| Guizhou Caohai is a typical and complete plateau wetland ecosystem,and is a wintering place for rare water birds such as black-necked cranes.As a typical grass type lake,aquatic plants play an important role in the Caohai ecosystem.In the past two years,aquatic plants in Caohai have experienced a decline.In order to explore the reasons for its decline,this study attempts to analyze the impact of sediment endogenous phosphorus release on the decline of aquatic plants from the perspective of phosphorus occurrence and release flux in sediments,thereby providing relevant theoretical support for scientific management of grassy lakes.In this study,four seasons of sampling were conducted for the overlying water,interstitial water,and surface sediments of the Caohai Sea,and the eutrophication degree of the overlying water was evaluated based on the comprehensive nutrient index method of the water body;Single factor standard index method and soil comprehensive nutrient index method were used to evaluate the pollution degree of organic matter and nitrogen and phosphorus nutrients in sediments;The spatiotemporal distribution characteristics of overlying water,interstitial water,and sediment were analyzed;Based on the phosphorus occurrence patterns and spatiotemporal distribution characteristics of surface sediments,the effects of sedimentary physicochemical factors on phosphorus occurrence patterns were compared;The static release flux of phosphorus was calculated from overlying water and interstitial water,and its annual flux and contribution rate to water phosphorus were estimated.The following conclusions were obtained through research:(1)The water quality of Caohai is in a moderately eutrophic state in winter,while it is in a slightly eutrophic state in spring,summer,and autumn.The maximum values in spring and summer have reached a moderately eutrophic state,and the water quality of Caohai has deteriorated significantly.(2)The organic matter and total nitrogen in the sediments of Caohai Lake are all of level 4 pollution in four seasons,while total phosphorus is of level 3 pollution in spring,and of level 2 pollution in summer,autumn,and winter.The comprehensive pollution index is of level 4 pollution in all four seasons.This indicates that Caohai has serious nitrogen and phosphorus pollution,and nitrogen pollution is higher than phosphorus pollution.(3)Although the total phosphorus content of Caohai sediment is not high,through the analysis of phosphorus forms,the proportion of organic phosphorus in the phosphorus forms of Caohai is as high as47.931%～72.286%,and the proportion of bioavailable phosphorus is25.52%～42.50%.The content of bioavailable phosphorus is high.When environmental conditions are suitable,bioavailable phosphorus will be released in large quantities,promoting algae proliferation,and deteriorating water quality.(4)The average contribution rate of static release to phosphorus in water is 5.80%.The average static release flux of phosphorus is 0.0275mg/(m~2·d),and the sediment generally represents a"source"of phosphorus.Static release has little impact on the release of endogenous phosphorus from Caohai sediment. |
