The sediment records of environmental changes under interactions of nature with mankind during last hundred years in the Yangpu Bay of Hainan, China

In the summer of 2005,the Second Institute of Oceanog raphy,State Oceanic Administration has investigated adjacent sea of Hainan Island for sediment and environment studies,and collected a sediment core in the Yangpu Bay.On the basis of the dated sediment core,the grain size,total organic carbon and stable organic carbon isotope (δ¹³C),total nitrogen and stable nitrogen isotope (δ¹⁵N),biogenic silica,heavy metals (nickel,cadmium,chromium,copper,zinc,lead),organochlorine pesticides (HCHs,DDTs) were analyzed.From 111 cm to surface,the concentrations of total organic carbon,total nitrogen and biogenic silica show increasing trends.Especially from 45 cm to surface,the trends are significant.So the conclusion can be obtained that accelerated entrophication occurred in the Yangpu Bay.The data of δ¹³ C and the atomicratio of total organiccarbon and total nitrogen reveal the mixing inputs of terrigenous and marine organic matter in the Yangpu Bay.And sediment organic carbon is dominated by terrigenous organic carbon.The corresponding relationship between terrigenous organic carbon and total organic carbon is good,and the value of the relationship coefficient is 0.917.From 23 cm to surface,δ¹³C was decreasing.From bottom to surface,δ¹⁵N was increasing.From 111 cm to surface,the concentrations of heavy metal and organochlorine pesticides show increasing trends.Analyzing all indicators of environmental evolution,the results showed that the development of Yangpu Bay environment during last hundred years can be divided into three stages:before the 1970s characterized by good biogenic environment;from the 1970s to the 1990s,the concentrations of heavy metals,organochlorine pesticides and biogenic elements are increasing;and from the 1990s to the beginning of the 21 century,the environment was polluted by all elements mentioned,and resulted in eutrophication.