Characteristics Of Nutrient Elements And Heavy Metal Pollution In Typical Lakes In Nansi Lake Basin

As the largest inland lake in Shandong Province,Nansi Lake is an important water storage area for South-North Water Diversion Project and an important water source area in the province.Sihe River and Dongyu River,as rivers entering the lake from Nansi Lake,are mainly used for surface water supply,agricultural irrigation and energy production.The water quality of the river into the lake also directly and indirectly affects the water ecological environment of Nansi Lake,so it is of great practical significance to study the water and sediment of the river into the lake for environmental governance.In this paper,Sihe River and Dongyu River,two inflow rivers of Nensi Lake,were selected As the research objects.The TN,TP,COD_Mn in the water and heavy metals（Cr,Ni,Zn,Cu,Pb,Hg,Cd,As,Mn）in the sediments of these two inflow rivers were analyzed statistically.Mainly studied the spatial distribution of heavy metals in sediment characteristics,the spatial distribution features of nutrient elements and interannual variability characteristics,the relationship between water and sediment of TN,TP,and uses the correlation analysis of mathematical statistics method,combining with river sediment,the physical and chemical properties of 9 kinds of heavy metals pollution in sediments of the ecological risk assessment,Finally,the sources of nutrient elements and heavy metals were discussed.The results are as follows:（1）Sihe has nine kinds of heavy metals in sediments and larger space heterogeneity,and poor correlation between each other,except the As and Mn other heavy metals in the middle reaches of yanzhou area（S2,S3）concentrations were significantly higher,including Hg,Cd in the ecological risk reached or high risk,shows that there are man-made pollution degree of heavy metals is higher,the study found that the main source may be koto region produced in the process of coal mining waste water,waste residue,waste gas and other pollutants.（2）The spatial distribution of heavy metals in the sediments of Dongyu River has a certain regularity,and most of the heavy metals have a good correlation with each other,and show similar spatial variation trends,which may be homologous pollution.Except for Hg and Cd,the concentrations of other heavy metals were significantly higher in the upstream and downstream,while the concentrations in the middle reaches were generally lower.The analysis showed that the main reasons for the higher concentrations in the upper and downstream were irrigation from the Yellow River and Nansi Lake water,respectively.The concentrations of heavy metals Hg and Cd were most seriously polluted at sampling points D3 and D4 in the middle reaches,and the application of high Hg pesticides and chemical fertilizers containing Cd in local agricultural activities was the main reason for the increase of concentrations of Hg and Cd.（3）The spatial variation of TN in Sihe River was significant,with a maximum of4.58mg·L^-1,while the overall concentrations of TP and COD_Mn were stable.In the past 10 years,the concentrations of the three groups had a similar change trend,all reaching the peak in 2012and decreasing rapidly with a fluctuating trend.The variation coefficient of TP in Dongyu River was close to 80%,and the maximum rate was 2.7 times of the average rate.The fluctuation of TN and COD_Mn concentrations was stable.The interannual variation trend showed that TN,TP and COD_Mn had opposite trends.The maximum TN concentration appeared from 2008 to 2011,while the peak of TP and COD_Mn appeared in 2016.（4）Sihe sediment and water TN and TP have strong correlation respectively,and the source is consistent,mainly from endogenous release,such as the decomposition of aquatic organisms.When the sedimentation conditions change,the TN and TP between the sediment and the water body will change each other,so the negative correlation is significant.The TN in the sediments and water of Dongyu River mainly comes from the internal recharge of the river,but the TP comes from a wide range of sources.The TP in the sediments mainly comes from the aquatic plant residues and land-based input,while the TP in the water comes from the untreated industrial and agricultural wastewater.