Yunnan Dianchi Lake Sediment Heavy Metal Element Distribution Law

Modern lakes are a complex dynamic system interacted by human and natural environments, especially when receiving large amounts of anthropogenic contaminants from nearby urban areas and industrial sites. Among the various contaminants, heavy metals are of particular concern due to their environmental persistence and biogeochemical recycling and ecological risks. However, high concentrations of heavy metals in lake sediments can come from natural environmental changes instead of anthropogenic contamination, depending on different background levels in parent materials in surrounding area and release/absorb equilibrium processes of the lake sediments. It is therefore that investigating spatial and temporal distribution of heavy metals in sediments usually concern not only element-geochemistry of lake sediments themselves but also of soil, bedrock from lake source region nearby.The study area is Dianchi Lake of Yungui Plateau, which is well known to the world for the increasingly serious environmental problems, such as algae blooms and water quality worsening. On the north of this lake, the city of Kunmin is located and is the most developed region in Yunnan Province.In this study, a total of 118 diverse 20-centimeter-long surface sediment cores have been collected from the whole Dianchi Lake. And 330 sediment samples are precisely analyzed for total concentrations of Al, Ca, Mg, Fe, Ti, Co, Cr, Cu, Ni, Pb, Cd, Hg, Zn, Mo, As, Ba by ICP analytical method.With the particle size analysis of the sediments, we find that the clay (>8) contents of sediment sample increase with its depth of the sediment profile, and the same law is discovered with the susceptibility.Correlation coefficients have been calculated to show the relationships between heavy metal concentrations and grain sizes. The concentrations of Fe, Co, Ti , Cu, Ni, Cr have weak positive correlations with the content of fine grained size of >8 in sediment sample, which results in that these elements' concentrations increase with its depth of the sediment profile (0-20cm). Those, which have negative correlations with the content of fine grained size of >8, such as Cd, Pb, Zn, Hg, show contrary distribution to Fe, Co, Ti, Cu, Ni, Cr in the sediment column.The Pearson correlation coefficients of the heavy metal and major metal and the Principle Component Analysis show that there are strong associations between Fe, Co, Ti , Cu, Ni and Cr, whereas Cd, Pb, Zn, Hg, As, Mo display different behavior from these metals. The former group is thought to be related with the Fe oxides colloid, whereas the later group may be dominated by organic matter.The low concentrations of Fe, Co, Ti in sediments of Caohai Lake is consistent with small value of magnetic susceptibility, which indicates that heavy metals dissolve because of high concentrations of organic matter.The concentrations of Cu, Ni, As, Hg, Zn, Cd, Pb in sediments of Caohai Lake are in general higher than those of Waihai Lake. The author thinks this is brought by the import of industrial waste water. We should pay attention to this, and adopt measurement to control the pollution source.