Sedimentary evidence for recent eutrophication in the northern basin of Lake Taihu, China: human impacts on a large shallow lake

Environmental change in Lake Taihu and its catchment since the early to middle part of the twentieth century has left a clear geochemical record in the lake sediments. The human activities in the lake and its catchment responsible for the change include agriculture, fisher, urbanisay tion, sewage and industrial waster disposal. Sediment cores were collected from Meilian Bay of northern Lake Taihu to investigate the record of anthropogenic impacts on the lake's ecosystem and to assess its natural, pre-eutrophication baseline state. Two marked stratigraphic sediment units were identified on the basis of total phosphorus concentration (TP), pigments, total organic carbon (TOC)/total nitrogen (TN), delta C-13 and delta N-15 corresponding to stages in the lake history dominated by phytoplankton, and by aquatic macrophytes. Results show that as TP loading increased from the early 1950s the lake produced sediments with increasing amounts of organic matter derived from phytoplankton. In the early 1950s, the first evidence for eutrophication at the Meilian Bay site is recorded by an increase in C/N values and in sediment accumulation rate, but there is little change in phosphorus concentrations, pigments, delta C-13 and delta N-15 at this time. After 1990 a more rapid increase in trophic status took place indicated by increased levels of phosphorus, pigments, delta N-15 and by decreased delta C-13 and TOC/TN values in the lake sediments. The first increase in trophic status of the early 1950s results mainly from agricultural development in the catchment. In contrast, the acceleration from ca. 1990 originates from the recent development of fisheries and the urbanisation and industrialisation of the catchment

Hydrological and Ecological Controls on Autochthonous Carbonate Deposition in Lake Systems: A Case Study From Lake Wuliangsu and the Global Perspective

Based on similar to 150-year of sedimentary records, we identify that autochthonous carbonate deposition in Lake Wuliangsu, in the upper reaches of the Yellow River, was independent of both hydrological and ecological variations before 1965, influenced by hydrological changes due to agricultural activities during 1965-1990, and slightly impacted by higher productivity under the eutrophication process after 1990. By comparing with data from lakes across the globe, we find that lake size and lake stratification control the contribution of recycled organic carbon to autochthonous carbonate deposition. Continuous mixing and aeration in shallow lakes facilitate the transformation of organic carbon into 29-45% of sedimentary carbonate, different from large and deep lakes (2-25%). Organic carbon recycling in lakes remains generally stable or decreases under the pressure of lake eutrophication, requiring further investigations on whether more organic carbon will be buried in the carbonate form