Nitrogen loading and natural pressures on the water quality of a shallow Mediterranean lake

Abstract The water quality of Koumoundourou Lake, a heavily modified, peri-urban, brackish and shallow lake near Athens, Greece, is under multiple stressors due to the industrial activities in the catchment area and natural pollution pressures. Although the broader area has undergone significant land use changes since the beginning of the 20th century converting it from rural to heavily industrialized, Koumoundourou Lake remained as one of the few habitats in Attica Region, for large numbers of aquatic birds. The water quality of the lake has been recently improved, which contributed to the increase of aquatic birds' population in the area and to the higher, in relation to the past, nitrogen inputs from natural sources. Therefore, a monitoring program has been implemented to assess the pollution pressure factors in the lake. A water quality model has been also used to simulate the lake's processes and estimate the nutrient mass budget focusing on the various nitrogen loading mechanisms (natural and anthropogenic). Based on the model output, the main polluting factor of the lake is the groundwater inflows. Aquatic birds affect slightly the lake's water quality, while the dry and wet atmospheric deposition contributes insignificantly to the total nitrogen loading.