The Change Characteristics Of Organic Carbon And Nitrogen In Surface Sediments And Water Quality Evaluation Of Lake Cibi

Lakes are important "sources" and "aggregations" of rock formations,influenced by various external natural factors and internal processes,and then constantly evolving,a correct understanding of the geochemical process of lakes is the basis for studying the changes of lake sediments and ancient climate and environment.According to the analysis of the spatial distribution characteristics of total nitrogen and phosphorus content,organic matter,TOC,and carbon and nitrogen isotopes in surface sediments of the lake,the present deposition process and pollution status of the lake were discussed,and the impacts of human activities in the basin on the lake area were effectively determined.In addition,according to the content of TN and TP in the water,environmental evaluation is conducted on the existing water quality status and sediment pollution in lake,providing reference for environmental research concerning the protection of Erhai Lake and the thorough investigation of Water quality in Cibi Lake.The results show that:(1)The particle size of surface sediment samples in Cibi Lake is divided into three types: clay,silty sand,and sand,and the content of clay components ranges from 5.985% to 32.162%,and is mainly distributed in the northwest of the lake under the influence of alluvial fans on hillsides.As the dominant particle size of silty sand in lake area,it is mainly affected by groundwater recharge and karst landform,and has no obvious regular distribution.The percentage of sand component varies from 0.36%to 28.758%.It is mainly distributed in the northern deep water area near the lakeside and the river inlet under the influence of the lake and human activities.The grain size frequency curve shows that the distribution of sediment is controlled by many factors.(2)The TP content of sediments ranged from 241.07 to 1814.33(mg/Kg),and the spatial distribution characteristics were high in the south and low in the north.The TN range ranged from 1571.54 to 5605.32(mg/Kg).The high value area was similar to the distribution area of sand components,and the sediments were greatly affected by exogenous input.The distribution of organic matter,TOC,sand components and total nitrogen content is similar,indicating that exogenous input is the main source ofsediment pollution.The value of 13 C isotope ranges from-32.073‰ to-25.34‰,and the average value is-29.725‰,indicating that the impact of land input is large in Cibi Lake,and part of the excess may be affected by internal lake sources.The impact is smaller than that of land input,and the entire central region in the spatial distribution is lower than that of the lake region,indicating that the lake region is affected more by external sources than the lake region.The change of 15 N value is between 1.237‰and 3.386‰,indicating that the nitrogen source in Bihu is mainly from the input of fertilizer.Combining the C/N value,we know that the input from the organic matter sources in Cibi Lake is affected both internally and externally,and the impact from external sources is greater than that from internal sources.(3)According to the classification,comprehensive pollution Cibi Lake surface sediment pollution is serious,basically do not have clean degree of the sample,a small number of the moderate pollution,most for severe pollution,even than high levels of pollution,organic pollution index evaluation,according to the standard Cibi Lake organic pollution in surface sediment pollution that may be in mild to moderate range,combined with the two methods of evaluation results,for the assessment of the overall to severe pollution.(4)The N/P analysis results show that almost all of the water in The lake is greater than 16,indicating that the amount of phosphorus in the lake is relatively low.According to the national standard of surface water environment quality monitoring standard(GB3838-2002),Ci keeps green lake water quality is good,for the national Ⅱ class water.Therefore,we should pay more attention to maintaining the stability of the sedimentary environment,strengthen supervision over the areas of human activities and the rivers entering the lake,reduce the use of chemical fertilizer in the farming land around the lake,and strive to maintain the quality of the water,so as to guarantee the quality of the water delivery of Erhai Lake.