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Page 11 2 Water Availability:Quantity and Quality In the twentieth century, there was often an unfortunate tendency to treat water-quantity and water-quality issues separately or to dismiss water-quality issues entirely. Although often done only for convenience, this artificial separation masks the importance of water quality in determining what water is available to serve what uses. Declines in water quality reduce the available water supply just as surely as does drought. Accordingly, water quality is treated here as an integral dimension of water availability in an effort to underscore the fact that water quality will have to be managed effectively to prevent water supplies from dwindling over time. The principal water problem in the early twenty-first century will be one of inadequate and uncertain supplies, both here and abroad (Postel, 1999). Intensifying scarcity is likely to be the rule, as growing demands from nearly all water-using sectors will compete for finite levels of developed supply and remaining free-flowing water that support environmental and other instream uses. Throughout the first two-thirds of the twentieth century, scarcity was thought to apply only to developed supplies (NRC, 1992a). This scarcity was managed primarily by developing and augmenting water supplies—for example, by the building of dams and the resultant creation of reservoirs. In the latter third of the century, more attention was paid to the opportunities offered by demand management as the expense and the negative environmental consequences of traditional water-development schemes became more widely and clearly understood (Michelsen et al., 1998; NRC, 1992a). Successful management of scarcity will require more systematic, comprehensive, and coordinated approaches. All the available techniques and options will need to be regarded as alternatives, and most solutions will involve combinations of alternatives. In planning for the management of scarcity, good hydrologic (including water-quality) data will be absolutely essential.
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Page 12 DEVELOPMENT OF SUPPLY-ENHANCING TECHNOLOGY As scarcity continues to intensify, the search for new supplies can be enhanced by (1) the development of new supply-enhancing technology and (2) reducing the costs of some existing technologies. There are three technologies that seem to hold considerable promise for the future. First, many of the wastewater treatment technologies that permit water to be recycled are already cost-competitive in many of the arid and semiarid regions of the West. Further reductions in cost will provide incentives for more widespread use of recycled water, thereby “expanding” the developed supply. Reductions in the capital and operating costs of such technologies will also permit municipalities and other water users to meet prevailing water quality discharge standards more inexpensively. A recent Water Science and Technology Board (WSTB) report evaluating potable reuse identified several issues that will have to be considered, including the need to improve toxicological testing of wastewater and exposure assessment methodologies to evaluate the health effects of using reclaimed wastewater for drinking (NRC, 1998). It will be necessary to improve public perception of recycled wastewater via research and educational programs in order for wastewater recycling to be successfully deployed. Research may be needed to identify other factors that influence adoption of reuse technologies, such as capital intensity and cost, reliability, and siting. Second, further development of desalting technology appears warranted under certain circumstances. Like wastewater treatment technology, some desalting technologies are now cost-competitive where source waters are brackish. In contrast, the promise of seawater desalting has remained elusive despite substantial investments made during the last half of the twentieth century. Energy will continue to be needed to convert seawater to freshwater and to lift and transport the water to sites often remote from the ocean. The problems associated with brine disposal are also likely to continue. Nevertheless, the development of new, more effective reverse osmosis membranes and improved technologies for pretreating water have the potential to reduce the cost of desalting to affordable levels in regions where energy is relatively inexpensive, brine disposal can be managed, and demand is local. Thus, research on pretreatment technologies for membrane desalting processes and on the causes for membrane fouling in seawater could go a long way in stimulating further progress. Third, many regions will need to augment storage to ensure adequate supplies of water during drought and dry seasons. Because surface water storage opportunities will be far less attractive than they were in the past for
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Page 13 ~ enlarge ~ New technologies for removing pathogens, such as this microfiltration unit, will be needed to help ensure that wastewater is safe for potable reuse. reasons of cost and environmental impact, there will be pressure to develop additional storage capacity by utilizing underground aquifers. Aquifer storage systems should be developed with extreme caution because water residence times in aquifers are usually longer than in surface water reservoirs. For this reason, it will be important to identify possible adverse environmental impacts and to devise management schemes to avoid or minimize those impacts. Substantive research is needed to address the practical problems of groundwater recharge and storage, such as when recharge should be done via percolation versus direct injection. Other issues include the potential for deterioration of groundwater quality because of recharge, deterioration of recharged water quality by minerals or contaminants in the aquifer, and the potential for recharge with surface water to damage the aquifer's storage capacity. The concept of aquifers as reactors and not merely as storage vessels needs to be developed to prevent problems as aquifer use increases.
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Page 14 The water resources research agenda for the twenty-first century should give priority to: developing new and innovative supply-enhancing technologies; improving existing technologies—particularly wastewater treatment, desalting technologies, and groundwater recharge and recovery schemes—so that both capital and operating costs will be lower; and assessing the safety of wastewater that has been treated for reuse as drinking water. WATER QUALITY:FUNDAMENTAL AND APPLIED STUDIES Future changes in land use will alter hydrologic and biogeochemical processes that control the quality of water derived from the nation's watersheds. As discussed in Chapter 1, current approaches to water-quality problems overlook important connections between local and regional hydrologic regimes. In particular, the monitoring and regulation of contaminants is currently carried out in a piecemeal manner that does not consider large-scale and long-range hydrologic and ecosystem processes or interactions between individual contaminants and major carbon and nutrient cycles. For these reasons, managing the quality of our water resources will require a holistic conceptual and modeling framework and will depend on more water-quality data and other hydrologic data acquired through in situ sensors and remote sensing. Development of this larger holistic framework will provide a means of better incorporating into water resource system management the results from several critical areas of water-quality research. It should be noted early on that preventing pollution is almost always less costly than cleaning it up after the fact. Nevertheless, the legacy of pollution that has already occurred must be addressed, in addition to the new sources of pollution that are currently going unabated. In particular, greater research is required on nonpoint source pollution, which accounts for nearly three-quarters of the contaminant loading to surface water and groundwater in the United States. Nonpoint source contaminants are delivered to waters via runoff, shallow groundwater, and atmospheric deposition. Nonpoint source pollution is a complex and spatially variable mixture of nutrients, toxic chemicals, sediment, and microorganisms from the land surface, and its transport is highly dependent upon the hydrologic regime, especially extreme events such as floods. Irrigated
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Page 15 agriculture is a particularly troublesome nonpoint pollution source because of salinization, erosion, and release of fertilizers, pesticides, and leachable minerals such as selenium, which can create toxic conditions in receiving waters. Controlling nonpoint source pollution requires identifying and quantifying the contributions of different land uses to pollutant loading, as well as implementing site-specific best management practices (such as forested buffers along waterways) to reduce pollutant loading. Unfortunately, identifying and quantifying nonpoint sources of pollution can be extremely difficult, especially for atmospheric deposition and other activities for which monitoring methods are inadequate. Significant efforts have been made to develop models that can predict pollutant loading from nonpoint sources given various land-use scenarios, but these models have yet to be tested thoroughly and verified for accuracy. Finally, best management practices used to reduce nonpoint source pollution are limited in their scope (what they can remove), efficiency (how much they can remove), and reliability (how well they work over time). Research is needed to improve monitoring methods and control technologies. Equally important is the development of a variety of societal approaches, including command and control regulatory regimes, voluntary and incentive-driven efforts, educational programs, landuse controls, and the control of pollution inputs to production processes. Research in these areas is typically expensive and time-consuming, but it will almost certainly be needed to undergird a workable national strategy for controlling nonpoint source pollutants. Indeed, problems of nonpoint source pollution are but one example of the need to integrate land-use and water polices. More knowledge is needed about the susceptibility and resilience of terrestrial and aquatic environments to contaminant loadings, as the long-term impacts of contaminant accumulation may eventually undermine overall ecological function. The successful management of water quality in the twenty-first century will require a more comprehensive understanding of the ways in which the environment processes contaminants, how those processes vary, and their robustness as contaminant loads grow. Research should lead to better assessments of the resistance and resilience of ecosystems to damage by waterborne contaminants and of the extent to which different biogeochemical processes either buffer organisms from the effects of contaminants or accentuate the bioaccumulation of contaminants by organisms in higher trophic levels. Studies relevant to this general category should include characterizing the susceptibility of organisms and ecosystems to acute and chronic contaminant exposure, evaluating the recovery times of ecosystems
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Page 16 following exposure to contaminants, and calculating residence times for pollutants. Under conditions of water scarcity, groundwater will take on greater importance as a water resource. In the past two decades, important advances have been made in understanding the geochemical and microbial processes occurring in the subsurface that control contaminant transport. For example, the roles of iron, manganese, and humic substances as electron acceptors have been demonstrated in laboratory and field settings. Field and modeling work can now be initiated to incorporate these processes into reactive transport modeling, which can be coupled with the advanced modeling approaches now used for groundwater flow systems. The protection, mitigation, and enhancement of groundwater quality will depend on a better understanding of the rates of chemical contaminant movement, of chemical, biochemical, and physical transformations of contaminants, and of potential remediation technologies. Some emphasis should be given to studies of the long-term availability of contaminants assimilated into soil and sediment. Understanding the implications of shallow groundwater contamination for hydrologically connected surface waters and for the long-term integrity of underlying deep groundwater can be used to evaluate trade-offs between surface water and groundwater resources on regional scales. These research needs apply not only to chemical contaminants but also to microbial pathogens. Microbial water pollution, which has always been an issue in developing nations, is a reemerging concern in the United States. Recent outbreaks of waterborne disease demonstrate the continued susceptibility of both surface water and groundwater supplies, from the E. coli outbreak in New York (CDC, 1999) to the Cryptosporidium outbreaks in Wisconsin and Nevada in which thousands were sickened, some fatally, from contaminated tap water (Smith and Rose, 1998). Microorganisms pose a particular concern in the water resources arena because of the very low tolerance exhibited for pathogens in water by humans, especially children, the elderly, and immunocompromised persons. Microbes originating from animal and human wastes are known to be present in surface source water, groundwater, and distribution systems (LeChevallier et al., 1999a,b). In a national survey, 30 percent of groundwater wells tested in the United States showed evidence of viral contamination (Abbaszadegan et al., 1999), and as much as 40 percent to 80 percent of surface waters tested contained parasites (Smith and Rose, 1998). Despite substantial advances in molecular biology (e.g., polymerase chain reaction and the promise of new techniques such as gene chip technology and bioinformatics), their application to water science
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Page 17 ~ enlarge ~ Contaminated sediments pose challenging problems in dealing with widespread sources that adversely affect water quality. The links between sediment biogeochemistry, contaminant availability, benthic organism feeding, and food web effects are not well understood. Thus, it is not possible to make reliable predictions, and, hence, experts disagree on management solutions. and technology has been minimal. Further research on microbial detection methods, the building of occurrence databases, the development of fate and transport models, and determinations of disease risks are needed. Development of a more integrated approach that couples water quantity and quality will provide critical knowledge for improving and redesigning the nation's water resource infrastructure to meet multiple objectives under an uncertain future climate. In the twenty-first century, attention must be given to the aging of the nation's water resource infrastructure and its effect on aquatic ecosystems and water quality. In addition to the changes in the operation of reservoirs and in the discharge of treated wastewater to surface waters or groundwaters previously mentioned, changes in drinking water treatment and distribution systems will be needed. A cornerstone of the drinking water industry's effort to provide safe water has been a “multiple
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Page 18barrier” approach, which includes watershed protection, water treatment, and distribution system integrity. Substantial gains have been made in the development of innovative treatment technologies and, very recently, significant progress has been made in protecting some watersheds (NRC, 2000). However, improving distribution system integrity has received little attention to date. Surveys of aging infrastructure suggest that substantial investments will be required to maintain distribution systems in the coming years and to limit their vulnerability to extreme hydrologic events through in-line infiltration. Moreover, contemporary regulations on disinfection and disinfection byproducts are likely to result in fundamental changes in disinfection practices. To support these changes, research will be needed to strengthen out understanding of the microbial ecology as well as the physical and chemical properties of distribution systems. Finally, in order for these new conceptual advances, data resources, and coupled transport models to be effectively used by decision-makers, basic research is needed to develop better risk assessment and risk management capabilities with respect to water quality. Little is known about the synergistic effects of chemical mixtures in aqueous environments or about the biological and human consequences of long-term exposure to low levels of many substances. Research efforts should be coordinated with additional research on human exposures and risk management itself. Specifically, more research is needed on methods for prioritizing risks and assessing multiple sources of risk on a relative basis. In addition, work is needed to understand the factors that affect individuals' views of water-related risks so that effective risk management and communication programs can be jointly implemented. In the water-quality arena, the water resources research agenda for the twenty-first century should give priority to: identifying physical, chemical, and microbial contaminants and understanding their fate and transport; identifying and developing innovative technologies for preventing pollution; controlling nonpoint source pollution; improving our ability to forecast the impact of land-use changes and best management practices on contaminant loading to surface water and groundwater; improving our ability to predict the impact of contaminant load changes on ecosystem sercices, biotic indices, and higher food chain organisms (fish and shellfish).
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Page 19 determining the role of the environment in processing and converting contaminants; developing better techniques and data for assessing the capacity of the environment to buffer organisms from contaminants and to recover from the effects of contamination; improving the integrity of drinking water distribution systems; and enhancing the scientific bases for risk assessment, risk management, and communication and decision-making regarding risk. IMPROVING HYDROLOGIC FORECASTING AND PREDICTION Because both short-term and seasonal weather play an increasing role in the nation's economy, short-term forecasting of precipitation and floods/ drought becomes important. Among other uses, forecasts are subsequently used to derive “temperature degree” days, which affect the energy market; to predict severe weather, which affects transportation and regional retail distribution centers; and to predict seasonal weather, which affects human health conditions such as West Nile encephalitis and malaria. Thus, there is substantial practical application for research aimed at improving methods of forecasting precipitation and streamflow, accurately assessing these predictions, and determining their usefulness for water management. Improvements can be made both in the accuracy of forecasts and in the length of time for which accurate forecasts can be made. Research should also focus on improving methods of predicting runoff, streamflow, and actual evapotranspiration on a regional basis, as these parameters directly affect water management. A better understanding of historic precipitation and streamflow patterns may lead to better predictions of future patterns of precipitation and steamflow and, importantly, the variability of these patterns—especially as they relate to climate anomalies such as El Niño. Because such large-scale weather patterns can induce extreme local conditions, methods to translate predictions of variability from the regional scale to the local scale are critical to water management. Although the average annual precipitation in the United States has not changed significantly over the last century, the incidence of heavy precipitation (and correlated high streamflow) has increased (Groisman et al., 2001), especially in the eastern portion of the country. Conversely, there is evidence of a retreat in spring snow cover extent over western regions of the country, which will affect water availability and possibly the occurrence of drought (Lettenmaier and Gan, 1990). Research that documents these
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Page 20 changes and identifies their causes (e.g., using remote sensing and in situ measurement of snow hydrology) could contribute to our ability to predict severe weather and thereby manage ensuing floods and droughts more effectively. Such research is especially needed to underpin risk-based evaluation of flood and drought response policies. In addition, work aimed at understanding why damage from floods and droughts has increased over time would be useful in evaluating past flood and drought management policies. Such evaluations could contribute much to the formulation of enlightened policies in the future. Finally, additional research to enhance our understanding of global climate change and its impacts will be needed. Changes in climate could exacerbate periodic and chronic shortfalls of water, particularly in arid and semiarid areas of the world. Such areas include many developing countries that already have limited resources with which to respond to water shortages. Climate change is leading to smaller snow packs and earlier melting (Lettenmaier and Gan, 1990), which puts at risk the water supply of semiarid regions of the western United States. For other regions, model simulations ~ enlarge ~ Flooding can be catastrophic in areas where waterways are heavily developed. Photograph courtesy of Elizabeth Rogers.
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Page 21of future climate change generally predict increased precipitation (Giorgi et al., 1998a), which increases the possibility of severe weather and flooding in temperate and humid regions and raises concerns about dam and levee failures, greater quantities of polluted runoff, and salinization of coastal aquifers. Global warming is likely to lead to sea level rise (on the order of a few meters) due to both thermal expansion of the oceans and melting of the Antarctic ice sheets. In the United States, an estimated 46 million people per year currently are at risk of flooding from storm surges, and climate change will exacerbate these problems, leading to potential impacts on coastal ecosystems and human coastal infrastructure (Watson et al., 1997). Finally, carbon storage in vegetation and soils is critical to global carbon cycling, and it ultimately relies on the availability of water to support vegetative growth (Tenhunen and Kabat, 1999). Disruption of this carbon storage, either by increased human water interception or altered rainfall patterns, could have serious repercussions for the global climate via carbon dioxide emissions to the atmosphere. Clearly, hydrologic issues related to global change should be included in the water resources research agenda (NRC, 1999a). The water resources research agenda for the twenty-first century should give priority to: improving our capacity to accurately forecast the hydrologic cycle (precipitation, actual evapotranspiration, and streamflow) over a range of time scales (days to seasons) and on a regional basis; better understanding and predicting the frequency and cause of severe weather that leads to floods and droughts; evaluating why damage from floods and droughts has grown over time; and improving our understanding of global change and its hydrologic impacts. NEED FOR ADEQUATE HYDROLOGIC DATA Intensifying water scarcity cannot be successfully addressed in the absence of reliable data about the quantity and quality of water over time and at different locations. The end-of-century trend of investing fewer and fewer dollars in data-gathering efforts—the declining number of stream gages is but one example—will need to be reversed if availability is to be adequately characterized. It is also important to recognize that the availability of water is random in nature and that the relative extent of water scarcity will be
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Page 22 influenced importantly by hydrologic variability. The hydrologic measurements needed to improve short-term hydrologic forecasting and water management will be qualitatively different from the types of measurements needed for water resources planning. Historically, data collection focused on long-term river discharge data for water supply planning, flood peak discharge data for flood control design, or precipitation data for flood prediction. In the decades ahead, there will be a greater need for data collected in near real time for water systems operations. This requires merging water quality and quantity data with predictions from weather and seasonal climate models. Currently, data collection systems are within the purview of different government agencies. Inasmuch as these agencies are frequently independent of each other, compiling data into coherent sets can sometimes be difficult. The need for adequate data is not limited to surface water. For much of the nation, too little is known about the rates of recharge to and extraction from groundwater aquifers. Groundwater supplies drinking water to approximately 50 percent of the U.S. population, and it can be critically important in the management and buffering of drought for all water using sectors. It will be crucial to understand how rates of recharge change over time, to identify the variables that influence recharge, and to determine sustainable rates of groundwater extraction (Alley et al., 1999). In addition, all groundwater aquifers are vulnerable to quality deterioration. Little is known about the rates of degradation and what they imply for the expected life of the aquifer in the absence of treatment (NRC, 1993). These rates need to be characterized and the contaminants in question and their sources identified. Such information is necessary to be able to preserve aquifers as resilient and robust components of the water supply system. Databases from research and monitoring programs should have the capacity to connect to each other through commonly accepted linking factors, such as latitude and longitude, in order to increase their availability and maximize their value for research and public purposes. In particular, water informatics is now quite feasible, given modern water information technologies and their links to emerging monitoring, visualization, and modeling technologies. The U.S. Environmental Protection Agency (EPA) is giving considerable attention to linking factors in the National Drinking Water Contaminant Occurrence Database, primarily for chemicals, thereby strengthening the nation's ability to understand the nature and scope of these threats to public health. However, no adequate occurrence database exists for microbial contaminants. The water resources research agenda for the twenty-first century should
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Page 23 give priority to: determining the country's hydrologic measurement needs and developing a program that will provide these measurements in an effective and efficient manner; further developing data collection and distribution in near real time for the improvement of weather forecasting, river discharge forecasting, and water resources operations; and developing technically improved methods of measuring water flows and water quality, both surface and subterranean. Appropriate attention should be given to remote sensing as well as in situ measurement techniques. Methods for optimally merging observations from different remote sensors (e.g., satellite, radar, and rain gages) and for estimating the uncertainty of the combined products are also needed.
Representative terms from entire chapter: