Nutrient budgets and the regulation of nutrient concentrations in a small sub‐arctic lake in northern Sweden

Abstract

SUMMARY. A 5‐year study was made of the hydrology and water chemistry in the watershed of Lake Stugsjön, a small lake in the sub‐arctic region of northern Sweden. Of the total yearly runoff, 80% occurs during the spring thaw in May and June and largely regulates the nutrient loading. The ice‐free period of the lake is June—October. Atmospheric deposition of nitrogen and phosphorus was among the lowest recorded anywhere, in spite of which it accounts for approximately half of the total summer nutrient loading. Dry fall‐out made up the major part of the total atmospheric deposition of nitrogen and phosphorus during the summer.Conductivity measurements showed that the major constituents were not influenced by processes within the lake.The nitrogen concentration in the lake during the summer was probably regulated by benthic algae which assimilated inorganic nitrogen from the sediments and released organic nitrogen to the lake water.Phosphorus loading and water temperature in combination showed a clear relationship with the mean concentration of chlorophyll‐α during the ice‐free period.