Seasonal nitrogen dynamics in a seepage lake receiving

Abstract

11 pages, 6 figures, 2 tablesStudies on nitrogen dynamics in seepage lakes are seldom undertaken, yet our understanding of the complex pattern of the nitrogen (N) cycle is complicated by its temporal and spatial heterogeneity. This research investigated temporal variation inNconcentration, considering different forms ofN(NO−3 ,NO−2 ,NH+4 , dissolved organicN, particulate organic N) in a Spanish flowthrough seepage lake (Colgada Lake) receiving high N loads. The study was based on monthly data collected over the period 2003–2005 from lake inputs and outputs, vertical profiles at a single representative site in the middle of the lake and fluxes of NH+4 and NO−3 at the sediment–water interface. The distribution of total N (TN) inputs and outputs did not follow a clear temporal pattern. TN inputs varied from 27.70 to 125 tonnes N month−1, 75–84% of which is NO−3 .Temporal variation of concentration profiles for different N forms measured showed significant differences owing to stratification. Ammonium always entered the sediment, whereas sediments acted as either a sink or source of NO−3 . Fluctuation in N dynamics in this lake was more influenced by external factors, such as the input variability, than by the turnover of nitrogenous substances in the water body. Comparing seasonal N dynamics, there seems to be temporal differences between seepage lakes and drainage lakes. In seepage lakes, dissolved inorganic nitrogen (DIN) peaks were reached in early spring and after overturn, whereas in drainage lakes, the autumn minimum gradually increased to maxima in late winter and during the stratification periodREN 2002-00558 Proyecto del Ministerio de Educación y Ciencia de EspañaPeer reviewe