Lakes and rivers are prominent features of the Arctic landscape and provide diverse habitats for plants, animals and microbes. In many places, these waters also provide important hunting and fishing grounds for Inuit communities, as well as drinking water supplies and a key resource for certain industries such as hydroelectricity, transport and mining. The Arctic contains an extraordinary diversity of lake types ranging from freshwater to saline, and from highly acidic to alkaline. Many of the lakes are crystal clear, while some are stained brown by coloured dissolved organic carbon (mostly humic materials) derived from the vegetation and wetlands in their surrounding catchments. The largest river in arctic Canada, the Mackenzie River, is especially rich in dissolved organic carbon and in suspended sediments, and much of its microbial activity appears to be associated with cells attached to sediment particles that are mixed through the water column.
One of the main channels of the Mackenzie River, Northwest Territories, Canada.
Water column profiling and sampling at meromictic Lake A, Northern Ellesmere Island, Nunavut, Canada
The northern coastline of Ellesmere Island, Nunavut, has a great variety of lakes, many of which are in the national park Quttinirpaaq (’Top of the World’ in Inuktitut). These include Ward Hunt Lake at lat 83 °N, a freshwater body overlain by 4 meters of multiyear ice. The shallow littoral waters of this lake melt out each year to reveal an extensive microbial mat dominated by highly pigmented cyanobacteria (Bonilla et al. 2005). Also in the region is a series of perennially ice-capped saline lakes that have been formed by the isostatic uplift of the landscape after retreat of the overlying ice sheet. The deep fiords became cut off from the sea and partially filled with freshwater resulting in «meromictic» conditions in which the lake is composed of multiple layers that differ in salinity, temperature, oxygen and other properties, and that never mix because of the salinity gradient and the near-permanent ice cover. These provide a diverse set of environments for the development of microbial communities (Van Hove et al. 2006). Given that the layered or «stratified» structure of these waterbodies depends on the persistence of their overlying ice, these ecosystems are likely to be strongly impacted by future climate change.
