Arctic Freshwater Habitats
Overall, the Arctic freshwater environment has experienced dramatic climatic shifts during the Holocene and Pleistocene, which have had enormous effects on the presence of biota today. They are also strongly influenced by extreme annual physical variations and limitations, namely temperature, available solar radiation and nutrients. Arctic freshwater systems, both with flowing and standing water, show a considerable variety in size, type, physical and chemical properties and biocomplexity (Christoffersen et al. 2008, Prowse et al. 2006).
Food webs in Arctic lakes can resemble that of temperate regions which include phototropic biota (algae and macrophytes), invertebrates (insects, crustaceans and rotifers) and fish, although with much fewer taxa and thus with a simpler food web structure than temperate lakes. Food webs might also be truncated, without larger predators (Christoffersen et al. 2008).
Running freshwaters are characterised by a dominance of glacial meltwater inputs, typically in large braided river systems with high sediment loads, highly irregular flows (even cessation after the main period of snow melt) and very low temperatures even in summer. However, in coastal, glacier-free areas, snowmelt, spring fed streams and lake outflows become important representatives of these systems (Füreder and Brittain, 2006). Here conditions can be more favourable, although many snowmelt streams dry up in summer.
Rivers in Arctic areas do not nescessarily flow whole year round: varying with local conditions and yearly variation, in Svalbard for example, river flow may start as late as late June to early July, in some places and years however as early as end of April/start of May. However, ice break-up tends to occur later in the season, from mid-July until late-August (Svenning and Gullestad, 2002).
The lakes and ponds in the archipelagoes of the Barents Sea are typically found in coastal, lowland areas as in most other Arctic regions (Rautio et al., 2011). Temporary thaw ponds, permanent shallow ponds and small lakes are numerous and, because of the low water depth (usually less than 2 m), these water bodies tend to freeze solid during winter and the shallower ones can dry out during summer. Apart from being unstable habitats due to large seasonal variations in water level, temperature and light, these shallow water bodies contain no fish populations. Larger and deeper lakes are also present on the Barents Sea archipelagoes, although not as numerous as, for example, in West Greenland and Alaska. Lakes with a water depth of more than 3 m are more stable, not freezing solid or drying out, and can host a permanent fish population.
However, the environmental conditions for organisms in High Arctic lakes are different from other northern climatic zones as the ice-free period is very short (typically 1-2 months), water temperatures and nutrient concentrations are constantly low and the intensity of ultraviolet radiation is often high compared to more temperate regions. Furthermore, there are physical barriers restricting colonization due to ice caps or remoteness. Consequently, the biodiversity of freshwater organisms in still waters in Svalbard and other isolated islands is expected to be low, even compared to High Arctic regions such as West Greenland and Alaska (Gíslason, 2005; Samchyshyna et al., 2008).
In a few areas, there are also hot springs, which have received particular attention from the chemical and microbiological perspective (Hammer et al., 2005; Jamtveit et al., 2006; Lauritzen and Bottrell, 1994). In Svalbard for example, hot springs can be found in two areas in the western part of Spitsbergen.