Catchment soil characteristics predict organic carbon, nitrogen, and phosphorus levels in temperate lakes

Allochthonous supply of dissolved organic matter (DOM) and nutrients from the catchment have a sub- stantial impact on the physical and chemical properties of lake water. Transport of DOM and nutrients is affected by different catchment characteristics, e.g., catchment area, soil and land cover, and population density. The aim of this study was to relate geological, hydrological, land-cover, and soil characteristics of 52 temperate catchments in Estonia to variability in DOM (measured as dissolved organic carbon [DOC]), total organic nitrogen (TON), and total phosphorus (TP) in lakes and to assess the relative importance of different land-cover and soil types as sources of these substances. DOC, TON, and TP were very diverse in the studied lakes. Strong positive correlation between DOC and TON indicated that these substances had similar concentration patterns and sources. Catchment soil cover was the best predictor of DOC, TON, and TP levels in lakes, explaining up to 43.8% of their variabilities. This obser- vation can partly be explained by different soil organic carbon (SOC) content: soils with higher SOC were associated with higher lake DOC and TON, whereas soils with low SOC corresponded to lower DOC and TON. Similar to other temperate lakes, bogs and peat soils were a major source of DOM in our studied lakes. DOC, TON, and color were positively associated with percentages of peat soils in the catchment. On the other hand, TP increased with the pro- portion of urban areas in the catchments, indicating the importance of human impact on its concentration. Under- standing the impact of different catchment characteristics on DOC, TON, and TP in temperate lakes is crucial for developing transport models used for predicting future levels of DOM and nutrients under changing climate and land use.

This study was funded by the Estonian Research Council grants PUTJD954, PRG709, and PRG1167, by the European Regional Development Fund through Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”, and by the European Union H2020 WIDESPREAD grant 951963 (TREICLAKE). The Estonian Ministry of Environment and the Estonian Environment Agency supported data collection in the national monitoring program.