Study On The Nutrient Occurrence Forms And The Structure Of Microbial Community In Sediments Of Hengshui Lake

Freshwater lakes are important natural resources in China,but most of the lakes are facing serious endogenous pollution.The enrichment of nitrogen and phosphorus in sediments is considered to be the main cause of lake endogenous pollution.Microorganism of lake sediments plays an important role in the transformation of organic matter and nutrients,microbial structure community characteristics are affected by various environmental factors.Hengshui Lake is located in Hengshui City of Hebei Province.As an important part of the South-to-north Water Diversion and Storage Project,it plays an important role in regulating temperature and humidity in surrounding areas and maintaining stable ecological conditions.In recent years,the external pollution of Hengshui Lake has been effectively controlled,and the external pollution sources such as industrial wastewater,rural life and livestock and poultry breeding have been basically eliminated.However,the eutrophication trend of Hengshui Lake is still not optimistic,and the internal pollution has become the main problem to be solved urgently in the current treatment and protection of Hengshui Lake.Therefore,to carry out research on the nutrient occurrence form and microbial community structure characteristics,which provided a theoretical basis for the water pollution governance,ecological protection and restoration in Hengshui Lake.Meanwhile,the research results provided a reference for environmental protection of the similar north freshwater lakes.Taking the sediments of Hengshui Lake as the research object,the nutrient content in sediments was determined by loss on ignition method,molybdenum antimony anti-spectrophotometry and persulfate oxidation method.The vertical distribution of nutrients in the columnar sediments of Hengshui Lake was further analyzed by measuring the content and occurrence forms of carbon,nitrogen and phosphorus nutrients in the sediments of different depths,revealing the deposition characteristics of pollutants in hengshui Lake in history,and carrying out risk assessment of nutrient pollution status.At the same time,based on high-throughput sequencing of 16S r RNA gene amplicon,the composition and diversity of sediment microbial community and its response relationship with environmental factors were analyzed.The main results are as follows:1.The degree of total nitrogen pollution in the columnar sediments of Hengshui Lake is moderate,and the degree of total phosphorus pollution is severe,so there are serious nitrogen and phosphorus pollution in the sediments of Hengshui Lake.The total phosphorus pollution problem is more serious,phosphorus release risk is relatively large,easy to cause water eutrophication.The distribution of carbon,nitrogen and phosphorus nutrients in the columnar sediments is significantly different.The spatial distribution of TN,NH₄⁺-N and TOC content is high in the central area and low in the northern area,while the spatial distribution of TP and IP content is high.High in southern regions and low in northern regions.From the perspective of vertical distribution,the contents of TN,NH₄⁺-N,TOC and TP in most sediments show a decreasing trend from shallow to deep.2.Hengshui Lake's columnar sediments have serious nutrient pollution,total nitrogen is at moderate pollution level(II),total phosphorus is at moderate pollution level(IV),and the comprehensive nitrogen and phosphorus pollution index is heavily polluted(IV).The evaluation results of nutrient pollution showed that phosphorus pollution in the whole lake is relatively serious.The evaluation results of organic pollution index showed,the organic index and organic nitrogen index of columnar sediments in Hengshui Lake are both grade III standards,and the environmental condition is still clean.3.The microbial community diversity in the various lake areas are the south area of lake>the center area of lake>the north area of lake.At the phylum level,Firmicutes,which was the dominant bacteria in other lakes frequently,had low relatively abundance in Hengshui lake.At the genus level,the proportion of norank-Anaerolineaceae in the sediment samples in the center area of lake was significantly higher than others.TOC content of the sediments was the key factor of microbial community structure in lake sediments,and is closely related to the organic pollution(Class?)of sediments.