| In order to understand the impact of human activities and natural environmental changes on the two lakes in Mengzi Basin,the biophysical parameters of sediments were used to analyze the physical and chemical properties of sediments,and the organic matter content of surface sediments of Lake Datun and Lake Changqiao were explored.The sediment particle size,total organic carbon?TOC?,total nitrogen?TN?,carbon and nitrogen stable isotope(?13C,?15N)of 75 sites were determined during the experiment.Meanwhile,the sediment particle size and hydrodynamic environment were discussed,and the effects of TOC and TN content were also analyzed.Moreover,the relative percentages of endogenous organic matter in terrestrial sources and lakes were discussed.At the same time,the organic index and organic nitrogen pollution were analyzed.?1?The surface sediments of the Lake Datun are mainly silt and clay,of which silt is the dominant size of the lake area,the type is clay silt,and some samples are sandy silt,silty sand and Sand-silt-clay.The surface sediments of the Lake Changqiao are mainly silt and clay.The silt is the dominant size of the lake area.The main types are clay silty sand and a few samples of silty clay.The intensity of human activities in lake basins also has an important influence on the variation of grain size components of lake sediments,forming concentric circles different from those under the influence of natural environment.?2?The total organic carbon?TOC?content in the surface sediments of the Lake Datun fluctuated between 1.91%and 8.78%,with an average content of 5.09%.The content is high in the middle and low in the periphery,forming a spatial distribution characteristic similar to a concentric circle structure.The surface sediments of Lake Changqiao are between 0.17%and 4.70%of total organic carbon?TOC?,with an average of 2.83%.In the center of the southeastern lake,there are more than 4%high-value central areas,and the core area gradually decreases toward the periphery,forming a spatial structure distribution similar to a concentric circle.?3?The total organic nitrogen?TN?content of the sediments in the Lake Datun ranged from 0.21%to 0.81%,with an average of 0.49%,forming a spatial distribution characteristic of a concentric structure.The spatial distribution characteristics of total organic nitrogen?TN?content in the surface sediments of the Lake Datun have the same trend as the spatial distribution characteristics of total organic carbon?TOC?content.The total organic nitrogen?TN?content in the surface sediments of Lake Changqiao is between 0.01%and 0.53%,and the fluctuation range is small,with an average value of 0.28%.The spatial distribution characteristics of total organic nitrogen?TN?content in the surface sediments of Lake Changqiao have the same trend as the spatial distribution characteristics of total organic carbon?TOC?content.The lake basin topography is the main controlling factor of the spatial distribution of organic matter.?4?The carbon/nitrogen ratio?C/N?of surface sediments in the Lake Datun is between 8.12 and 12.55 with an average of 10.12.The carbon/nitrogen ratio?C/N?of surface sediments in Lake Changqiao is between 8.63 and 14.80,with an average of10.80.The organic carbon isotope(?13C)of Lake Datun is between-30.49-21.46,with an average of-26.62.The organic carbon isotope(?13C)of Lake Changqiao is between-30.42-21.7,with an average of-26.31.?5?The nitrogen isotope(?15N)of the sediments in the Lake Datun is between4.11and 9.07with an average of 6.99;the nitrogen isotope(?15N)of the Lake Changqiao sediment is between 8.43and 13.97,with an average.The value is10.83,the western coast is larger than the south coast,and the northwest is larger than the southwest.The Shadian River is larger than the eastern coast and larger than the northeast.The surface erosion is serious and human activities are frequent.The organic nitrogen in the study area mainly comes from the nitrate of soil organic matter in the land source and the domestic sewage discharged by human beings,and the internal source mainly comes from the phytoplankton in the lake,and some of it comes from the artificial fertilization on the agricultural land around the lake.A small part of the Changqiao Lake has C3 plants from terrestrial sources.?6?The organic matter contributed by terrestrial soil sources in the organic matter of the Lake Datun sediments accounted for 097.36%,and the contribution value accounted for 26.6%of the total organic matter of sediments.The organic matter of endophytic phytoplankton in the sediments of the Lake Datun is 067.35%,and the contribution value accounts for 32.93%of the total organic matter of sediments.The organic matter of terrestrial human activity sewage in the organic matter of the Lake Datun sediment is 0-98.16%,and the contribution value accounts for 40.95%of the total organic matter of sediment.The contribution rate of the three endmembers is:f sew>f p>f soil,and the organic matter of sewage is the main source of organic matter in the sediments of the Lake Datun.The organic matter contributed by terrestrial soils in the organic matter of Lake Changqiao sediments accounted for 089.64%,and the contribution of soil organic matter accounted for 39.85%of the total organic matter of sediments.The organic matter contributed by the source of phytoplankton in the lake accounted for090.71%,and the contribution value accounted for 28.31%of the total organic matter of sediment.The organic matter from the sewage is between 093.82%,and the contribution value accounts for 32.75%of the total organic matter of the sediment.The contribution rate of the three endmembers is:f soil>f sew>f p,the soil organic matter is the main source of organic matter in the Lake Changqiao sediment,and the organic matter of the sewage is second. |
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