Climate Change and...

Annotated Bibliography

Effects of Climate Change

Freshwater Ecosystems

Haak, A.L., Williams, J.E., Isaak, D., Todd, A., Muhlfeld, C., Kershner, J.L., Gresswell, R., Hostetler, S., and Neville,H.M., 2010, The potential influence of changing climate on the persistence of salmonids of the inland west: U.S. Geological Survey Open-File Report 2010–1236, 74 p.

Warming during the 20th century drove a series of environmental trends that have profound implications for many aspects of salmonid habitat including disturbance regimes, such as wildfire, and unfavorable changes to thermal and hydrologic properties of aquatic systems. As dramatic and extensive as climatic and environmental trends are for salmonid habitats, global climate models (GCMs) project that many of these trends will continue and even accelerate until at least the middle of the 21st century.

Matthews, W.J., E.G. Zimmerman (1990). Potential effects of global warming on native fishes of the southern Great Plains and the Southwest. Fisheries 15 (6): 26-32

ABSTRACT: Fish in streams of the southern Great Plains and southwestern North America may be particularly vulnerable to extirpation or extinction due to global warming. Streams of this region already have some of the hottest free-flowing water on earth (summer maxima of 38–40°C), and even now fish live at times very near their lethal thermal limits. Unlike many terrestrial and marine organisms or fishes of some rivers, fishes in these prairie stream systems cannot migrate northward to cooler temperatures in the event of global warming. If warming of 3–4°C occurs, a substantial number of species endemic to this region could face extinction unless they adapt behaviorally or genetically for thermal increases. Existing evidence suggests little likelihood of successful behavioral adjustments. Data on thermal tolerance of local populations provide conflicting evidence: one widespread species of the Great Plains shows no difference in thermal tolerance across its range, whereas another shows adaptation to environmental temperatures at the local level. Because of the evolutionarily brief time predicted for global warming, it is unlikely that genetic options can arise rapidly enough through mutation to allow species to cope with hotter environments. Species that survive major increases in environmental temperature will likely be ones with adequate existing genetic variation to allow survival and selection of at least some individuals. Overall, the outlook for native fishes of the Great Plains and southwest is bleak, if predicted temperature increases occur.

J. D. Meisner (1990). Effect of climatic warming on the southern margins of the native range of brook trout,Salvelinus fontinalis . Canadian Journal of Fisheries and Aquatic Sciences 47 (6): 1065-1070

ABSTRACT: Stream inventories of brook trout (Salvelinus fontinalis ) habitat show that the minimum altitude of a brook trout stream in the southern part of the native range rises steadily from sea level at about 39° 12′N, to approximately 640 m at about 34° 40′N at the southern margin of the range. Using this empirical lower stream boundary and a statistical model of the influence of altitude and latitude on groundwater temperature, I suggest that the lower altitudinal margin of the southern part of the native range is shaped by the 15 °C groundwater isotherm. I used the climate warming scenario of the Goddard Institute for Space Studies, GISS, to estimate the increase in groundwater temperature in the native brook trout range, and to estimate the increase in the altitude of the lower stream boundary in a "warmer" climate. The GISS scenario projects a 3.8 °C increase in mean annual air temperature for the southern part of the native brook trout range in the next century, which leads to increases of up to 714 m in the altitude of the lower stream boundary, and to significant reductions in area available for brook trout.

C. E. Williamson, W. Dodds, T. K. Kratz, M. A. Palmer (2008). Lakes and streams as sentinels of environmental change in terrestrial and atmospheric processes. Frontiers in Ecology and the Environment 6 (5): 247-254

ABSTRACT: Recent advances in our understanding of the importance of continental- to global-scale connectivity among terrestrial and aquatic ecosystems make consideration of aquatic–terrestrial linkages an urgent ecological and environmental issue. Here, we describe the role of inland waters as sentinels and integrators of the impact of humans on terrestrial and aquatic ecosystems. The metabolic responses of lakes and streams (ie the rates at which these systems process carbon) are proposed as a common metric to integrate the impacts of environmental change across a broad range of landscapes. Lakes and streams transport and alter nutrients, contaminants, and energy, and store signals of environmental change from local to continental scales over periods ranging from weeks to millennia. A carefully conceived and well-integrated network that includes monitoring and experimental approaches to terrestrial–aquatic connectivity is critical to an understanding of basic ecosystem-level processes and to forecasting and mitigating future environmental impacts at the continental scale.

W.R. Rouse, M.S.V. Douglas, R.E. Hecky, A.E. Hershey, G.W. Kling, L.E> Lesack, P. Marsh, M. McDonald, B.J. Nicholson, N.T. Roulet, J.P. Smol (1997). Effects of climate change on the freshwaters of Arctic and subarctic North America. Hydrological Processes 11 (8): 873-902

ABSTRACT: Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO2 scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect of the environment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water supply of lakes in delta regions and which determines the availability of habitat for aquatic organisms. Climate warming or river damming and diversion would probably lead to the complete drying of many delta lakes. Climate warming would also change the characteristics of ponds that presently freeze to the bottom and result in fundamental changes in their limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the chemical, mineral and nutrient status of lakes and most likely have deleterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive. Extensive wetlands and peatlands are an important component of the global carbon budget, and warmer and drier conditions would most likely change them from a sink to a source for atmospheric carbon. There is some evidence that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation patterns; to model the thermal behaviour of wetlands, lakes and rivers; to understand better the interrelationships of cold region rivers with their basins; to begin studies on the very large lakes in the region; to obtain a firm grasp of the role of northern peatlands in the global carbon cycle; and to link the terrestrial water balance to the thermal and hydrological regime of the polar sea. Overall, there is a strong need for basic research and long-term monitoring.

D. Hope, M.F. Billett, R. MIlne, T.A.W. Brown (1997). Exports of organic carbon in British rivers. 11 (3): 325-344

ABSTRACT: This study provides the first detailed estimate of riverine organic carbon fluxes in British rivers, as well as highlighting major gaps in organic carbon data in national archives. Existing data on organic carbon and suspended solids concentrations collected between 1989 and 1993, during routine monitoring by the River Purification Boards (RPBs) in Scotland and the National River Authorities (NRAs) in England and Wales, were used with annual mean flows to estimate fluxes of dissolved and particulate organic carbon (DOC and POC) in British rivers. Riverine DOC exports during 1993 varied from 7·7-103·5 kg ha-1 year-1 , with a median flux of 31·9 kg ha-1 year-1 in the 85 rivers for which data were available. There was a trend for DOC fluxes to increase from the south and east to the north and west. A predictive model based on mean soil carbon storage in 17 catchments, together with regional precipitation totals, explained 94% of the variation in the riverine DOC exports in 1993. This model was used to predict riverine DOC fluxes in regions where no organic carbon data were available. Calculated and predicted fluxes were combined to produce an estimate for exports of DOC to tidal waters in British rivers during 1993 of 0·68±0·07 Mt. Of this total, rivers in Scotland accounted for 53%, England 38% and Wales 9%. Scottish blanket peats would appear to be the largest single source of DOC exports in British rivers. An additional 0·20 Mt of organic carbon were estimated to have been exported in particulate form in 1993, approximately two-thirds of which was contributed by English rivers. It is suggested that riverine losses of organic carbon have the potential to affect the long-term dynamics of terrestrial organic carbon pools in Britain and that rivers may regulate increases in soil carbon pools brought about by climate change.

Chatters, J.C., V.L. Butler, M.J. Scott, D.M. Anderson, D.A. Neitzel (1992). A paleoscience approach to estimating the effects of climatic warming on salmonid fisheries of the Columbia River Basin. U.S. Department of Energy, Pacific Northwest Lab

ABSTRACT: Efforts to estimate the effect of climate change on fisheries are hampered by the lack of models that project realistic aquatic habitat conditions at the regional scale. Data from the paleosciences are a suitable alternative both for environmental scenario development and model validation. We are using a paleoscience approach to calculate the potential effect of global warming on anadromous salmonid stocks of the Columbia River Basin, northwestern America. First, archaeologically dated fluvial sediments and bivalves were used with terrestrial paleoecological data to reconstruct the flow, flow patterns, temperatures, and bed conditions 6000-7000 years ago, when paleoclimatic indicators and atmospheric models suggest regional temperatures were up to 2°C warmer. Next, these conditions were imposed on Columbia system subbasins and their effects on salmon stocks were modeled using the Northwest Power Planning Council's computer-based Tributary Parameter Model and System Planning Model. Results thus far indicate a 30 to 60% decline in salmon stocks relative to current conditions. Finally, fish remains from archaeological sites were analyzed for evidence of actual salmon production under the reconstructed stream conditions to assess the validity of model projections. Preliminary findings are comparable to model predictions. Important side benefits of using paleoscience data are that they allow a direct measurement of climatic effects on resources of concern, and are readily understood by both policymakers and the public.

J. E. Williams, A. L. Haak, H. M. Neville, W. T. Colyer (2009). Potential consequences of climate change to persistence of cutthroat trout populations. North American Journal of Fisheries Management 29 (3): 533-548

ABSTRACT: Warmer water, changes in stream flow, and the increasing frequency and intensity of other disturbances are among the factors associated with climate change that are likely to impact native trout populations in the western USA. We examined how three of these factors—increased summer temperatures, uncharacteristic winter flooding, and increased wildfires—are likely to affect broad-scale population persistence among three subspecies of cutthroat troutOncorhynchus clarkii . Our results suggest that as much as 73% of the habitat currently occupied by Bonneville cutthroat troutO. c. utah , 65% of that occupied by westslope cutthroat troutO. c. lewisi , and 29% of that occupied by Colorado River cutthroat troutO. c. pleuriticus will be at high risk from one or more of the these three factors. Within the next 50 years, wildfire, floods, and other disturbances may have a greater impact on population persistence than increasing water temperature alone. Our results also suggest that the risk will vary substantially within subspecies. For each subspecies, our analyses identified large portions of their ranges where all populations either currently fail to meet basic persistence criteria, are at high risk from climate change, or both, indicating a high likelihood of losing the genetic and life history diversity in those areas. Stress from climate change is likely to compound existing problems associated with habitat degradation and introgression from introduced salmonids. Recognition of the increased risk from climate change may warrant altering the management paradigm of isolation and require increased control efforts for invasive nonnative species. Regardless of the management avenue chosen, more populations are likely to become isolated and vulnerable in the near future. Our results argue for immediate restoration actions within certain subbasins to increase the resistance and resilience of at-risk populations and habitats to additional disturbances caused by rapid climate change.

Condron, A., DeConto, R., Bradley, R. S., Juanes, F. (2005). Multidecadal North Atlantic climate variability and its effect on North American salmon abundance. Geophysical Research Letters 32 (23): L23703

ABSTRACT: Climate variability is now known to play a key role in the abundance of marine fisheries, and must be accounted for to implement sustainable management strategies. We show that North American Atlantic salmon abundance has fluctuated in parallel with the Atlantic Multidecadal Oscillation (AMO); a basin-wide, low frequency climate mode producing cold-warm-cold sea surface temperatures over the last century. During the AMO warm (cool) phase salmon abundance is lower (higher). Changes in sea surface temperature associated with the AMO are most pronounced in the winter season near the Grand Banks of Newfoundland, a known overwintering area for salmon and an important time for determining survival. A moratorium on salmon fishing was established in 1992, but has so far contributed few signs of improvement in stock size. This may be explained by a shift in the AMO to a positive phase, producing persistently warm temperatures in the marine environment. Our findings show that a continued warming near the Grand Banks of Newfoundland will have a detrimental impact on this already depleted stock despite the reduction in commercial fishing.

Greenwald, D.N., L. B. Brubaker (2001). A 5000-year record of disturbance and vegetation change in riparian forests of the Queets River, Washington, U.S.A.. Canadian Journal of Forest Research 31 (8): 1375-1385

ABSTRACT: We used fossil pollen, charcoal, and sediment stratigraphy in three small hollows to investigate disturbance events and changes in the composition of riparian forests on a small section of the Queets River floodplain, Olympic Peninsula, Washington. The records ranged in age from approximately 500 years at two sites 300 and 550 m from the river, to 5000 years at a site 800 m from the river. Approximately 400–600 years BP, the two sites nearest the river were either inundated by a very large flood or covered by the active channel, which would have occupied a substantially different position than its present course. Following inundation or channel movement, the pollen record suggests thatAlnus rubra Bong., the primary mesic forest colonizer in the Pacific Northwest, increased and was then replaced byPicea sitchensis (Bong.) Carrière andTsuga heterophylla (Raf.) Sarg. At the site farthest from the river, two fires occurred within the last ca. 4500 years. One of the fires was followed by a period of shrub dominance and succession toTsuga heterophylla . The other fire did not cause a change in the pollen record. A recent unprecedented rise inTsuga heterophylla pollen, which began ca. 1000 years BP, might be in response to cooling during the Little Ice Age. Overall, the small hollow records highlight the complex effect of floods, fire, and possibly climate change on riparian forests of the Queets River.

B.B. Wolfe, T.L. Karst-Riddoch, S.R. Vardy, M.D. Falcone, R. I. Hall, T.W.D. Edwards (2005). Impacts of climate and river flooding on the hydro-ecology of a floodplain basin, Peace-Athabasca Delta, Canada since A.D. 1700. Quaternary Research 64 (2): 147-162

ABSTRACT: Multi-proxy paleolimnological analyses on lake sediment cores from “Spruce Island Lake” (58° 50.82' N, 111° 28.84' W), a perched basin in the northern Peace sector of the Peace-Athabasca Delta (PAD), Canada, give insights into the relative roles of flow regulation of the Peace River and climatic variability on the basin hydro-ecology. Results indicate substantial variability in basin hydro-ecology over the past 300 years ranging from seasonal to periodic desiccation in the 1700s to markedly wetter conditions during the early 1800s to early 1900s. The reconstruction is consistent with (1) dry climatic conditions that defined the peak of the Little Ice Age and subsequent amelioration evident in conventional ring-width and isotopic analyses of tree-ring records located hydrologically and climatically upstream of the PAD, and (2) Peace River flood history inferred from sub-annual magnetic susceptibility measurements from another lake sediment record in the Peace sector of the PAD. Although regulation of the Peace River for hydroelectric power generation since 1968 has long been considered a major stressor of the PAD ecosystem leading to reduced frequency of ice-jam and open-water flooding and an extended period of drying, our results show that current hydro-ecological status is not unprecedented as both wetter and drier conditions have persisted for decades in the recent past under natural climatic variability. Furthermore, paleolimnological evidence from Spruce Island Lake indicates that recently observed dryness is part of a longer trend which began some 20–40 years prior to Peace River regulation.

Wigand, P.E., D. Rhode, R. Hershler, D.B. Madsen, D.R. Curry (2002). Great Basin vegetation history and aquatic systems: the last 150,000 years. Smithsonian Institution Press: 309-367

ABSTRACT: The 14 papers collected herein treat diverse aspects of the aquatic history of the Great Basin of the western United States and collectively attempt to summarize and integrate portions of the vast body of new information on this subject that has been acquired since the last such compilation was published in 1948. In the first section, four papers (Lowenstein, Negrini, Reheis et al., Sack) focus on the physical aspects of the Great Basin paleolake histories, whereas a fifth paper (Oviatt) summarizes the contributions to the study of Bonneville Basin lacustrine history made by two early giants of the field, Grove Karl Gilbert and Ernst Antevs. In the second section, four papers synthesize perspectives on Great Basin aquatic history provide by diatoms and ostracods (Bradbury and Forester), fishes (Smith et al.), aquatic insects (Polhemus and Polhemus), and aquatic snails (Hershler and Sada), whereas a fifth (Sada and Vinyard) summarizes the conservation status of the diverse aquatic biota that is endemic to the region. In the final section, three papers integrate terrestrial biotic evidence pertaining to Great Basin aquatic history derived from pollen from cores (Davis), floristics (Wigand and Rhode), and the mammal record (Grayson), whereas a fourth (Madsen) examines the relationship between Great Basin lakes and human inhabitants of the region. Although diverse in scope and topic, the papers in this volume are nonetheless linked by an appreciation that integration of geological, biological, and anthropological evidence is a necessary and fundamental key to a mature understanding of Great Basin aquatic systems history.

C. A. Gibson, J. L. Meyer, N. L. Poff, L. E. Hay, A. Georgakakos (2005). Flow regime alterations under changing climate in two river basins: implications for freshwater ecosystems. River Research and Applications 21 (8): 849-864

ABSTRACT: We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee-Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river-floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee-Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee-Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability of the river to assimilate wastewater treatment plant effluent. Our study illustrates the types of changes that river ecosystems might experience under future climates.

Cooney, S.J., A. P. Covich, P.M. Lukacs, A. L. Harig, K.D. Fausch (2005). Modeling global warming scenarios in Greenback cutthroat trout (Oncorynchus clarki stomias ) streams: implications for species recovery. Western North American Naturalist 65 (3): 371-381

ABSTRACT: Changes in global climate may exacerbate other anthropogenic stressors, accelerating the decline in distribution and abundance of rare species throughout the world. We examined the potential effects of a warming climate on the greenback cutthroat trout (Oncorhynchus clarki stomias), a resident salmonid that inhabits headwater streams of the central Rocky Mountains. Greenbacks are outcompeted at lower elevations by nonnative species of trout and currently are restricted to upper-elevation habitats where barriers to upstream migration by nonnatives are or have been established. We used likelihood-based techniques and information theoretics to select models predicting stream temperature changes for 10 streams where greenback cutthroat trout have been translocated. These models showed high variability among responses by different streams, indicating the usefulness of a stream-specific approach. We used these models to project changes in stream temperatures based on 2 °C and 4 °C warming of average air temperatures. In these warming scenarios, spawning is predicted to begin from 2 to 3.3 weeks earlier than would be expected under baseline conditions. Of the 10 streams used in this assessment, 5 currently have less than a 50% chance of translocation success. Warming increased the probability of translocation success in these 5 streams by 11.2% and 21.8% in the 2 scenarios, respectively. Assuming barriers to upstream migration by nonnative competitors maintain their integrity, we conclude that an overall habitat improvement results because greenbacks have been restricted through competition with nonnatives to suboptimal habitats, which are generally too cold to be highly productive.

N. L. Poff, S. Tokar, P. Johnson (1996). Stream hydrological and ecological responses to climate change assessed with an artificial neural network. Limnology and Oceanography 41 (5): 857-863

ABSTRACT: An artificial neural network (ANN) was used to evaluate the hydrological responses of two streams in the northeastern U.S. having different hydroclimatologies (rainfall and snow + rain) to hypothetical changes in precipitation and thermal regimes associated with climate change. For each stream, historic precipitation and temperature data were used as input to an ANN, which generated a synthetic daily hydrograph with high goodness-of-fit (r2 > 0.80). Four scenarios of climate change were used to evaluate stream responses to climate change: + 25% precipitation, -25% precipitation, 2x the coefficient of variation in precipitation regime, and +3°C average temperature. Responses were expressed in hydrological terms of ecological relevance, including flow variabilitiy, baseflow conditions, and frequency and predictability of floods. Increased average precipitation induced elevated runoff and more frequent high flow events, while decreased precipitation had the opposite effect. Elevated temperature reduced average runoff. Doubled precipitation variability had a large effect on many variables, including average runoff, variability of flow, flooding frequency, and baseflow stability. In general, the rainfall-dominated stream exhibited greater relative response to climate change scenarios than did the snowmelt stream.

Dahm, C.N., M.A. Baker, D. I. Moore, J. R. Thibault (2003). Coupled biogeochemical and hydrological responses of streams and rivers to drought. Freshwater Biology 48 (7): 1219-1231

ABSTRACT: 1. Severe or extreme droughts occurred about 10% of the time over a 105-year record from central New Mexico, U.S.A., based on the Palmer Drought Severity Index.

2. Drought lowers water tables, creating extensive areas of groundwater recharge and fragmenting reaches of streams and rivers. Deeper groundwater inputs predominate as sources of surface flows during drought. Nutrient inputs to streams and rivers reflect the biogeochemistry of regional ground waters with longer subsurface residence times.

3. Inputs of bioavailable dissolved organic carbon to surface waters decrease during drought, with labile carbon limitation of microbial metabolism a byproduct of drought conditions.

4. Decreased inputs of organic forms of carbon, nitrogen and phosphorus and a decrease in the organic:inorganic ratio of nutrient inputs favours autotrophs over heterotrophs during drought.

5. The fate of autotrophic production during drought will be strongly influenced by the structure of the aquatic food web within impacted sites.

G. R. McMurray, R. J. Bailey (1998). Change in Pacific Northwest coastal ecosystems. NOAA Coastal Ocean Program: 342 pp.

EXECUTIVE SUMMARY: Over the past one hundred and fifty years, the landscape and ecosystems of the Pacific Northwest coastal region, already subject to many variable natural forces, have been profoundly affected by human activities. In virtually every coastal watershed from the Strait of Juan de Fuca to Cape Mendocino, settlement, exploitation and development of resources have altered natural ecosystems. Vast, complex forests that once covered the region have been largely replaced by tree plantations or converted to non-forest conditions. Narrow coastal valleys, once filled with wetlands and braided streams that tempered storm runoff and provided salmon habitat, were drained, filled, or have otherwise been altered to create land for agriculture and other uses. Tideflats and saltmarshes in both large and small estuaries were filled for industrial, commercial, and other urban uses. Many estuaries, including that of the Columbia River, have been channeled, deepened, and jettied to provide for safe, reliable navigation. The prodigious rainfall in the region, once buffered by dense vegetation and complex river and stream habitat, now surges down simplified stream channels laden with increased burdens of sediment and debris. Although these and many other changes have occurred incrementally over time and in widely separated areas, their sum can now be seen to have significantly affected the natural productivity of the region and, as a consequence, changed the economic structure of its human communities.

This activity has taken place in a region already shaped by many interacting and dynamic natural forces. Large-scale ocean circulation patterns, which vary over long time periods, determine the strength and location of currents along the coast, and thus affect conditions in the nearshore ocean and estuaries throughout the region. Periodic seasonal differences in the weather and ocean act on shorter time scales; winters are typically wet with storms from the southwest while summers tend to be dry with winds from the northwest. Some phenomena are episodic, such as El Niño events, which alter weather, marine habitats, and the distribution and survival of marine organisms. Other oceanic and atmospheric changes operate more slowly; over time scales of decades, centuries, and longer. Episodic geologic events also punctuate the region, such as volcanic eruptions that discharge widespread blankets of ash, frequent minor earthquakes, and major subduction zone earthquakes each 300 to 500 years that release accumulated tectonic strain, dropping stretches of ocean shoreline, inundating estuaries and coastal valleys, and triggering landslides that reshape stream profiles. While these many natural processes have altered, sometimes dramatically, the Pacific Northwest coastal region, these same processes have formed productive marine and coastal ecosystems, and many of the species in these systems have adapted to the variable environmental conditions of the region to ensure their long-term survival. The combination of these many natural processes has resulted in highly productive marine and coastal ecosystems that are adapted to the widely variable conditions of the region.

The economy and culture of the Pacific Northwest coastal region continue to depend to a large degree upon natural resources. As the landscape and coastal resources continue to be developed and, in some cases, depleted, the economic and social systems that depend on a stable, predictable set of environmental conditions to provide goods and services are increasingly vulnerable to environmental change, whether natural, human-caused, or both. Changes in environmental conditions and consequent disruptions of ecosystem functions trigger reactions in political, social, and economic systems that can consume immense amounts of social, political, and economic capital. The decline of coastal salmon stocks, for instance, has resulted in a significant effort by the Oregon and Washington state governors and agencies, Federal agencies, and local communities to find "the cause", and "restore" these stocks in coastal streams. Developing and carrying out resource management programs that are ecosystem-sensitive and have public support requires that scientists and managers work together to significantly improve understanding of the function and variability of coastal ecosystems, the effects of management practices, and the economic and social, as well as ecological, consequences of change.

Crozier, L.G., R.W. Zabel (2006). Climate impacts at multiple scales: evidence for differential population responses in juvenile Chinook salmon. Journal of Animal Ecology 75 (5): 1100-1109

SUMMARY: 1. We explored differential population responses to climate in 18 populations of threatened spring–summer Chinook salmonOnchorynchus tshawytscha in the Salmon River basin, Idaho.

2. Using data from a long-term mark–release–recapture study of juvenile survival, we found that fall stream flow is the best predictor of average survival across all populations.

3. To determine whether all populations responded similarly to climate, we used a cluster analysis to group populations that had similar annual fluctuations in survival. The populations grouped into four clusters, and different environmental factors were important for different clusters.

4. Survival in two of the clusters was negatively correlated with summer temperature, and survival in the other two clusters was positively correlated with minimum fall stream flow, which in turn depends on snow pack from the previous winter.

5. Using classification and regression tree analysis, we identified stream width and stream temperature as key habitat factors that shape the responses of individual populations to climate.

6. Climate change will likely have different impacts on different populations within this metapopulation, and recognizing this diversity is important for accurately assessing risks.

Hauer, F. R., J.S. Baron, D.H. Campbell, K.D. Fausch, S.W. Hostetler, G.H. Leavesley, P.R. Leavitt, D.M. McKnight, J.A. Stanford (1997). Assessment of climate change and freshwater ecosystems of the Rocky Mountains, USA and Canada. Hydrological Processes 11 (8): 903-924

ABSTRACT: The Rocky Mountains in the USA and Canada encompass the interior cordillera of western North America, from the southern Yukon to northern New Mexico. Annual weather patterns are cold in winter and mild in summer. Precipitation has high seasonal and interannual variation and may differ by an order of magnitude between geographically close locales, depending on slope, aspect and local climatic and orographic conditions. The region's hydrology is characterized by the accumulation of winter snow, spring snowmelt and autumnal baseflows. During the 2-3-month spring runoff period, rivers frequently discharge > 70% of their annual water budget and have instantaneous discharges 10-100 times mean low flow.

Complex weather patterns characterized by high spatial and temporal variability make predictions of future conditions tenuous. However, general patterns are identifiable; northern and western portions of the region are dominated by maritime weather patterns from the North Pacific, central areas and eastern slopes are dominated by continental air masses and southern portions receive seasonally variable atmospheric circulation from the Pacific and the Gulf of Mexico. Significant interannual variations occur in these general patterns, possibly related to ENSO (El Niño-Southern Oscillation) forcing.

Changes in precipitation and temperature regimes or patterns have significant potential effects on the distribution and abundance of plants and animals. For example, elevation of the timber-line is principally a function of temperature. Palaeolimnological investigations have shown significant shifts in phyto- and zoo-plankton populations as alpine lakes shift between being above or below the timber-line. Likewise, streamside vegetation has a significant effect on stream ecosystem structure and function. Changes in stream temperature regimes result in significant changes in community composition as a consequence of bioenergetic factors. Stenothermic species could be extirpated as appropriate thermal criteria disappear. Warming temperatures may geographically isolate cold water stream fishes in increasingly confined headwaters. The heat budgets of large lakes may be affected resulting in a change of state between dimictic and warm monomictic character. Uncertainties associated with prediction are increased by the planting of fish in historically fishless, high mountain lakes and the introduction of non-native species of fishes and invertebrates into often previously simple food-webs of large valley bottom lakes and streams. Many of the streams and rivers suffer from the anthropogenic effects of abstraction and regulation. Likewise, many of the large lakes receive nutrient loads from a growing human population.

We concluded that: (1) regional climate models are required to resolve adequately the complexities of the high gradient landscapes; (2) extensive wilderness preserves and national park lands, so prevalent in the Rocky Mountain Region, provide sensitive areas for differentiation of anthropogenic effects from climate effects; and (3) future research should encompass both short-term intensive studies and long-term monitoring studies developed within comprehensive experimental arrays of streams and lakes specifically designed to address the issue of anthropogenic versus climatic effects.

F.M.R. Hughes, A. Colston, J. O. Mountford (2005). Restoring riparian ecosystems: the challenge of accommodating variability and designing restoration trajectories. Ecology and Society 10 (1): 22 pp.

ABSTRACT: Flood disturbance processes play a key role in the functioning of riparian ecosystems and in the maintenance of biodiversity along river corridors. As a result, riparian ecosystems can be described as mobile habitat mosaics characterized by variability and unpredictability. Any river restoration initiative should aim to mimic these attributes. This paper suggests that there needs to be an increased institutional capacity to accept some levels of both variability and unpredictability in the ecological outcomes of river restoration projects. Restoration projects have frequently used some form of historical or contemporary reference system to define objectives and to help in the evaluation process. Using these reference systems can give a false sense of the predictability of ecological outcomes. We suggest that reference systems need to be used with caution for six reasons: (1) there are often no appropriate reference systems to use, (2) many catchment parameters have changed since the times of chosen historic reference systems, (3) climate change has been continuous throughout the Holocene, (4) projected climate change is of uncertain magnitude, (5) alien species cannot be avoided, and (6) landscape context changes through time. As well as defining short-term objectives, we suggest that river restoration projects should also formulate longer-term (decadel) restoration trajectories that are less predictable but more representative of real system attributes. Restoration trajectories could be defined using a range of ecological outcomes to accommodate interannual variability. The challenges of defining what levels of variability are important for restoring European floodplain forests are used to demonstrate the difficulties of broadening approaches and creating trajectories. In particular, the changing significance of variability at different spatial and temporal scales is discussed. An account is given of a restoration project at Wicken Fen in the United Kingdom in which nondeterministic approaches to goal setting have been initiated.

Jager, H.I., W. Van Winkle, B.D. Holcomb (1999). Would hydrologic climate changes in Sierra Nevada streams influence trout persistence?. Transactions of the American Fisheries Society 128 (2): 222-240

ABSTRACT: We predicted the consequences of climate change for sympatric populations of brown troutSalmo trutta and rainbow troutOncorhynchus mykiss in an upstream and a downstream reach of a Sierra Nevada stream with the help of an individual-based trout population model. The model evaluated the ecological effects of two anticipated responses to climate change: (1) a shift in peak flows from spring to winter and (2) an increase in stream temperature. Changes in temperature and flow regime both influenced simulated persistence of the two trout species. We hypothesized a decrease in the fall-spawning brown trout population as a result of winter floods that scour brown trout redds. Although scouring mortality showed the expected pattern, effects of seasonal shifts in flow on simulated dewatering of redds was equally important and tended to compensate for scouring. Because trout are coldwater fishes, we hypothesized that a rise in mean stream temperature would be harmful to both species, particularly in downstream reaches. We found that a climate change scenario with a 2°C increase in average stream temperature benefited both species in the cooler upstream reach but was harmful in the warmer downstream reach. Overall, our results supported the hypothesis that climate change will restrict trout to higher elevations in the Sierra Nevada. Finally, the combined effects of elevated temperature and shifted flow differed from the effect of elevated temperature alone. In combination, the two climatic factors produced threshold effects in rainbow trout abundance by shifting the age at first maturation. Complex interactions between the period of incubation and various causes of redd mortality (dewatering, scouring, and temperature-related mortality) also lead to nonadditive effects of the two climatic factors on abundances. We conclude that focusing on one factor alone (i.e., temperature) may not be sufficient to predict climate change effects in the stream environment.

Kukulka, T., Jay, D. A. (2003). Impacts of Columbia River discharge on salmonid habitat: 2. Changes in shallow-water habitat. Journal of Geophysical Research - Oceans 108 (C9): 3294

ABSTRACT: This is the second part of an investigation that analyzes human alteration of shallow-water habitat (SWH) available to juvenile salmonids in the tidal Lower Columbia River. Part 2 develops a one-dimensional, subtidal river stage model that explains ~90% of the stage variance in the tidal river. This model and the tidal model developed in part 1 [Kukulka and Jay, 2003] uncouple the nonlinear interaction of river tides and river stage by referring both to external forcing by river discharge, ocean tides, and atmospheric pressure. Applying the two models, daily high-water levels were predicted for a reach from rkm-50 to rkm-90 during 1974 to 1998, the period of contemporary management. Predicted water levels were related to the bathymetry and topography to determine the changes in shallow-water habitat area (SWHA) caused by flood control dikes and altered flow management. Model results suggest that diking and a >40% reduction of peak flows have reduced SWHA by ~62% during the crucial spring freshet period during which juvenile salmon use of SWHA is maximal. Taken individually, diking and flow cycle alteration reduced spring freshet SWHA by 52% and 29%, respectively. SWHA has been both displaced to lower elevations and modified in its character because tidal range has increased. Our models of these processes are economical for the very long simulations (seasons to centuries) needed to understand historic changes and climate impacts on SWH. Through analysis of the nonlinear processes controlling surface elevation in a tidal river, we have identified some of the mechanisms that link freshwater discharge to SWH and salmonid survival.

McIntosh, B. A., J.R. Sedell, J.E. Smith, R.C. Wissmar, S.E. Clarke, G.H. Reeves, L.A. Brown (1994). Management history of eastside ecosystems: changes in fish habitat over 50 years, 1935 to 1992. USDA Forest Service, Pacific Northwest Research Station: 55 pp.

DESCRIPTION: From 1934 to 1942, the Bureau of Fisheries surveyed over 8000 km of streams in the Columbia River basin to determine the condition of fish habitat. To evaluate changes in stream habitat over time, a portion of the historically surveyed streams in the Grande Ronde, Methow, Wenatchee, and Yakima River basins were resurveyed from 1990 to 1992. Streams were chosen where the primary impacts were natural disturbance (unmanaged), such as wilderness and roadless areas, and where human impacts (managed) were the major disturbances. In addition, historical changes in land-use, stream flow, and climate regimes were also analyzed. Many of these streams had been degraded from land-use activities (riparian timber harvest, splash dams, stream channelization, livestock grazing, and mining) prior to the historical survey. While the general trend throughout the Columbia River basin has been towards a loss in fish habitat on managed lands and stable or improving conditions on unmanaged lands, the data for these four river basins suggest there is a regional pattern to this change. Based on this information, along with data on the status of anadromous fish runs in these basins, fish habitat has shown some improvement from past abuses in eastern Washington, while continuing to decline in eastern Oregon. This appears to be the result of different land-use histories in the two regions. The river basins of eastern Washington apparently had a period of recovery after World War I from past land-use practices, as the impacts of development decreased. In contrast, river basins of eastern Oregon have been affected continuously by land-use practices over the entire development period (1850-present). From this information, it is clear that land-use practices have degraded fish habitat throughout eastern Washington and Oregon. Strategies to protect, restore, and maintain anadromous and resident fish populations and their habitat, must be based on a watershed approach that protects the remaining habitat and restores historical habitats.

Melack, J. M., J. Dozier, C.R. Goldman, D. Greenland, A. M. Milner, R.J. Naiman (1997). Effects of climate change on inland waters of the Pacific coastal mountains and western Great Basin of North America. Hydrological Processes 11 (8): 971-992

ABSTRACT: The region designated as the Pacific Coastal Mountains and Western Great Basin extends from southern Alaska (64°N) to southern California (34°N) and ranges in altitude from sea level to 6200 m. Orographic effects combine with moisture-laden frontal systems originating in the Pacific Ocean to produce areas of very high precipitation on western slopes and dry basins of internal drainage on eastern flanks of the mountains. In the southern half of the region most of the runoff occurs during winter or spring, while in the northern part most occurs in summer, especially in glaciated basins. Analyses of long-term climatic and hydrological records, combined with palaeoclimatic reconstructions and simulations of future climates, are used as the basis for likely scenarios of climatic variations. The predicted hydrological response in northern California to a climate with doubled CO2 and higher temperatures is a decrease in the amount of precipitation falling as snow, and substantially increased runoff during winter and less in late spring and summer. One consequence of the predicted earlier runoff is higher salinity in summer and autumn in San Francisco Bay. In saline lakes, the incidence of meromixis and the associated reduction in nutrient supply and algal abundance is expected to vary significantly as runoff fluctuates. In subalpine lakes, global warming will probably will lead to increased productivity. Lacustrine productivity can also be altered by changes in wind regimes, drought-enhanced forest fires and maximal or minimal snowpacks associated with atmospheric anomalies such as El Niño-Southern Oscillation (ENSO) events. Reduced stream temperature from increased contributions of glacial meltwater and decreased channel stability from changed runoff patterns and altered sediment loads has the potential to reduce the diversity of zoobenthic communities in predominately glacier-fed rivers. Climatic warming is likely to result in reduced growth and survival of sockeye salmon in freshwater, which would, in turn, increase marine mortality. Further research activities should include expanded studies at high elevations and of glacier mass balances and glacial runoff, applications of remote sensing to monitor changes, further refinement of regional climatic models to improve forecasts of future conditions and continued analyses of long-term physical, chemical and biological data to help understand responses to future climates.

J. L. Meyer, M. J. Sale, P.J. Mulholland, N. LeRoy Poff (1999). Impacts of climate change on aquatic ecosystem functioning and health. Journal of the American Water Resources Association 35 (6): 1373-1386

ABSTRACT: We review published analyses of the effects of climate change on goods and services provided by freshwater ecosystems in the United States. Climate-induced changes must be assessed in the context of massive anthropogenic changes in water quantity and quality resulting from altered patterns of land use, water withdrawal, and species invasions; these may dwarf or exacerbate climate-induced changes. Water to meet instream needs is competing with other uses of water, and that competition is likely to be increased by climate change. We review recent predictions of the impacts of climate change on aquatic ecosystems in eight regions of North America. Impacts include warmer temperatures that alter lake mixing regimes and availability of fish habitat; changed magnitude and seasonality of runoff regimes that alter nutrient loading and limit habitat availability at low flow; and loss of prairie pothole wetlands that reduces waterfowl populations. Many of the predicted changes in aquatic ecosystems are a consequence of climatic effects on terrestrial ecosystems; shifts in riparian vegetation and hydrology are particularly critical. We review models that could be used to explore potential effects of climate change on freshwater ecosystems; these include models of instream flow, bioenergetics models, nutrient spiraling models, and models relating riverine food webs to hydrologic regime. We discuss potential ecological risks, benefits, and costs of climate change and identify information needs and model improvements that are required to improve our ability to predict and identify climate change impacts and to evaluate management options.

P.J. Mulholland, G.R. Best, C.C. Coutant, G.M. Hornberger, J.L. Meyer, P.J. Robinson, J. R. Steinberg, R.E. Turner, F. Vera-Herrera, R.G. Wetzel (1997). Effects of climate change on freshwater ecosystems of the southeastern United States and the Gulf of Mexico. Hydrological Processes 11 (8): 949-970

ABSTRACT: The south-eastern United States and Gulf Coast of Mexico is physiographically diverse, although dominated by a broad coastal plain. Much of the region has a humid, warm temperate climate with little seasonality in precipitation but strong seasonality in runoff owing to high rates of summer evapotranspiration. The climate of southern Florida and eastern Mexico is subtropical with a distinct summer wet season and winter dry season. Regional climate models suggest that climate change resulting from a doubling of the pre-industrial levels of atmospheric CO2 may increase annual air temperatures by 3-4°C.

Changes in precipitation are highly uncertain, but the most probable scenario shows higher levels over all but the northern, interior portions of the region, with increases primarily occurring in summer and occuring as more intense or clustered storms. Despite the increases in precipitation, runoff is likely to decline over much of the region owing to increases in evapotranspiration exceeding increases in precipitation. Only in Florida and the Gulf Coast areas of the US and Mexico are precipitation increases likely to exceed evapotranspiration increases, producing an increase in runoff. However, increases in storm intensity and clustering are likely to result in more extreme hydrographs, with larger peaks in flow but lower baseflows and longer periods of drought.

The ecological effects of climate change on freshwaters of the region include: (1) a general increase in rates of primary production, organic matter decomposition and nutrient cycling as a result of higher temperatures and longer growing seasons: (2) reduction in habitat for cool water species, particularly fish and macroinvertebrates in Appalachian streams; (3) reduction in water quality and in suitable habitat in summer owing to lower baseflows and intensification of the temperature-dissolved oxygen squeeze in many rivers and reservoirs; (4) reduction in organic matter storage and loss of organisms during more intense flushing events in some streams and wetlands; (5) shorter periods of inundation of riparian wetlands and greater drying of wetland soils, particularly in northern and inland areas; (6) expansion of subtropical species northwards, including several non-native nuisance species currently confined to southern Florida; (7) expansion of wetlands in Florida and coastal Mexico, but increase in eutrophication of Florida lakes as a result of greater runoff from urban and agricultural areas; and (8) changes in the flushing rate of estuaries that would alter their salinity regimes, stratification and water quality as well as influence productivity in the Gulf of Mexico.

Many of the expected climate change effects will exacerbate current anthropogenic stresses on the region's freshwater systems, including increasing demands for water, increasing waste heat loadings and land use changes that alter the quantity and quality of runoff to streams and reservoirs. Research is needed especially in several critical areas: long-term monitoring of key hydrological, chemical and biological properties (particularly water balances in small, forested catchments and temperature-sensitive species); experimental studies of the effects of warming on organisms and ecosystem processes under realistic conditions (e.g. in situ heating experiments); studies of the effects of natural hydrological variation on biological communities; and assessment of the effects of water management activities on organisms and ecosystem processes, including development and testing of management and restoration strategies designed to counteract changes in climate.

Poff, N. L., M.M. Brinson, J.W. Day, Jr. (2002). Aquatic ecosystems and global environmental change. Pew Center on Global Climate Change: 45 pp.

EXECUATIVE SUMMARY: Climate change of the magnitude projected for the United States over the next 100 years will cause significant changes to temperature regimes and precipitation patterns across the United States. Such alterations in climate pose serious risks for inland freshwater ecosystems (lakes, streams, rivers, wetlands) and coastal wetlands, and they may adversely affect numerous critical services they provide to human populations.

The geographic ranges of many aquatic and wetland species are determined by temperature. Average global surface temperatures are projected to increase by 1.5 to 5.8°C by 2100 (Houghton et al., 2001), but increases may be higher in the United States (Wigley, 1999). Projected increases in mean temperature in the United States are expected to greatly disrupt present patterns of plant and animal distributions in freshwater ecosystems and coastal wetlands. For example, cold-water fish like trout and salmon are projected to disappear from large portions of their current geographic range in the continental United States, when warming causes water temperature to exceed their thermal tolerance limits. Species that are isolated in habitats near thermal tolerance limits (like fish in Great Plains streams) or that occupy rare and vulnerable habitats (like alpine wetlands) may become extinct in the United States. In contrast, many fish species that prefer warmer water, such as largemouth bass and carp, will potentially expand their ranges in the United States and Canada as surface waters warm.

The productivity of inland freshwater and coastal wetland ecosystems also will be significantly altered by increases in water temperatures. Warmer waters are naturally more productive, but the particular species that flourish may be undesirable or even harmful. For example, the blooms of “nuisance” algae that occur in many lakes during warm, nutrient-rich periods can be expected to increase in frequency in the future. Large fish predators that require cool water may be lost from smaller lakes as surface water temperatures warm, and this may indirectly cause more blooms of nuisance algae, which can reduce water quality and pose potential health problems.

Warming in Alaska is expected to melt permafrost areas, allowing shallow summer groundwater tables to drop; the subsequent drying of wetlands will increase the risk of catastrophic peat fires and the release of vast quantities of carbon dioxide (CO2 ) and possibly methane into the atmosphere.

In addition to its independent effects, temperature changes will act synergistically with changes in the seasonal timing of runoff to freshwater and coastal systems. In broad terms, water quality will probably decline greatly, owing to expected summertime reductions in runoff and elevated temperatures. These effects will carry over to aquatic species because the life cycles of many are tied closely to the availability and seasonal timing of water from precipitation and runoff. In addition, the loss of winter snowpack will greatly reduce a major source of groundwater recharge and summer runoff, resulting in a potentially significant lowering of water levels in streams, rivers, lakes, and wetlands during the growing season.

The following summarizes the current understanding regarding the potential impacts of climate change on U.S. aquatic ecosystems:

1. Aquatic and wetland ecosystems are very vulnerable to climate change. The metabolic rates of organisms and the overall productivity of ecosystems are directly regulated by temperature. Projected increases in temperature are expected to disrupt present patterns of plant and animal distribution in aquatic ecosystems. Changes in precipitation and runoff modify the amount and quality of habitat for aquatic organisms, and thus, they indirectly influence ecosystem productivity and diversity.

2. Increases in water temperature will cause a shift in the thermal suitability of aquatic habitats for resident species. The success with which species can move across the landscape will depend on dispersal corridors, which vary regionally but are generally restricted by human activities. Fish in lowland streams and rivers that lack northward connections, and species that require cool water (e.g., trout and salmon), are likely to be the most severely affected. Some species will expand their ranges in the United States.

3. Seasonal shifts in stream runoff will have significant negative effects on many aquatic ecosystems. Streams, rivers, wetlands, and lakes in the western mountains and northern Plains are most likely to be affected, because these systems are strongly influenced by spring snowmelt and warming will cause runoff to occur earlier in winter months.

4. Wetland loss in boreal regions of Alaska and Canada is likely to result in additional releases of CO2 into the atmosphere. Models and empirical studies suggest that global warming will cause the melting of permafrost in northern wetlands. The subsequent drying of these boreal peatlands will cause the organic carbon stored in peat to be released to the atmosphere as CO2 and possibly methane.

5. Coastal wetlands are particularly vulnerable to sea-level rise associated with increasing global temperatures. Inundation of coastal wetlands by rising sea levels threatens wetland plants. For many of these systems to persist, a continued input of suspended sediment from inflowing streams and rivers is required to allow for soil accretion.

6. Most specific ecological responses to climate change cannot be predicted, because new combinations of native and non-native species will interact in novel situations. Such novel interactions may compromise the reliability with which ecosystem goods and services are provided by aquatic and wetland ecosystems.

7. Increased water temperatures and seasonally reduced streamflows will alter many ecosystem processes with potential direct societal costs. For example, warmer waters, in combination with high nutrient runoff, are likely to increase the frequency and extent of nuisance algal blooms, thereby reducing water quality and posing potential health problems.

8. The manner in which humans adapt to a changing climate will greatly influence the future status of inland freshwater and coastal wetland ecosystems. Minimizing the adverse impacts of human activities through policies that promote more science-based management of aquatic resources is the most successful path to continued health and sustainability of these ecosystems. Management priorities should include providing aquatic resources with adequate water quality and amounts at appropriate times, reducing nutrient loads, and limiting the spread of exotic species.

Overall, these conclusions indicate climate change is a significant threat to the species composition and function of aquatic ecosystems in the United States. However, critical uncertainties exist regarding the manner in which specific species and whole ecosystems will respond to climate change. These arise both from uncertainties about how regional climate will change and how complex ecological systems will respond. Indeed, as climate change alters ecosystem productivity and species composition, many unforeseen ecological changes are expected that may threaten the goods and services these systems provide to humans.

P.S. Rand, S. G. Hinch, J. Morrison, M.G.G. Foreman, M.J. MacNutt, J.S. Macdonald, M. C. Healey, A.P. Farrell, D.A. Higgs (2006). Effects of river discharge, temperature, and future climates on energetics and mortality of adult migrating Fraser River sockeye salmon. Transactions of the American Fisheries Society 135 (3): 655-667

ABSTRACT: We evaluated the effects of past and future trends in temperature and discharge in the Fraser River on the migratory performance of the early Stuart population of sockeye salmonOncorhynchus nerka . Fish of lower condition exhibited disproportionately higher mortality during the spawning run, elucidating a critical link between energetic condition and a fish's ability to reach the spawning grounds. We simulated spawning migrations by accounting for energetic demands for an average individual in the population from the time of entry into the Fraser River estuary to arrival on the spawning grounds (about 1,200 km upstream) and estimated energy expenditures for the average migrant during 1950–2001. The model output indicates relatively high interannual variability in migration energy use and a marked increase in energy demands in recent years related to unusually high discharges (e.g., 1997) and warmer than average water temperature (e.g., 1998). We examined how global climate change might effect discharge, water temperature, and the energy used by sockeye salmon during their spawning migration. Expected future reductions in peak flows during freshets markedly reduced transit time to the spawning ground, representing a substantial energy savings that compensated for the effect of the increased metabolic rate resulting from exposure to warmer river temperatures. We suggest that such watershed-scale compensatory mechanisms may be critical to the long-term sustainability of Pacific salmon, given expected changes in climate. However, such compensation will probably only be applicable to some stocks and may be limited under extremely high temperatures where nonenergetic factors such as disease and stress may play a more dominant role in defining mortality. Our results further indicate that a long-term decline in the mean mass of adult sockeye salmon completing their marine residency could erode their migratory fitness during the river migration and hence jeopardize the sustainability of sockeye salmon and the fishery that targets them.

H. A. Regier, J. D. Meisner (1990). Anticipated effects of climate change on freshwater fishes and their habitat. Fisheries 15 (6): 10-15

ABSTRACT: We sketch an iterative assessment process for the effects of climate change on freshwater fisheries that uses water temperature, water quantity, and water quality variables to link the atmosphere to fishery resources. Iterative interaction among atmospheric, ecological, and fisheries scientists clarifies the information needs of each discipline and progressively improves the assessments of effects. The process incorporates information at different scales, i.e., organism/laboratory, species/habitat, and population/ecosystem. We illustrate the operation of the iterative assessment process with recent work done on the water temperature linkage, and sketch some linkages through water quantity and water quality variables. A Wild Salmonid Watch (WSW) could provide a framework for monitoring climate change and its effects on salmonid stocks on a hemispheric scale. We discuss the initial steps required to mobilize a WSW for climate change and its role as climate change develops in the decades ahead.

Rieman, B.E., D. Isaak, S. Adams, D. Horan, D. Nagel, C. Luse, D. Myers (2007). Anticipated climate warming effects on Bull trout habitats and populations across the interior Columbia River Basin. Transactions of the American Fisheries Society 136 (issue in progress): 1552-1565

ABSTRACT: A warming climate could profoundly affect the distribution and abundance of many fishes. Bull troutSalvelinus confluentus may be especially vulnerable to climate change given that spawning and early rearing are constrained by cold water temperature creating a patchwork of natal, headwater habitats across river networks. Because size and connectivity of patches also appear to influence persistence of local populations, climate change could lead to increasing fragmentation of remaining habitats and accelerated declines of this species. We modeled relationships between lower elevation limits of small bull trout and mean annual air temperature as functions of latitude and longitude across the species’ potential range within the interior Columbia River basin of the United States. We used our results to explore implications of climate warming expected in the next 50+ years. We found a strong association between the lower limits of bull trout distributions and longitude and latitude that was consistent with patterns in mean annual air temperature. We concluded that climate does strongly influence regional and local bull trout distributions and modeled bull trout response to a range of projected climate warming effects. Even modest warming may produce substantial loss and fragmentation of thermally suitable habitat. Additionally, the loss of moderate to large patches would be more dramatic than loss of total area and changes are unlikely to be uniform across the species’ range. Climate warming could lead to an accelerated loss of bull trout populations disproportionate to the simple loss of watershed area and some populations appear to face higher risks than others. Predictions like these could provide a foundation for regional prioritization in conservation management.

B. R. Scanlon, D. G. Levitt, R. C. Reedy, K. E. Keese, M. J. Sully (2005). Ecological controls on water-cycle response to climate variability in deserts. Proceedings of the National Academy of Sciences 102 (17): 6033-6038

ABSTRACT: The impact of climate variability on the water cycle in desert ecosystems is controlled by biospheric feedback at interannual to millennial timescales. This paper describes a unique field dataset from weighing lysimeters beneath nonvegetated and vegetated systems that unequivocally demonstrates the role of vegetation dynamics in controlling water cycle response to interannual climate variability related to El Niño southern oscillation in the Mojave Desert. Extreme El Niño winter precipitation (2.3-2.5 times normal) typical of the U.S. Southwest would be expected to increase groundwater recharge, which is critical for water resources in semiarid and arid regions. However, lysimeter data indicate that rapid increases in vegetation productivity in response to elevated winter precipitation reduced soil water storage to half of that in a nonvegetated lysimeter, thereby precluding deep drainage below the root zone that would otherwise result in groundwater recharge. Vegetation dynamics have been controlling the water cycle in interdrainage desert areas throughout the U.S. Southwest, maintaining dry soil conditions and upward soil water flow since the last glacial period (10,000-15,000 yr ago), as shown by soil water chloride accumulations. Although measurements are specific to the U.S. Southwest, correlations between satellite-based vegetation productivity and elevated precipitation related to El Niño southern oscillation indicate this model may be applicable to desert basins globally. Understanding the two-way coupling between vegetation dynamics and the water cycle is critical for predicting how climate variability influences hydrology and water resources in water-limited landscapes.

Bachuber, F.W. (1989). The occurence and paleolimnologic significance of cutthroat trout (Oncorhynchus clarki ) in pluvial lakes of the Estancia Valley, central New Mexico. Geological Society of America Bulletin 101 (12): 1543-1551

ABSTRACT: Cutthroat trout (Oncorhynchus clarki ) fossils in the Quaternary-age lacustrine sediment of the Estancia Valley provide insight into the paleolimnologic history of the valley. The presence of fish is evidence that a pluvial system overflowed into the Pecos River watershed. Most likely, the overflow occurred during the expansion of Early Lake Estancia, an Illinoian or pre-Illinoian pluvial lake known only in subcrop. Once established in the Estancia watershed, trout occupied headwater streams and only intermittently migrated and resided in developing lake systems. The headwater streams served as refugia through the Sangamon(?) and early and middle Wisconsin time when a fresh-water lake did not exist in the valley. With the advent of full-pluvial conditions during the late Wisconsin, trout migrated from headwater streams into the first of three fresh-water phases of Late Lake Estancia. On two occasions, climate shifted to warmer and drier conditions, causing significant lake-level drawdown. Salinity increased and trout were eliminated from the lake, only to be reintroduced during the next fresh-water phase. Near the close of the late Wisconsin, Late Lake Estancia waned and desiccated, but headwater streams remained as fish refugia. Following the interpluvial episode, the basin again filled, culminating in Lake Willard, considered to be of latest Wisconsin age. With evolution into a fresh-water body, trout migrated into a lake environment for the last time. Ensuing hot/dry conditions brought about the desiccation of Lake Willard and severely impacted the headwater streams. This factor, in possible combination with human fishing activity, led to the elimination of fish from the Estancia Valley after a continuous occupation of at least 130,000 yr.

J. Battin, M. W. Wiley, M.H. Ruckelshaus, R. N. Palmer, E. Korb, K. K. Bartz, H. Imaki (2007). Projected impacts of climate change on salmon habitat restoration. Proceedings of the National Academy of Sciences 104 (16): 6720-6725

ABSTRACT: Throughout the world, efforts are under way to restore watersheds, but restoration planning rarely accounts for future climate change. Using a series of linked models of climate, land cover, hydrology, and salmon population dynamics, we investigated the impacts of climate change on the effectiveness of proposed habitat restoration efforts designed to recover depleted Chinook salmon populations in a Pacific Northwest river basin. Model results indicate a large negative impact of climate change on freshwater salmon habitat. Habitat restoration and protection can help to mitigate these effects and may allow populations to increase in the face of climate change. The habitat deterioration associated with climate change will, however, make salmon recovery targets much more difficult to attain. Because the negative impacts of climate change in this basin are projected to be most pronounced in relatively pristine, high-elevation streams where little restoration is possible, climate change and habitat restoration together are likely to cause a spatial shift in salmon abundance. River basins that span the current snow line appear especially vulnerable to climate change, and salmon recovery plans that enhance lower-elevation habitats are likely to be more successful over the next 50 years than those that target the higher-elevation basins likely to experience the greatest snow–rain transition.

Nikolaidis, N. P., H.L. Hu, C. Ecsedy, J.D. Lin (1993). Hydrologic response of freshwater watersheds to climatic variability: Model development. Water Resources Research 29 (10): 3317-3328

ABSTRACT: To evaluate the hydrologic and biogeochemical response of freshwater watersheds to climatic variability properly, a mathematical model with detailed parameterization in describing the hydrologic and thermal processes in a watershed is needed. For this purpose, the Enhanced Trickle Down model was modified to predict the hydrologic and thermal responses of freshwater watersheds to various climate change scenarios. Modifications of the model included the incorporation of an energy transfer submodel, an improved hydraulic conductivity scheme, and the coupling with a point source snowmelt model. The results of calibration and verification of the model using 8 years of field data collected at the Agricultural Research Service, W-3 watershed, located near Danville, Vermont, are presented.

T. Beechie, E. Buhle, M. Ruckelshaus, A. Fullerton, L. Holsinger (2006). Hydrologic regime and the conservation of salmon life history diversity. Biological Conservation 130 (4): 560-572

ABSTRACT: Life history diversity of imperiled Pacific salmonOncorhynchus spp. substantially contributes to their persistence, and conservation of such diversity is a critical element of recovery efforts. Preserving and restoring diversity of life history traits depends in part on environmental factors affecting their expression. We analyzed relationships between annual hydrograph patterns and life history traits (spawn timing, age at spawning, age at outmigration, and body size) of Puget Sound Chinook salmon (Oncorhynchus tshawytscha ) to identify environmental indicators of current and historic diversity. Based on mean monthly flow patterns, we identified three hydrologic regimes: snowmelt-dominated, rainfall-dominated, and transitional. Chinook populations in snowmelt-dominated areas contained higher proportions of the stream-type life history (juvenile residence >1 year in freshwater), had older spawners, and tended to spawn earlier in the year than populations in rainfall-dominated areas. There are few extant Puget Sound populations dominated by the stream-type life history, as several populations with high proportions of stream-type fish have been extirpated by construction of dams that prevent migration into snowmelt-dominated reaches. The few extant populations are thus a high priority for conservation. The low level of genetic distinction between stream-type and ocean-type (juvenile residence <1 year in freshwater) life histories suggests that allowing some portion of extant populations to recolonize habitats above dams might allow re-expression of suppressed life history characteristics, creating a broader spatial distribution of the stream-type life history. Climate change ultimately may limit the effectiveness of some conservation efforts, as stream-type Chinook may be dependent on a diminishing snowmelt-dominated habitat.

Knowles, N., D. Cayan (2002). Potential effects of global warming on the Sacramento/San Joaquin watershed and the San Francisco estuary. Geophysical Research Letters 29 (18): 1891, doi:10.1029/2001GL014339

ABSTRACT: California's primary hydrologic system, the San Francisco estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. Projected temperature anomalies from a global climate model are used to drive a combined model of watershed hydrology and estuarine dynamics. By 2090, a projected temperature increase of 2.1°C results in a loss of about half of the average April snowpack storage, with greatest losses in the northern headwaters. Consequently, spring runoff is reduced by 5.6 km3 (~20% of historical annual runoff), with associated increases in winter flood peaks. The smaller spring flows yield spring/summer salinity increases of up to 9 psu, with larger increases in wet years.

Independent Scientific Advisory Board, (2007). Climate change impacts on Columbia River Basin fish and wildlife. Independent Scientific Advisory Board for the Northwest Power Planning Council, the Columbia River Basin Indian Tribes, and the National Marine Fisheries Service: 146 p.

EXECUTIVE SUMMARY (partial): Warming of the global climate is unequivocal. Evidence includes increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level. Eleven of the last twelve years (1995 -2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). The linear warming trend over the last 50 years (0.13 +/- 0.03°C per decade) is nearly twice that for the last 100 years. The total global average temperature increase from 1850 – 1899 to 2001 – 2005 is 0.76 +/- 0.19°C.

Climate records show that the Pacific Northwest has warmed about 1.0 ºC since 1900, or about 50% more than the global average warming over the same period. The warming rate for the Pacific Northwest over the next century is projected to be in the range of 0.1-0.6° C/decade. Projected precipitation changes for the region are relatively modest and unlikely to be distinguishable from natural variability until late in the 21st century. Most models project long-term increases in winter precipitation and decreases in summer precipitation. The changes in temperature and precipitation will alter the snow pack, stream flow, and water quality in the Columbia Basin:

-Warmer temperatures will result in more precipitation falling as rain rather than snow
-Snow pack will diminish, and stream flow timing will be altered
-Peak river flows will likely increase
-Water temperatures will continue to rise

These changes will have a variety of impacts on aquatic and terrestrial habitats in the Columbia Basin.

Naiman, R.J., M.G. Turner (2000). A future perspective on North America's freshwater ecosystems. Ecological Applications 10 (4): 958-970

ABSTRACT: Fresh waters are central to society and to the environment. Nevertheless, ongoing and projected changes in the distribution, abundance, and quality of water resources and freshwater ecosystems represent a serious threat to the integrity of the environment as well as the vitality of human cultures. Nearly every country in the world experiences regular water shortages, agriculture uses most of the world's available fresh water, and most illnesses in developing countries result from waterborne parasites and pathogens. Unfortunately, often hidden in these and other depressing statistics are the needs of the environment for adequate water to maintain vibrant ecosystems. Understanding the abilities and limits of freshwater ecosystems to respond to human-generated pressures is becoming a central issue for cultures and a challenge for science. This article explores trends in alterations to freshwater ecosystems, discusses the ecological consequences of biophysical alterations expected to occur in the next 20–30 years, and identifies some of the major scientific challenges and opportunities to effectively address the changes. Topics discussed include altered hydrological regimes, biogeochemical cycles, altered land use, riparian management, life history strategies, and relations between climate change and water resource management.

Saunders, J.F., III, M. Murphy, M. Clark, W. M. Lewis, Jr. (2004). The influence of climate variation in the estimation of low flows used to protect water quality: a nationwide assessment. Journal of the American Water Resources Association 40 (5): 1339-1349

ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro-Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection.

Mote, P. W., D. J. Canning, D. L. Fluharty, R.C. Francis, J. F. Franklin, A. F. Hamlet, M. Hershman, M. Holmberg, K. N. Ideker, W. S. Keeton, D. P. Lettenmaier, L. R. Leung, N. J. Mantua, E. L. Miles, B. Noble, H. Parandvash, D. W. Peterson, A. K. Snover, S. R. Willard (1999). Impacts of climate variability and change, Pacific Northwest. National Atmospheric and Oceanic Administration, Office of Global Programs, and JISAO/SMA Climate Impacts Group: 110 pp.

OVERVIEW: Experience of the recent past illustrates the impacts that the climate variations have on the Pacific Northwest, and illustrates that there are both winners and loser when the climate is different from the “average.” The mild winter and spring of 1997—98 saw an early snow melt, which strained regional water supplies during the summer and fall months. An especially warm and dry summer, coupled with the early melt, led to exceptionally low flows and high temperatures in many Northwest streams. These conditions in turn caused severe difficulties for salmon. However, 1997—98 also had benefits for the region, which avoided the damage and disruption caused by heavy snow fall and winter flooding during the previous two winters.

Climate is not a constant, and yet many aspects of human infrastructure and activities are planned with the assumption that it is constant. But what happens when climate produces a surprise? What if, furthermore, there are long-term changes in climate? Humans have altered the composition of Earth’s atmosphere to such an extent that climate itself appears to be changing. The consequences of a changing climate may be beneficial for some places and activities, and detrimental for others.

This report describes the possible impacts of human-induced climate change and of natural climate variability like El Niño, focusing on the water resources, salmon, forests, and coasts of the Pacific Northwest (PNW). It has been prepared largely by the Climate Impacts Group (CIG) at the University of Washington. The CIG, under the direction of Professor Edward L. Miles, is an interdisciplinary group of researchers from the physical, biological, and social sciences working together to understand the impacts of climate variability and change on the Northwest.

Looking at the recent past, much of the climate history of the PNW can be described by a few recurring patterns. The strongest pattern highlights the tendency for winter climate to be either relatively cool and wet or relatively warm and dry. Cool-wet winters are generally associated with increased risks of flooding and landslides, abundant summer water supply, more abundant salmon, reduced risk of forest fires, and improved tree growth (except at high elevation). Warm-dry winters are often followed by summer water shortages, less abundant salmon, and increased risk of forest fires. The occurrence of the cool-wet or warm-dry winter pattern is influenced by two main climate variations in the Pacific Basin: ENSO (El Niño-Southern Oscillation) primarily on year-to-year timescales and PDO (the Pacific Decadal oscillation) primarily on decade-to-decade timescales. ENSO and PDO cause variation sin snowpack and streamflow, and hence the ability to meet water resource objectives; with respect tot he region’s water resources, ENSO and PDO can reinforce or cancel each other. In contrast, the response of forests and salmon is correlated more strongly with the PDO than with ENSO. The magnitude of seasonal anomalies of temperature and precipitation leading to the above effects is strikingly small, but these past anomalies enable us to calibrate the possible responses to long-term climate change.

Looking to the future, computer models of climate generally agree that the PNW will become, over the next half century, gradually warmer and wetter, with most of the precipitation increase in winter. These trends mostly agree with observed changes over the past century. Wetter winters would likely mean more flooding of certain rivers, and landslides on steep coastal bluffs. The region’s warm, dry summers may see slight increases in rainfall, according to the models, but the gains in rainfall will be more than offset by losses due to increases in evaporation. Loss of moderate-elevation snowpack in response to warmer winter temperatures would have enormous and mostly negative impacts on the region’s water resources, forests, and salmon. Among these impacts are a diminished ability to store water in reservoirs for summer use, more drought-stressed tress leading to reductions in forested area, and spawning and rearing difficulties for salmon.

Knowing what changes might occur is only part of the challenge, however. This knowledge must make its way from the realm of research to the realm of decisions, and be used in decisions. Large practical and, in some cases, legal constraints prevent climate information from being fully utilized. Meeting the challenges posed by climate variations and climate change will require considerable revision of the policies and practices concerning how the region’s natural resources are managed. An indication of the scope of such revisions comes from considering how government agencies have handled climate-related stresses in the past, like droughts and coastal erosion. In many cases, agencies cannot even make use of a good seasonal forecast in making short-term planning decision: the operating assumption is often that climate is constant and extremes do not occur. There are wide variations among the four sectors considered here in how management presently makes use of climate information.

Milner, A. M., Brown, L. E., Hannah, D. M. (2009). Hydroecological response of river systems to shrinking glaciers. Hydrological Processes 23 (1): 62-77

ABSTRACT: Aquatic ecosystems in high latitude and altitude environments are strongly influenced by cryospheric and hydrological processes due to links between atmospheric forcing, snowpack/glacier mass-balance, river discharge, physico-chemistry and biota. In the current phase of global climate warming, many glaciers are shrinking. Loss of snow and ice-masses will alter spatial and temporal dynamics in bulk basin runoff with important changes in the relative contributions of snowmelt, glaciermelt and groundwater to stream flow. Accordingly, altered water source contributions will be accompanied by changes to fluvial, solute, sediment and thermal regimes and, thus, channel stability and habitat. The projected reduction in sediment load, warmer water temperature and increased channel stability will drive significant shifts in the floral and faunal composition of glacier-fed rivers. This paper hypothesizes a general increase in the richness and production of micro-organisms, algae, macroinvertebrates and fish as glacier hydrological influence shrinks under a warmer climate. With reduced glacial influence, macroinvertebrate species trait diversity will increase with more organisms possessing larger body size, less specialized body shape and lower adult mobility. In larger river systems, potential reduction of meltwater inputs will have a significant influence on off-channel habitats (e.g. side-channels and sloughs) that depend on glacial runoff to sustain habitat availability and connectivity, particularly for fish. Some species such as cold stenothermic taxa (including some endemic macroinvertebrates) may be vulnerable to extinction and therefore gamma (regional) diversity will be reduced. These sensitive macroinvertebrate taxa may be important biological indicators of environmental change in glacierized river basins. Moreover, high climatic sensitivity and low human perturbation make glacially influenced river basins early indicator systems for identifying hydrological and ecological responses to climate change/variability. It is concluded that glacier shrinkage and associated changes in runoff amount and timing, water source contributions and physico-chemical habitat will be a major driver of the future biodiversity of stream communities in cold environments. Research imperatives and future directions are proposed for investigation of glacier-fed river hydroecology.

J. G. Eaton, R. M. Scheller (1996). Effects of climate warming on fish thermal habitat in streams of the United States. Limnology and Oceanography 41 (5): 1109-1115

ABSTRACT: The effects of climate warming on the thermal habitat of 57 species of fish of the U.S. were estimated using results for a doubling of atmospheric carbon dioxide that were predicted by the Canadian Climate Center general circulation model. Baseline water temperature conditions were calculated from data collected at 1,700 U.S. Geological Surveys stream monitoring stations across the U.S. Water temperatures after predicted climate change were obtained by multiplying air temperature changes by 0.9, a factor based on several field studies, and adding them to baseline water temperatures at stations in corresponding grid cells. Results indicated that habitat for cold and cool water fish would be reduced by ~50%, and that this effect would be distributed throughout the existing range of these species. Habitat losses were greater among species with smaller initial distributions and in geographic regions with the greatest warming (e.g. the central Midwest). Results for warm water fish habitat were less certain because of the poor state of knowledge regarding their high and low temperature tolerance; however, the habitat of many species of this thermal guild likely will also be substantially reduced by climate warming, whereas the habitat of other species will be increased.

D. W. Schindler (2001). The cumulative effects of climate warming and other human stresses on Canadian freshwaters in the new millennium. Canadian Journal of Fisheries and Aquatic Sciences 58 (1): 18-29

ABSTRACT: Climate warming will adversely affect Canadian water quality and water quantity. The magnitude and timing of river flows and lake levels and water renewal times will change. In many regions, wetlands will disappear and water tables will decline. Habitats for cold stenothermic organisms will be reduced in small lakes. Warmer temperatures will affect fish migrations in some regions. Climate will interact with overexploitation, dams and diversions, habitat destruction, non-native species, and pollution to destroy native freshwater fisheries. Acute water problems in the United States and other parts of the world will threaten Canadian water security. Aquatic communities will be restructured as the result of changes to competition, changing life cycles of many organisms, and the invasions of many non-native species. Decreased water renewal will increase eutrophication and enhance many biogeochemical processes. In poorly buffered lakes and streams, climate warming will exacerbate the effects of acid precipitation. Decreases in dissolved organic carbon caused by climate warming and acidification will cause increased penetration of ultraviolet radiation in freshwaters. Increasing industrial agriculture and human populations will require more sophisticated and costly water and sewage treatment. Increased research and a national water strategy offer the only hope for preventing a freshwater crisis in Canada.

M. A Palmer, C. A. Reidy Liermann, C. Nilsson, M. Flörke, J. Alcamo, P. S. Lake, N. Bond (2008). Climate change and the world's river basins: anticipating management options. Frontiers in Ecology and the Environment 6 (2): 81-89

ABSTRACT: Major rivers worldwide have experienced dramatic changes in flow, reducing their natural ability to adjust to and absorb disturbances. Given expected changes in global climate and water needs, this may create serious problems, including loss of native biodiversity and risks to ecosystems and humans from increased flooding or water shortages. Here, we project river discharge under different climate and water withdrawal scenarios and combine this with data on the impact of dams on large river basins to create global maps illustrating potential changes in discharge and water stress for dam-impacted and free-flowing basins. The projections indicate that every populated basin in the world will experience changes in river discharge and many will experience water stress. The magnitude of these impacts is used to identify basins likely and almost certain to require proactive or reactive management intervention. Our analysis indicates that the area in need of management action to mitigate the impacts of climate change is much greater for basins impacted by dams than for basins with free-flowing rivers. Nearly one billion people live in areas likely to require action and approximately 365 million people live in basins almost certain to require action. Proactive management efforts will minimize risks to ecosystems and people and may be less costly than reactive efforts taken only once problems have arisen.

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