Characteristics And Evaluation Of Nutrient And Heavy Metal Pollution In Sediments From Dongting Lake

Dongting Lake is the second largest freshwater lake in China.It is located in the middle reaches of the Yangtze River,and its water exchange has an important correlation with the Yangtze River.Due to its geographical location,ecological function,shipping,other related social and economic values.In the past 30 years,the input of heavy metals such as copper,zinc,lead and cadmium into the Dongting Lake,the corresponding risks and toxicityhas increased significantly,and its level also continued to increase.In order to reflect the heavy nutrient salt,metal pollution level,spatial distribution characteristics and risk assessment of Dongting Lake,this paper completed the investigation and analysis of the sediment cores of the Dongting Lake,the sedimentary cores into the lake and the lake center,and the research results are specific.as follows:(1)The average total organic carbon content in the surface sediments of Dongting Lake was 13.26 mg/g,the total nitrogen content was 1046 mg/kg,and the total phosphorus content was 242.19 mg/kg.The spatial distribution generally shows a decreasing distribution from west to east.The organic index and organic nitrogen evaluation of the environmental conditions of the Dongting Lake sediments indicate that organic nitrogen pollution exists in the sediments of Dongting Lake.The organic index evaluation results show that there is no serious pollution at all points,which is consistent with or better than the cleanliness level.It is worthwhile to compare the isotope characteristics of the pollution source.Soil organic matter is the main source of organic matter in the surface sediments of Dongting Lake.(2)The spatial distribution of heavy metal concentration in sediments showed a decreasing trend from west to east.The spatial characteristics of heavy metal elements showed that the concentration of rivers in the lake was higher than that in the lake center.In addition,the results of the evaluation of heavy metals in the Dongting Lake sediment by the cumulative index method and the potential ecological safety index show that the single element pollution degree is Cd> Cr> Pb> Cu> Zn,and the order of single potential ecological risk is Cd> Pb> Cu> Cr> Zn,in which Cd contributes a lot to the comprehensive ecological risk index of Dongting Lake sediments,and is the main ecological risk contribution factor.(3)In the columnar sediments of the lake center,the input of terrigenous organic matter in the sediments of the South lake center and the West lake center is significant,while the East lake center is an endogenous source.In the historical sedimentary characteristics,the historical sedimentary changes of nutrient salts are not significant,and the historical deposition of heavy metals has a significant increasing trend.The organic matter has homology with total phosphorus and total nitrogen.The heavy metals Cu,Zn,Pb,Cd and Cr all show homology.Characteristics,and the input of terrestrial sources plays an important role in the cumulative increase of nutrients and heavy metals.