Sustaining Healthy Freshwater Ecosystems
Sustaining Healthy Freshwater Ecosystems Issues in Ecology Published by the Ecological Society of America Number 10, Winter 2003
Issues in Ecology Number 10 Winter 2003 Sustaining Healthy Freshwater Ecosystems SUMMARY Fresh water is vital to human life and economic well-being,and societies extract vast quantities of water from rivers,lakes,wetlands,and underground aquifers to supply the requirements of cities,farms,and industries.Our need for fresh water has long caused us to overlook equally vital benefits of water that remains in stream to sustain healthy aquatic ecosyste There isgrowingre gnition that functionally intact and biologicallyc mplexfres provide many econor mically servicestos es include contro transportation,recreation,purification of human and industrial wastes,habitat for plants and animals,and production of fish and other foods and marketable goods.Over the long term,intact ecosystems are more likely to retain the adaptive capacity to sustain production of these goods and services in the face of future environmental disruptions such as climate change.These ecosystem benefits are costly and often impossible to replace when aquatic systems are degraded.For this reason,deliberations about water allocation should always include provisions for maintaining the integrity of freshwater iificeidee indicats thatqi cystem can be protected or restored byrthe oll Rivers,lakes,wetlands,and their connecting ground waters are literally the "sinks"into which landscapes drain.Far from being isolated bodies or conduits,freshwater ecosystems are tightly linked to the watersheds or catchments of which each is a part,and they are greatly influenced by human uses or modifications of land as well as water.the stream network itself is important to the continuum of river processes Dynamic patterns of flow that are maintained within the natural range of variation will promote the integrity nd sust nab y of fr aquatic system Aquatic ecosystem sadditionally require that sedim nts and orelines,heat and light properties,chemical an nutrient inputs,and plant and animal populations fluctuate within natural ranges,neither experiencing excessive swings beyond their natural ranges nor being held at constant levels. Failure to provide for these natural reauirements results in loss of species and ecosystem services in wetlands rivers.and lakes.Scientifically definina requirements for protectina or restoring aquatic ecosystems.however.is only a first step new policy and man proaches will equired.Current piecemeal and consumption-oriented o water policy ca olve th e problems r inc easingly degraded freshwat ecosystems begin to ress how wat is viewed and anage in the United States 1e0 1)Framing national,regional,and local water management policies to explicitly incorporate freshwater ecosystem 2)Defining water resources to include watersheds.so that fresh waters are viewed within a landscape or ecosystem context instead of by political iurisdiction or in geographic isolation. 3)Increasing communication and education across disciplines,especially among engineers,hydrologists. economists,and ecologists,to facilitate an int grated view of freshwater orts using well-grounded ecolo 月gn Maintaining and protecting remaining freshwater ecosystems that have high integrity. Cover-(1)Rio Grande at Bandelier National Monument,New Mexico.Photo courtesy Jim Thibault,University of New Mexico Biology Department:(2)Rio Grande near Bernalillo,New Mexico.Photo courtesy Anders Molles,son of Manuel C.Molles,Jr. University of New Mexico Biology Department:(3)Dry Rio Grande at Bosque del Apache National Wildlife Refuge,July 17. 2002.Photo courtesy Jennifer Schuetz,University of New Mexico Biology Department
1 Issues in Ecology Number 10 Winter 2003 Sustaining Healthy Freshwater Ecosystems SUMMARY Fresh water is vital to human life and economic well-being, and societies extract vast quantities of water from rivers, lakes, wetlands, and underground aquifers to supply the requirements of cities, farms, and industries. Our need for fresh water has long caused us to overlook equally vital benefits of water that remains in stream to sustain healthy aquatic ecosystems. There is growing recognition, however, that functionally intact and biologically complex freshwater ecosystems provide many economically valuable commodities and services to society. These services include flood control, transportation, recreation, purification of human and industrial wastes, habitat for plants and animals, and production of fish and other foods and marketable goods. Over the long term, intact ecosystems are more likely to retain the adaptive capacity to sustain production of these goods and services in the face of future environmental disruptions such as climate change. These ecosystem benefits are costly and often impossible to replace when aquatic systems are degraded. For this reason, deliberations about water allocation should always include provisions for maintaining the integrity of freshwater ecosystems. Scientific evidence indicates that aquatic ecosystems can be protected or restored by recognizing the following: • Rivers, lakes, wetlands, and their connecting ground waters are literally the “sinks” into which landscapes drain. Far from being isolated bodies or conduits, freshwater ecosystems are tightly linked to the watersheds or catchments of which each is a part, and they are greatly influenced by human uses or modifications of land as well as water. The stream network itself is important to the continuum of river processes. • Dynamic patterns of flow that are maintained within the natural range of variation will promote the integrity and sustainability of freshwater aquatic systems. • Aquatic ecosystems additionally require that sediments and shorelines, heat and light properties, chemical and nutrient inputs, and plant and animal populations fluctuate within natural ranges, neither experiencing excessive swings beyond their natural ranges nor being held at constant levels. Failure to provide for these natural requirements results in loss of species and ecosystem services in wetlands, rivers, and lakes. Scientifically defining requirements for protecting or restoring aquatic ecosystems, however, is only a first step. New policy and management approaches will also be required. Current piecemeal and consumption-oriented approaches to water policy cannot solve the problems confronting our increasingly degraded freshwater ecosystems. To begin to redress how water is viewed and managed in the United States, we recommend: 1) Framing national, regional, and local water management policies to explicitly incorporate freshwater ecosystem needs. 2) Defining water resources to include watersheds, so that fresh waters are viewed within a landscape or ecosystem context instead of by political jurisdiction or in geographic isolation. 3) Increasing communication and education across disciplines, especially among engineers, hydrologists, economists, and ecologists, to facilitate an integrated view of freshwater resources. 4) Increasing restoration efforts using well-grounded ecological principles as guidelines. 5) Maintaining and protecting remaining freshwater ecosystems that have high integrity. 6) And recognizing human society’s dependence on naturally functioning ecosystems. Cover—(1) Rio Grande at Bandelier National Monument, New Mexico. Photo courtesy Jim Thibault, University of New Mexico Biology Department; (2) Rio Grande near Bernalillo, New Mexico. Photo courtesy Anders Molles, son of Manuel C. Molles, Jr., University of New Mexico Biology Department; (3) Dry Rio Grande at Bosque del Apache National Wildlife Refuge, July 17, 2002. Photo courtesy Jennifer Schuetz, University of New Mexico Biology Department
Issues in Ecology Number 10 Winter 2003 Sustaining Healthy Freshwater Ecosystems by Jill S.Baron,N.LeRoy Poff,Paul L.Angermeier,Clifford N.Dahm,Peter H.Gleick,Nelson G.Hairston,Jr..Robert B. Jackson,Carol A.Johnston,Brian D.Richter,Alan D.Steinmar INTRODUCTION that focuses primarily on maintaining the lowest acceptable water quality and minimal flows,and protecting single species Fresh water is vital to human life and economic well- rather than aquatic communities.A fundamental change in being,and societies draw heavily on rivers,lakes,wetlands, water management policies is needed,one that embraces a and underground aquifers to supply water for drinking. much broader view of the dynamic nature of freshwater irrigating crops,and running ndustrlal processes.Ihe benenit resources and the short-and long-term benefits they provide of these extractive uses of fresh water have traditionally Our current educational practices are as inadequat f water that remains as management policies to the cha es Hydrologis engineer managers, e who design and ma 96 th eco wa d rarely d00 ut the o taught (Figur seque sider the c tical role of ter ir tra society or to d the human and industrial wastes habitat for institutions that manage wate plants and animals and production of fish omists dev Der and politician and other foods and marketable aoods seldom project far enough into the futur These human benefits are what ecologists Figure 1-Freshwater ecosystems pro to fully account for the potential call ecolonical services defined as "the vide economically valuable commodities ecological costs of short-term plans.Few conditions and processes through which and services to humans (drinking water. Americans are aware of the infrastructure natural ecosystems,and the species that rrigation.transportation.recreation etc.).as well as habitat for plants and that brings them pure tap water or make them up,sustain and fulfill human r wastes away and fewer stil life."Over the lona term.healthy freshwater animals. carries their understand the ecological tradeoffs tha ecosvstems are likely to retain the adaptive are made to allow these conveniences capacity to sustain production of these ecological services in the Although the requirements of healthy freshwate face of future environmental disruptions such as climate change ecosystems are often at odds with human activity.this conflic Ecological services are costly and often impossible need not be inevitable The challenge is to determine how to replace when aquatic ecosystems are degraded Yet today. society can extract the water resources it needs whil aquatic ecosystems are being severely altered or destroyed protec ting the important natural complexity and adaptiv at a greaterrate than at any other time in h nan history capacity or tre hwater ecosystems en scientifi and far faster han they are b ing restored.Debates involving nding ma possible to outline here sustainab wate resour e qua y. esnwat osysten timing the ru ate hat ust b onside mong the c tin ecosyste will b erent polic ty. Ame natura pu e informatio ab anageme society d States are able tom po appro thi sed the overall of different rnment entities have y in what wa condition nized that can be discharged into water or how water is used a water movement thro uthe biosphere is highly redistributed.and the goals of one are often at cros altered by human activities purposes with those of others.U.S.laws and water is intensively used by humans concerning water are implem ented in a manaoe ement context poor water quality is pervasive
2 Issues in Ecology Number 10 Winter 2003 Sustaining Healthy Freshwater Ecosystems by Jill S. Baron, N. LeRoy Poff, Paul L. Angermeier, Clifford N. Dahm, Peter H. Gleick, Nelson G. Hairston, Jr., Robert B. Jackson, Carol A. Johnston, Brian D. Richter, Alan D. Steinman INTRODUCTION Fresh water is vital to human life and economic wellbeing, and societies draw heavily on rivers, lakes, wetlands, and underground aquifers to supply water for drinking, irrigating crops, and running industrial processes. The benefits of these extractive uses of fresh water have traditionally overshadowed the equally vital benefits of water that remains in stream to sustain healthy aquatic ecosystems. There is growing recognition that functionally intact and biologically complex freshwater ecosystems provide many economically valuable commodities and services to society (Figure 1). The services supplied by freshwater ecosystems include flood control, transportation, recreation, purification of human and industrial wastes, habitat for plants and animals, and production of fish and other foods and marketable goods. These human benefits are what ecologists call ecological services, defined as “the conditions and processes through which natural ecosystems, and the species that make them up, sustain and fulfill human life.” Over the long term, healthy freshwater ecosystems are likely to retain the adaptive capacity to sustain production of these ecological services in the face of future environmental disruptions such as climate change. Ecological services are costly and often impossible to replace when aquatic ecosystems are degraded. Yet today, aquatic ecosystems are being severely altered or destroyed at a greater rate than at any other time in human history, and far faster than they are being restored. Debates involving sustainable allocation of water resources should recognize that maintenance of freshwater ecosystem integrity is a legitimate goal that must be considered among the competing demands for fresh water. Coherent policies are required that more equitably allocate water resources between natural ecosystem functioning and society’s extractive needs. Current water management policies in the United States are clearly unable to meet this goal. Literally dozens of different government entities have a say in what wastes can be discharged into water or how water is used and redistributed, and the goals of one agency are often at crosspurposes with those of others. U. S. laws and regulations concerning water are implemented in a management context that focuses primarily on maintaining the lowest acceptable water quality and minimal flows, and protecting single species rather than aquatic communities. A fundamental change in water management policies is needed, one that embraces a much broader view of the dynamic nature of freshwater resources and the short- and long-term benefits they provide. Our current educational practices are as inadequate as management policies to the challenge of sustainable water resource management. Hydrologists, engineers, and water managers, the people who design and manage the nation’s water resource systems, are rarely taught about the ecological consequences of management policies. Likewise, ecologists are rarely trained to consider the critical role of water in human society or to understand the institutions that manage water. Economists, developers, and politicians seldom project far enough into the future to fully account for the potential ecological costs of short-term plans. Few Americans are aware of the infrastructure that brings them pure tap water or carries their wastes away, and fewer still understand the ecological tradeoffs that are made to allow these conveniences. Although the requirements of healthy freshwater ecosystems are often at odds with human activity, this conflict need not be inevitable. The challenge is to determine how society can extract the water resources it needs while protecting the important natural complexity and adaptive capacity of freshwater ecosystems. Current scientific understanding makes it possible to outline here in general terms the requirements for adequate quantity, quality, and timing of water flow to sustain the functioning of freshwater ecosystems. A critical next step will be communication of these requirements to a broader community. The American public, when given information about management alternatives, supports ecologically based management approaches, particularly toward fresh water. Several previous studies that have addressed the overall condition of freshwater resources have recognized that • water movement through the biosphere is highly altered by human activities; • water is intensively used by humans; • poor water quality is pervasive; Figure 1—Freshwater ecosystems provide economically valuable commodities and services to humans (drinking water, irrigation, transportation, recreation, etc.), as well as habitat for plants and animals
Issues in Ecology Number 10 Winter 2003 Table 1-Changes in hydrologic flow,water quality,wetland area,and species viability in U.S.rivers,lakes,and wetlands since Euro-American settlement. U.S.Freshwater Resources Pre-settlement Condition Current Conditions Source Undammed rivers (in 48 contiguous states) 5.1 million km 4.7 million km Echeverria et al.1989 Free-flowing rivers that qualify for wild 5.1 million km o 0001 million km USD011982 and scenic status (in 48 contiquous states) Number of dams>2m 0 75.000 CE01995 Volume of water diverted from surface waters 0 10 million mday(1985) Solley et al.1998 Total daily U.S.water use Unknown 1.5 million mday(1995 Solley et al.1998 Sediment inputs to reservoirs not applicable 1.200 million m/year Stallard 1998 River water quality(1.1 million km surveyed) Unimpaired 402.000 km impaired* EPA 1998 Lake water quality*(6.8 million ha surveyed) Unimpaired 2.7million ha impaired" EPA 1998 Wetland acreage(in48 contiguous states) 87 million ha 35 million ha van der Leeden et al.1990 Number of native freshwater fish species 822 species Stein and Flack 1997 Number of native freshwater mussel specie 305 species 157 imperiled or extinct Stein and Flack 1997 Number of native crayfish species 330 species 111 imperiledor extinc Stein and Flack 1997 Number of native amphibian species 242 species 64 imperiled or extinct Stein and Flack 1997 Only 19%(1,16,00 km)of total river km in U.S.were surveyed out of a total of ,792,00 km.Only 0%(6.8 million ha)of tota lake area (16.9 million ha)were surveyed. and freshwater plant and animal species are at maintain natural habitat dynamics that support production greater risk of extinction from human activities and survival of species. Variability in the timing and rate of compared with all other species. water flow strongly influence the sizes of native plant and These and other analyses indicate that freshwater ecosystems animal populations and their age structures,the presence of es,the interact are needed In this paper we describe the requirements for water of ecosystem processes. Periodic and episodic sufficent quaity.amount.timng.and variability patterns alsc quality.physic habita ec al dynamics tha nne in aqu cosy have evol ve ting and ing ter of fre d to the wate REOUIREMENTS FOR FRESHWATER catehmants of which th Water flowing thr FCOSYSTEM INTEGRITY the landscape on its way to the se a moves in three di linking upstream to downstream stream channels to Freshwater ecosystems differ greatly from one floodplains and riparian wetlands and surface waters to another depending on type.location. and around water.materials genera ted across the landscan nevertheless share important features.For one,lake ultimately make their way into rivers lakes and othe wetlands rivers and their connerted around waters share a freshwater ecosystems Thus these systems are areatly common need for water within a certain range of quantity influenced by what happens on the land,including human and quality.In addition,because freshwater ecosystems are activities. dynamic,all require a range of natural variation or We have identified five dynamic environmental factors disturbance to maintain viability or resilience.Water flows that regulate much of the structure and functioning of any that vary both season to season and year to year,for example, aquatic ecosystem,although their relative importance varies are needed to support plant and animal communities and among aquatic ecosystem types(Figure 2).The interaction
3 Issues in Ecology Number 10 Winter 2003 • and freshwater plant and animal species are at greater risk of extinction from human activities compared with all other species. These and other analyses indicate that freshwater ecosystems are under stress and at risk (Table 1). Clearly, new management approaches are needed. In this paper we describe the requirements for water of sufficient quality, amount, timing, and flow variability in freshwater ecosystems to maintain the natural dynamics that produce ecosystem goods and services. We suggest steps to be taken toward restoration and conclude with recommendations for protecting and maintaining freshwater ecosystems. REQUIREMENTS FOR FRESHWATER ECOSYSTEM INTEGRITY Freshwater ecosystems differ greatly from one another depending on type, location, and climate, but they nevertheless share important features. For one, lakes, wetlands, rivers, and their connected ground waters share a common need for water within a certain range of quantity and quality. In addition, because freshwater ecosystems are dynamic, all require a range of natural variation or disturbance to maintain viability or resilience. Water flows that vary both season to season and year to year, for example, are needed to support plant and animal communities and maintain natural habitat dynamics that support production and survival of species. Variability in the timing and rate of water flow strongly influence the sizes of native plant and animal populations and their age structures, the presence of rare or highly specialized species, the interactions of species with each other and with their environments, and many ecosystem processes. Periodic and episodic water flow patterns also influence water quality, physical habitat conditions and connections, and energy sources in aquatic ecosystems. Freshwater ecosystems, therefore, have evolved to the rhythms of natural hydrologic variability. The structure and functioning of freshwater ecosystems are also tightly linked to the watersheds, or catchments, of which they are a part. Water flowing through the landscape on its way to the sea moves in three dimensions, linking upstream to downstream, stream channels to floodplains and riparian wetlands, and surface waters to ground water. Materials generated across the landscape ultimately make their way into rivers, lakes, and other freshwater ecosystems. Thus these systems are greatly influenced by what happens on the land, including human activities. We have identified five dynamic environmental factors that regulate much of the structure and functioning of any aquatic ecosystem, although their relative importance varies among aquatic ecosystem types (Figure 2). The interaction Table 1— Changes in hydrologic flow, water quality, wetland area, and species viability in U.S. rivers, lakes, and wetlands since Euro-American settlement. *Only 19% (1,116,500 km) of total river km in U. S. were surveyed out of a total of 5,792,400 km. Only 40% (6.8 million ha) of total lake area (16.9 million ha) were surveyed. U. S. Freshwater Resources Pre-settlement Condition Current Conditions Source Undammed rivers (in 48 contiguous states) 5.1 million km 4.7 million km Echeverria et al. 1989 Free-flowing rivers that qualify for wild 5.1 million km 0.0001 million km US DOI 1982 and scenic status (in 48 contiguous states) Number of dams >2m 0 75,000 CEQ 1995 Volume of water diverted from surface waters 0 10 million m3 day-1(1985) Solley et al. 1998 Total daily U. S. water use Unknown 1.5 million m3 day-1(1995) Solley et al. 1998 Sediment inputs to reservoirs not applicable 1,200 million m3 /year Stallard 1998 River water quality*(1.1 million km surveyed) Unimpaired 402,000 km impaired* EPA 1998 Lake water quality*(6.8 million ha surveyed) Unimpaired 2.7 million ha impaired* EPA 1998 Wetland acreage (in 48 contiguous states) 87 million ha 35 million ha van der Leeden et al. 1990 Number of native freshwater fish species 822 species 202 imperiled or extinct Stein and Flack 1997 Number of native freshwater mussel species 305 species 157 imperiled or extinct Stein and Flack 1997 Number of native crayfish species 330 species 111 imperiled or extinct Stein and Flack 1997 Number of native amphibian species 242 species 64 imperiled or extinct Stein and Flack 1997
Issues in Ecology Number 10 Winter 2003 of these drivers in space and time defines the dynamic nature Focusina on one factor at a time will not vield a of freshwater ecosy stems true picture of ecosystem functioning.Evaluating freshwater 1.The flow pattern defines the rates and pathways ecosystem integrity requires that all five of these dynamic by which rainfall and snowmelt enter and circulate within environmental factors be integrated and considered jointly. river channels,lakes,wetlands,and connecting ground waters,and also determines how long water is stored in Flow Patterns these ecosystems. 2 Sediment and organic matter inouts provide raw An evaluation of the characteristics required for healthy materials that create physical habitat structure,refugia, functionina can beain with a description of the natural or substrates,and spawning grounds and supply and store historical flow pattermns for streams,rivers,wetlands and lakes nutrients that sustain aquatic plants and animals. Certain aspects of these patterns are critical for regulating Temperature and light characteristics requlate biological productivity (that is,the growth of algae or the metabolic processes.activity levels,and productivity of phytoplankton that form the base of aquatic food webs)and aquatic organisms. biological diversity.particularly for rivers.These aspects include Chemical and nutrient conditions regulate pH. base flow,annual or frequent floods,rare and extreme flood plant and animal productivity,and water quality. events. seasonality of flows,and annual variability (BOX 1) The plant and anima assemblage influences Sucn ractors are also relevant for evaluating the integrity o ecosystem proces community structure and because flow patterns and hydrope (tha ations in water le these factors vary within deine the yea ates,as well as types a aqu such as nd and 2in atter or ences uctivity and is ann ogen highsr lows in flows.te erature.and other surroundin LOW REGIME WATER QUALITY Sediment Biotic The rmal/Light Assemblage Chemical/Nutrier Inputs Flux Functional Aquatic Ecosystems Short-term ng-term Sustainability Goods and Services And Adaptive Capacity Figure 2-Conceptual model of major forces that influence freshwater ecosystems
4 Issues in Ecology Number 10 Winter 2003 of these drivers in space and time defines the dynamic nature of freshwater ecosystems: 1. The flow pattern defines the rates and pathways by which rainfall and snowmelt enter and circulate within river channels, lakes, wetlands, and connecting ground waters, and also determines how long water is stored in these ecosystems. 2. Sediment and organic matter inputs provide raw materials that create physical habitat structure, refugia, substrates, and spawning grounds and supply and store nutrients that sustain aquatic plants and animals. 3. Temperature and light characteristics regulate the metabolic processes, activity levels, and productivity of aquatic organisms. 4. Chemical and nutrient conditions regulate pH, plant and animal productivity, and water quality. 5. The plant and animal assemblage influences ecosystem process rates and community structure. In naturally functioning freshwater ecosystems, all five of these factors vary within defined ranges throughout the year, tracking seasonal changes in climate and day length. Species have evolved and ecosystems have adjusted to accommodate these annual cycles. They have also developed strategies for surviving – and often requiring — periodic hydrologic extremes caused by floods and droughts that exceed the normal annual highs or lows in flows, temperature, and other factors. Focusing on one factor at a time will not yield a true picture of ecosystem functioning. Evaluating freshwater ecosystem integrity requires that all five of these dynamic environmental factors be integrated and considered jointly. Flow Patterns An evaluation of the characteristics required for healthy functioning can begin with a description of the natural or historical flow patterns for streams, rivers, wetlands and lakes. Certain aspects of these patterns are critical for regulating biological productivity (that is, the growth of algae or phytoplankton that form the base of aquatic food webs) and biological diversity, particularly for rivers. These aspects include base flow, annual or frequent floods, rare and extreme flood events, seasonality of flows, and annual variability (BOX 1). Such factors are also relevant for evaluating the integrity of lakes and wetlands because flow patterns and hydroperiod (that is, seasonal fluctuations in water levels) influence water circulation patterns and renewal rates, as well as types and abundances of aquatic vegetation such as reeds, grasses, and flowering plants. Furthermore, the characteristic flow pattern of a lake, wetland, or stream critically influences algal productivity and is an important factor to be considered when determining acceptable levels of nutrient (nitrogen and phosphorus) runoff from the surrounding landscape. Figure 2— Conceptual model of major forces that influence freshwater ecosystems. FLOW REGIME WATER QUALITY Sediment Flux Chemical/Nutrient Flux Thermal/Light Inputs Biotic Assemblage Functional Aquatic Ecosystems Short-term Goods and Services Long-term Sustainability And Adaptive Capacity
Issues in Ecology Number 10 Winter 2003 Human alterations of river flow have seldom taken BOX 1- DEFINING FLOW CONDITIONS FOR RIVERS AND STREAMS into account the ecological consequences."Many rivers now resemble elaborate plumbing works,with the timing and Base flow conditions characterize neriods of low flov amount of flow completely controlled.like water from a faucet hotwoon storms They define the minimum quantity so as to maximize the rivers'benefits for humans,"wrote of water in the channel.,which directly influences water policy expert Sandra L.Postel."But while modern habitat availability for aquatic organisms as well as engineering has been remarkably successful at getting wate the depth to saturated soil for riparian species.The to people and farms when and where they need it,it has magnitude and duration of hase flow varies areatly failed to protect the fundamental ecological function of rivers among different rivers,reflecting differences in climate and aquatic systems. geology.and vegetation in a watershed. in the U..West are prime Frequent(that is,two-year return interval)floods human manipul tion o reset the system by flus damages to riverban streambed,thus promoting higher production during nming rivers a and da base flow period High flows may also facilitate dispersal o organis hghf6anudo contribute 0 e ate which used to bopsanadmahpaianegeatondynanie e adja support diverse riparian Sediment and Organic Matter Inputs tant reformative events for systems They transnort large amounts of sedimer In river systems the move ement of sediments and often transferring it from the main channel to influxes of organic matter are impd ortantc ponents of habita floodolains Habitat diversity within the river structure and dynamics.Natural on ganic matter inputs include increased as channels are scoured and reformed and seasonal runoff and debris such as leaves and decaying plan successional dynamics in riparian communities and material from land-based communities in the watershed floodplain wetlands are reset. Large flows can also Especially in smaller rivers and streams.the organic matte remove species that are poorly adapted to dynamic that arrives from the land is a particularly important source river environments such as upland tree species or non of eneray and nutrients.and tree trunks and other woody native tish species.The success of non-native invaders materials that fall into the water provide important substrates is often minimized by natural high flows. and the and habitats for aquatic organisms.Natural sediment restriction of major floods by reservoirs plays ar movements are those that accompany natural variations in important role in the establishment and proliferation water flows In lakes and wetlands.all but the finest inflowind of exotic species in many river systems. sediment falls permanently to the bottom,so that over tim Seasonal timing of flows, especially high flows, these systems fill.The invertebrates,algae,bryophytes ritical for d to epro e high flow runs Alon rs cotto ood trees seeds during peak snowmelt to maximize the negative consequences for aquatic and ripariar communities Annual variation in flow is an important factor influencing river systems.For example,year-to-year variation in runoff volume can maintain high species diversity.Similarly.ecosystem productivity and foodweb structure can fluctuate in response to this This variation also ensures Figure 3-Livestock use of streams can have impacts on speci n different years.thus the amount of sediment and nutrients inputs.Photo cour promoing iversity. tesy the U.S.Geological Survey.South Platte National Water Quality Assessment Program (NAWOA)
5 Issues in Ecology Number 10 Winter 2003 Human alterations of river flow have seldom taken into account the ecological consequences. “Many rivers now resemble elaborate plumbing works, with the timing and amount of flow completely controlled, like water from a faucet, so as to maximize the rivers’ benefits for humans,” wrote water policy expert Sandra L. Postel. “But while modern engineering has been remarkably successful at getting water to people and farms when and where they need it, it has failed to protect the fundamental ecological function of rivers and aquatic systems.” Rivers in the U.S. West are prime examples of how human manipulation of water flows can lead to multiple damages to riverbank and floodplain processes and communities. Damming rivers and dampening natural variations in flow rates by maintaining minimum flows year round have contributed to widespread loss of native fish species and regeneration failure of native cottonwood trees, which used to support diverse riparian communities (BOX 2). Sediment and Organic Matter Inputs In river systems, the movement of sediments and influxes of organic matter are important components of habitat structure and dynamics. Natural organic matter inputs include seasonal runoff and debris such as leaves and decaying plant material from land-based communities in the watershed. Especially in smaller rivers and streams, the organic matter that arrives from the land is a particularly important source of energy and nutrients, and tree trunks and other woody materials that fall into the water provide important substrates and habitats for aquatic organisms. Natural sediment movements are those that accompany natural variations in water flows. In lakes and wetlands, all but the finest inflowing sediment falls permanently to the bottom, so that over time these systems fill. The invertebrates, algae, bryophytes, BOX 1— DEFINING FLOW CONDITIONS FOR RIVERS AND STREAMS Base flow conditions characterize periods of low flow between storms. They define the minimum quantity of water in the channel, which directly influences habitat availability for aquatic organisms as well as the depth to saturated soil for riparian species. The magnitude and duration of base flow varies greatly among different rivers, reflecting differences in climate, geology, and vegetation in a watershed. Frequent (that is, two-year return interval) floods reset the system by flushing fine materials from the streambed, thus promoting higher production during base flow periods. High flows may also facilitate dispersal of organisms both up- and downstream. In many cases moderately high flows inundate adjacent floodplains and maintain riparian vegetation dynamics. Rare or extreme events such as 50- or 100-year floods represent important reformative events for river systems. They transport large amounts of sediment, often transferring it from the main channel to floodplains. Habitat diversity within the river is increased as channels are scoured and reformed and successional dynamics in riparian communities and floodplain wetlands are reset. Large flows can also remove species that are poorly adapted to dynamic river environments such as upland tree species or nonnative fish species. The success of non-native invaders is often minimized by natural high flows, and the restriction of major floods by reservoirs plays an important role in the establishment and proliferation of exotic species in many river systems. Seasonal timing of flows, especially high flows, is critical for maintaining many native species whose reproductive strategies are tied to such flows. For example, some fish use high flows to initiate spawning runs. Along western rivers, cottonwood trees release seeds during peak snowmelt to maximize the opportunity for seedling establishment on floodplains. Changing the seasonal timing of flows has severe negative consequences for aquatic and riparian communities. Annual variation in flow is an important factor influencing river systems. For example, year-to-year variation in runoff volume can maintain high species diversity. Similarly, ecosystem productivity and foodweb structure can fluctuate in response to this year-to-year variation. This variation also ensures that various species benefit in different years, thus promoting high biological diversity. Figure 3—Livestock use of streams can have impacts on the amount of sediment and nutrients inputs. Photo courtesy the U.S. Geological Survey, South Platte National Water Quality Assessment Program (NAWQA)
Issues in Ecology Number 10 Winter 2003 vascular plants.and bacteria that populate the bottoms of seas freshwater systems are highly adapted to the specific sediment and organic matter conditions of their environment as are many fish species.and do not persist if changes in the type uator an size.or frequency of sediment inputs occur.The fate of these gradients in turn influence organisms is critical to sustaining freshwater ecosystems since dis and both the distributi they are responsible for much of the work of water purification,decomposition,and nutrient cycling. can chano dramatically dow emof dams (BOX 2). Humans have severely altered the natural rates of Utah's Green River.mean mo thly water temper sediment and organic matter supply to aquatic systems, het veen 2 degrees Celsius(C)in winter and 18 dearee C in increasing some inputs while decreasing others (Figure 3) summer before completion of the Flaming Gorge Dam in 1962 Poor agricultural,logging,or construction practices,for After dam closure the annual range of mean monthly wate example,promote high rates of soil erosion.In many areas temperatures below the dam was greatly narrowed,to betweer small streams or wetlands have even been completely 4 C and 9 C.As a result.species richness declined and 18 eliminated through filling.paving.or re-ouingnto artificia genera (that is arouns of related species)of insects were lost channels The U.S.Environmental Protection Agency (EPA other species,notably freshwater shrimp.came to dominate the orts that in one rter of all lakes with sub-standard water ranks of invertebrate animals.Aquatic insects have not recovere ause of impairm despite 20 years of partia tering fror temperature restoration achieve by releasing water from warme reservoir water layers. Wate temperature also dropped in th Colorado River after closure of the Glen Canyon Dam in 1963.and the fo B ty nov 1 cubic meters of sediment build up each year in U.S. (Table 1) in tum cuts off normal sand.silt. d e and gravel supplies to downstream reaches causing streambed erosion Figure 4-Eutrophication from irrigation return flows. ation to月 that both degrades in-channel Photo courtesy the U.S.Geological Survey,South Platte National Water Quality Assessment Program(NAWOA). t the to of an habitat and isolates floodplain and ommonly found much riparian wetlands from the channel further north. during rejuvenating high flows.Channel straightening overgrazing of river and stream banks,and clearing of streamside Nutrient and Chemical Conditions vegetation reduce organic matter inputs and often increase erosion. Natural nutrient and chemical conditions are those that reflect local climate.bedrock,soil,vegetation type.and Temperature and Light topography.Natural water conditions can range from clear nutrient-poor rivers and lakes on crystalline bedrock to much The light and heat properties of a body of water are more chemically enriched and algae-producing freshwaters nflue as by in catchments with organic matter-rich soils or limestone charac r th vity.Water bedrock.This natural regional diversity in watershed characteristics,in turn,sustains high biodiversity. ons,the mela at A condition known as cultural eutrophication occurs ite proces when additional nutrients,chiefly nitrogen and phosphorus.from d human activities enter freshwater ecosystems (Figure 4). fit nd h the living community in a body of water varies from season al species can increase well beyond astern lakes such as Lakes
6 Issues in Ecology Number 10 Winter 2003 vascular plants, and bacteria that populate the bottoms of freshwater systems are highly adapted to the specific sediment and organic matter conditions of their environment, as are many fish species, and do not persist if changes in the type, size, or frequency of sediment inputs occur. The fate of these organisms is critical to sustaining freshwater ecosystems since they are responsible for much of the work of water purification, decomposition, and nutrient cycling. Humans have severely altered the natural rates of sediment and organic matter supply to aquatic systems, increasing some inputs while decreasing others (Figure 3). Poor agricultural, logging, or construction practices, for example, promote high rates of soil erosion. In many areas small streams or wetlands have even been completely eliminated through filling, paving, or re-routing into artificial channels. The U.S. Environmental Protection Agency (EPA) reports that in one quarter of all lakes with sub-standard water quality, the cause of impairment is silt entering from agricultural, urban, construction, and other non-point (widely dispersed) sources. Dams alter sediment flows both for the reservoirs behind them and the streams below, silting up the former while starving the latter. By one estimate, another 1.2 billion cubic meters of sediment builds up each year in U. S. reservoirs (Table 1). This sediment capture in turn cuts off normal sand, silt, and gravel supplies to downstream reaches, causing streambed erosion that both degrades in-channel habitat and isolates floodplain and riparian wetlands from the channel during rejuvenating high flows. Channel straightening, overgrazing of river and stream banks, and clearing of streamside vegetation reduce organic matter inputs and often increase erosion. Temperature and Light The light and heat properties of a body of water are influenced by climate and topography as well as by the characteristics of the water body itself: its chemical composition, suspended sediments, and algal productivity. Water temperature directly regulates oxygen concentrations, the metabolic rate of aquatic organisms, and associated life processes such as growth, maturation, and reproduction. The temperature cycle greatly influences the fitness of aquatic plants and animals and, by extension, where species are distributed in the system and how the living community in a body of water varies from season to season. In lakes particularly, the absorption of solar energy and its dissipation as heat are critical to development of temperature gradients between the surface and deeper water layers and also to water circulation patterns. Circulation patterns and temperature gradients in turn influence nutrient cycling, distribution of dissolved oxygen, and both the distribution and behavior of organisms, including game fishes. Water temperature can change dramatically downstream of dams (BOX 2). In Utah’s Green River, mean monthly water temperatures ranged between 2 degrees Celsius (C) in winter and 18 degrees C in summer before completion of the Flaming Gorge Dam in 1962. After dam closure, the annual range of mean monthly water temperatures below the dam was greatly narrowed, to between 4 C and 9 C. As a result, species richness declined and 18 genera (that is, groups of related species) of insects were lost; other species, notably freshwater shrimp, came to dominate the ranks of invertebrate animals. Aquatic insects have not recovered despite 20 years of partial temperature restoration achieved by releasing water from warmer reservoir water layers. Water temperature also dropped in the Colorado River after closure of the Glen Canyon Dam in 1963, and there was a dramatic increase in water clarity. Water clarity now routinely allows visibility to greater than 7 meters, whereas prior to dam closure, the water column was opaque with suspended sediments. The colder, clearer waters have allowed a nonnative trout population to flourish, at the top of an unusual food web more commonly found much further north. Nutrient and Chemical Conditions Natural nutrient and chemical conditions are those that reflect local climate, bedrock, soil, vegetation type, and topography. Natural water conditions can range from clear, nutrient-poor rivers and lakes on crystalline bedrock to much more chemically enriched and algae-producing freshwaters in catchments with organic matter-rich soils or limestone bedrock. This natural regional diversity in watershed characteristics, in turn, sustains high biodiversity. A condition known as cultural eutrophication occurs when additional nutrients, chiefly nitrogen and phosphorus, from human activities enter freshwater ecosystems (Figure 4). The result is a decrease in biodiversity, although productivity of certain algal species can increase well beyond original levels. Midwestern and Eastern lakes such as Lakes Michigan, Huron, Erie, and Figure 4—Eutrophication from irrigation return flows. Photo courtesy the U.S. Geological Survey, South Platte National Water Quality Assessment Program (NAWQA)
Issues in Ecology Number 10 Winter 2003 Ontario demonstrate the consequences of excess inputs of the potential to push functionally intact freshwater ecosystems nutrients and toxic contaminants.as well as non-native species beyond the bounds of resilience or sustainability.threatening introductions and over-fishing (BOX 3).Onondaga Lake,New their ability to provide important goods and services on both York,which was polluted with salt brine effluent from a soda short and long time scales.Further,introduction of non-native ash industry,likewise responded with marked changes in the species that can thrive under the existing or altered range of plankton and fish communities,including invasions by non-native environmental variation can contribute to the extinction of native fish species.Among U.S.lakes identified by the EPA as impaired species,severely modify food webs,and alter ecological processe in 1996,excess nutrients contributed to more than half of the such as nutrient cycling.Exotic species are often successful in water quality problems. More than half of agricultural and modified systems,where they can be difficult to eradicate urban streams sampled by the U. Geological Survey were trations that exceed quidelines TOOLS AVAILABLE FOR RESTORATION Plant and Animal Assemblages ecosyst h a more na y of species that lives in any give and susta prevent in The sullablly ofae One tech that riv ecosystem for any particular species is dictated by the environmental conditions management tar ts for streamflow that is water flow sediment variability over time temperature.light,and nutrient patterns sed for several rivers.including th -and the presence of,and interactions among.other species in the system.Thus River in North Carolina,and the vast both the habitat and the biotic Colorado River system in the West Thes community provide controls and variable streamflow techniques seek a feedbacks that maintain a diverse range balance between water delivery needs for of species.The high degree of natural power generation or irrigation.and ir variation in environmental conditions in stream ecoloaical needs for flow variabilit -Freshwater ecosystems fresh waters across the United States Figure 5- that displays a certain timing.frequency provide habitats to plants and ani promotes high biological diversity.In fact. Human activities duration,and rate of change characteristi North American fresh water use plac ater habitats are virtually unrivaled in diversity of fish, many of these reshwater species of the natural system(Figure 6).Restoring crayfish,amphibian,and aquatic xtinction. Photo courte this flow variability helps to reconnec reptile olog Survey. South dynamic riparian and groundwater systems enabling water to mov he Program(NAWQA). more naturally through all dim are processe decomp aegoasgnaa of water Other restor tion,both fron often perfo point sou age pipe off fron with capacity to adap sources is a kind of i Water Act nd Safe Dr tinue durin en ntal stross and toxin to this is connectivity am water bodies.which allows ply the maiority of pollutants to freshwater ecos species to move to more suitable habitat as environmental some situatio ns best manao conditions change Human activities that alter freshwater environmental practices includeer sion contro and moderate application conditions can greatly change both the identity of the species of fertilizers.pesticides and herbicides. Best ma in the community and the functioning of the ecosystem(Figure practices require willing farmers,however.and willingness is 5).Excessive stressor simplification of natural complexity has often a response either to economic incentives or to stringent
7 Issues in Ecology Number 10 Winter 2003 Ontario demonstrate the consequences of excess inputs of nutrients and toxic contaminants, as well as non-native species introductions and over-fishing (BOX 3). Onondaga Lake, New York, which was polluted with salt brine effluent from a soda ash industry, likewise responded with marked changes in the plankton and fish communities, including invasions by non-native fish species. Among U.S. lakes identified by the EPA as impaired in 1996, excess nutrients contributed to more than half of the water quality problems. More than half of agricultural and urban streams sampled by the U. S. Geological Survey were found to have pesticide concentrations that exceed guidelines for the protection of aquatic life. Plant and Animal Assemblages The community of species that lives in any given aquatic ecosystem reflects both the pool of species available in the region and the abilities of individual species to colonize and survive in that water body. The suitability of a freshwater ecosystem for any particular species is dictated by the environmental conditions – that is, water flow, sediment, temperature, light, and nutrient patterns — and the presence of, and interactions among, other species in the system. Thus, both the habitat and the biotic community provide controls and feedbacks that maintain a diverse range of species. The high degree of natural variation in environmental conditions in fresh waters across the United States promotes high biological diversity. In fact, North American freshwater habitats are virtually unrivaled in diversity of fish, mussel, crayfish, amphibian, and aquatic reptile species compared with anywhere else in the world. The biota, in turn, are involved in shaping the critical ecological processes of primary production, decomposition, and nutrient cycling. Within a body of water, species often perform overlapping, apparently redundant roles in these processes, a factor that helps provide local ecosystems with a greater capacity to adapt to future environmental variation. High apparent redundancy (that is, species richness or biodiversity) affords a kind of insurance that ecological functions will continue during environmental stress. Critical to this is connectivity among water bodies, which allows species to move to more suitable habitat as environmental conditions change. Human activities that alter freshwater environmental conditions can greatly change both the identity of the species in the community and the functioning of the ecosystem (Figure 5). Excessive stress or simplification of natural complexity has the potential to push functionally intact freshwater ecosystems beyond the bounds of resilience or sustainability, threatening their ability to provide important goods and services on both short and long time scales. Further, introduction of non-native species that can thrive under the existing or altered range of environmental variation can contribute to the extinction of native species, severely modify food webs, and alter ecological processes such as nutrient cycling. Exotic species are often successful in modified systems, where they can be difficult to eradicate. TOOLS AVAILABLE FOR RESTORATION Despite widespread degradation of freshwater ecosystems, management techniques are available that can restore these systems to a more natural and sustainable state and prevent continued loss of biodiversity, ecosystem functioning, and ecological integrity. One technique, for example, involves restoring some of the natural variations in stream flow, based on the understanding that river systems are naturally dynamic. New statistical approaches to setting management targets for streamflow variability over time have been applied to or proposed for several rivers, including the Flathead River in Montana, the Roanoke River in North Carolina, and the vast Colorado River system in the West. These variable streamflow techniques seek a balance between water delivery needs for power generation or irrigation, and instream ecological needs for flow variability that displays a certain timing, frequency, duration, and rate of change characteristic of the natural system (Figure 6). Restoring this flow variability helps to reconnect dynamic riparian and groundwater systems with surface flows, enabling water to move more naturally through all the spatial dimensions that are essential to fully functional ecosystems. Other restoration efforts target pollution, both from point sources such as effluent from industrial or sewage pipes and nonpoint sources such as fertilizer runoff from urban lawns and rural croplands. Point sources of water pollution are readily identified, and many have been controlled, thanks in large part to the federal Clean Water Act and Safe Drinking Water Act. Nonpoint sources of nutrients and toxins now supply the majority of pollutants to freshwater ecosystems. In some situations, best management practices have succeeded in reducing runoff of agricultural pollutants. These practices include erosion control and moderate applications of fertilizers, pesticides and herbicides. Best management practices require willing farmers, however, and willingness is often a response either to economic incentives or to stringent Figure 5—Freshwater ecosystems provide habitats to plants and animals. Human activities and water use place many of these freshwater species at risk of extinction. Photo courtesy the U.S. Geological Survey, South Platte National Water Quality Assessment Program (NAWQA)
Issues in Ecology Number 10 Winter 2003 BOX 2-THE COLORADO RIVER The Colorado River is one of the most highly sed rive s in the world.Two reservoirs lakes Powell and Mead along with 12 other larne equations desianed to maximize both hydroelectric generation and water supplies for.domestic.and industrial use in seven states acre oss the Western lnited state s and Mexico.More than 30 million people depend on Colorado River water.The original Colorado River Compact of 198 llocated all water for societal use.(Actually it over-allocated because typical water volumes were overestimated while year-to-year variability was ignored.) Physical changes to the river below the dams have been profound.Flow in the Colorado River is snowmelt driven.and pre-dam flow patterns were dominated by large discharges from Apri vs in late summe and fall. The river carried tremendou rom nighly erodible Colorado Plateau, temperatures were melt,and peak ur in any m ases as gree ic me vital role rapped behin and the waters below are wate the bo ers of most reservoirs, ature or hundreds w th the natur 、the upper reversal of Colora re water is release Ecological responses to the dams have been equally profound.The clear,cold tail waters below the dams,in conjunction with widespread introduction of non-native species,have promoted food webs that are alien to the Colorado River.Prior to regulation,the organic matter that fueled the river food web primarily originated on land and was carried into the river during large runoft events.Now,organic matter is supplied largely by luxuriant mats of algae that grow on the bottom of the river.The algae are consumed by insects and other invertebrates that historically occurred only in the much colder tributanes or the Colorado;these insects and invertebrates are in turn eaten by non-native rainbow and brown trout.Below the Glen Canyon Dam that holds Lake Powell,only four out of eight indigenous fish species rema hes,many of which either compete witl or directly feed on the endangered native fish 00 ning because the trees are upstream res f annual floods prever are more tolerant of these modified conditions have The effects of 14 major dams and hundreds of water diversions have been felt all the way to the river mouth.Since completion of the Glen Canyon Dam in 1963,measurable flows from the Colorado River into the Sea of Cortez have occurred only infrequently.The wetland area at the mouth of the river has decreased from a historical average of 250,000 hectares to 5,800 to 63,000 hectares(depending on the year).In the Sea of Cortez,the lack of freshwater inflows has contributed to the endangerment of a large number of species.and the loss of algal productivity has caused the abundance of bivalve mollusk populations to drop 94 percent from 1950 values. gical Act of 19 Canyon Prote n Monitor rch Center to are Iof which are od o p05 experimental flood was generated to help scientists and managers i vestigate the effects of hiab flows on sedim rg ort and biolonical cultural and socioec Another set of experimental floods is nla d alon with aggressive efforts to reduce non-native trout onulations There is also discussion of installing a the nperatures below it.Partial restoration of historic ten tures below below the dam.More than 20 vears later.the number of species is as low or lower than before the restoration efforts began Further downstream,the number of insect taxa did increase,but only because warmer summer temperatures occurred in combination with periodic floods and sediment inputs from a tributary
8 Issues in Ecology Number 10 Winter 2003 BOX 2 — THE COLORADO RIVER The Colorado River is one of the most highly regulated and heavily used river systems in the world. Two principal reservoirs, Lakes Powell and Mead, along with 12 other large reservoirs store and release water according to complicated equations designed to maximize both hydroelectric generation and water supplies for agricultural, domestic, and industrial use in seven states across the Western United States and Mexico. More than 30 million people depend on Colorado River water. The original Colorado River Compact of 1928 allocated all water for societal use. (Actually it over-allocated because typical water volumes were overestimated while year-to-year variability was ignored.) Physical changes to the river below the dams have been profound. Flow in the Colorado River is snowmelt driven, and pre-dam flow patterns were dominated by large discharges from April through July, followed by low flows in late summer and fall. The river carried tremendous amounts of sediment from the highly erodible Colorado Plateau, and river temperatures were seasonally warm. Today, river flow is nearly decoupled from natural snowmelt, and peak discharges can occur in any month, often November to January. Daily changes in water releases as great as 566 cubic meters per second occur regularly for hydropower generation. Alluvial sediment, which once played a vital role in creating inchannel habitat, is now trapped behind the dams, and the waters below are clear and sediment-starved. Also, because water is released from the bottom waters of most reservoirs, water temperatures for hundreds of kilometers below the dams are very cold throughout the summer and relatively warm during the winter, a reversal of the natural seasonal cycle. (An exception is Flaming Gorge Reservoir on the Green River in the upper Colorado basin, where water is released from multiple reservoir layers.) Ecological responses to the dams have been equally profound. The clear, cold tail waters below the dams, in conjunction with widespread introduction of non-native species, have promoted food webs that are alien to the Colorado River. Prior to regulation, the organic matter that fueled the river food web primarily originated on land and was carried into the river during large runoff events. Now, organic matter is supplied largely by luxuriant mats of algae that grow on the bottom of the river. The algae are consumed by insects and other invertebrates that historically occurred only in the much colder tributaries of the Colorado; these insects and invertebrates are in turn eaten by non-native rainbow and brown trout. Below the Glen Canyon Dam that holds Lake Powell, only four out of eight indigenous fish species remain, along with 22 non-native fishes, many of which either compete with or directly feed on the endangered native fish. Native cottonwood trees and the animal community they support are declining because the trees are unable to take root under variable flows. Also, upstream reservoirs that reduce the magnitude of annual floods prevent the establishment of cottonwoods higher on the riverbanks. Other shrubs and trees that are more tolerant of these modified conditions have grown profusely, including non-natives such as tamarisk. The effects of 14 major dams and hundreds of water diversions have been felt all the way to the river mouth. Since completion of the Glen Canyon Dam in 1963, measurable flows from the Colorado River into the Sea of Cortez have occurred only infrequently. The wetland area at the mouth of the river has decreased from a historical average of 250,000 hectares to 5,800 to 63,000 hectares (depending on the year). In the Sea of Cortez, the lack of freshwater inflows has contributed to the endangerment of a large number of species, and the loss of algal productivity has caused the abundance of bivalve mollusk populations to drop 94 percent from 1950 values. To reduce the impact of dam operations on the river’s ecological resources, Congress passed the Grand Canyon Protection Act of 1992. A large group of Colorado River stakeholders now work with a Department of Interior sponsored Grand Canyon Monitoring and Research Center to attempt through adaptive management to protect and restore riparian areas and native fishes, several of which are threatened or endangered. In 1996, after nearly 15 years of study, a large experimental flood was generated to help scientists and managers investigate the effects of high flows on sediment transport and biological, cultural, and socioeconomic resources. Another set of experimental floods is planned, along with aggressive efforts to reduce non-native trout populations. There is also discussion of installing a thermal control device on Glen Canyon Dam to raise water temperatures below it. Partial restoration of historic temperatures below Flaming Gorge Dam on the Green River, however, have not improved conditions for aquatic insects directly below the dam. More than 20 years later, the number of species is as low or lower than before the restoration efforts began. Further downstream, the number of insect taxa did increase, but only because warmer summer temperatures occurred in combination with periodic floods and sediment inputs from a tributary
Issues in Ecology Number 10 Winter 2003 Is it possible to manage a river as highly regulated as the Colorado in ways that protect and improve environmental conditions for the native biota?Only time will tell,but an important first step is recognizing that key processes and conditions must be allowed to fluctuate within a range of natural variability. co SAN JUAN GILA Photo credits,clockwise from top center:Green River,22 May 1871:John Wesley Powell Photographs/#17234 Grand Canyon National Park Museum Collection:Loch Vale Watershed,CO:J.Baron:Colorado River:K.Henry Grand Canyon ca.1872.John Wesley Powell Photographs/#17248,Grand Canyon National Park Museum Collection Colorado River delta:Jennifer Pitt,Environmental Defense:Lake Mead:National Park Service:Hoover Dam,2002:P Nagler:Glen Canyon Dam:Bureau of Reclamation,Upper Colorado Region. reaulations to help in determinina best management standards for a pollutant are established within each ecoregion practices.the EPA has recently published quidelines for based on comparison with relatively unpolluted watersor establishing acceptable nutrient runoff criteria for different if few or no unpolluted waters re main in a region on regions of the United States,recognizing the inherent natural waters with the lowest pollution levels (Figure )Once a variability in local and regional availability of nutrients.The standard is set,management practices can be enacted to guidelines are based on Total Maximum Daily Load (TMDL). reduce inputs of unwanted pollutants. a calculation of the maximum amount of a pollutant that a Another large source of nonpoint pollution is water body can receive and still meet water quality atmospheric deposition of nitrogen and other contaminants standards.To allow for natural variation,water quality that fall as acid rain or dry pollutants.These could be
9 Issues in Ecology Number 10 Winter 2003 Photo credits, clockwise from top center: Green River, 22 May 1871: John Wesley Powell Photographs / # 17234, Grand Canyon National Park Museum Collection; Loch Vale Watershed, CO: J. Baron; Colorado River: K. Henry; Grand Canyon ca. 1872, John Wesley Powell Photographs / # 17248, Grand Canyon National Park Museum Collection; Colorado River delta: Jennifer Pitt, Environmental Defense; Lake Mead: National Park Service; Hoover Dam, 2002: P. Nagler; Glen Canyon Dam: Bureau of Reclamation, Upper Colorado Region. Is it possible to manage a river as highly regulated as the Colorado in ways that protect and improve environmental conditions for the native biota? Only time will tell, but an important first step is recognizing that key processes and conditions must be allowed to fluctuate within a range of natural variability. regulations. To help in determining best management practices, the EPA has recently published guidelines for establishing acceptable nutrient runoff criteria for different regions of the United States, recognizing the inherent natural variability in local and regional availability of nutrients. The guidelines are based on Total Maximum Daily Load (TMDL), a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards. To allow for natural variation, water quality standards for a pollutant are established within each ecoregion based on comparison with relatively unpolluted waters or – if few or no unpolluted waters remain in a region — on waters with the lowest pollution levels (Figure 7). Once a standard is set, management practices can be enacted to reduce inputs of unwanted pollutants. Another large source of nonpoint pollution is atmospheric deposition of nitrogen and other contaminants that fall as acid rain or dry pollutants. These could be