Catchment vegetation can trigger lake dystrophy through changes in runoff water quality

Surface runoff can supply lakes with a variety of chemical substances - their type and quantity may significantly vary and depend on the characteristics of the catchment area: geomorphology, phytocoenosis type and degree of human impact. In this study we investigated the physicochemical properties of the surface runoff water collected from the wooded catchment of Lake Piaseczno Duze (LPD, Drawa National Park, Poland) covered by a monoculture of Scots pine (Pinus sylvestris) and mixed forest with white birch (Betula pubescens) as the dominant tree. Experimentally, we also aimed to study the leaching of nutrients from pine and birch litter. Throughout the investigated period runoff waters had low pH, brown colour and high levels of dissolved organic carbon (DOC) - most likely induced by humic acids. Furthermore, considerable levels of nitrogen (N) and phosphorus (P) were found. The highest concentrations of nutrients were observed in runoff collected after heavy rainfall and snow melting. Runoff from the coniferous area contained significantly higher levels of DOC but lower concentrations of N and P compared to runoff collected from the birch-dominated forest. Similar physicochemical conditions were observed in the leaching experiment. Moreover, it was found that the release of chemical substances from both coniferous and deciduous litter was rapid. Our study indicates that surface runoff from forest areas can significantly affect lake chemistry. Based on the simultaneous analyses of littoral water chemistry we suggest that it may contribute to LPD dystrophication through the transportation of high levels of acidic compounds.