Contribution of surface runoff from forested areas to the chemistry of a through-flow lake

The role of surface runoff from forested areas in chemical cycling and freshwater ecology is still not completely understood. Changes in total precipitation and increase in heavy rainfalls may, however, in some regions promote the effect of runoff in aquatic environments. In this study, we aimed to investigate the physicochemical properties of the surface runoff occurring within the wooded catchment area of a through-flow lake (Poland, Europe). Samples were collected over a 2-year period from slopes overgrown by the monoculture of Scots pine (Pinus sylvestris) or mixed forest dominated by European beech (Fagus sylvatica) and Scots pine. At the same time, the chemical properties of littoral and pelagic zones were analysed. Waters overflowing both slopes were found to have low pH, high colour and relatively high content of dissolved organic carbon and nutrients. Compared to coniferous site, the runoff from mixed forest was represented by significantly higher concentrations of organic matter, nitrogen, phosphorus and calcium ions. The greatest changes of the studied chemical parameters were noted in runoff occurring during heavy rainfall and snow melting (coniferous slope) or after shedding of leaves (the mixed forest slope). Surface runoff was revealed to be less important source of chemical loads in basins with direct river inflow but for more isolated basins it may be a significant factor affecting water quality.