| Sediment dredging is an effective measure for controlling internal pollution in lakes,but it can significantly alter the physicochemical properties of sediment,thereby changing the properties of organic matter,especially dissolved organic matter(DOM),in sediment.DOM is particularly important for the release of internal pollutants,which inevitably affect aquatic biodiversity.However,previous studies have focused mainly on the release of pollutants from sediment and their effects on biodiversity,without delving into the role of DOM in this process.Therefore,studying the mechanisms of pollutant release caused by changes in the physicochemical properties of DOM during sediment dredging and its relationship with algal and benthic biodiversity can provide a new perspective for assessing the environmental effects of sediment dredging,which is crucial for lake management after dredging.This study focuses on the physicochemical properties of DOM in the sediment of Dianchi Lake,as well as the effects of dredging on the pollution characteristics of conventional pollutants(nitrogen,phosphorus,and heavy metals)and microplastics.The desorption characteristics of pollutants and the relationship between DOM and algal or benthic biodiversity were systematically analyzed.The main findings of this study are as follows:(1)Dredging can reduce suspended solids,conductivity,and oxidation-reduction potential of the water in Dianchi Lake.However,the pollutants in interstitial water and the total phosphorus and nitrogen in surface sediment increase after dredging.There is a negative correlation between the particle size distribution of sediment in Dianchi Lake and the content of conventional pollutants.Furthermore,the higher the organic matter content in sediment,the higher the content of heavy metals and nitrogen pollutants.The ecological hazard of heavy metals in the surface sediment of Dianchi Lake is generally mild,and dredging can reduce the risk index of heavy metals.Dredging has little effect on the color and type compositions of microplastics in the sediment of Dianchi Lake,but it can change the morphological structure of microplastics.Dredging can reduce the content of microplastics in the sediment and may potentially decrease the ecological risk of microplastics.(2)The desorption of pollutants from dissolved organic matter(DOM)can be divided into two stages:fast and slow reactions,and the desorption process is strongly affected by pH.Joint desorption experiments have shown that ammonia nitrogen can promote the desorption of lead,while phosphate inhibits it.The lower the aromaticity and humification of DOM,the more easily it releases pollutants such as nitrogen,phosphorus,and heavy metals.(3)According to the identification of algae and benthic biomass in Dianchi Lake,the cyanobacteria(Microcystis and Oscillatoria)are found to be dominant in algal abundance in the phylum Cyanobacteria.The gastropod Paraprososthenia costata dominates the benthic biomass,but both algal and benthic animal biodiversity is low.In addition,the physicochemical properties of DOM in the Dianchi Lake sediment were significantly correlated with the biodiversity of algae and benthic biomass.The lower the aromaticity and humification of DOM,the fewer species and the lower diversity of algae and benthic animals,with increased density and uniformity.This study clarifies the effects of dredging on the water quality,sediment physicochemical properties,and pollutant distribution characteristics in Dianchi Lake,elucidates the desorption mechanism of internal pollutants by DOM in sediment,analyzes the relationship between DOM physicochemical properties and pollutant release processes,and the biodiversity of aquatic organisms.The research results can provide data support and theoretical guidance for subsequent dredging of Dianchi Lake sediment,new information on the impact of DOM in dredging on lake ecosystems and a new perspective for the environmental impact assessment of dredging. |
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