The arctic freshwater environment experienced dramatic climatic shifts during the Holocene (10,000 years ago to present) and Pleistocene, which has had enormous effects on the presence of biota today. The freshwater ecosystems are strongly influenced by annual physical variations and limitations, namely temperature, solar radiation and nutrients. Arctic freshwater systems, with both flowing and standing water, show considerable variation in size, biocomplexity, and physical and chemical properties (Christoffersen et al. 2008, Prowse et al. 2006).
Food webs in arctic lakes can resemble those of temperate regions which include phototropic biota (algae and macrophytes), invertebrates (insects, crustaceans and rotifers) and fish. However, in the Arctic there are far fewer taxa and thus, the food web structure is simpler than in 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 the Arctic do not necessarily flow the 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 archipelagos 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. Because of their low water depth (usually less than 2 m), these water bodies tend to freeze solid during winter, while the shallower ones can dry out during summer. Because these habitats are unstable 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 archipelagos, 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, do not freeze solid or dry out, and can host a permanent fish population.
The environmental conditions for organisms in High Arctic lakes are different from other northern climatic zones. 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 hot springs, which have received particular attention from a 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.
The crustacean Lepidurus arcticus, or commonly known as tadpole shrimp, may look prehistoric but is very much alive. As an omnivore it can have a significant impact on the structure of communities in many localities. In particular in shallow localities, where it rarely co-occur with fish, and is a significant predator of smaller crustaceans like Daphnia (Christoffersen, 2001).
Video showing a Lepiderus arcticus in a lake in Svalbard. Two eggs can bee seen attached to her legs. (Video: Simen S. Hjelle, 2022)
The Arctic char is the only fresh water fish present in Svalbard.