4
Water and the Environment

The significance of the environment—including ecosystem services—to the sustainability of water supplies is often ignored in addressing the study area's water-resource planning. This chapter provides evidence, first that environmental quality depends on maintaining water quality and quantity, and second, that high-quality water supplies depend on environmental quality. To a large degree, environmental quality refers to the area's ecosystems, and without the goods and services of natural ecosystems, sustaining supplies of high-quality water for people will be extremely difficult and expensive. Environmental concerns are central to sustainable water resource planning. Water-resource planners in the study area should recognize that the relationships among ecosystem goods and services and water are dynamic and interactive.

In reviewing the relationships among these services, biodiversity, and water supply and quality, this chapter makes four major points. First, maintaining and enhancing ecosystem goods and services is essential for the economic development and welfare of the study area, especially over the medium and longer terms. This stewardship will enhance the quality of life of the study area's inhabitants; and it will maintain environmental quality, including water quality. Second, to achieve such benefits, it is essential to maintain, and where possible, restore ecosystem structure and functioning (sometimes referred to as ecosystem integrity). Third, biological diversity has great moral, cultural, and aesthetic importance to many societies, as reflected in laws and international agreements that express commitments to protect it. In addition, many ecologists believe



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--> 4 Water and the Environment The significance of the environment—including ecosystem services—to the sustainability of water supplies is often ignored in addressing the study area's water-resource planning. This chapter provides evidence, first that environmental quality depends on maintaining water quality and quantity, and second, that high-quality water supplies depend on environmental quality. To a large degree, environmental quality refers to the area's ecosystems, and without the goods and services of natural ecosystems, sustaining supplies of high-quality water for people will be extremely difficult and expensive. Environmental concerns are central to sustainable water resource planning. Water-resource planners in the study area should recognize that the relationships among ecosystem goods and services and water are dynamic and interactive. In reviewing the relationships among these services, biodiversity, and water supply and quality, this chapter makes four major points. First, maintaining and enhancing ecosystem goods and services is essential for the economic development and welfare of the study area, especially over the medium and longer terms. This stewardship will enhance the quality of life of the study area's inhabitants; and it will maintain environmental quality, including water quality. Second, to achieve such benefits, it is essential to maintain, and where possible, restore ecosystem structure and functioning (sometimes referred to as ecosystem integrity). Third, biological diversity has great moral, cultural, and aesthetic importance to many societies, as reflected in laws and international agreements that express commitments to protect it. In addition, many ecologists believe

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--> that maintaining biological diversity is important to sustain ecosystem functioning, although the information on this matter is still very sparse and unclear. Fourth, all these achievements require that, in plans for providing and allocating the study area's water resources, a balance must be struck among environmental, short-term economic, and other objectives. To assess these balances and identify appropriate tradeoffs, a significant amount of new scientific information will be needed. Ecosystem Services Ecosystem services are ecosystem processes and functions beneficial to humans, primarily in contributing to the sustainability of people's lives and their intensively managed ecosystems. When activities destroy or impair the ability of natural ecosystems to provide these goods and services, the goods and services must be replaced by artificial means. Examples of such replacements are wastewater treatment plants, water filtration and purification systems, erosion control programs, and so on. Wide experience has shown that the artificial replacements for natural ecosystem goods and services are usually very expensive and often inferior to the natural ones. Because natural ecosystems provide these goods and services at no immediate financial cost, they appear to be free and their value and importance are often underestimated or overlooked entirely. For example, the value of ground water properly includes its extractive values (e.g., municipal, industrial, and agricultural uses) as well as the natural, in-situ services it provides (e.g., providing habitat and supporting biota, preventing subsistence of land, buffering against periodic water shortage, and diluting or assimilating ground-water contaminants) (NRC, 1997). To take advantage of these crucial services, they must be understood and protected. Ecosystem services can be classified into those related to air, soil, and water. One particular service, absorbing and detoxifying pollutants, can be related to air, soil, water, or some combination of the three. Some services are global in extent and of crucial survival value, namely, the maintenance of the gaseous composition of the atmosphere, and regulation of global air temperatures and global and local climatic patterns. Although increasing quantities of cash crops are produced on soilless substrates in the study area (using growth chambers, or ''greenhouses"), soil is one universal substrate for terrestrial biological production. Soils are produced by weathering of rocks in the Earth's crust. Organisms directly affect this weathering and also mediate the effects of water and air on weathering. Thus, one important ecosystem service is production and maintenance of soil. Soil can be lost by wind and water erosion at a rate orders of magnitudes faster than it is generated. Normally, soil erosion

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--> is slowed down or even totally prevented by vegetation cover. The vegetation of the drylands, through sparse, plays a similar role, which is augmented by a biogenic and soil crust, produced by photosynthetic bacteria, algae, lichens, and mosses (Boeken and Shachak, 1994). Soil retention is linked to water-related ecosystem services, and these are directly related to sustainable water supplies. Another important ecosystem service is the maintenance of the hydrological cycle. Plants are important for this service, which is especially valuable in drylands. Plant architecture, growth form, and phenology jointly influence the fate of raindrops (i.e., what is retained by the soil, what runs off, and what is returned to the atmosphere) and generate shade, which reduces topsoil evaporation. The overall effect of the vegetation on the water balance of the ecosystem, or even of a country or region, depends on the plant community structure. A plant community is composed of all the species populations that inhabit the ecosystem. The spatial combination of the individuals of all species in the community determines the effect of the vegetation on the water balance of the ecosystem, and effects on the water balance of adjacent and even distant ecosystems as well. The water-related services above are "input" services, which include soil moisture recharge and retention, aquifer recharge, and control of soil salinization and erosion. With respect to "output," one important ecosystem process is returning water to the atmosphere. On a global dimension, this process is clearly a service. However, on the local and regional scale in dryland countries like those of the study area, this is more a "disservice." The balance of this "service''/"disservice" is not known. For Israel, Stanhill (1993) calculated that 10,000 years ago, when the dry subhumid part of the country (receiving 400 to 800 mm annual rainfall) was mostly a natural, scrubland ecosystem, the potential water yield (volume of rain falling in a given year on a given surface area, minus volume of water returned to the atmosphere from the same area and year) was 1,590 km3/year, lower than the current 1,846 km3/year, with most of the area consisting of cropland, a highly managed ecosystem. Natural scrubland ecosystems appear to evaporate more soil water than intensively managed ecosystems in Israel. However, the positive contributions of that scrubland and other less managed ecosystems—such as scrubland's contribution in recharging aquifers—to the water balance of Israel, compared to the contributions of intensively managed ecosystems, must be calculated too, and weighed against the losses due to evapotranspiration from the same ecosystems.

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--> Services Provided by Water Bodies Open-water body ecosystems are spatially more homogeneous and better delimited than most terrestrial ecosystems. Being mostly a dryland, the study area is inherently poor in water bodies. Furthermore, many of these aquatic ecosystems are under intensive management or have been totally replaced by terrestrial ones. The following section addresses ecosystem services of the study area's streams, lakes, and wetlands. Streams Currently, the most significant ecosystem service of streams is the natural treatment of wastewater. The wastewater-treating service of most of the aquatic organisms in streams is facilitated by the oxidizing properties of the stream current and its velocity. Other components of the food web, such as aquatic herbivores and predators, are instrumental in regulating the populations of these wastewater-treating species, and in this way become involved in the quality of the wastewater treatment service of streams. Lakes Of the two study area's major lakes, one (the Dead Sea) is globally unique in its apparent lifelessness, and the other (Lake Kinneret, Lake Tiberias, or Sea of Galilee) serves as an operational open water reservoir for supplying water of drinking quality to most parts of Israel, with recent allocations to Jordan and the West Bank and Gaza Strip. The "service" of this ecosystem is thus to store water and to help maintain its quality as drinking water. Lakes in general, including Lake Kinneret/Lake Tiberias/Sea of Galilee, also provide the ecosystem service of wastewater treatment, although not as effectively as streams. Wetlands Wetlands are lands where the water table is usually at or near the surface, or lands covered by shallow water, that have characteristic physical, chemical, and biological features reflecting recurrent or sustained inundation or saturation (Cowardin et al., 1979; NRC, 1995a). Most major wetlands of the study area have been drained totally (coastal wetlands of Israel) or partially (Hula in Israel, Azraq in Jordan). Others, especially around the Dead Sea, are still relatively intact, though small. Wetlands are characterized by the slow rate of water movement in them. This

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--> feature reduces their oxidizing capacity, making them ineffective in wastewater treatment. However, the slow water movement promotes the deposition of suspended material and provides ample time for the complete biological mineralization of organic compounds and biodegradation of synthetic toxic chemicals (NRC, 1992). The slow water movement also supports typical wetland vegetation, which further slows water movement, and reduces the depth of the wetland, thus contributing to its spatial expansion. This expansion provides a unique ecosystem service: water storage during floods and a slow downstream release. Wetlands therefore lower flood peaks and their detrimental economic and environmental effect, such as soil erosion (NRC, 1992). While this service is not provided by landlocked wetlands such as Azraq, it was an important (although underestimated) function of the Hula wetland before its drainage. Artificial Aquatic Ecosystems All types of artificial open water bodies function as intensively managed ecosystems. These bodies include fish ponds (mainly in Israel), wastewater treatment plants (e.g., the Shifdan plant in Israel), water carrying systems' open canals and reservoirs (the National Water Carrier in Israel and the Ghor Canal in Jordan), and other open air reservoirs (e.g., floodwater reservoirs in Jordan and Israel). Soon after construction, such bodies are colonized by aquatic microorganisms, plants, and invertebrates, and they are used by waterfowl and insectivorous bats (Carmel and Safriel, 1998). Thus, the water bodies, constructed for the sole function of water treatment or supply, become intensively managed ecosystems, with ecosystem functions shaped by the wild species that successfully colonize them. Like natural and less intensively managed ecosystems, constructed aquatic ecosystems provide the ecosystem service of promoting wastewater treatment. Many of these water bodies are also important habitat for birds, especially birds that migrate or that use it for wintering. Constructed wetlands for wastewater treatment can also provide wildlife habitat (U.S. EPA, 1993). In Israel, the major wastewater treatment facility, Shifdan, has become a waterfowl sanctuary that attracts hundreds of bird-watchers every year and is used to university teaching. Nearly all constructed water bodies in the study area significantly support bird and other aquatic and riparian biodiversity. Biological Diversity Biological diversity means the diversity of genotypes within a species, species diversity, and the diversity of ecological communities: in short,

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--> biological diversity (often abbreviated to biodiversity) is the diversity of life on Earth. (See the similar definition by the 1992 United Nations Convention on Biological Diversity [Anonymous, 1992]). The protection of endangered species and biodiversity in general has been important to many people for a long time, and as a result, many have looked to science to provide quantitative assessments of the value of biodiversity. Although that endeavor has been difficult, there are other good reasons to protect biodiversity. For example, Sagoff (1996) described how difficult it is to establish on a purely economic basis that biodiversity or indeed most individual species should be protected, but he argued that the best reasons—and they are very powerful—for protecting biodiversity in most cases are ethical, moral, cultural, and aesthetic. Societies around the world have, in their laws and international treaties, reflected this view. Thus the United States's Endangered Species Act of 1973 declares it "to be the policy of Congress that all Federal departments and agencies shall seek to conserve endangered species and threatened species…" (Section 2 {b [c]}). The act further specifies that the determination as to whether a species is endangered or threatened must be based "solely on the basis of the best scientific and commercial data available," i.e., without reference to economic considerations (Section 4 {b[1]) (see NRC 1995b for a description and history of the act and its scientific underpinnings). In the study area, Annex IV of the Israel-Jordan Peace Treaty (see Appendix A) includes commitments to protect natural resources and biodiversity; the presence of parks and other protected areas throughout the study area is further indication of the study area's commitment to protecting biodiversity. The above discussion does not suggest that biodiversity has no economic value or that it is not important in maintaining ecosystem goods and services. Clearly, some species have enormous economic value and ecological importance, and some ecosystems have economic—especially tourism—value because of their biodiversity. Within the study area, several ecosystems have recreational and hence economic value. For example, woodland ecosystems are relatively rare in the study area, but their sharp contrast with the more common deserts make them important recreationally and inspirationally. Aquatic ecosystems are even more valuable in these respects, especially when they occur in deserts, such as the Azraq Oasis or wetlands and oases around the Dead Sea. Lake Kinneret/Lake Tiberias/Sea of Galilee, although it is in a relatively fertile area, is a major site for tourism and leisure activities, especially in summer. On the other hand, the study area's deserts and their own biodiversity contrast sharply with the landscapes that are home to most foreign tourists in the study area, and hence deserts are major sources of tourist income. Without some minimum amount of biodiversity, ecosystems would

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--> function poorly, even if the general relationship between biodiversity and ecosystem functioning is unclear (see Grime, 1997 for a clear summary of this matter and citations to recent literature). In addition, many have cautioned that just because we cannot at present quantify relationships between biodiversity and ecosystem functioning, that does not mean we should be cavalier about extinctions: a species lost is gone forever, and we might discover too late that it had great ecological or economic importance (e.g., Perrings, 1991). Sagoff (1988) warned that if we wait to establish the economic and survival value of biodiversity, it may be irreversibly lost. For all the above reasons, the committee concludes that it is important to protect biodiversity, and that water-resource planning should take this into account. Furthermore, protecting biodiversity often requires the protection of ecosystems, as does the protection of ecosystem goods and services. Thus, maintaining biodiversity and ecosystem goods and services can often be treated as a single goal, as the committee does in the following sections of this chapter. Economic Values of Individual Species In general, economic values of species derive from their provision of food, fuel, and fiber. In addition, some species provide medicinal, ornamental, and aesthetic goods. All human food consists of species and their direct products. Most of the species consumed by the global human population are domesticated and cultivated, which is also to say derived from species provided by biodiversity, or wild species. Many domestic species, and especially the food species, do not exist anymore in non-manipulated ("natural") ecosystems, namely, in the wild. But their progenitors, and more often their wild relatives, still occur in natural ecosystems. It is the genetic diversity of these progenitors and relatives that is one of the most critical benefits of biodiversity. Ironically, domestic species are the most endangered species, despite the huge sizes of their populations and their large geographical extent. Efforts to increase their production have led to erosion of their genetic variability. These species gradually lose their resistance to environmental changes, competitors, pests, and parasites. The high densities and uninterrupted spatial expanses of their populations, and the "globalization" that leads to widespread uniformity of their genetic structure and to high transmissibility of their mortality agents, make them increasingly prone to extinction (Hoyt, 1992). Their wild progenitors and relatives provide a repository of transferable genetic variability, variability that can counteract the ongoing genetic erosion of the domestic species, thus reducing their extinction risks.

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--> The study area of this report is one of the Earth's richest areas in progenitors and relatives of domesticated species (Zohary, 1983). Land uses depending on supplies of irrigation water deny these biogenetic resources their natural habitats where they dynamically evolve under our changing environment (Zohary, 1991). Because this genetic diversity is the insurance against agricultural disasters, its loss through excess water use jeopardizes the long-term sustainability and contributes to non-sustainability in the use of the study area's water supplies. Many wild species, both terrestrial and aquatic, are of commercial value. Wild plant species are often heavily sought, collected whole or for their parts, for their herbal, aromatic, medicinal, and ornamental properties. Many wild plant species are labeled prime pasture species, because they are critical for range-dependent livestock. Expansion of irrigated agriculture is at the expense of this economically significant biodiversity. At the same time, most species do not have current, short-term economic value. Of the approximately 266,000 species of plants known (Raven and Johnson, 1992), about 5,000 are used as food plants, 2,300 are domesticated, and 20 provide most of the food for the global human population (Frankel and Soulé, 1981). Food production is currently limited by land and water resources and losses to pests, but not by the lack of food species. However, should current food species fail because of the risks identified above, alternative species, currently wild, will be sought for domestication. The natural species pool is thus a repository of potential food and utility species for humans. Farmers often view the natural ecosystems adjacent to their croplands as sources of pests. But these and other natural ecosystems are also, and sometimes mostly, sources of enemies of agricultural pests. Thus, natural ecosystems provide important services that have economic value. Use of synthetic chemicals to control pests also controls their enemies, so this potential ecosystem value (pest control) is often not realized. Conflicts Between Water Resource Development and Ecosystem Goods and Services All species of realized or potential economic benefit to humans, globally and in the study area, are land users, and this type of land use competes with irrigated cropland. Improved water supplies for the study area may reduce not only the economic benefit of any expanded agriculture, but also the sustainability of existing irrigated and rain-fed agricultural production. This potential conflict requires evaluating that part of biodiversity that is of economic significance, but even the fraction and magnitude of that part of biodiversity have not yet been anywhere identified (Lawton, 1991). All species and their different populations must be

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--> considered possible members of this economically important class, at least until a large part of the useful species are identified as such. Their benefits must then be weighed against the benefits of developments driven by water supplies in the study area. Water Supplies, Biodiversity, and Desertification There is a critical relationship between ecosystems, desertification, loss of biodiversity, and climate change in the context of sustainable water supplies. Desertification is land degradation in drylands caused by mismanagement and overexploitation. Overpopulation and increased demands, mostly in semiarid regions, bring about overstocking and overgrazing and trampling, transformation of woodland to rangeland (e.g., the deforestation for railway ties and fuel in the study area by Turkish forces in the early part of the century) and the overexploitation of rangeland for the fire wood. The reduced vegetation cover and breakage of the soil crust, lead to water and wind erosion of the topsoil, and with it an irreversible loss of productivity-desertification. The loss of vegetation cover reduces aquifer recharge and increases losses of floodwater. At the same time the loss of vegetation cover reduces the global carbon sink, thus exacerbating global warming. Another type of land degradation is associated with the transformation of rangelands with year-round vegetation cover, to croplands that if not irrigated, have only intermittent cover, leading to further soil erosion. If the croplands are irrigated, irrigation brings about salinization of the topsoil: water scarcity does not permit application of quantities sufficient for leaching, and the high evaporation leaves the salt in the topsoil. Such croplands, when abandoned due to salinization, cannot revert to their original function as rangeland, since most range species are intolerant of the increased salinity. Thus, either due to loss of topsoil or due to salinization or both, land degradation may reach the point of irreversible desertification. To conclude, increasing the water supply allows the intensified use of rangelands and their conversion to croplands in semiarid regions. This leads to loss of biodiversity, reduced ecosystem services such as soil conservation, aquifer recharge, and the maintenance of carbon sink, thus exacerbating desertification and global warming. Desertification often has roots, typically a large external disturbance (Puigdefabregas, 1995), that began some years, or even decades, before crises manifest themselves (e.g., the Dust Bowl in the United States in the 1930s and the Sahel crisis in the 1970s). For this reason, it is important to try to prevent desertification by avoiding nonsustainable use of water, before it manifests itself by loss of biodiversity and the impaired provision

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--> of ecosystem services such as aquifer recharge, leading to reduced sustainability of water supplies. Environmental Costs of Water-Resource Development Policy makers, planners, and individuals in the study area need to make many decisions about activities ranging from international development projects to individual actions concerning water use, waste disposal, and what to plant in a garden or field. To make decisions about these activities and allocate water resources to different uses in the study area, a balance must be struck among environmental, economic, and other objectives when those objectives do not represent the same uses of water. To assess the balance and to identify acceptable tradeoffs, current scientific information should be used; a significant amount of new scientific information will also be needed. The preceding sections explained how environmental quality depends on the goods and services provided at no cost by natural ecosystems and explained how economic well-being, quality of life, and maintenance of water supplies depend on environmental quality. This section describes some of the specific consequences that follow from failure to maintain ecosystem goods and services by losing the land that is needed for ecosystems to persist. The section illustrates some of the factors that must be considered in making assessments and identifying sound tradeoffs, by describing interactions among environments, ecosystem goods and services, water quality and quantity, and human activities in the study area. First, we characterize the study area's biodiversity in the context of water supplies, we then describe the effects of water-resource development in biodiversity and on ecosystem services; and finally, we address ways to mitigate negative effects in achieving sustainable water supplies for the study area. Biodiversity of the Study Area Biodiversity relevant to water use in the study area has the following features: The ecology of the study area as a whole is that of hyperarid, arid, semiarid, and dry subhumid dryland ecosystems. The area's biodiversity is therefore that of drylands, with terrestrial vegetation directly limited by water, and all other components of biodivesity affected directly or indirectly by the variability and the unpredictability of water availability (Noy-Meir, 1973).

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--> Humans have had an extremely long and persistent influence on the environment. It is highly likely that the recent evolution of the study area's biota took place in the presence of humankind, and that human activities and practices have acted as selection agents, like other agents of natural selection. Attributes (1) and (2) imply that many of the study area's species have been selected to withstand water scarcity, fluctuations in water supply, and human interventions, and hence that the study area's ecosystems are resistant and resilient. The study area is not only a crossroads of continents (Africa, Asia, and Europe), but also of biogeographical regions—the Saharo-Arabian (African), Irano-Turanian (Asian), and Mediterranean. The area also shows intrusions and relicts of Euro-Siberian (northern European and Ethiopian (tropical African) species. Attributes (1) and (3) have three implications: overall species richness is very high; most species are presented by peripheral populations, and, although most of the species are not unique (endemic) to the region, the communities, that is, the regional assemblages of species, are. In this region, species of Asian steppes interact in the study area with species of Saharan deserts, for example. Effects of Water Use on Regional Biodiversity and Ecosystem Services It is clear from the preceding that biota and ecosystem services depend on water. Water-resource development in the study area usually entails six major practices: transportation of water from lakes and river sources; pumping from sources of springs as well as impounding springs by enclosing them in concrete structures; drainage of wetlands and large ponds; drainage of ephemeral ponds; pumping from aquifers; and damming floodwater courses to construct floodwater reservoirs. Each of these practices has notable effects on biodiversity and ecosystem services of the area, as discussed below. Management of Lakes and River Sources. Large water-development projects have dramatically affected the regional economy by promoting year-round intensive, pressure-irrigated agriculture as well as urban development. These development projects are associated with the management of river systems. The coastal Yarkon River1 fed by Ein Afek springs at the Judean foothills generated the Yarkon-Negev Line. The Rift Valley's Jordan River Basin management generated the Israeli National Water

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--> or water quality of aquatic ecosystems in the area could cause the extirpation of more than 35 percent of their vertebrate and plant species (and probably a high number of invertebrate species as well). It is not known which regional ecosystems are more prone to species loss through reduction in size, nor what their thresholds are below which species are lost (see Appendix C). Thus, the fact that the number of extinctions in terrestrial ecosystems of the study area known so far is insignificant is not a cause for complacency. To conclude, the appropriation of land by agricultural and urban development impairs at least one water-related ecosystem service—recharge—and also jeopardizes regional biodiversity. A troubling example of the loss of biodiversity is the loss of natural ecosystems in the Negev desert. In the 1950s, Israel promoted "greening the desert," resulting in a transformation of traditional rangeland to irrigated cropland, adversely affecting peripheral populations of plants and animals of rich within-species (genetic) diversity (Safriel et al., 1994). Increased urbanization, technological advances in wastewater treatment, recognition that agriculture in the central coastal plain endangers the coastal aquifer, and irrigation via the Israeli National Water Carrier all encourage this shift of Israeli agriculture from relatively wet, fertile regions to semiarid regions. But this shift accelerates the loss of biodiversity, and probably the provision of some ecosystem services. Thus, it is not sustainable over the long term. The loss of natural ecosystems and biodiversity occasioned through Israel's policy of greening the desert gives cause for concern about the potential adverse effects of Jordan's Badia Program to develop its eastern desert. Effects of Fragmentation An agricultural plot that dissects a natural ecosystem, or even a road cutting through that ecosystem, can split a large and hence safe ecosystem into two smaller, extinction-prone ones. Migration between two small ecosystems can offset the risk of species extinction in each, at least in any ecosystem that functions as a sink for migrants from another. But the development that caused the fragmentation often serves as a barrier for migration. Similarly, this barrier can erode within-species genetic variability, further contributing to risks of species extinction (Tilman et al., 1994). Statistics on road casualties of endangered species suggest that roads function as effective barriers between ecosystems. But the effects of fragmentation on the study area's biodiversity has not been studied. Effects of Pesticides Pesticides are applied rather generously in the study area; for example, 15,000 metric tons are applied every year in Israel. Especially when applied from the air, the effect of pesticides on

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--> natural ecosystems adjacent to agricultural land is evident. Pesticides and herbicides are often concentrated at each link of food webs, sometimes at up to lethal concentrations in top trophic levels. Top-down effects on ecosystems may be highly significant, hence pesticides cause a great concern. Pesticides are also transported by runoff affecting aquatic ecosystems. The recent reductions in cotton production in Israel, for example, not only save water, but also reduce the pesticide damage to aquatic and other ecosystems. Effects of Fertilizers Fertilizers too are applied in large quantities in the study area, often in the irrigation water. Fertilizers reach aquatic ecosystems, where they can cause eutrophication, and they also contaminate ground water. Thus, water drawn from lakes, rivers, and aquifers for agriculture contaminates and alters ecosystem functioning. Again, such indirect effects of water use may be environmentally more significant than their direct effects. Because dryland ecosystems are limited not just by water but also by nutrients, the enrichment of fertilizers "escaping" from desert agriculture may dramatically change the functioning and structure of these ecosystems. Effects of Trace Elements Effects of trace elements have not received sufficient attention in the study area. However, the experience of irrigated agricultural development in the San Joaquin Valley in California (NRC, 1989) suggests that harmful trace elements, especially selenium, are abundant in agricultural drainage water, and these can be further concentrated in the food web, damaging wildlife and humans. Mitigation What is being done and what should be done to mitigate adverse effects on natural ecosystems and their biodiversity, as they are caused by current and future water-resource development in the study area? Mitigation activities are of four types: restoration of damaged aquatic ecosystems; securing allocation of water for aquatic ecosystems, thus guaranteeing their ecosystem services for the future; development and implementation of a system for environmental impact assessment of planned major water-management projects in the study area; and development of regional planning policies that integrate water-resource development, agricultural development, and the functioning of natural ecosystems, to promote overall sustainability.

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--> Wastewater for Restoration of Freshwater Ecosystems Until 1991, the prevailing notion was that aquatic ecosystems should be rehabilitated by elimination of all effluents, ensuring flow of freshwater only. But the realities of water scarcity in the study area made it clear that rivers will dry up completely if the discharge of high-quality effluents back to them is not permitted when freshwater allocations are unavailable. For example, the Hula Nature Reserve in Israel has been found to function even when much of its water is effluent. The notion of using wastewater to help support biodiversity is based also on the belief that natural ecosystem can "serve themselves" by processing the wastewater. Many data have been accumulated, for example, along the course of the Yarkon River, to evaluate the treatment capacity of this river. For the month of June 1994, self-purification during the passage of water through measured sections of the river was evident in reductions of 0.1 to 0.5, 0.5 to 0.6 and 0.2 microgram/liter/second respectively in biological oxygen demand, chemical oxygen demand, and ammonium concentration—a high rate of self-purification, typical of an eastern Mediterranean climate (Rahamimov, 1996). Similar values have been measured in the plains section of the Soreq stream, and much higher values in the mountainous sections of this sewage stream. To increase the self-purification potential of the Yarkon, small dams have been constructed and the slowed-downstream above them is artificially oxygenated. An Israeli National River Administration was established in 1993 and charged with coordinating the restoration of river ecosystems, including the use of wastewater for this purpose. Though the main motivation for such action is recreation, the rehabilitated rivers promote biodiversity and provide ecosystem services. These restorations require water allocation of wastewater of specified quality, as well as freshwater allocation. This freshwater is not necessarily water lost to agriculture, because most of the allocation can be impounded at the lower reaches of the rivers, and the fraction lost by seepage recharges aquifers. Balancing Water Resource Development with Biodiversity and Ecosystem Services Regional Planning Using Advanced Technologies Intensifying water-resource development puts the study area's biodiversity and ecosystem services at risk. It is therefore necessary to evaluate the benefits of the development against the lost biodiversity and services. The risk of loss can be reduced by striking an optimal balance between land allocation for development and for biodiversity. Remote-sensing

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--> and geographic information systems (GIS) technologies are now available to carry out this mission by means of the following steps. Taking stock of current land uses, classed by development (e.g., urban areas, industrial areas, rural settlements, agriculture, and infrastructure) and biodiversity (e.g., protected areas, open areas not legally protected, rangelands, and some types of extensive agriculture). Thus, the first GIS map layer can plot current development and existing biodiversity. Ranking the various types of existing biodiversity (e.g., an indigenous woodland of a given successional state or of a semiarid watershed) in terms of ecological value—i.e., provision of ecosystem goods and services and support of biodiversity—and the different sizes of each of these types. Assessing the relative value of existing biodiversity areas identified in step 1 using the rankings obtained in step 2. For highly developed sections of the study area, the biodiversity areas will be scattered patches of natural ecosystems within a matrix of development, with the size of each patch and its distance from adjacent patches contributing significantly to its relative value. In nondeveloped areas, patches of development will be interspersed within a matrix of natural ecosystems, and the relative value of each type of patch will be less affected by size and distances to similar patches. Relative values can be expressed as colors or color tones in a second GIS map layer. Estimating the dimensions and identifying the areas required for additional, forecasted water-driven development. The economic benefits of water-resource development of each of these areas can then be assessed and expressed in a third GIS layer. Overlaying the third map layer on the second layer is the first step in an iterative process leading to optimization. Given that biodiversity areas cannot be recreated, optimization will entail adjusting the development areas such that, for example, low-benefits development areas will not be overlain on high-value diversity areas. The optimization process, though, may be more complicated than just that. The major undertaking is step 2 above, namely the ranking of biodiversity and ecosystem services. This ranking has never been done in the study area in an objective, methodical manner, and ideally should be preceded by sufficient research. However, this fact should not discourage carrying out the exercise in current and future planning. Demand simply grows faster than the pace of the required research. It is therefore necessary to use existing knowledge, and improve the valuation as knowledge accumulates.

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--> Evaluation of Terrestrial Biodiversity and Ecosystem Services The biota of an area can be evaluated by three criteria: its ability to provide ecosystem services; the number of species of realized and potential direct economic benefit that it includes; and its ability to absorb anthropogenic disturbances without loss in its ecosystem services or biodiversity (resistance), along with its potential for rehabilitation following disturbance (resilience; Safriel, 1987). Each of these criteria can be quantified by applying current knowledge, paradigms, or prevailing notions, as follows. Provision of Ecosystem Services Water-related ecosystem services depend on the property of the ecosystem and its placement within the watershed. Concerning properties, working hypotheses are that the larger the number of vegetation layers, the greater is the infiltration potential and the smaller the risk of soil erosion and intense surface runoff; and the larger the number of species, the greater the number of vegetation layers. Although the exact number of species in most of the study area's ecosystems is not known, these ecosystems can still be ranked in species richness. Woodlands and scrublands, for example, are richer than rangelands in the number of their perennial species (in dry subhumid areas), and stabilized sand dunes are richer than salt pans (in semiarid and arid areas). Vegetation maps that depict the major plant formations, such as those just mentioned, are available for most parts of the study area (Zohary, 1973), and the numbers of their species are also available in various sources. It is therefore possible to rank all of these major plant formations of the area by their number of plant species. With respect to the placement of the ecosystem within the watershed, the higher the elevation of an ecosystem within the watershed, the greater the value of its services. For example, loss of woodland at the top of a watershed, where rainfall in the area is more abundant, will generate more destructive floods, with a greater loss to aquifers, than similar loss at the bottom of the watershed. Ecosystems can therefore also be scored according to their elevation above the bottom of the watershed. Species of Potential Economic Value An ecosystem with a large number of species is also likely to have a relatively large number of species of potential economic significance. An ecosystem can be ranked by its number of species not only to evaluate its biodiversity, but also to assess the potential economic value of its biodiversity. Sometimes, it is even possible to identify particular species whose potential is already realized. The following groups of species can be ranked by their realized or potential economic value, the top rank being most valuable: (1) progenitors of

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--> cultivated species; (2) wild relatives of cultivated species; (3) noncultivated species currently collected for nutritional, medicinal, ornamental, aromatic, energy production, and industrial purposes; (4) high-quality forage species; (5) low-quality forage species; (6) species represented by peripheral populations; (7) species already identified by IUCN revised criteria under the categories of vulnerable and rare (including species whose economic significance is not yet known, but whose extinction would prevent the discovery of their significance); (8) species of inspirational and recreational value (which often translate to economic benefits); (9) species of scientific interest (which also have economic value, including through scientific discoveries); and (10) species that provide or manipulate habitats for other species, or are ecosystem engineers (Jones et al., 1994). An ecosystem can be scored by the number of its species in each of the above categories, multiplied by the rank of the category. Resistance and Resilience Resilience and resistance are positively (but not linearly) correlated with area. The risk of extinction is reduced with greater population size, population size increases with area, number of species increases with area, and the large perimeter-to-surface ratio of small areas makes their species highly vulnerable to surrounding development. However, it is difficult to prescribe the threshold size for an area to be nonresistant or nonresilient. Hence, in the study area, which as a whole is small, the larger the area allotted to natural ecosystems, the better. Rehabilitation of biodiversity and ecosystem services following disturbance is faster when there are sources of immigrants. These sources are other natural ecosystems, so their significance increases as they are closer to the disturbed area. The penetrability of the surrounding areas for propagules interacts with their distance: the greater the penetrability of the areas, the farther the propagules can travel. For example, for many species, an extensive surrounding agricultural area is more penetrable than a surrounding urban region. To conclude, the most valuable ecosystem is one with highest number of species, many of which are of potential economic significance; one that performs unusual or particularly valuable services; and a large ecosystem, especially if it is connected by a corridor to another similar natural ecosystem. Evaluation of Aquatic Biodiversity The study area is relatively poor in aquatic ecosystems. Therefore, in evaluating biodiversity, a higher score should be attributed to areas that contain aquatic ecosystems, or to each aspect of an aquatic ecosystem,

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--> than to a terrestrial ecosystem otherwise having the same scores. Thus, the value of an aquatic ecosystem in the study area with a given number of species will be higher than that of a terrestrial ecosystem of the same number of species and the same size. The following identifies some guidelines for evaluating aquatic ecosystems. In their provision of ecosystem services and number of species, aquatic ecosystems can be ranked as follows from greatest to less great: lakes, wetlands, ephemeral ponds, springs, perennial rivers, and streams. The higher the elevation of an aquatic ecosystem within a watershed, the greater the value of its services. Aquatic ecosystems also affect biodiversity of adjacent terrestrial ecosystems, by providing water for terrestrial vegetation, and water and food for terrestrial fauna. With respect to species' economic value, the category of forage species in the previous list of terrestrial ecosystems should be replaced by species of fisheries significance. Special features of aquatic ecosystems that confer resistance and resilience, apart from features described for terrestrial ecosystems, are the distance of the ecosystem from polluting sources, which should be great, and the existence of corridors, such as streams, between isolated water bodies. Using these sets of rules, it should be possible to evaluate regional biodiversity, and to use this evaluation as a tool to determine the extent of desirable water-resource development, such that this development is sustainable. Even if knowledge is incomplete, any serious attempt to rank areas in this fashion is likely to lead to better decisions. Recommendations This chapter has shown that maintaining and enhancing ecosystem goods and services will help—not hinder—most aspects of economic development and welfare in the study area. These goods and services enhance the quality of life of the study area's inhabitants; and they are required to maintain environmental quality, including water quality. The chapter has shown that biological diversity is important as well, and protecting it is likely to protect the structure and functioning of ecosystems to achieve those benefits; maintaining ecosystem goods and services will also protect biodiversity. The two points above require that, in plans for providing and allocating water resources among various uses in the study area, a balance is needed among environmental, economic, and other objectives when they do not lead to the same priorities for water use. Two types of recommendations follow. The first outlines the scientific information needed to better understand the relationships among ecosystem goods and services, ecosystem structure and functioning, and biodiversity, and also the information needed to assess the balances and

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--> tradeoffs among various objectives. The second set of recommendations outlines ecologically based methods for improving the sustainability of water supplies, based on scientific information already in hand. Research Recommendations Identify and quantify the services provided by each of the study area's ecosystem types, distinguishing between water-related services, and other services. Study and quantify the optimal and minimal water allocations (quantity and quality, in time and space) for each of these ecosystems to sustain the provision of each of their services. Determine which of the ecosystem types within the study area's landscapes play landscape-relevant keystone roles and investigate ways to maintain natural processes, and hence diversity at the landscape and region scale, while meeting the human demands of these landscapes. Identify species of the study area that are endangered or at risk of becoming endangered, assess the contribution of each to water-related ecosystem services, identify the causes for the endangerment of these species, and explore means to reduce the risks. Compare local water losses from evapotranspiration of natural and moderately managed major ecosystems of the study area to regional water gains from each of the ecosystem services, including increasing infiltration and reducing surface runoff and its associated topsoil erosion. Assess the study area's biodiversity components (species, ecotypes, and populations) of current and potential economic significance, especially in aquatic habitats and climatic transition zones inhabited by peripheral populations, and determine the water allocation and the land area and configuration required for their conservation. Assess the economic and biodiversity significance of the study area's indigenous dryland trees, especially the desert acacia, and the effects of current and potential relevant development projects (wells, dams, and roads) on the sustainability of the trees. Conduct long-term studies to evaluate the effects of damming stormwater on biodiversity at the lower reaches of watersheds, especially in hyperarid and arid regions, and use the results to prescribe amounts of water that must be released to reduce damages to downstream biodiversity. Evaluate the amount of water lost through regional appropriation of natural watersheds by agriculture and urban development, to generate guidelines for land use allocation in areas still not developed and for changes in current land use. Study the rate of extinctions of species populations in the study area resulting from fragmentation, transformation, and reductions in size

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--> of natural ecosystems, and use the results to provide guidelines for water management and related development projects. Evaluate the amounts of water allocated to nature reserves and other ways of protecting biodiversity that go to recharging aquifers after these uses. Study the role of the area's natural ecosystems in treating wastewater of various quality, the degree to which freshwater allocated to natural ecosystems can be replaced by treated wastewater, and the technologies appropriate for this substitution. Conduct the research required to define improved criteria for evaluating the significance of the area's biodiversity in providing ecosystem goods and services. Operational Recommendations The sustainability of water supplies requires that the area's natural ecosystems be treated as one of the legitimate users of the study area's water resources. Because water-resource development and the further development it promotes can damage biodiversity and therefore impair the provision of ecosystem services, development in the study area should be carried out so that the gains of water-resource development clearly outweigh lost ecosystem services and reduced biodiversity. Precise objectives should be set for all aquatic, riparian, and other water-dependent sites in the study area, specifying the type of biodiversity to be maintained and the type of ecosystem service the site can provide and whose continuance should be ensured. These objectives should be used to determine the minimal required allocation of water quantity and quality. Indicators, benchmarks, and monitoring programs for each water-allocation site should be developed to review and update the allocations. In future land-use planning, as in water-resource planning, the benefits of proposed developments should be evaluated against the cost of lost biodiversity and reduction of ecosystem services. When the study area's climatic transition areas (rich in within-species or genetic diversity), as well as other areas rich in progenitors and relatives of domestic crops, are targeted for water-driven development, it would be prudent to consider setting aside within them protected areas sufficiently large to serve as repositories of genetic resources. The costs and benefits of avoiding, reducing, or mitigating the effects of fragmentation of natural ecosystems should be considered when planning water development and allocation and the additional development they promote.

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--> References Anonymous. 1992. UN Convention on Biological Diversity. Geneva, Switzerland: United Nations Environmental Program Ashkenazi, S. 1995. Acacia trees in the Negev and the Arava, Israel. Leisrael, Jerusalem: Hakeren Hakayemet (Hebrew with English summary). Ben-David, Z. 1987. Taninim River, nearly the end of the road. Tel Aviv, Israel: The Society for the Protection of Nature in Israel, report (in Hebrew). Boeken, B., and M. Shachak. 1994. Desert plant communities in human-made patches, implications for management. Ecological Applications 4:702-716. Carmel, Y., and U. Safriel. 1998. Habitat use by bats in a Mediterranean ecosystem in Israel, conservation implications. Biological Conservation 84:245-250. Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of Wetlands and Deep Water Habitats of the United States. Washington, D.C.: Office of Biological Services, Fish and Wildlife Service, U.S. Department of the Interior. Frankel, O. H., and M. E. Soulé. 1981. Conservation and Evolution. Cambridge, U.K.: Cambridge University Press. Gazith, A., and Y. Sidis. 1981. Report on a survey of coastal ephemeral pools 1979/80. Tel Aviv, Israel: Institute of Nature Conservation Research, Tel Aviv University. Grime, J. P. 1997. Biodiversity and ecosystem function: The debate deepens. Science 277:1260-1261. Hoyt, E. 1992. Conserving the wild relatives of crops. Rome, Italy: IBPGR. Jones, C. G., J. H. Lawton, and M. Shachak. 1994. Organisms as ecosystem engineers. Oikos 69:373-386. Lawton, J. H. 1991. Are species useful? Oikos 62:3-4. Mador-Haim, Y. 1987. Brechat Ya'ar Pool. Teva Vearetz (Nature and Land) 29(3):45-47 (in Hebrew). McArthur, R. H., and E. O. Wilson. 1967. The Theory of Island Biogeography. Princeton, N.J.: Princeton University Press. Moskin, Y. 1992. The Influence of Mankind on Aquatic Ecosystems. An unpublished dissertation, submitted to the Hebrew University of Jerusalem (in Hebrew). Nathan, R., U. N. Safriel, and H. Shirihai. 1996. Extinction and vulnerability to extinction at distribution peripheries: An analysis of the Israeli breeding avifauna. Israel Journal of Zoology 42:361-383. National Research Council (NRC). 1989. Irrigation-Induced Water Quality Problems. Washington, D.C.: National Academy Press. National Research Council (NRC). 1992. Restoration of Aquatic Ecosystems. Washington, D.C.: National Academy Press. National Research Council (NRC). 1995a. Wetlands: Characteristics and Boundaries. Washington, D.C.: National Academy Press. National Research Council (NRC). 1995b. Science and the Endangered Species Act. Washington, D.C.: National Academy Press. National Research Council (NRC). 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, D.C.: National Academy Press. Noy-Meir, I. 1973. Desert ecosystems. Environment and producers. Annual Review of Ecology and Systematics 4:25-51. Perrings, C. 1991. Reserved rationality and the precautionary principle: Technological change, time and uncertainty in environmental decision making. Pp. 153-166 in Ecological Economics, R. Costanza, ed. New York: Columbia University Press. Puigdefabregas, J. 1995. Desertification: stress beyond resilience, exploring a unifying process structure. Ambio 24:311-313.

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