Lakes in the Boreal Region

The boreal region covers a large part of Europe, and the lake density is high. Consequently, the lake types representative of the boreal region may also be the most common ones of Europe as a whole. The lakes of the region are usually small and shallow, and of glacial origin. They range from low to high contents of humic substances, depending on catchment characteristics and hydraulic retention time. The most common lake type in the boreal region in the northeast of Europe, especially in the two countries with the highest lake density, Finland and Sweden, is a humic lake, also known as brown water or dystrophic lake (Figure 5). Lakes become humic as a result of soils in the catchment containing high levels of organic matter. Upland peaty catchments and forest dominated catchments give a perfect prerequisite for

Shallow Lakes Ecosystem

Figure 4 Biogeographical regions of Europe. The map has been taken from the European Environmental Agency at http:// dataservice.eea.europa.eu/atlas/.

Alpine

Anatolian

Arctic

Atlantic

Black sea

Boreal

Continental

Macaronesia

Mediterranean

Pannonian

Steppic

Figure 4 Biogeographical regions of Europe. The map has been taken from the European Environmental Agency at http:// dataservice.eea.europa.eu/atlas/.

Figure 5 Example of a humic lake in the Boreal Region (Oppsveten, Sweden). Photograph: Cristian Gudasz.

high humic contents in lake waters. Humic lakes are usually characterized by brownish water with a low pH, low nutrient concentrations, and poor underwater light conditions. The flora and fauna is adapted to these conditions with dominance of flagellates that are able to survive under poor light conditions.

Humic substances result in high levels of dissolved organic carbon in lake waters, influencing the pathways of energy and nutrient flow within a lake ecosystem. Dissolved organic carbon in the water absorbs ultraviolet radiation, which has far-reaching consequences for aquatic organisms. Recently, an increase in dissolved organic carbon has been observed across northern Europe. This increase has been coupled to changes in the climate and atmospheric deposition. It has been identified as problematic for society since drinking water rich in dissolved organic carbon can produce carcinogens when chlorinated.

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