| The construction of the reservoir will inevitably have a certain impact on the water power,sediment and riverbed boundary of the natural river,and change the original water and sediment conditions and riverbed shape,which cause the reservoir sedimentation.The reservoir water level fluctuation zone is the area of environmental change caused by the periodic fluctuation of the reservoir water level,which is the most sensitive area for the scour and sedimentation of the reservoir sediments,and also the most important area affecting the water environment of the reservoir.It is very important to accurately evaluate the quality of reservoir water environment that the change of water level causes the erosion and deposition of sediment and the calculation.Therefore,based on the characteristics of water storage and drainage in the drawdown zone,and combined with the characteristics of hydrology and water level change,this paper takes Biliuhe reservoir of Dalian City as the research object,applying the improved sediment discharge method to calculate the sedimentation.According to the sedimentary process,the temporal and spatial characteristics of phosphorus in sediments were analyzed.With economic development,population growth and other factors,the impact of human activities on the environment has increased,which is also the main factor for the increase of phosphorus and other nutrients or pollutants.Based on the above background and research content,this paper analyzes and studies from three aspects:the calculation of deposition amount,the analysis of phosphorus spatiotemporal change and the influence of human factors on phosphorus change.The results are as follows.(1)In terms of the calculation of the sedimentation amount in the reservoir water dissipation area.Based on the area surrounded by the water level and the method of flow sediment combination,the siltation amount of the analysis area D1 at the inlet of Biliuhe reservoir is calculated.The results show that the analysis area D1 takes 60m as the boundary point of erosion and siltation.From the establishment of Biliuhe reservoir to 2017,the time when the water level is higher than 60m elevation accounts for 72%,and the flow and sediment concentration of flood in flood season account for 72%.There was a significant positive correlation(>0.7)between them,and the siltation mainly occurred during the flood.Combined with the improved sediment transport formula,the sediment deposition in analysis area D1 is 1.59×106m~3,and the average sediment deposition is 4839m~3/a(2)In the aspect of temporal and spatial analysis of phosphorus in sediment.The vertical distribution of total phosphorus,organic phosphorus and inorganic phosphorus in column samples was analyzed based on the calculation of silting layer and the experimental data of total phosphorus.The total phosphorus content increased first,then decreased and then increased from deep to shallow,and reached the maximum at the depth of 45-50cm.In the depth of 0-20cm,the content of total phosphorus in the surface layer is higher than that in the depth of 20cm.The content of total phosphorus changes in the range of 345.95-947.65mg/kg,and the main content is inorganic phosphorus,the change range is 335.36-885.68mg/kg.This stage mainly occurs in 2004-2014.The change range of total phosphorus reserves is0.057-0.132kg/m2,and that of inorganic phosphorus reserves is 0.056-0.124kg/m2.Through calculation and analysis of phosphorus distribution,it can be seen that phosphorus is obviously enriched in recent years.(3)In human factor analysis.Through SPSS principal component analysis,three principal components were obtained,the eigenvalues were 4.016,1.771 and 1.196respectively.Paddy field,dry land,forest land,rural residential area and vegetation coverage have higher load on the first principal component,farmland productivity,population spatial distribution and GDP have higher load on the second principal component and the third principal component respectively,and the cumulative contribution rate of the first,second and third principal components is 87%.Through the calculation of the comprehensive principal component value f of different years by the principal component comprehensive model,we can see that the order of the impact degree of human activities is successively 2015>2005>2010>1995>2000>1990,and the most serious impact is 2015,which shows that the human factor dominated by land use is the main driving force for the increase of phosphorus content,in addition,the economic and other factors also affect the change of phosphorus content It has a direct impact. |
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