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Wetland is the conjunction of lake and terrene where human activities are concentrated. From the viewpoints of material transport and cycling in the terrene-lake system, wetland is the buffer where sand and mud, heavy metals, pollutants and nutrients are tarried. In this paper, we provide a case study based on the temporal and spatial distribution of elements in the Wangling River catchment, a small sub-catchment of Longgan Lake in the middle reaches of the Yangtze River. We have found that wetland can buffer major heavy metals such as Cr, Cu, etc. significantly, but has a little buffer function to some active elements such as Fe and Mn, which are always transported as solutions. Human activities not only influence the distribution of elements, but also weaken the buffer function of wetland. Intensive human activities in the Longgan Lake area in the past 70 years have been recorded in stream, wetland and lake sediments, especially the human activity events such as deforesting and reclaiming on a large scale in 1958 and the 1980’s. Human activities caused the increase of sedimentation rates since the 1950’s, as well as the increase of elements’ concentrations. The extensive use of fertilizers and pesticides since the 1960’s have led to the increase of total P concentrations. Increasing SO2 emission accelerate the process of cation exchange in soil, and enhance the leaching of Mn out of soils. Permanent storing of water causes the soil gleyification that also intensifies the leaching of Mn. These are two major reasons for the obvious increase of manganese concentrations in recent 20 years in Longgan Lake. Intensive human activities since the 1950s’ have intensified the population in this region and thus destroyed the buffer function of wetland.

Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment, organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Chenghai, a closed, eutropic lake in southern China, provide information on lake historical eutrophication. During the last 660 years, great changes have taken place in productivity and eutrophication of Lake Chenghai in response to human activities. In 1690, the productivity of the lake began to increase as Lake Chenghai became closed from agriculture in the lake’s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, nitrogen, CaCO3, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, intensive human activities induced modem lacustrine productivity and eutrophic level. Human-induced trophic changes during the past few decades have affected the Lake Chenghai ecosystem to such an extent that it has never experienced before in the last 660 years.

Lake Xingcuo is a small closed, hard-water lake, situated on eastern Tibet Plateau. Stable isotope data (δ18O and δ13C) from the freshwater snailGyraulus sibirica (Dunker) in a 34 cm long, radioactive isotope-dated sediment core represent the last 200 years of Lake Xingcuo environmental history. Carbon and oxygen isotope ratios in the shells of the freshwater snail bear information on the isotopic composition of the water in which the shells were formed, which in turn characterizes the climatic conditions prevailing during the snail’s life span. Whole-shell and incremental growth data were collected from modern and fossil shells from Lake Xingcuo. The δ18O values of modern shells from Lake Xingcuo are in equilibrium with those of modern waters, while δ13C values are indicative of snail dietary carbon and a lake with high δ13CTDIC By calibrating δ18O and δ13C in the shellGyraulus sibirica (Dunker) with instrument measured data for the period 1954 – 1992, we found that the δ18O of the snail shells is an efficient indicator to reveal air temperature in the warmer half year instead of that around the whole year, and that there is a certain positive correlation between index δ18O and the running average temperature in the warmer half-year period. Climatic variability on eastern Tibet Plateau, for the last two centuries, has been successfully inferred from the δ18O record in freshwater snails in the sediments of Lake Xingcuo. As such, the last 200 years of palaeoclimatic record for this region can be separated into three periods representing oscillations between warming and cooling, which are confirmed by the Guliya ice record on the Tibet Plateau.