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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology (1996)

Chapter: 3 Contemporary Water Management: Role of Limnology

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Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 66
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 67
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 68
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 69
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 70
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 71
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 72
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 73
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 74
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 75
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 76
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 77
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 78
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 79
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 80
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 81
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 82
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 83
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 84
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 85
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 86
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 87
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 88
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 89
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 90
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 91
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 92
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 93
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 94
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 95
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 96
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 97
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 98
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 100
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 101
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 102
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 103
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 104
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 105
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 106
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 107
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
×
Page 108
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 109
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 110
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 111
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 112
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 114
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 115
Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Suggested Citation:"3 Contemporary Water Management: Role of Limnology." National Research Council. 1996. Freshwater Ecosystems: Revitalizing Educational Programs in Limnology. Washington, DC: The National Academies Press. doi: 10.17226/5146.
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Page 117

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CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 65 3 Contemporary Water Management: Role of Limnology Understanding how aquatic systems function is complex because of the interdependencies among chemicals in the water and sediments, populations of aquatic organisms, water temperature, the shape of the water body, and the nature of the surrounding landscape. When one considers humans as a part of aquatic ecosystems, the dynamics of these systems becomes even more difficult to comprehend. Nearly every human activity—from farming and gardening to road building, shipping, fishing, and fuel combustion—affects rivers, lakes, and wetlands in some way. Limnology provides the tools necessary for understanding how water bodies behave in environments without significant human influence and how they are affected by the full range of human activities. This chapter highlights risks to North American surface waters and describes the role of limnologists and scientists in closely allied disciplines in improving understanding and stewardship of these waters. The contributions of limnologists range from establishing a detailed understanding of the extent and causes of an environmental problem to developing techniques to solve the problem or minimize its impact. Although limnologists, often drawing on the work of water scientists in fields such as environmental engineering and hydrology, have made major contributions toward understanding and solving the major problems of freshwater ecosystems during the past few decades, much remains to be learned. Consequently, the chapter also describes how additional limnological research would be helpful in defining and solving problems. The chapter divides problems in aquatic ecosystems according to whether they originate from modifications in the watershed or physical characteristics of the water body; from changes in the water's chemical composition; or from alterations in the ecosystem's biological communities.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 66 It is critical to realize, however, that the physics, chemistry, and biology of a water body are interrelated. Changes in the physical landscape surrounding water bodies can affect the chemical inputs to them, which in turn can affect aquatic biota. Similarly, changes in the chemical composition and biota of an aquatic ecosystem can affect the physical landscape. Much of the research described in this chapter has been conducted in response to problems caused by human activities. In a general sense, this research could be considered goal oriented (or directed research) rather than basic research conducted for the pursuit of knowledge itself. Nonetheless, much of this work has contributed to the understanding and solution of aquatic ecosystem problems because it advanced understanding of the fundamental behavior of these ecosystems. Similarly, many of the research needs identified in this chapter address basic limnological questions even though the results could be applied toward the solution of practical problems. (For more detailed information about research needs in limnology, see Naiman et al., 1995, and background papers at the end of this report.) PHYSICAL CHANGES IN WATERSHEDS AND WATER BODIES In many locations, the most serious causes of water quality decline are not direct inputs of pollutants but indirect effects resulting from changes in the landscape and atmosphere surrounding the water body and alteration of the water's natural flow path. Countless freshwater systems also have been affected by direct physical alterations to the shoreline or shape of the water body. For example, vegetation along lake and stream banks often is cleared to allow recreational or commercial access. Outlets to lakes often are dammed to provide downstream flow controls and allow water-level regulation in the lake. Channels are constructed between lakes and rivers, and littoral areas of lakes are dredged to allow ship and boat traffic. In addition, wetlands often are drained for agriculture and forestry. These physical changes can have subtle or dramatic impacts on the structure and functions of aquatic ecosystems, depending on the severity of the change. In many cases, the impacts are caused by excessive diversion of water from a stream for crop irrigation or other water supply purposes to the extent that so-called in-stream uses of the water (for example, maintenance of fish populations) may be impaired. Limnologists have made and continue to make critical contributions toward understanding how water bodies are disrupted by physical changes to the water bodies themselves or to their watersheds. Dam and Impoundment Building More than 80,000 dams exist in the United States (Frederick, 1991), creating impoundments that range in size from small millponds to large

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 67 multipurpose reservoirs. Until recently, dams were viewed as good, clean ways to generate hydroelectric power (Abelson, 1985; Bourassa, 1985), control floods, and provide storage for water supplies. Hence, their environmental impacts were not understood, evaluated, or monitored. Recently, society has become more aware of these impacts and the economic value of resources, such as fisheries, that have been damaged by dam construction. Limnologists, along with hydrologists and fisheries biologists, have been involved in documenting how dam building affects river ecosystems in several ways (National Research Council, 1987): • Temperature alterations: Because the water passing through reservoirs often originates from points near the middle or bottom of the water column, it may be much colder during the summer months than natural flows would have been. Sustained low temperatures during the warm months may support cold-water fisheries for species such as trout in streams and rivers that otherwise would not provide appropriate temperature regimes for these fish. At the same time, however, temperature alteration may suppress important native fish (Minckley, 1991) and other aquatic animals (Ward and Stanford, 1979). • Changes in dissolved oxygen, nutrient, and suspended solids concentrations: Dams may affect the amounts of oxygen, suspended solids, and nutrients in water flowing downstream (Gordon et al., 1992). The concentrations of dissolved oxygen in the lower water column of reservoirs may be low or zero in some instances, hampering the development of fisheries or altering the native fauna below dams (Petts, 1984). Further, water released from dams is likely to have a lower sediment content than water entering a reservoir (Andrews, 1991), causing substantial biotic changes such as enhanced growth of algae (Blinn and Cole, 1991) as well as physical changes in the downstream sediment balance (Simons, 1979). • Hydraulic modifications: Dams may stabilize the natural variation in the flow of rivers, alter seasonal extremes, or induce entirely new patterns. In addition, hydropower production facilities associated with some dams may establish a regular daily pulse in stream discharge and mean depth. These hydraulic peculiarities in turn can have significant biological effects. For example, decreased variability in streamflow below dams may cause habitat losses for fish and other aquatic organisms (Kellerhals and Church, 1989). In addition, wetland areas can suffer massive losses of important habitats (Baumann et al., 1984). The Atchafalaya Delta of the Mississippi River and the Peace-Athabasca Delta in northern Alberta are important examples. Aquatic scientists have estimated that the latter delta, which supports many unique species of wildlife and several hundred indigenous people, will disappear in fewer than 50 years unless Bennett Dam is decommissioned (see Box 3-1).

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 68 BOX 3-1 BENNETT DAM AND THE DISAPPEARANCE OF THE PEACE-ATHABASCA DELTA In the past, most dams and reservoirs were constructed without adequate study of their consequences for aquatic ecosystems, which has lead to irreparable or costly damage. One example is the installation of Bennett Dam on the Peace River. The Peace River flows from headwaters in northern British Columbia across Alberta to Lake Athabasca. Historically, the spring melt flood of the Peace backed up water into the lake and delta of the Athabasca River, flooding small, perched lakes and wetlands along the dendritic channels in the delta. The area was rich in wildlife and was home to more than 1,500 indigenous people. Except in 1974, when an ice jam caused flooding, there has been no flooding of the Peace-Athabasca Delta since 1969, when Bennett Dam was constructed on the Peace River near the British Columbia-Alberta border. Muskrat, the staple of a thriving trapping industry, disappeared within a few years. Rich fisheries declined. Waterfowl numbers decreased dramatically as marshlands were invaded by willows and other trees. Many of the dendritic channels filled in, making boat travel impossible. Grazing lands for wood bison declined as range quality deteriorated after the annual deposition of rich sediments ceased (Carbyn et al., 1993). Few indigenous people now live on the land. Most remain in the community of Fort Chipeweyan, where their use of natural foods is being replaced by less-nutritious alternatives (Wein et al., 1991). Damming of the river has resulted in the end of a traditional way of life for people in the area. Studies done to document the deleterious downstream impacts of the Bennett Dam provide resource managers and water resource planners with knowledge about the consequences of dam building so that these problems can be avoided in the future. • Increase in mercury levels: In some cases, the construction of reservoirs has caused the mercury content of fish to increase rapidly to values that exceed guidelines for human consumption, as shown in the example in Figure 3-1 (Bodaly et al., 1984; Rosenberg et al., 1995). Increased mercury levels have led to losses of commercial, recreational, and subsistence fisheries. The increase appears to be largely the result of low oxygen concentrations caused by the decay of flooded vegetation. Such conditions promote the increased activity of bacterial species that transform inorganic mercury into the methylated form, which is greatly biomagnified (Rudd, 1995). • Release of greenhouse gases: The release of the greenhouse gases carbon dioxide (CO2) and methane (CH4) following the flooding of forests and peatlands is another major concern identified by limnologists and other environmental scientists. The total area of reservoir surface in North

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 69 FIGURE 3-1 Mercury concentrations in pike and walleye flesh from two Canadian reservoirs after impoundment. LG2 is part of the James Bay Phase 1 development in Quebec. SIL is Southern Indian Lake on the Churchill River in northern Manitoba. SOURCE: Reprinted, with permission, from Rosenberg et al. (1995). © 1995 by Global Environmental Change.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 70 America is substantial, roughly equivalent to that of Lake Ontario (Rudd et al., 1993). Under natural conditions, wetlands are significant sinks for CO2 and major sources of CH4, while forests are minor sinks for CH4 and about in equilibrium with atmospheric CO2 (Rudd et al., 1993; Gorham, 1995). Following flooding, these areas become strong net sources of greenhouse gases for several years. The rate of greenhouse gas emission per unit of hydropower production may be comparable to emissions from a fossil fuel plant producing an equivalent amount of power, depending on the area of land that is flooded to create the hydroelectric facility (Rudd et al., 1993). The broad range of effects of dams on water quality, physical habitat, and biotic communities presents numerous research opportunities relevant to resource management that are now being actively explored with the involvement of limnologists (National Research Council, 1987; Cheslak and Carpenter, 1990). For example, multiple-level outlet structures can be used to manipulate water temperature (Larson et al., 1980) or to mix waters of various oxygen or nutrient contents at the dam. Input from limnologists and other aquatic scientists can help to ensure that management of existing dams is optimized. As dams age and fill with sediment, their utility decreases and so does the economic incentive to maintain them. However, removing dams can create severe problems from remobilization of upstream sediment, which is likely to be rich in nutrients and oxygen-consuming organic matter deposits and may contain hazardous chemicals. Limnologists can help assess and avoid such problems when dams are removed. Wetlands Destruction Wetlands were long regarded by many as wastelands fit for nothing until ''reclaimed" by human manipulation. In recent times, however, human societies have begun to recognize the broad array of values that wetlands can provide (Greeson et al., 1979; Richardson, 1989, 1994; National Research Council, 1992, 1995). Among the physical values of wetlands are such properties as shoreline stabilization, flood-peak reduction, and ground water recharge. Wetlands also function as filters, transformers, and sinks for materials delivered to them by human activities, thus improving water quality. For instance, they can filter 60 to 90 percent of suspended solids from wastewater and as much as 80 percent of sediment in runoff from agricultural fields (Richardson, 1989). In addition to these important physical and chemical functions, wetlands provide a great variety of biological benefits. Riparian wetlands serve as protective

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 71 nurseries and food sources for young fish before they move out into open water. The microorganisms and vegetation in wetlands are essential on both local and global scales in cycling carbon, nitrogen, and sulfur between the earth and the atmosphere. In addition, wetlands provide commercial products such as lumber, cranberries, marsh hay, wild rice, waterfowl, muskrat, beaver, and mink. Despite their benefits, wetlands in many parts of the world are disappearing at an alarming rate due to human activity. In the contiguous United States, more than 50 percent of the original wetlands had been destroyed by the 1970s, and an additional 2.6 percent were lost through the 1980s (Frayer, 1991). In some states—such as California, Ohio, and Iowa—less than 10 percent of the original wetlands remain, with consequent losses of waterfowl, furbearing animals, and fish. The largest human uses of wetlands are for forestry and agriculture (Kivinen, 1980). Across large sections of the Midwest, for example, drainage tiles have been installed beneath wetlands to allow use of their fertile soils for crop production. Urban development also has led to the dredging and filling of many wetlands. Others have been flooded or drained by Example of a wetland: a patterned peatland in the Hudson Bay Lowlands in Canada. Because of upwelling ground water, large peatlands such as this often develop intricate landscape patterns, which represent perhaps the most delicate mutual interaction between hydrology and vegetation on the earth's surface (Sjörs, 1961; Heinselman, 1963; Wright et al., 1992). SOURCE: Paul H. Glaser, Limnological Research Center, University of Minnesota.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 72 highway construction. Stormwater and wastewater diversion to wetlands has added both nutrients and toxic materials (Environmental Protection Agency, 1994), leading to major alterations of flora and fauna. The United States currently has a policy of "no net loss" of wetlands, which has spawned work in restoring damaged wetlands and attempting to construct artificial wetlands to replace natural ones that have been destroyed. As presently practiced, however, wetland restoration is a very imperfect science (Mitsch and Gosselink, 1993). The best candidates for restoration are early successional wetlands such as cattail marshes. Restoration of natural prairie wetlands also may be possible in some cases. Restoration of forested wetlands is difficult, given the long lives of trees, and restoration of the large patterned peatlands of the boreal zone— developed over millennia by interactions of local and regional hydrology—must be regarded as essentially impossible once they are seriously degraded. Replacing mature wetlands that have taken centuries or millennia to develop with cattail marshes cannot be considered in compliance with the no-net-loss policy because it results in a major shift in biodiversity and ecological function. Construction of new wetlands, allowed in the United States under Section 404 of the Clean Water Act (Kusler and Kentula, 1989), to replace ones that have been destroyed for development is even more difficult than restoration of damaged wetlands. There often is no record of what the destroyed wetland was like. Moreover, follow-up investigations of created wetlands are rare, so that the success of mitigation efforts is seldom evaluated (Erwin, 1991). In a rare follow- up study, Erwin reported very limited success for wetland mitigation in South Florida. According to Bedford (in press), adequate attention has been given neither to reproducing the original wetland hydrology nor to establishing specific types of plant communities. Further fundamental limnological research is essential for managing, restoring, and creating wetlands and for developing a workable no-net-loss policy. Additional scientific understanding is needed to address issues such as the following: • What have been the spatial patterns of wetland development through the centuries? • To what degree has wetland development been controlled by environmental factors (hydrology, in particular), and to what degree has it resulted from autogenic processes such as peat accumulation? • Do environmental changes generally cause slow and steady changes in wetlands, or do threshold phenomena dictate relatively sudden responses to environmental stresses (natural or anthropogenic) that build up over time? • How will global warming affect wetlands, particularly peatlands, and vice versa?

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 73 • How are wetlands linked ecologically and biogeochemically to other aquatic and terrestrial ecosystems? Limnological research to answer such questions is critical in the quest to protect and manage the remnants of the valuable wetland resource in North America. Other Modifications to Watersheds For millennia, humans have been modifying watersheds in ways other than by building dams and draining wetlands, often with adverse consequences for aquatic biota and water quality (Solbe, 1986; Harriman et al., 1994). Forests and grassland have been transformed to agricultural fields or urban pavements as societies have established themselves around water bodies; forest ecosystems have been replaced with tree plantations designed to meet human needs for timber. Studies by limnologists and their fellow water scientists have provided valuable insights about impacts of human development on water bodies. Examples of limnological work in this area include the following: • Effects of early agricultural and urban activities: Studies by limnologists have shown that even the earliest stages of agricultural and urban development caused changes in water quality. Fires built by native people significantly altered the landscape of North America (Lewis and Ferguson, 1988). Work by several limnologists has indicated that fire changes water quality, causing increases in runoff of water, nutrients, and mineral ions (Schindler et al., 1980; Bayley et al., 1992 a,b; MacDonald et al., 1993). Paleolimnological studies by Hutchinson et al. (1970) showed that construction of the Appian Way (Via Appia) by the Romans in the second century A.D. changed drainage patterns for Lago di Monterosi in Italy in such a way that the lake became eutrophic. Similarly, Frey (1955) showed that early agrarian societies in the catchment of Längsee, Austria, caused the lake to become meromictic (meaning the bottom waters no longer mix with the remainder of the lake) through land clearning and associated activities. • Changes in nutrient loads caused by land use: Limnological studies have shown that land-use changes alter the yield of nutrients from watersheds to lakes. For example, Dillon and Kirchner (1975) showed that the transformation of forested land into pasture causes a considerable increase in nutrient yields from catchments to lakes. Transformation to agricultural land causes still greater increases. Sorrano et al. (in press) showed that urbanization increases nutrient inputs and that in addition to land use, the proximity of modified land to stream edges is an important factor controlling nutrient inputs to Lake Mendota, Wisconsin. • Effects of forestry: Clearcut logging is well known to increase water yield and the transport of nutrients, sediments, and other substances to

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 74 streams (Bosch and Hewlett, 1982; Murphy et al., 1986; Harr and Fredriksen, 1988; Harriman et al., 1994). Likens et al. (1970) demonstrated that when catchments are not revegetated, the yield of nutrients, sediments, and other substances can increase manyfold. Even managed forestland can affect aquatic ecosystems. For example, when deciduous forests in catchments are transformed into conifer plantations, soils, ground water, and runoff typically become more acidic because of the increased trapping of strong acids from the atmosphere by conifers and the acidifying effect on soils of decomposing conifer needles (Feger, 1994); the result is modification in the acid-base balance of lakes whose watersheds encompass the forestland. Even when no changes are made in species of vegetation, different stages of the growth and harvest cycle cause differences in the chemistry of streams (Harriman et al., 1994; Kreuzer, 1994). Global Warming Most atmospheric scientists agree that average global temperatures are likely to rise as a result of increasing levels of greenhouse gases, particularly CO2 and CH4, in the atmosphere (Houghton et al., 1995). Although scientists who believe that global warming is occurring or will soon occur outnumber the dissenters, there is disagreement about how much the temperature might increase and how fast (American Society of Limnology and Oceanography and North American Benthological Society, 1994; Houghton et al., 1995). Despite this disagreement, it is widely accepted that substantial changes in the temperature of the earth are likely to have significant effects on inland aquatic ecosystems (see Box 3-2). Atmospheric CO2 concentrations have been rising since the industrial revolution as the result of fossil fuel burning. Deliberate burning of forests as land is cleared is an important second source (Houghton et al., 1995). Levels of CH4 in the atmosphere also have been increasing, but for reasons that are not well understood. Although the abundance of CH4 in the atmosphere is much lower than that of CO2, it is 7.5 to 62-times more effective as a greenhouse gas, depending on the time scale under consideration (Houghton et al., 1995). Important CH4 sources include wetlands, rice paddies, termites, and domestic animals such as cows. Wetland limnologists have contributed greatly to understanding the role of wetlands in CH4 production (Bartlett and Harriss, 1993; Harriss et al., 1993), but a mechanism that fully explains the increase in the atmosphere still needs to be found (Houghton et al., 1995). Research has scarcely begun on an alternative explanation that CH4 is increasing because human activities have slowed the mechanisms removing it from the atmosphere. Refined estimates of the magnitudes and rates of global warming are problematic because of uncertainties in emissions from human activities and variabilities in different storage mechanisms for carbon. For example,

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 75 seawater, organic detritus, and vegetation all tie up large amounts of carbon. Furthermore, cloud cover, aerosol haze, and oceanic circulation all affect the rate and degree of change, thereby complicating predictions. Recently, Mitchell et al. (1995) modeled the global interactions of greenhouse gases, aerosols, and ocean circulation and concluded that, overall, aerosols will reduce the warming expected from greenhouse gases by about one-third. These many uncertain factors will have to be better understood before the timing and extent of global warming can be predicted. Limnological research can help to reduce these uncertainties. Unless properly designed with appropriate vegetative buffers, clearcuts can be a source of sediments and nutrients to aquatic ecosystems. SOURCE: Elizabeth Rogers, White Water Associates, Inc. Limnologists have been centrally involved in evaluating the effects of climate warming on fresh waters and have described a wide range of effects that climatic warming is likely to have on lakes and streams (Firth and Fisher, 1992; Schindler et al., in press, a,b). Increased temperature will increase evapotranspiration, so that lower soil moisture, ground water flows, and stream flows are likely to result (except where climatic warming is accompanied by large increases in rainfall). Stream temperatures track air temperatures reasonably closely; therefore, some streams may become too warm for some organisms. Periods when small streams are dry may increase dramatically. The early melting of snow will cause less pronounced spring flow pulses, which are vital to the maintenance of wetland and riparian habitats. The reduction in water flows, coupled with the

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 76 decrease in weathering of rocks and soils, may cause decreased export of chemicals—including nutrients, base cations, strong acid anions, silica, and dissolved organic carbon—to lakes and larger rivers (Schindler et al., in press a,b). In lakes, longer ice-free seasons, warmer water temperatures, and deeper thermoclines may cause dramatic increases in habitat warmth (measured as degree-days) and decreases in habitat suitable for cold-water species such as trout, thus affecting the composition of fish communities (Magnuson et al., 1990; Stefan et al., 1995). BOX 3-2 HOW CLIMATE CHANGE AFFECTS LAKES Freshwater lake temperatures respond to changed atmospheric conditions, and changes in lake water temperatures and temperature stratification dynamics may have a profound effect on fish and other aquatic organisms (Meisner et al., 1987; Coutant, 1990; Magnuson et al., 1990; Stefan et al., 1995). The response of lake water temperatures to climate changes can be investigated by several methods. One approach is to examine long-term records. In a few lakes, such as those in the Experimental Lakes Area in Ontario, Canada, and Lake Mendota in Wisconsin, weekly and biweekly vertical profiles of water quality and biological parameters have been collected for many decades (Robertson, 1989; Schindler et al., 1990). Observations from such lakes indicate rising average surface water temperatures, increased evaporation, and increases in transparency and diversity of phytoplankton. Such trends can be determined, however, only if lake temperature records are long enough. Where records are short but detailed, a second approach is to compare individual warm and cold or wet and dry years (Hondzo and Stefan, 1991). A third approach, useful for extrapolating to lakes of different geometries and latitudes and to possible future climates, involves numerical simulation models. Such models calculate heat transfer from the atmosphere to the water and within the lake water column (Blumberg and DiToro, 1990; Croley, 1990; McCormick, 1990; Schertzer and Sawchuk, 1990). In one investigation using a numerical modeling method to simulate daily water temperatures in 27 classes of lakes characteristic of the north-central United States, Hondzo and Stefan (1993) determined that a doubling of atmospheric CO2 would increase surface water temperatures by less than the corresponding air temperature increase but that bottom water temperatures in seasonally stratified lakes would be largely unchanged. The effect on fish would be a decrease in habitat for cold-water species and an increase in habitat for species that prefer warmer water, with the greatest effects on lakes in southern latitudes (Stefan et al., 1995). Atmospheric warming also would increase evaporative loss of lake water by as much as 300 mm for the season (Hondzo and Stefan, 1993). Limnologists have shown that in addition to affecting lakes and streams, global change will markedly affect the balance of productivity

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 77 and decomposition in wetland ecosystems (Billings, 1987; Gorham, 1995). Peatland ecosystems sequester an estimated 4 × 1014 kg of carbon, about one- quarter of the total soil pool (Woodwell et al., 1995) and thus play a major role in the global carbon cycle. A general warming would lead to longer growing seasons and might simultaneously increase net primary productivity in wetlands. Under wetter conditions, production and emission of CH4 in wetlands would increase relative to production and emission of CO2. In contrast, if climatic warming leads to a drawdown of wetland water tables, CO2 emissions are likely to increase and CH4 emissions to decline. The possibility of melting of the extensive permafrost beneath northern peatlands complicates this scenario (Gorham, 1995). Fire is another significant variable in this context because if droughts become increasingly frequent and severe, surface peats may catch fire and smolder for years, releasing both CO2 and CH4 to the atmosphere (Gorham, 1995). Continued limnological research is needed to reduce the large uncertainties—whether water tables will rise or fall, whether CH4 levels will increase or decrease, how much fire frequency and intensity may increase— about how global warming will affect wetlands and how wetlands, in turn, will affect global warming. Long-term records of climatic, hydrological, and ecological variables are invaluable for analyzing and evaluating the effects of climate change. For example, long-term studies of ice records (Assel and Robertson, 1994, in press) and the changes in lakes and streams (Schindler et al., 1990, 1992, in press a) under climatic warming have greatly increased understanding of the effects of climate change on aquatic ecosystems and on land-water linkages, as have paleoecological studies of wetlands. Experimental studies in limnology are particularly needed to assess the secondary effects of climate alteration (mediated through heating, erosion, nutrient alterations, etc.) on organisms and biogeochemical processes in aquatic communities. CHEMICAL CHANGES IN AQUATIC ECOSYSTEMS Humans have long used the water bodies beside which they have settled as receptacles for their wastes. For example, archaeological investigations in the Indus River Basin have uncovered brick sewer systems dating back as early as 2500 B.C. (McHenry, 1992). As the human population has grown and concentrated in urban areas, the quantity of wastes discharged to water bodies has increased, changing the chemistry of the receiving waters in ways that, in turn, affect aquatic organisms. Emissions of contaminants to the air through combustion also have caused significant changes in the chemistry and, in turn, the biology of aquatic systems. A wide variety of limnological research addresses the problems created by chemical changes in water bodies.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 78 Municipal, Industrial, and Agricultural Waste Discharges Municipal wastewater treatment plants currently discharge more than 110 million cubic meters (30 billion gallons) of sewage per day into U.S. water bodies (van der Leeden et al., 1990). Manufacturing industries discharge an additional 91 million cubic meters (24 billion gallons) per day (van der Leeden et al., 1990). More difficult to manage than these point sources of pollution, however, are diffuse sources of pollution such as agricultural and urban runoff. For example, state water resource managers identified agricultural runoff as a cause of impairment of 49 percent of the damaged lakes, rivers, and streams they assessed; they identified urban runoff as a factor in the decline of 24 percent of damaged lakes and 10 percent of damaged rivers and streams (Environmental Protection Agency, 1994). Three of the major impacts of excessive waste loadings to surface waters are loss of dissolved oxygen, cultural eutrophication, and buildup of toxic compounds. Loss of Dissolved Oxygen Excess discharges of organic wastes cause the depletion of the receiving water's oxygen supply. Low oxygen levels threaten the survival of desirable sport fish species such as trout, salmon, and bass, which may be replaced by populations of catfish and carp. If the oxygen level drops low enough, even catfish and carp cannot survive. In the worst cases, when the oxygen concentration reaches zero for extended periods, no higher organisms can survive, and the only life remaining in the water body consists of anaerobic bacteria that produce gases such as CH4 and hydrogen sulfide. Much of the earliest aquatic science research focused on understanding the effects of sewage and other organic waste discharges on dissolved oxygen concentrations. As a result of these early efforts, the effects of adding excess organic matter to a water body are well understood. For example, in 1884, Dupré recognized that oxygen depletion in a stored bottle of water occurred because of the activity of microscopic organisms, which he called "microphytes" (Phelps, 1944). By the early decades of this century, scientists had developed standardized procedures to determine the amount of oxygen that organisms will use when degrading a given waste; this amount is known as "biochemical oxygen demand" (BOD) (Streeter and Phelps, 1925). H. W. Streeter, a Public Health Service researcher, and E. B. Phelps, a professor of stream sanitation at Columbia University, developed an equation that predicts how much the oxygen concentration of a river will decline at given points downstream of a waste discharge (Streeter and Phelps, 1925). This equation is historically important as the first mathematical model used to predict water quality. It predicts oxygen levels based on rates of two processes: microbial oxygen

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 79 demand (that is, BOD), which is a sink or loss term, and atmospheric reaeration, which is a source term. The output of this equation is known as the "oxygen sag curve," because the oxygen concentration decreases downstream of a waste discharge and, further downstream, increases again once the waste is biodegraded (see Box 3-3 and Figure 3-2). Although BOX 3-3 RECOVERY OF THE MISSISSIPPI RIVER NEAR MINNEAPOLIS-ST. PAUL Early in the twentieth century, the Mississippi River near Minneapolis-St. Paul, Minnesota, was severely polluted. The discharge of large amounts of untreated sewage from the Twin Cities, combined with construction of a dam that reduced the naturally cleansing river currents, had resulted in the near elimination of dissolved oxygen from the portion of the river flowing through the Twin Cities region (Johnson and Aasen, 1989). As shown in the lower curve on Figure 3-2, mean August dissolved oxygen concentrations were near zero between St. Paul and Lock and Dam 2 in 1926; the oxygen concentration increased below the dam due to biodegradation of the pollutants upriver and natural reaeration of the water. The low dissolved oxygen levels in the reach of river between the Twin Cities and the dam encouraged the proliferation of pollutant-degrading bacteria that produce hydrogen sulfide and methane gases, creating an unbearable stench and lifting mats of sludge to the water surface (Johnson and Aasen, 1989). In addition, native fish and other pollution-sensitive organisms died off. Research by A. H. Wiebe in the late 1920s documenting the poor condition of the Mississippi encouraged the Twin Cities to plan their first sewage treatment plant (Johnson and Aasen, 1989). Following the opening of the plant (the first on the Mississippi River) in 1938, water quality improved markedly. As shown in Figure 3-2, mean August dissolved oxygen concentrations increased to more than 4.0 mg per liter from 1942 to 1955. However, during the 1950s the population of the Twin Cities expanded dramatically, and river flows decreased at the same time. By 1960, water quality had declined again between the cities and the dam, as shown in Figure 3-2. Because of the drop in dissolved oxygen levels and the increase in pollution levels, the only life present in the portion of the river near the sewage treatment plant was tubified worms (Johnson and Aasen, 1989). Following a significant increase in the capacity of the wastewater treatment plant and upgrades in the type of treatment provided in 1966, water quality improved again. Dissolved oxygen levels rose to more than 4.0 mg per liter (Johnson and Aasen, 1989). With the addition of more advanced treatment technology in the mid-1980s, water quality improved still further. Mean August dissolved oxygen levels now greatly exceed 5.0 mg per liter (the current water quality standard) along the full stretch of river through the Twin Cities (see Figure 3-2). Pollution-sensitive species such as mayflies have returned after a 50-year absence (Fremling, 1989).

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 80 Phelps did not call himself a limnologist, he identified himself as an expert in "the science of rivers"—with knowledge of the biology, chemistry, and geology of river systems (Phelps, 1944). His work helped to advance the field of stream limnology. FIGURE 3-2 Mean August dissolved oxygen concentrations in the Mississippi River below St. Paul, Minnesota. Note the ''sag" in the curves: the oxygen level decreases immediately downstream of the city due to oxygen consumption by microorganisms that degrade wastes; it increases again further downstream due to atmospheric reaeration once the wastes are biodegraded. SOURCE: Reprinted, with permission, from Johnson and Aasen (1989). © 1989 by the Journal of the Minnesota Academy of Science. Early research on how sewage affects streams was an important source of the scientific basis for federal legislation to control water pollution. For example, the opening paragraphs of the 1972 Clean Water Act state that its objective is "to restore and maintain the chemical, physical, and biological integrity of the nation's waters." The act requires states to issue permits— known as National Pollutant Discharge Elimination System (NPDES) permits— to municipalities and industries that discharge wastes to waterways. For municipal sewage treatment plants, two primary requirements specified in the permits are reductions in BOD (the basis for the Streeter-Phelps equation) and suspended solids in the waste to levels that are based on the capabilities of standard sewage treatment technologies. Thus, the early work by Streeter, Phelps, and others examining the effects of pollution on streams helped to provide the technical basis for this permit system.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 81 Although the goals of the Clean Water Act have not been fully achieved (see Chapter 1), the act has been effective in reducing discharges of untreated municipal sewage and, as a consequence, in combating oxygen depletion in waterways. In 1960, for example, 110 million of 180 million U.S. residents were served by sewage systems, but only 36 percent of the sewage was treated before discharge to a water body. For the remaining 64 percent, waterways were used as conduits for raw sewage. By 1984, 170 million of 236 million U.S. residents were served by sewers, and the sewage was treated for 169 million (more than 99 percent) of those served (van der Leeden et al., 1990). By 1992, the 50 states reported to the Environmental Protection Agency (EPA) that municipal sewage posed a "major" problem in just 2 percent of rivers they assessed and 3 percent of assessed lake acres (EPA, 1994). Similarly, the states reported that dissolved oxygen depletion is a major source of impairment in 2 percent of assessed rivers and 3 percent of assessed lakes (EPA, 1994). The work by river specialists and other aquatic scientists has been a major factor underlying the success of the Clean Water Act in addressing the dissolved oxygen depletion problem. Cultural Eutrophication Cultural eutrophication, the detrimental increase of nutrient inputs to lakes by humans, has been one of the major freshwater problems of the twentieth century. Typical symptoms include the development of nuisance blooms of algae and aquatic macrophytes, with associated problems of taste, odor, and even toxicity; the depletion of deep-water oxygen due to increased decomposition; and the loss of species of fish and invertebrates that require high oxygen concentrations (see Box 3-4). Limnologists began documenting these problems as early as the mid-nineteenth century, but paleolimnological studies have revealed that the problem existed at least as early as the second century (Hutchinson, 1969). By the early twentieth century, limnologists had developed a system for classifying lakes relative to their degree of eutrophication (Thienemann, 1925). By the mid-twentieth century, cultural eutrophication was recognized as a pervasive problem in much of western Europe and North America. Despite early recognition that nutrients were responsible for eutrophication, many questions were unresolved in the early 1960s, which prevented the adoption of effective prevention, management, and restoration strategies. Public concern about the problem led governments in many countries to establish large-scale research programs to address it. Important questions that needed answers were (1) the role of various nutrients in contributing to eutrophication problems; (2) the quantitative importance of various natural and cultural sources of nutrients; (3) the extent to which natural factors such as lake shape and water renewal rates influence the ability of a lake to assimilate nutrient inputs without developing

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 82 undesirable symptoms of eutrophication; (4) the relative importance of internal nutrient cycling versus external nutrient loading in causing or maintaining symptoms of eutrophication; and (5) the degree to which controlling external nutrient sources would result in rapid improvements in water quality conditions or whether additional in-lake restorative measures would be needed for most lakes. There was a lack of consensus among limnologists even on a question as basic as "How should eutrophication be defined?" Limnologists responded rapidly to the challenge of these questions, stimulated by the widespread occurrence of eutrophication problems and the availability of government research funds. Proceedings of several important symposia during this period (e.g., National Research Council, 1969; Likens, 1972) document the breadth of research BOX 3-4 THE CULTURAL EUTROPHICATION OF LAKE GEORGE Lake George, located in the eastern Adirondack Mountains of New York State, is sometimes called the "queen of American lakes." Its water clarity is among the highest of natural lakes in the United States. Most of the lake's watershed is forested, but the southwestern shore has residential developments, and a major commercial area is located on the lake's southern tip. The year-round population is about 5,000, but in summer the population increases to about 50,000. Residents and visitors use the lake for recreation and potable water. As the population surrounding Lake George has increased, the lake's characteristics have changed. Projected future development of the basin has raised concerns about increasing eutrophication, because the recreation-based economy of the area depends heavily on maintaining the lake's water quality. Limnological studies of Lake George identified a logarithmic increase in algal production between 1974 and 1978. Distinct spatial water quality patterns were observed, with lower transparencies, lower dissolved oxygen concentrations in deep waters, higher phosphorus and chlorophyll-a concentrations, and a greater occurrence of blue-green algal blooms in the southern portion of the lake than in the undeveloped northern portion. In addition, fecal coliform counts in the southern end of the lake were five times above permissible levels for contact recreation. Of the 80 streams draining into the lake, those in the southern basin, nearest to human developments, had significant problems with sedimentation, affecting lake water quality and the fish spawning areas in the streams and the lake. The studies attributed the reduction in water quality to runoff from urban developments. As an example, the Lake George National Urban Runoff Program project determined that the increased algal production was due to phosphorus (EPA, 1982). Because there are no point-source discharges, the phosphorus loading was attributed to urban runoff. The study estimated that urban runoff accounted for 20 percent of the annual phosphorus load in the southern basin.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 83 activities aimed at solving the problem. Such symposia played key roles in exchange of information and ideas among limnologists and in the development of recommendations for how eutrophication might be controlled. Within a decade, many of the most critical issues had been resolved, at least to the extent that effective management programs could be established. For example, limnologists developed ways to express the consequences of eutrophication quantitatively in terms of changes in lake transparency and chlorophyll content of phytoplankton (e.g., Carlson, 1977), and they developed quantitative predictive models in the late 1960s and early 1970s (e.g., Vollenweider, 1969; Dillon and Rigler, 1975) that facilitated the determination of loading criteria for phosphorus. A key limnological study of an early lake restoration effort on Lake Washington in Seattle resolved questions regarding the reversibility of eutrophication. W. T. Edmondson, a University of Washington limnologist, demonstrated that this lake recovered rapidly following diversion of nutrient-rich sewage effluent from the lake (Edmondson, 1970) (see Box 3-5). However, it should be noted that control of external nutrient sources is not sufficient to alleviate the symptoms of eutrophication in all lakes. In many cases, in-lake treatment to decrease the rate of phosphorus recycling from bottom sediments or to restore damaged habitat also is necessary to reverse long-term and severe impacts of excess nutrient loadings. A hotly debated controversy developed over the role of phosphorus in eutrophication (see Box 3-6). Members of the detergent industry (a major source of phosphorus in sewage) proposed that carbon dioxide was the primary nutrient controlling phytoplankton blooms in eutrophied lakes and that phosphorus was of little importance (Edmondson, 1991). Confusion about which nutrients to control ultimately was resolved through a variety of field experiments, laboratory studies, and modeling exercises that identified phosphorus as the critical element in most lakes.1 Limnologists at Canada's Experimental Lakes Area in the late 1960s and early 1970s designed whole-lake experiments to resolve the controversy. An early experiment in one lake showed that controlling carbon sources would have little effect on eutrophication, because even in the most severely carbon-limited lakes, sufficient carbon could be drawn from the atmosphere by photosynthesis to allow the development of large algal blooms (Schindler et al., 1972). A second experiment in another lake showed that phosphorus control was effective at preventing eutrophication and that other nutrients would not cause eutrophication in the absence 1 Lakes in glaciated regions of the northeastern and north-central United States are phosphorus limited in the absence of anthropogenic nutrient loadings. Coastal waters and lakes in some other geographic regions may be nitrogen limited. A well-known example of a nitrogen-limited inland lake is Lake Tahoe in the Sierra Nevada.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 84 of phosphorus (Schindler, 1974). Overall, these experiments demonstrated that atmosphere-water exchanges of carbon and nitrogen could correct algal deficiencies of these elements. They also supported newly developed quantitative models relating phosphorus input and water renewal rates to eutrophication; these models form the basis for modern eutrophication control strategies (Vollenweider, 1969, 1975, 1976; Dillon and Rigler, 1975). Following these limnological discoveries, in North America and most European countries, phosphorus inputs to lakes from sewage and detergents were controlled in an effort to solve eutrophication problems. BOX 3-5 RECOVERY OF LAKE WASHINGTON Lake Washington serves as a remarkable example of the use of basic scientific research in a public action to protect environmental quality. The lake began to show a response to eutrophication in 1955. Although its condition was not bad at that time, the lake was protected by public action before serious deterioration took place. The action involved passage of a special law by the state legislature, creation of a new kind of municipal government organization, a public education campaign, and a public vote in which the community agreed in effect to tax itself to protect the lake. The lake had been receiving increasing amounts of nutrient-rich secondary sewage effluent since 1941. By 1955, the daily input was about 75,000 cubic meters (20 million gallons). In that year there was a modest bloom of Oscillatoria rubescens, a species of cyanobacteria that had appeared early in the eutrophication of several European lakes. The bloom served as an early warning signal. W. T. Edmondson, at the University of Washington, started a research program designed as a basic scientific, experimental study of lake fertilization. At the same time, public awareness of a number of pollution problems in the area was growing. The mayor of Seattle appointed a committee of public-spirited citizens to study the problems and propose solutions. Meanwhile, Edmondson's studies led him to predict that Lake Washington would develop nuisance conditions in a few years and that diversion of sewage effluent would not only protect the lake against further deterioration but permit it to recover from the damage already shown. The committee proposed diversion of the effluent in such a way as not to cause the same problem elsewhere. Two difficulties had to be overcome. First, since sewage was coming from several cities around the lake, financing would have to be shared. State law In many cases, the control of point sources of nutrients alone has not been enough to prevent or reverse eutrophication. As nutrient control measures took effect on municipal effluents, the relative importance of contributions from nonpoint sources began to rise. By 1980, nonpoint sources contributed approximately 95 percent of the total nitrogen load and 98 percent of the total phosphorus load to surface waters (van der Leeden et al., 1990). Also, as population and industry continue to grow,

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 85 at that time did not provide for such financial arrangements among municipalities, so the first hurdle was to get a new law passed by the state legislature. A persuasive presentation of the case was made by a state senator who later became governor and was well aware of the limnological situation. The enabling legislation permitted the formation of a governmental entity, the Municipality of Metropolitan Seattle (Metro), to deal with several kinds of problems associated with urbanization. The next step was to persuade the citizens to work for Metro and to commit $125 million for the diversion project, essentially a tax on themselves; there would also be a monthly fee for each household for treatment. Opposition to the Metro project developed, based on financial and political considerations. In 1958, federal funding was not available for such a project. An educational campaign was launched with lectures and with debates presenting both sides of the issue. It made full use of the limnological information and predictions coming from Edmondson's laboratory, as well as the results of an engineering study. After a positive vote in favor of Metro and the sewage diversion, five years passed while plans were drawn up and construction began. During that time cyanobacterial populations increased and transparency decreased, a condition widely noticed by the public. Diversion took five more years to complete. With the first partial diversion, the lake stopped deteriorating and then improved to a condition better than it had been in 1950, five years before the Oscillatoria bloom. A full account of the limnological situation and the public action is given by Edmondson (1991), and recent developments are described in Edmondson (1994). atmospheric precipitation and windblown dust have become sources large enough to aggravate the problem (e.g., Brezonik, 1976; Hendry et al., 1981). In some cases, atmospheric inputs of nitrogen have exceeded "critical loads" to natural catchments, causing saturated ecosystems to release excess nitrogen to lakes and streams, where both acidification (via nitric acid) (Nilsson and Grennfelt, 1988) and eutrophication (in nitrogen-limited waters such as Lake Tahoe and the Baltic Sea) result (Rosenberg et al., 1990). Nitrate concentrations in the Great Lakes and in lakes of Scandinavia have increased dramatically in the past few decades (Bennett, 1986; Henriksen and Brakke, 1988). Even with increasing land-use controls to prevent excess nutrient discharges, the eutrophication problem will not be eliminated entirely. Limnologists have shown that in some cases; internal recycling of nutrients from bottom sediments can help to maintain eutrophic conditions in lakes for long time periods after external loading rates are controlled (e.g., Chapra and Canale, 1991). Limnologists have experimented with altering the structure of food

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 86 BOX 3-6 THE GREAT CARBON CONTROVERSY During the 1960s, considerable public concern developed over the rapidly increasing incidence and intensity of algal blooms in lakes of Europe and North America, including the Great Lakes. Dr. R. A. Vollenweider, a limnologist, spent several years reviewing possible causes of this eutrophication. In a widely circulated report, he concluded that increased inputs of phosphorus and nitrogen were the most probable causes of the problem (Vollenweider, 1968). His report convinced the International Joint Commission (a joint U.S.-Canadian body that recommends Great Lakes management strategies) to recommend that phosphorus be removed from sewage effluents and eliminated from laundry detergents, the major sources of the element to the lower Great Lakes. The soap and detergent industry resisted this recommendation. Industry representatives argued that laboratory experiments with Great Lakes water had shown carbon, not phosphorus, to be limiting to algal growth. They also presented other calculations, based on the amount of carbon in lake water, suggesting that carbon would limit algal production and that the carbon in sewage effluents, rather than the increasing phosphorus, was causing the eutrophication problem. A whole-lake experiment was conducted to resolve the carbon-phosphorus controversy. Limnologists at Canada's Experimental Lakes Area (ELA) selected a small oligotrophic lake containing a very low concentration of inorganic carbon (much lower than concentrations in the Great Lakes and typical eutrophic lakes). They added phosphorus and nitrogen to the lake in order to determine whether carbon limitation would prevent the lake from becoming eutrophic. Within weeks after fertilization began, an enormous algal bloom developed in the lake, proving that low carbon would not limit eutrophication (Schindler et al., 1973). Further studies in the lake showed that the carbon necessary to produce and maintain the algal bloom was entering the lake as carbon dioxide from the atmosphere (Schindler et al., 1972). The laboratory experiments used as evidence by proponents of the carbon limitation theory had provided erroneous results. The experiments had been carbon limited because carbon dioxide was prevented from entering the test vessels. The atmosphere had been ignored as a carbon source. This important limnological experiment provided strong evidence to refute the carbon limitation theory. In subsequent whole-lake experiments using combinations of phosphorus, nitrogen, and carbon, limnologists at ELA were able to show that phosphorus control would indeed control eutrophication in most lakes (Schindler, 1974, 1977). In most parts of the world, control of phosphorus input is now used as the basis for controlling eutrophication.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 87 webs, termed "biomanipulation," to reduce populations of nuisance algae in situations where nutrient and water inputs cannot be altered sufficiently (Shapiro et al., 1975; Shapiro and Wright, 1984; Shapiro, 1995). Biomanipulation controls algal blooms by maximizing the population of grazing zooplankton. The zooplankton population can be increased by minimizing the population of zooplanktivorous fish by establishing large populations of piscivorous predators. Carpenter et al. (1985) developed a set of specific predictions on the cascading impacts of shifting populations of large piscivores on the primary producers of lakes and tested the predictions through a series of whole-lake experiments (Carpenter and Kitchell, 1993). These experiments supported the basic biomanipulation concept, although some limnologists have criticized it (see Shapiro, 1995). The efficacy of biomanipulation as a management tool is currently being explored in Lake Mendota, Wisconsin, through a collaborative effort involving the University of Wisconsin–Madison and the Wisconsin Department of Natural Resources (Kitchell, 1992). The response of limnologists to improve understanding of the eutrophication problem is one of the important success stories in ecological science. Key investigations involved both fundamental and applied science. Practical solutions were implemented that reversed the trend of increasing eutrophication in many important lakes, including Lakes Erie, Michigan, and Tahoe. However, many lakes continue to suffer from eutrophication problems in part because of the economic difficulties involved in implementing effective controls on nonpoint nutrient sources. Development of cost-effective strategies for controlling nonpoint sources of nutrients, minimizing their effects, and restoring degraded lakes remains a key research need. Moreover, many fundamental and practical limnological questions remain unanswered or incompletely resolved. For example, limnologists cannot predict which specific assemblage of blue-green algae will result from specific nutrient loadings, nor can they predict which other algae will replace them when nutrient levels are decreased or biomanipulation is used. Accumulation of Toxic Pollutants Municipal and industrial waste discharges, urban runoff, and agricultural runoff all contain trace concentrations of toxic compounds (Novotny and Chesters, 1981; Lazaro, 1990). Often present in these discharges are organochlorine compounds, some of which are among the most toxic substances known to humans. Examples include dioxins and PCBs (poly- chlorinated biphenyls), which enter waterways from industrial sources, as well as DDT, toxaphene, and many other pesticides, which enter lakes and streams via runoff from agricultural lands and managed forests. Originally, people believed that release of toxic compounds in trace

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 88 quantities caused little harm to the environment because concentrations in water were very low—usually in the part per billion, trillion, or even quadrillion range. However, such views did not account for biomagnification in aquatic food chains (Gilbertson, 1988; Peakall, 1993). Many limnological studies have shown that in the passage up food chains, organochlorine compounds can accumulate in predatory fish or fish-eating birds and mammals at concentrations up to 10 million times greater than those in lake water. Even in very remote areas, the concentrations of organochlorine compounds in fish and marine mammals can be high enough to require that consumption by humans be limited. Much of the runoff of toxic pollutants is episodic in nature, yet past research has focused mostly on long-term ambient conditions. Limnologists are developing better approaches for capturing episodic pulses, identifying their consequences, and determining the synergistic effects of multiple contaminants and sources (Davies, 1991; Herricks et al., 1994). Limnologists also continue to study long-term, sublethal effects of toxic compounds on organisms and populations; many management decisions are based on lethal doses, whereas the true long-term consequences may result from more subtle effects. Finally, limnologists are advancing knowledge of the effects of toxic compounds that have accumulated in the sediments of rivers and lakes, but much more needs to be learned about the long-term effects of these compounds. It is known, however, that some pesticides have subtle, even intergenerational effects on endocrine systems (Colborn and Clement, 1992; Colborn et al., 1993). In summary, limnologists, along with other water scientists, have a long history of identifying the sources, routes, and consequences of pollutants from urban, industrial, and agricultural areas. Limnologists have been and will continue to be instrumental in identifying the linkages among waste discharges, runoff, water quality, and ecosystem functioning (see Box 3-7) Their involvement in developing solutions to the problems of nonpoint-source pollution from runoff will be especially critical as these problems increase. Acid Rain and Toxic Air Pollutants Acid rain has been known as a localized problem resulting from industrial development since the middle of the nineteenth century; in this century it has become recognized as a broad regional to global environmental problem, with major occurrences in Europe, eastern North America, the former Soviet Union, and more recently in East Asia. It is a consequence of two major human activities. One is the use of fossil fuel. For example, many sources of coal contain substantial amounts of sulfur, which upon combustion is released to the atmosphere as sulfur dioxide (SO2). In addition, the high-temperature combustion of all fossil fuels,

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 89 BOX 3-7 INVOLVEMENT OF LIMNOLOGISTS IN IMPROVING LAKE WATER QUALITY: TWO EXAMPLES Two places where limnologists have helped develop plans to improve lake water quality are Lake Tahoe, in the Sierra Nevada of northern California, and Lake Mendota, in Madison, Wisconsin. Lake Tahoe, the third-deepest lake in North America, is known for its high water clarity. Because of its unique scenic beauty, the basin surrounding the lake became an attraction for naturalists and developers. Since 1960, when Lake Tahoe hosted the winter Olympics, the resident population has grown from 20,000 to more than 50,000. Each year, more than 12 million tourists visit the lake. The development of Lake Tahoe during the 1960s brought with it a reduction in water clarity and a doubling of phytoplankton production. By the late 1960s, water clarity had decreased from 40 meters (130 feet) to 30 meters (100 feet); today, water clarity is close to 24 meters (80 feet). Extensive algal mats developed along the shoreline in late spring, creating a decaying scum. The visible signs of eutrophication concerned citizens and conservationists. Charles Goldman, a limnologist at the University of California, Davis, determined that the nitrogen content of the lake had increased with urbanization, and this had promoted the growth of excess algae (Goldman, 1981, 1985, 1988, 1989). With the increase in urbanization had come an increase in nitrogen from septic systems, lawn fertilizers, stormwater runoff from impervious surfaces, and erosion of topsoil associated with land clearing and development (Goldman, 1981, 1985, 1988, 1989). Goldman's work led to the development of a new sewage disposal plan for the basin. Working with a group of environmental engineers, he facilitated conversion of the septic system to a municipal sewage treatment network that incorporated special facilities for removing nitrogen from the sewage. Goldman's work continues to provide a basis for educating the public and is the foundation of conservation efforts to control the effects of future development on Lake Tahoe. Lake Mendota, a prominent feature of the landscape of Madison, Wisconsin, has a long history of limnological research (Brock, 1985; Kitchell, 1992). Despite some major successes in mitigating the effects of pollutants from point sources, the lake's water quality continues to have undesirable attributes that are direct consequences of nutrients entering the lake from nonpoint sources of pollution. Two Wisconsin limnologists, Patricia Soranno and James Kitchell, are involved in efforts to reduce the impact of these excess nutrients. One program involves manipulating the food web to increase water clarity by increasing the number of predators of zooplankton-consuming organisms, thus lowering the populations of these secondary consumers and increasing the populations of algae-eating zooplankton (Kitchell, 1992). A second effort involves an assessment of the effects of land use on nonpoint-source pollutants. Because agricultural land use dominates the Lake Mendota watershed (presently accounting for 86 percent of the surface area), it contributes most of the basin's nonpoint-source nutrient loading. Current land-use trends are to urbanize existing agricultural land, and these changes are expected to degrade water quality further (Soranno et al., in press). These shifts are being evaluated in a major project sponsored by the Wisconsin Department of Natural Resources.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 90 especially in internal combustion engines of automobiles and trucks, partially oxidizes atmospheric nitrogen to the compounds nitric oxide (NO), and nitrogen dioxide (NO2) (collectively referred to as NOx). Once released to the atmosphere, sulfur and nitrogen oxides are oxidized further to sulfuric acid and nitric acid. The other major human activity leading to acid rain is the smelting of sulfide ores of various metals—including iron, copper, and lead—which releases SO2 to the atmosphere. Sulfur dioxide and NOx have residence times in the atmosphere of up to a few days, by which time they can spread hundreds of kilometers from their sources. In this way, they are able to create broad patches of air pollution over, for instance, much of Europe and most of eastern North America (National Research Council, 1981). The arctic haze phenomenon also is caused by sulfate aerosols, which are carried north in winter from industrial sites in Eurasia (Barrie, 1986; Welch et al., 1991). The polar ice caps show evidence of increasing deposition of sulfate and nitrate beginning with the industrial revolution (Boutron and Delmas, 1980; Wolf and Peel, 1985). Acid rain is neutralized readily if it falls on fertile soils rich in bases, the more so if the soils contain particles of calcium carbonate weathered from soft limestone rocks. If, however, it falls on infertile soils, poor in bases and derived from hard, slowly weathering rocks such as granite and quartzite, the acid is neutralized only partly by soil bases and by microbial and plant uptake of nitrate. The remainder, chiefly sulfuric acid, is washed into streams and lakes, where further neutralization may take place owing to sulfate reduction in lake sediments and loss of nitrate by algal assimilation or denitrification in the sediments (Cook et al., 1986; Brezonik et al., 1987; Rudd et al., 1988) (see Box 3-8). If neither soils nor aquatic sediments can neutralize acid rain completely, the pH of the lake or stream water declines, causing a variety of deleterious effects. marked changes occur in the species abundance and composition of all types of aquatic communities, including open-water and shoreline algae, larger aquatic plants, open-water microscopic zooplankton, bottom-living invertebrates, and fish. For instance, increasing acidity can interfere with spawning, so that the population fails to reproduce (Dillon et al., 1984). Alternatively, embryonic development or the development of species in juvenile life stages may not take place normally (Rosseland and Staurnes, 1994). Acidification of lake and stream water also releases toxic forms of aluminum (Al 3+ and AlOH2+) that clot the mucus on fish gills, interfering with their function. Finally, acidification can alter food webs. For example, acidification may lead to a reduction in prey species of minnows and invertebrates so that predators such as lake trout starve to death (Schindler et al., 1985). Minns et al. (1990, 1992) estimate that acid precipitation has eliminated many species of organisms in thousands of sensitive lakes in eastern Canada alone. They further

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 91 predict that recently imposed controls on sulfur oxide emissions will reduce acidification damage only to about half of that caused by emissions at early 1980s levels. BOX 3-8 INTERNAL ALKALINITY GENERATION In the early 1970s it was widely believed that lakes acidified by acid precipitation would not recover. Geological materials in the catchments of lakes were believed to be the primary source of alkalinity for neutralizing acid in rain and snow. It was thought that these would become exhausted, after which neutralization of incoming acids could not occur. Early acidification models were constructed on this belief. This view was peculiarly at variance with limnological studies. More than 30 years earlier, G. E. Hutchinson (1941) and C. H. Mortimer (1941-1942) had published observations showing that alkalinity was produced by anoxic lake sediments, although the mechanisms by which this occurred were not elucidated. A whole-lake experiment at Canada's Experimental Lakes Area quantified the extent of in-lake alkalinity production and revealed that when sulfuric acid was the primary strong acid added, microbial reduction of sulfate to sulfide was the most important process (Cook and Schindler, 1983; Cook et al., 1986). Subsequent whole- lake experiments with nitric acid showed that algal uptake of nitrate and microbial denitrification to N2 similarly neutralized incoming nitric acid (Rudd et al., 1990). Investigations of lakes in other regions showed that the acid-neutralizing processes are widespread in lakes (Baker et al., 1986; Rudd et al., 1986; Schindler, 1986; Brezonik et al., 1987). Although the microbial in-lake acid neutralizing mechanisms are not 100 percent efficient, they greatly reduce the effect of acid precipitation and allow lakes to recover when acid precipitation is reduced. Limnologists have developed successful models to predict the rate of internal alkalinity generation in different lakes with different inputs of sulfuric and nitric acids (Kelly et al., 1987; Baker and Brezonik, 1988). Limnologists have shown that the degree of biological change occurring in aquatic communities as a result of acid rain can be related clearly to the degree of acidification (Brezonik et al., 1993), but in only a few cases can the chain of cause and effect be specified in detail; these cases relate chiefly to fish of recreational and economic importance, in particular salmonids (Baker et al., 1994). Simple direct responses by individual species to changes in chemical conditions can be ruled out as the mechanisms underlying many organismal responses to acidification (Webster et al., 1992). Likewise, it has been shown that standard laboratory bioassays are of limited use in predicting organismal responses to acidification in actual ecosystems (Gonzalez and Frost, 1994). Despite expenditures of many millions of dollars on research related to acidic deposition, especially

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 92 during the 1980s, information about the full range of ecosystem effects of acid rain is lacking for nearly all groups of aquatic organisms other than commercially important fish. Therefore, it still is not possible to predict with great accuracy the long-term consequences for the functioning of aquatic ecosystems of the alterations brought about by acid stress, and further research is needed. Vinyl curtain being placed in a lake for an experiment on acidification. The curtain divides the lake into two basins. One will be treated to lower the pH, and the other will be used as an experimental control. SOURCE: Dave Cornelius, University of Wisconsin, Center for Limnology. Studies by paleolimnologists show that many ecosystems have not come to equilibrium with the acid loading now affecting them (Charles et al., 1990). Limnologists have also shown that climatic warming and acid deposition may have synergistic effects (Bayley et al., 1992a; Lazerte, 1993; Schindler et al., in press, b). Therefore, ecological and biogeochemical responses induced by acid rain can be revealed only by whole-ecosystem experiments and long-term studies over several decades. Too few such studies have been carried out, and more are needed in different terrains with differing biotic communities. Now that many, but by no means all, countries have passed legislation to partially control emissions of sulfur, the continuation of studies of ecological effects of acid rain has been curtailed severely, as have studies of the recovery of ecosystems damaged by acid deposition. For example, research funds to study acidification problems have plummeted in the

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 93 United States since 1990, when Congress passed the Clean Air Act Amendments, which call for a decrease in sulfur oxide emissions by about 50 percent by the end of the century. Even with controls on sulfur emissions, long- term atmospheric deposition of nitrate- and ammonia-nitrogen remains an uncontrolled threat to many aquatic (and other) ecosystems. The effects of nitrogen deposition have received far less study than the toxic effects associated with the deposition of sulfate and its associated hydrogen ions, and increased attention to this issue is warranted. Indeed, the EPA recently announced that it would not propose a new acid deposition standard to protect sensitive areas from nitrogen deposition because ''scientific uncertainty" makes it "difficult to determine the appropriate level of a standard or standards at this time" (EPA, 1995). This inaction is of particular importance to individuals in New York who are concerned about protecting vulnerable areas in the Adirondack Mountains (Renner, 1995). Along with sulfur and nitrogen, fossil fuels contain a variety of toxic metals, among them mercury, lead, and cadmium. Upon combustion these are emitted to the atmosphere on particulate matter that can be transported over long distances. Smelters add to the atmospheric loading of these metals. In addition, the combustion of fossil fuels produces a variety of polycyclic aromatic hydrocarbons that can be transported in the atmosphere by particulate matter. Some of these, such as benzo-a-pyrene (also present in tobacco smoke), are extremely toxic. Other organic micropollutants distributed regionally through the atmosphere are a consequence of the agricultural use of herbicides and insecticides. Still other organic micropollutants (such as dioxins and PCBs) are emitted to the atmosphere—as well as directly to aquatic ecosystems—as a result of industrial activity. Although PCBs and many chlorinated insecticides have been banned from manufacture and use in the United States, the legacy of past use still provides a source of these materials. Some banned insecticides such as DDT are still used in other countries, such as Mexico, and enter U.S. ecosystems as a result of long-range atmospheric transport. The deleterious effects of these metal and synthetic organic compounds upon inhabitants and users of aquatic ecosystems are less well documented than those of acid rain. However, in the case of mercury and PCBs, warnings have been issued in more than 30 states concerning the consumption by humans of fish from numerous lakes and rivers, including many in the Great Lakes states. Atmospheric transport and deposition is the major source of mercury in these regions (Swain et al., 1992). Eisenreich and coworkers (1979) have shown that the principal mechanism by which PCBs enter Lake Superior is long-range atmospheric transport and deposition by rain, snow, and dryfall. Dioxins and PCBs also have been found in sediments and biota of Siskiwit Lake, an otherwise pristine water body on Isle Royale in Lake Superior (Swackhamer and Hites, 1988). Isle Royale,

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 94 a U.S. national park, has no permanent human inhabitants, and the watershed for Siskiwit Lake is wholly forested. Thus, there are no sources of organochlorine compounds in the watershed; long-range atmospheric transport of these compounds is the only logical explanation for their presence in the lake. In Canada, airborne contamination of lakes has resulted in consumption advisories for fish throughout Ontario and in regions as remote as the Yukon Territories (Kidd et al., 1995b) (see Box 3-9). The presence of metals and synthetic organic compounds is a concern because many of them may cause birth defects, cancer, or immunological and reproductive disorders (Colborn and Clement, 1992; Colborn et al., 1993). Many bioaccumulate to such high levels that they are toxic to the end-members of aquatic food chains. In the case of mercury, rules of the U.S. Food and Drug Administration state that fish cannot be sold if the concentration exceeds 1 part per million (ppm). In Canada, the corresponding threshold for commercial sale is 0.5 ppm; that value is exceeded in many areas, most notably in reservoirs (Rosenberg et al., 1995). The Minnesota Department of Health recommends that pregnant women eat no more than one meal per month of fish containing more than 0.15 ppm of mercury. Minnesota has a lake water standard for mercury concentration BOX 3-9 LONG-RANGE TRANSPORT OF TOXIC COMPOUNDS TO LAKE LABERGE, YUKON TERRITORIES Lake Laberge is widely regarded as a symbol of remote northern wilderness as the result of the popular poem "The Cremation of Sam McGee," written by Robert W. Service during the Yukon gold rush. The catchment of the lake is still largely uninhabited except for the city of Whitehorse, above the lake on the Yukon River. The lake is large (200 km2) and served as an important source of protein for local indigenous peoples. In 1992, the fishery of the lake was closed because of high toxaphene concentrations in the fish. Concentrations of DDT and PCBs also were higher than in other large lakes of the Yukon. Initially, investigators hypothesized that the contamination was caused by surreptitious dumping of toxaphene in the lake. However, detailed studies of toxaphene concentrations and stable isotopes of nitrogen in Laberge and other lakes of the area, which had lower toxaphene concentrations, showed that the higher toxaphene concentrations in Laberge fish may be explained by the fact that food chains were one step longer in Laberge than in other lakes of the area (Kidd et al., 1995a,b). The toxaphene entered the lake via contaminated rainfall from the United States and Eurasia and then accumulated in the fatty tissues of aquatic organisms, with higher levels of toxaphene found at higher levels of the food chain (see Figure 3-3).

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 95 FIGURE 3-3 Toxaphene concentrations in species at various levels of the food chain in three Yukon lakes: Laberge (○, solid line), Fox (•, dash-dot line), and Kusawa (▪, dashed line). The stable nitrogen isotope (§ 15N) value shown on the horizontal axis is a surrogate measure for position on the food chain; § 15N increases from prey to predator by an average of 3.4 per trophic level. The data show that species at the highest level of the food chain accumulate the largest amount of toxaphene and that lake trout and burbot in Lake Laberge are nearly a trophic level higher (and thus several times more contaminated) than in other lakes. Organisms shown on the figure are as follows: LT, lake trout; BT, burbot; LW, lake whitefish; RW, round whitefish; CL, least cicso; LS, longnose sucker; ZO, zooplankton; GA, Gammarus sp.; CH, chironomid (subfamilies Tanypodinae, Prodiamesinae, and Chironomidae); SN, snail (family Lymnaeidae); and TR, tricopteran (family Limnephilidae). SOURCE: Reprinted, with permission, from Kidd et al. (1995b). © 1995 by Science. of only 7 nanograms (ng) per liter, intended to protect humans from the consumption of contaminated fish. In parts of the state, this standard may be inadequate because in some lake waters with mercury levels of only 2 ng per liter, the concentration in fish exceeds 0.45 ppm—three times the consumption advisory for pregnant women. Larger, older predatory fish at the top of the aquatic food chain are of particular concern

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 96 because they accumulate the highest levels of mercury. Figure 3-4 provides an example of advisory recommendations for an individual lake in northern Minnesota contaminated by atmospheric deposition of mercury. Wildlife, of course, cannot respond to fish advisories, nor do all humans heed the warnings. Birds such as belted kingfishers, common loons, ospreys, and bald eagles consume large amounts of fish, as do mink and river otters among the mammals. In Minnesota there is evidence that mercury accumulation may be impairing reproduction by common loons. There is also an indication that walleye reproduction may be affected. Elevated concentrations of mercury have been detected in some mink and river otters. Researchers attributed the death of a Florida panther—a rare and endangered species—in the Everglades in 1989 to elevated levels of mercury found in the animal's liver, leading to concern about mercury pollution throughout the south Florida ecosystem (Jordan, 1990). In the Great Lakes and below pulp mills, organochlorine compounds delivered via the air and other routes have been linked with reproductive FIGURE 3-4 Minnesota fish consumption advisory, 1994. "Vacation" refers to those who eat the particular fish species only during short vacations; "season" refers to those who consume the fish seasonally; and "annual" refers to those who consume the fish year-round. SOURCE: Minnesota Department of Health, 1994.

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 97 problems—including sterility, birth defects, unsuccessful hatching, and deformities in offspring—in fish-eating birds (Gilbertson et al., 1991). In northern Canada, indigenous peoples who eat large quantities of aquatic organisms often have unacceptably high concentrations of mercury in their blood and hair (Lockhart, 1995). The likelihood of synergistic interactions among diverse pollutants from atmospheric sources needs far more investigation. For example, a number of organochlorine compounds are now known to have similar effects on enzyme and hormone systems, indicating that they may have additive or synergistic effects (Colborn and Clement, 1992). Another example of such synergism is mercury and acid rain. Bioaccumulation of mercury along food chains depends in the first instance on its transformation by microbes from the inorganic form to methylmercury, which has greatly increased mobility and biological uptake. Several studies have shown that the rate of methylation increases upon lake acidification (Xun et al., 1987; Ramlal et al., 1993); this may provide an explanation for the typically higher concentrations of mercury observed in fish from lakes with low pH (Wiener et al., 1990). Limnologists, in association with a variety of other scientists (fisheries biologists, toxicologists, aquatic chemists, hydrologists, atmospheric scientists), have been centrally involved in the study and solution of problems caused by acid rain and airborne toxic compounds. Table 3-1 chronicles some of the key scientific discoveries concerning the effects of acid rain and toxic air pollutants on aquatic ecosystems. BIOLOGICAL CHANGES IN AQUATIC ECOSYSTEMS All of the physical and chemical changes described above can markedly affect the populations that inhabit inland waters. Physical changes (such as dam construction and global warming) and chemical inputs (from acid rain, runoff, direct waste discharges, airborne toxic compounds, etc.) can change the structure of the aquatic food web and create conditions in which native species cannot survive. In addition to causing biological changes via physical and chemical changes, humans have affected aquatic biota in more direct ways: by introducing exotic species, altering aquatic communities to support game fish, and causing the extinction of native species. Exotic Species Introduction Sometimes intentionally and sometimes inadvertently, humans have substantially expanded the geographic ranges of many species. For example, about 20 percent of the 5,523 vascular plant species of eastern North America have been introduced (Fernald, 1950). In many cases, species

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 98 have been introduced into regions to which they are foreign. Other cases involve the shifting of species distributions within narrower geographic regions. In either situation, introduced species can have substantial effects on aquatic habitats; they may shift the occurrence or abundance of native species, change important ecosystem functions, and interfere with desired human uses of the water body. Limnologists are important in developing assessments of the consequences of inadvertent introductions. They also can play a key role in the development of realistic predictions for intentional introductions. Finally, limnologists can help create management strategies to minimize the impacts of introductions that have already taken place. TABLE 3-1 Some Significant Discoveries Concerning the Effects of Atmospheric Deposition On Aquatic Ecosystems, 1957-1995 Date Reference Topic 1957 Mackereth Showed the degree of acidification of English lakes to be related to substrate geology 1959 Dannevig Recognized the relationship among acid rain, surface water acidity, and disappearance of fish in Norway 1967 Woodwell et al. Reported biological magnification of DDT in aquatic food chains 1971 Winchester and Nifong Indicated atmospheric precipitation as an important source of trace metals in Lake Michigan 1974 Almer et al. Showed a reduction of biodiversity in phytoplankton, zooplankton, and fish in acidified Swedish lakes 1977 Murphy and Rzeszuko Found atmospheric deposition to be an important source of PCBs to Lake Michigan 1978 Ferguson et al. Implicated air pollution and associated acid deposition in the disappearance of Sphagnum mosses from northern English bogs during the industrial age 1979 Cronan and Schofield Showed toxicity to fish of aluminum released from soils by acid deposition 1980 Davis and Berge Inferred pH profiles in dated cores of lake sediment from diatom stratigraphy 1985 Schindler et al. Demonstrated that adverse effects of acid deposition on fish can occur via harm to food organisms 1992 Wright et al. Showed rapid recovery of catchments following reduced acid loading 1995 Muir et al. Demonstrated high concentrations of organochlorine contaminants in arctic marine fauna due to long-range transport and bioaccumulation Many exotic species, including the sea lamprey, alewife, and zebra mussel, have invaded the Great Lakes over the past century. In response, a variety of nonnative fish species have been introduced intentionally, in some cases to control invading species and in other cases to replace fish eliminated by the invaders. Many of the invading species entered the

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 99 lakes after large canals and locks were constructed to allow oceangoing commercial ship traffic in the upper lakes. In essence, the Great Lakes have served as an unintentional laboratory for investigating the effects of invading and introduced exotic species because so many have established themselves there (Mills et al., 1994). One exotic organism that has received considerable recent attention is the zebra mussel, Dreissenia polymorpha (Herbert et al., 1991). Zebra mussels were introduced to the Great Lakes in 1986, when a ship from Europe discharged its ballast water into the St. Clair River between Lakes Huron and Erie (Roberts, 1990). The zebra mussel was not detected until 1988, when two Canadian students discovered the species in a sample from Lake St. Clair. By that time, the mussel had already moved downstream into Lake Erie, where its population exploded. Since then, the mussel has spread throughout the Great Lakes and into other waterways, including the Mississippi and Hudson rivers. Zebra mussels have a wide variety of effects on invaded water bodies. They filter vast quantities of water to obtain phytoplankton for their diet. Zebra mussel filtering is likely responsible for a recent doubling in water clarity in Lake Erie (Holland, 1993). Not all effects are positive, however. The National Biological Service estimates that this invader will cost $5 billion to industries, municipalities, and private citizens by the year 2000 because of its ability to attach to almost any hard surface. Negative effects range from clogging of water intake pipes for industries and water treatment plants to loss of important native mussels and clams that cannot compete with the invader. For example, at a water treatment plant on Lake Erie, a combination of zebra mussels and ice completely blocked the intake, so that the city of Monore, Michigan, had to impose emergency water conservation measures and close businesses and schools. Reopening the water intake cost $250,000; completely retrofitting the system to prevent such problems in the future will cost $6 million (Roberts, 1990). Zebra mussels also threaten native clams and fish spawning beds because they can literally cover them and thereby get first access to the food supply. The mussels' phenomenal numbers (a mature, thumbnail-sized female can produce a million eggs) and prodigious appetite have been found to produce three striking effects on waters they inhabit: (1) precipitous drops in phytoplankton populations, (2) increased water transparency, and (3) greatly enhanced growths of filamentous algae. The net effect is a shift in algal community structure, which can impact higher trophic levels (including fish) in aquatic food webs. Since 1991, the federal government has appropriated $10.3 million to the Sea Grant program for university-based research on zebra mussels and public education efforts to help control their spread; various water management agencies at the federal and state levels (such as the U.S. Army Corps of Engineers) also have research programs related to this

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 100 pest. Sea Grant's zebra mussel research has been conducted in six areas: (1) biology and life history, (2) effects on ecosystems, (3) socioeconomic analyses, (4) control and mitigation, (5) prevention of new introductions, and (6) reduction of spread. Limnologists at academic institutions have been involved in a wide range of research efforts within these categories. For example, limnologists have found Dreissenia polymorpha to be genetically highly diverse; this may allow it to spread and adapt to new environments. Laboratory- reared larvae have been observed to postpone settlement and attachment and to prolong their free-swimming period for an additional seven weeks beyond their normal time in this life form. These delays could have profound effects on the dispersal characteristics of zebra mussels. Although it is not possible to eliminate zebra mussels from water bodies where they have become established, limnologists are studying a variety of physical, chemical, and biological control measures. These include the use of ultraviolet radiation to kill larval forms of zebra mussels, application of high-voltage fields on water intake pipes, use of various chemicals to kill adults or prevent larval attachment, and isolation of bacteria that inhibit larval attachment or cause disease in zebra mussels. Another invader of the Great Lakes from Europe via oceangoing vessels is Bythotrephes cederstroemi, a large crustacean zooplankton. This species is less conspicuous to the public eye than the zebra mussel but is nevertheless capable of causing significant economic damage. A voracious predator of other zooplankton, Bythotrephes was first observed in Lake Huron in December 1984, detected soon after that in Lake Erie, and present in all of the Great Lakes by 1988. It spread rapidly throughout Lake Michigan after its first appearance in the north end in 1986, and it has moved into lakes connected to the Georgian Bay of Lake Huron and into northern Minnesota, which is outside the drainage basin of the Great Lakes. Several groups of limnologists are investigating the role of Bythotrephes in the Great Lakes ecosystem (Lehman, 1991). Changes in the zooplankton population of Lake Michigan immediately followed the increase of Bythotrephes. The abundance of Daphnia decreased sharply, with changes occurring in body size that would be expected from selective predation by Bythotrephes. Daphnia is an important food for several species of game fish, so the change may threaten the vitality of important fish populations. Bythotrephes is a poor food for small game fish because it has a stiff tail spine, a centimeter long in the largest individuals. However, it is eaten freely by the alewife (Alosa pseudoherengus), an undesirable exotic fish species in the Great Lakes. Since the production of a full-grown Bythotrephes involves the consumption of many Daphnia, the net effect on the production of game fish could be negative. Apart from its indirect effect on fisheries, Bythotrephes is a direct nuisance to net fisherman. Its long tail spines stick to nylon nets, and animals accumulate on nets in slimy masses, making the nets difficult and unpleasant to

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 101 handle. There is no obvious technology to control Bythotrephes, and there appears to be no predator in the Great Lakes capable of controlling it, except perhaps the alewife, itself an undesirable exotic species whose population is now controlled by large predatory nonnative fish (salmon) that have been stocked in the lakes. Whereas the zebra mussel and Bythotrephes were introduced to the Great Lakes accidentally, introductions of nonnative species are often intentional. Stocking of fish, and in some cases fish food, in particular, is a common management practice. More than 25 percent of inland fish caught in the United States are nonnative stocks (Moyle et al., 1986). The effects of such introductions often are poorly anticipated and adverse to native populations. Spencer et al. (1991) described a case in which the negative effects of the stocking the opossum shrimp (Mysis relicta), a forage species for fish, extended out of Flathead Lake, Montana, one of the largest natural lakes in the western United States, to eagles and bears that inhabit the area around it. Eagle and bear populations declined markedly as the introduced shrimp reduced the number of salmon, on which the animals had depended as a major food source. The salmon decline was linked to direct competition between juvenile salmon and opossum shrimp, which ultimately depend on the same prey species. Another major example of the purposeful introduction of nonnative species is the widespread stocking of salmonid fish into lakes in the mountains of western North America. Fishless alpine lakes were stocked with eastern brook trout, European brown trout, Atlantic salmon, arctic char, smallmouth bass, and many other species. Up to 80 percent of the fishless alpine lakes in the U.S. Rocky Mountains and 20 percent of the lakes in Canadian mountain national parks have been stocked with nonnative populations (Donald, 1987; Bahls, 1992). Limnologists have demonstrated that in fishless lakes, the original invertebrate predators, such as large calanoid copepods, benthic crustaceans, and midge larvae, were extirpated by stocked fish (Lamontagne and Schindler, 1994; Paul and Schindler, 1994); this set off changes in communities that increased algal biomass in lakes, even in pristine areas (Leavitt et al., in press). In lakes where fish were present, introduced species often displaced native stocks, in some cases eliminating them completely (see Box 3-10). In other cases, native species were eliminated prior to stocking by deliberately treating the lake with rotenone or toxaphene (Miskimmin and Schindler, 1993, 1994; Miskimmin et al., 1995). Pacific salmon have also been introduced into the Great Lakes. The salmon were initially intended to replace native lake trout that were lost largely because of the effects of the sea lamprey, which entered the Great Lakes from the Atlantic Ocean through ship canals built in the nineteenth and early twentieth centuries (Christie, 1974). The salmon are maintained only through active management programs. A substantial portion of their

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 102 forage base involves two other species that invaded the Great Lakes, the alewife and the rainbow smelt, each of which has had large-scale effects on the lakes' food webs. The mechanism for the alewife's introduction to the Great Lakes is unclear (Scott and Crossman, 1973). Rainbow smelt were successfully introduced into Crystal Lake, a small lake connected to Lake Michigan by a stream, in 1912 after several failed attempts at direct establishment in the Great Lakes (Evans and Loftus, 1987). This population eventually expanded throughout the Great Lakes. Once established, rainbow smelt and alewife ultimately caused a substantial reduction in populations of native fish species (such as bloaters, lake whitefish, and cisco) through the combined effects of competition and predation (Crowder, 1980; Evans and Loftus, 1987; Crossman, 1991; McClain, 1991). Rainbow smelt are currently spreading through inland lakes throughout the Midwest with as yet unknown but likely important consequences for native species and food webs (Evans and Loftus, 1987). BOX 3-10 EFFECTS OF FISH STOCKING IN NORTH AMERICAN ALPINE LAKES Even alpine lakes at high elevations in national parks of the West have not been spared the introduction of exotic species. In the early twentieth century, brown trout from Europe, brook trout and Atlantic salmon from eastern North America, rainbow trout from several regions, golden trout from the southwestern United States, arctic char, rainbow trout from several locations, and several races of cutthroat trout, especially the Yellowstone cutthroat, were widely introduced into waters where they were not native, including naturally fishless alpine lakes (Donald, 1987; Bahls, 1992). Although there were few studies of aquatic communities done in conjunction with the stocking, the few contemporary studies (Anderson, 1980) and later paleoecological studies (Miskimmin and Schindler, 1993; Lamontagne and Schindler, 1994) showed the impoverishment of invertebrate communities by stocked fish. In some cases, the eliminated species did not return (Paul and Schindler, 1994). Similar effects, dating to pre-World War I times, have been identified by paleolimnological studies (Pechlaner, 1984). Mosquitofish introduced in 1924 to control biting insects and other tropical fish released by hobbyists into the hot springs of Banff National Park eliminated the rare Banff longnose dace. The native bull trout is now endangered or eliminated from much of the West by interbreeding with introduced brook trout. The hybrids are sterile. Important invasions of aquatic ecosystems have not been limited to animal species. Several important cases, dating back many decades, involve the spread of plant species. The North American aquatic plant Elodea canadensis was introduced into Europe in the early 1800s and had

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 103 enormous economic effects (Hutchinson, 1975). Its populations extended widely throughout canals that were major arteries for shipping industries at the time and made their navigation by horse-drawn barges very difficult. The favor was returned when the Eurasian water milfoil, Myriophyllum spicatum, was introduced to North America in the early twentieth century. This species has proliferated throughout shallow water regions of many lakes, limiting their recreational use and leading to the development of extensive and costly aquatic weed control programs. it also has caused substantial reductions in the populations of many native plants. A range of problems has been associated with the human-caused spread of the water hyacinth, Eichhornia crassipes , from South America throughout much of the world (Sculthorpe, 1967). This free-floating plant proliferates quickly and has seriously clogged many waterways and lakes in the southeastern United States. Similar problems have followed the introduction of other floating plant species, such as Pistia stratiotes (water lettuce) and Salvinia auriculata, which also can cause public health problems by providing refuges for disease-bearing mosquitoes. Purple loosestrife, Lythrum salicaria , which was introduced to North America from Eurasia in the early 1800s, has monopolized wetlands and displaced native plant species throughout the United States and Canada (Stuckey, 1980; Thompson et al., 1987). The plant has attractive flowers that, along with their use as a pollen source for honeybees, are probably responsible for the plant's spread. Community changes caused by such nonnative plants have important deleterious effects on many waterfowl and insect species, which lose access to plant species that had provided their forage base; thus, they are the subjects of active limnological research. An important lesson to be derived from exotic species invasions and introductions is that aquatic communities often are delicately balanced. Shifts caused by invading species can have substantial effects on ecosystem and community structure, as well as on fundamental ecosystem processes, and often these shifts have impacts that are not desirable. For example, Lamarra (1975) showed that common carp, perhaps the most widely distributed nonnative fish in North America, vastly enhances phosphorus return from lake sediments, enhancing eutrophication. Limnologists, along with fisheries biologists, are essential in evaluating such effects and predicting the occurrence and results of future invasions. Addressing the problems caused by exotic species will require a fundamental understanding of a wide range of aquatic ecosystem features, including factors dictating community structures and ecosystem processes that are the basis for much limnological research. Species Extinction Taken to the extreme, the net impact of the varied forms of human effects on inland aquatic ecosystems can threaten entire species with

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 104 extinction. The Nature Conservancy classifies at least 30 percent of all North American fish species as rare, extinct, or at risk of extinction (Master, 1990). The proportion of species in these categories is even higher for crayfish (65 percent) and unionid mussels (73 percent) (Master, 1990). Some aquatic insect species face similar risks of extinction. About one-third of rare, threatened, and endangered species in the United States are associated with wetlands (Niering, 1988). In general, the danger of extinction for a species is related to its distribution. Threats of extinction due to human-caused environmental effects are most severe for species that occur in only a small number of habitats. In some cases, however, threatened species can be distributed fairly widely. Causes of extinction include physical disruption of habitats, the generation of chemical stress across ecosystems, and the introduction of species that are major predators, parasites, or competitors of native species. These various mechanisms sometimes interact. For example, the impact of invaders on native fish species in California streams is more severe where the natural flow regime in a stream has been modified by humans (Baltz and Moyle, 1993). Introduction of nonnative species, often through fisheries management practices, appears to be a widespread cause of threatened extinctions (Lodge, 1993). Limnologists are addressing the problem of species extinction in two ways. First, they are gathering information on the distribution of native species and on factors that influence their densities in their habitats. This information can be used to develop management practices that minimize both the occurrence of extirpation within particular habitats and, ultimately, overall species extinctions. Second, limnologists are working to develop an understanding of aquatic ecosystems sufficient to predict the effects of the loss of a species on the entire community and on ecosystem processes. Although some ecosystem processes are fairly immune to the loss of a single species (Frost et al., 1995), in other situations fundamental ecosystem patterns and processes are influenced strongly by the presence or absence of a single species (Huntly, 1995). Developing general understanding of linkages between ecosystems and species is currently an area of substantial research interest in aquatic and terrestrial ecology (Jones and Lawton, 1995). ENHANCING THE ROLE OF LIMNOLOGY IN FRESHWATER ECOSYSTEM MANAGEMENT In summary, limnologists have played important roles in the development of scientific knowledge needed to manage and protect freshwater ecosystems. Limnologists have provided scientific input on questions such as how land use affects water quality, how wetlands influence global warming and the global cycling of carbon, how wastewater discharges

CONTEMPORARY WATER MANAGEMENT: ROLE OF LIMNOLOGY 105 affect water quality and aquatic communities, how fossil fuel emissions lead to the degradation of aquatic systems, and what mechanisms lead to the deterioration of lakes and rivers via cultural eutrophication. Advances in knowledge achieved by limnologists and aquatic scientists in related fields have led to plans for long-term management of important aquatic ecosystems (see, for example, Box 3-11). In limnology as in other fields of science, answering some questions reveals additional complexities of the systems under study and creates BOX 3-11 ROLE OF LIMNOLOGISTS IN GREAT LAKES MANAGEMENT Limnologists have played important roles in cleanup and management of the Great Lakes. In the early 1960s, pollution was rampant in the lower Great Lakes. Al Beeton, a limnologist at the University of Michigan, showed from historical records how much the chemistry and biology of the lower Great Lakes had changed since the early part of the twentieth century (Beeton, 1965). In response to this and other expressions of concern, the governments of the United States and Canada wrote a formal ''letter of reference" to the International Joint Commission (IJC) asking the commission to examine whether the lower Great Lakes were polluted and, if so, to identify the causes and cures. Richard Vollenweider, a Swiss limnologist who moved to Canada in 1969, had earlier identified phosphorus and nitrogen as the principal causes of eutrophication, which was occurring in the lower Great Lakes. Vollenweider's model of eutrophication became the scientific basis for the phosphorus control program that led to restoration of Great Lakes water quality (Vollenweider, 1968). Jack Vallentyne, a Canadian limnologist, was instrumental in focusing on the need to remove phosphates from detergents as part of the control program (Vallentyne, 1970). This work led directly to the signing in 1972 of the Great Lakes Water Quality Agreement between Canada and the United States. However, by 1978 it was apparent that water quality could not be controlled by looking at water alone. Vallentyne, working as a head of the Ecosystem Committee of the IJC Great Lakes Science Advisory Board, proposed that an ecosystem approach to water quality be used—one that examined water in the context of all the interacting components of air, water, soil, and living organisms in the Great Lakes basin (Great Lakes Research Advisory Board, 1978). Subsequently, the IJC incorporated an ecosystem approach to environmental management into the Great Lakes Water Quality Agreement of 1978 (Vallentyne and Beeton, 1988). The ecosystem approach had been used by limnologists since Lindeman (1942) applied it to Cedar Creek Bog, Minnesota. However, it was not until the signing of the 1978 Great Lakes agreement that the approach entered the political domain (Vallentyne and Beeton, 1986). Now, the ecosystem approach is accepted as management policy in the United States, Canada, and Europe.

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To fulfill its commitment to clean water, the United States depends on limnology, a multidisciplinary science that seeks to understand the behavior of freshwater bodies by integrating aspects of all basic sciences—from chemistry and fluid mechanics to botany, ichthyology, and microbiology. Now, prominent limnologists are concerned about this important field, citing the lack of adequate educational programs and other issues.

Freshwater Ecosystems responds with recommendations for strengthening the field and ensuring the readiness of the next generation of practitioners. Highlighted with case studies, this book explores limnology's place in the university structure and the need for curriculum reform, with concrete suggestions for curricula and field research at the undergraduate, graduate, and postdoctoral levels. The volume examines the wide-ranging career opportunities for limnologists and recommends strategies for integrating limnology more fully into water resource decision management.

Freshwater Ecosystems tells the story of limnology and its most prominent practitioners and examines the current strengths and weaknesses of the field. The committee discusses how limnology can contribute to appropriate policies for industrial waste, wetlands destruction, the release of greenhouse gases, extensive damming of rivers, the zebra mussel and other "invasions" of species—the broad spectrum of problems that threaten the nation's freshwater supply. Freshwater Ecosystems provides the foundation for improving a field whose importance will continue to increase as human populations grow and place even greater demands on freshwater resources. This volume will be of value to administrators of university and government science programs, faculty and students in aquatic science, aquatic resource managers, and clean-water advocates—and it is readily accessible to the concerned individual.

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