18.104.22.168 Impacts on aquatic productivity and biodiversity
Projected changes in runoff, river- and lake-ice regimes, and seasonal and interannual water balance and thermal characteristics will alter biodiversity and productivity relationships in aquatic ecosystems (Walsh et al., 2005; Prowse et al., 2006b; Wrona et al., 2006a). Ultimately the dispersal and geographical distribution patterns of aquatic species will be altered, particularly for fish (Reist et al., 2006a). Extension of the ice-free season may lead to a decline in fish habitat availability and suitability, particularly affecting species such as lake trout (Salvelinus namaycush) that prefer colder waters (Hobbie et al., 1999; Reist et al., 2006b). The projected enhanced river flows will also increase sediment transport and nutrient loading into the Arctic Ocean, thereby affecting estuarine and marine productivity (Carmack and Macdonald, 2002).
Increased permafrost thawing and deepening of the active layer will increase nutrient, sediment and carbon loadings, enhancing microbial and higher trophic level productivity in nutrient-limited systems. As water-column dissolved organic carbon (DOC) concentration increases, penetration of damaging UV radiation and photochemical processing of organic material would decline, although not as prominently in highly productive systems (Reist et al., 2006b; Wrona et al., 2006a). Enhanced sediment loadings will negatively affect benthic and fish-spawning habitats by increasing the biological oxygen demand and hypoxia/anoxia associated with sedimentation, and contribute to habitat loss through infilling (Reist et al., 2006a). Whether freshwater systems will function as net carbon sinks or sources depends on the complex interactions between temperature, nutrient status and water levels (Frey and Smith, 2005; Flanagan et al., 2006). Initial permafrost thaw will form depressions for new wetlands and ponds interconnected by new drainage networks. This will allow for the dispersal and establishment of new aquatic communities in areas formerly dominated by terrestrial species (Wrona et al., 2006b). As the permafrost thaws further, surface waters will increasingly drain into groundwater systems, leading to losses in freshwater habitat.
Southerly species presently limited by temperature/ productivity constraints will probably colonise Arctic areas, resulting in new assemblages. Many of these, particularly fishes, will be likely to out-compete or prey upon established Arctic species, resulting in negative local effects on these (Reist et al., 2006a). These southern emigrants to the Arctic will also bring with them new parasites and/or diseases to which Arctic species are not adapted, thereby increasing mortality (Wrona et al., 2006b). Direct environmental change combined with indirect ecosystem shifts will significantly impact local faunas by reducing productivity, abundance and biodiversity. Such effects will be most severe for freshwater fish that rely entirely upon local aquatic ecosystems (Reist et al., 2006c). Distributions of anadromous fish, which migrate up rivers from the sea to breed in freshwater, will probably shift as oceanic conditions and freshwater drainage patterns are affected (Reist et al., 2006c); as will the geographical patterns of habitat use of migratory aquatic birds and mammals (Wrona et al., 2005). Important northern fish species such as broad whitefish (Coregonus nasus), Arctic char (Salvelinus alpinus), inconnu (Stenodus leucichthys), Arctic grayling (Thymallus arcticus) and Arctic cisco (Coregonus autumnalis) will probably experience population reductions and extirpations (e.g., due to reproductive failures), contraction of geographical ranges in response to habitat impacts, and competition and predation from colonising species (Reist et al., 2006a, b, c).