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2_23 A dltliirial The general effects of climate change on freshwater systems will likely include increased water tempera- tures, decreased dissolved oxygen levels, and increased toxicity of pollutants thereby altering the availability and quality of habitat for aquatic biota (reviews in Mulholland et al. 1997, Allan et al. 2005, Ficke et al. 2007). Meyer et al. (1999) identified characteristics of aquatic ecosystems that are particularly sensitive to climate change (Table 2 -5). These highlight the range of impacts climate change poses to the biota of freshwater systems — ranging from loss of habitat and the resulting shifts in species composition to changes in nutrient cycling that affect oxygen and nutrient availability —and the indirect effects of synergies with other stressors. Changes in global climate affect primary produc- tion and the nutrient concentration of inland waters (reviewed in Ficke et al. 2007). Increased produc- tivity resulting from warmer temperatures can lead to oxygen depletion in bottom waters as algae and organic matter settle out of surface waters and decompose. Water quality is also likely to be influ- enced by climate - induced changes, with potential consequences for aquatic organisms (reviewed in Murdoch et al. 2000). Warming of surface waters and longer growing seasons have the potential to increase primary production, organic matter decom- position, and nutrient cycling (Mulholland et al. 1997), particularly in systems with sufficient nutri- ent and oxygen supplies. Productivity will be affect- ed by changes in the hydrologic cycle that impact nutrient loading and residence times. For example, more frequent storm events may flush nutrients and sediment into surface waters. In addition, warmer water temperatures may increase productivity as a result of increased metabolic rates. During drier climatic periods, decreased stream flow may increase the residence time and concentrations of nutrients and pollutants in surface waters. However, in oxygen poor systems, decreased oxygen holding capac- ity associated with warmer water temperatures may actually exacerbate low oxygen availability and limit productivity. Table 2 -5. Some properties of aquatic ecosystems that are particularly sensitive to climate change (Source: Meyer et al. 2002, © Wiley Interscience, used with permission). Lakes Streams Wetlands Mixing Regime Flow Regime Altered Water Balance Leading to Wetland Losses Nutrient and DOC Inputs Sediment Transport/ Channel Fire Frequency Alterations Habitats Meeting Temperature and Nutrient Loading and Rates of Altered Rates of Exchanges of Oxygen Requirements Nutrient Cycling Greenhouse Gases Productivity Fragmentation and Isolation of Cold Vegetation Species Composition Water Habitats Top Predator Changes Leading to Altered Rxchanges with the Riparian Reproductive Success of Many Trophic Cascades Zone Animal Species Abundance of Cold- and Warm- Life History Characteristics of Many Sensitivity to Invasion by Tropical Water Fish Species Aquatic Insects Exotic Species