Some sediment-geochemical evidence for the recent environmental changes of the lakes from the middle and lower Yangtze River basin, China

The lakes along the middle-lower Yangtze River Basin have undergone dramatic water quality deterioration and eutrophication during recent decades. The nutrient and metal accumulation in the lake sediments through time were investigated using the sedimentary-geochemical records of the drilling cores from several typical lakes. The results showed a general increase in total organic carbon and total nitrogen concentration with lower depth in the profiles. Increased delivery of organic matter to the lake system could be responsible for the nutrient enrichments in the lake bottom sediments. The general trend of nutrients matter enriched upwards in the core indicated that these lakes had become eutrophic since the mid-1950s (macrophyte-type lake), or late 1980s (algae-type lake). In addition, the results have also shown that human activities have exerted a great influence on the past lake environmental changes since the 1950s, inferred from the changes in the sedimentary rate and the anthropogenic metal accumulation in the sediment cores. Enhanced human activities seem to occur around the early 1970s.