| Summary: | The study focuses on chemical composition of stream and subsurface water in the catchments of two small arctic alpine lakes in the Kilpisjärvi area (northwest Finland). Differences and changes in chemical components of both water types are followed in order to detect spatial variability and impact of environmental factors. To achieve this, ion compositions of subsurface water and streams were measured at 12 sites in the catchments of Lakes Saana and Saanalampi during four years (2008–2010, and again in 2017). In the Lake Saanalampi catchment, the salinity of stream water (7.0 to 12.7 μS·cm−1) corresponded to that of snow. In the catchment of Lake Saana, however, the conductivity in stream water was much higher (40 to 220 μS·cm−1), connected mainly to the increase of SO42− and less with Mg2+ and Ca2+ contents, especially in the western part of the Saana catchment. These results demonstrate that arctic conditions do not preclude intense chemical weathering where conditions are favourable. Although chemical composition of the soil fluid does not match the geochemical signal from the local soil, rock composition, especially the presence of pyrite, is the main controller of chemical weathering rates of the rocks on the area. This supports earlier views that the character of precipitation mostly controls water chemistry of local lakes in the Kilpisjärvi area.
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