| Lake has multiple functions as an important terrestrial ecosystem,whose health situation has a close relationship with regional economic development and people's living standard.In recent years,with rapid economic development and unreasonable human activities,a large number of sewage from industry,agriculture,and living is discharged into lake and resulted in increased levels of lake nutrients and caused significant eutrophication of lake water,which has a serious influence on regional social economic development and the improvement of people's living standards.After the arsenic pollution in 2008 in Lake Yangzong,many scholars have carried out a lot of researches focusing on heavy metal pollution and achieved many achievements.However,researches on the input of lake nutrients and its impacts on the ecological environment are less involved.Therefore,based on 36 samples from surface sediment,through the analysis of organic matter and their stable isotope,combined with the water quality proxies,we analyzed the spatial distribution of organic matter and the material source of organic and its influence factors,and evaluated the environment status of surface sediment.Here are the conclusions:(1)Based on the analysis of water quality parameters,we found out that Lake Yangzong is a seasonal stratified lake and possesses seasonal hypoxia at the bottom,whose stratification is mainly caused by the changes of temperature.In addition,TN and TP contents' change indicates that water is nutritional state.And the content of nitrogen and phosphorus in bottom is higher than that of upper.(2)The characteristics of granularity show that the main type of sediment is clayey-silt,and the silt is the dominant ingredient from 52.951% to 67.793%.Meanwhile,the each ingredient in surface sediment has an obvious distribution feature.The clay is higher in the north and south but lower in the central and western regions.There is a significant negative correlation between silt and clay content(p<0.01,r=-0.922).As for the median grade,the distribution is the same to the clay content.(3)Compared with other lakes,the contents of TOC and TN are relatively higher.The contents of TOC and TN have an obvious distribution feature,which shows that higher in the south but lower in the north.The content is reducing form the south to north,which suggests the source should come from south area of the lake.Moreover,the C/N is between 16.267 and 27.270,with an average value of 22.130,whose distribution is opposed to the content of TOC and TN.Additionally,the distribution of ?13C is similar to the C/N,but the distribution of ?13C is opposed to the ?15N.Consequently,we conclude that the source of organic matter is mainly related to the input of the south side of the lake.The land-borne matter carried by the river shows a decreasing trend from south to north under the action of water flow.(4)Based on the analysis of the ecological organic index,the surface sediments belong to organic pollution and organic nitrogen pollution,except for the sampling points 1 and 2.Of course,the status of pollution is different,such as relatively sever pollution in south part and relatively light pollution in north part.Above proxies suggest that the change of ecological environment change has an obvious spatial distribution characteristics,hence we should takes proper steps on agricultural activities near the south lake. |
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