Long-term changes of water physicochemical conditions and benthic microbial processes in a small lake associated with land use in the catchment

Abstract

Changes in land use in the catchments and areas near the shorelines of lakes may have undesirable consequences for the functioning of lake ecosystems. We studied temporal changes in physicochemical parameters and benthic microbial processes within the small Lake Gulbinas (Lithuania) in relation to the type of land use in the catchment. We compared the period when agriculture activity decreased and increased urban development commenced (2001–2002, transition period) with periods of intense urban land use (2007, 2014–2015). The results were compared to reference data from earlier agricultural periods (1962, 1987–1989). The highest nutrient concentrations in the water were observed during the period of agriculture activity, while increased phosphate concentrations in the near-bottom water and increased organic carbon content and microbial activity in the lake sediments were observed during the period of intense urban land use. Throughout the latter period, anaerobic mineralization of organic carbon via sulfate reduction in bottom sediments was significantly higher than that during the transition period. The intensification of benthic sulfate reduction led to sulfide increase and, thus, to a higher phosphate mobility re-fertilizing the water. Our study suggests that, with a shift of land usage in catchment areas from agricultural to urban, increasing sedimentary organic carbon and its intensive anaerobic mineralization may stimulate internal eutrophication of small lakes.