Ecological Assessment Of Freshwater Aquaculture Environment And Sediment Pollution Restoration Around The Taihu Lake In Jiangsu Province

The freshwater aquaculture around the Taihu Lake in Jiangsu Province is an important component of the socio-economic development of the Taihu Lake basin.While providing significant economic benefits to the basin,freshwater aquaculture has also caused a series of water ecological health problems.These problems not only threaten the quality and efficiency of aquaculture but also become important factors restricting pollution control and eutrophication management of the Taihu Lake basin.Based on the health monitoring results of freshwater aquaculture around the Taihu Lake in Jiangsu Province from September 2020 to August 2021,this paper constructed an evaluation index system based on the PSR model and conducted an impact factor identification combining with the obstacle degree model.The study systematically evaluated the current status of the ecosystem health of freshwater aquaculture around the Taihu Lake in Jiangsu Province.Furthermore,the study explored the removal effect of pollutants in the aquaculture sediment under different restoration methods（adding Ca O₂,adding Ca（NO₃）₂,intermittent aeration,adding Bacillus,adding Lactobacillus）and analyzed their microbial response mechanisms.The main conclusions of this paper are as follows:（1）The TN concentration of the water ranged between 0.85-8.11mg/L,and the NH₄⁺-N concentration ranged between 0.10-6.51mg/L throughout the year.The winter TN and NH₄⁺-N concentrations were generally higher than in other seasons.The TP and TN concentrations in the lake aquaculture water were lower than those in pond aquaculture water.The seasonal variation trend of COD_Mnwas not significant,and the Chl.a content showed the characteristics was spring>summer>autumn>winter.In the comprehensive water quality index evaluation results,Class III water accounted for47.73%,and Class IV water accounted for 36.36%.The comprehensive pollution index evaluation results of the aquaculture sediment showed that the pollution level was severe in summer,followed by autumn,winter,and spring.Mild pollution accounted for 15.91%,and severe pollution accounted for 65.91%.The nutritional status index of planktonic plants was highest in summer and lowest in winter.The trend of changes in the density of planktonic animals was summer>spring>autumn>winter,and pond aquaculture>lake aquaculture.（2）The PSR model was used to construct the ecosystem health evaluation system of freshwater aquaculture around the Taihu Lake in Jiangsu Province.The evaluation results showed that the ecosystem health level of lake aquaculture was higher than that of pond aquaculture.Among them,the highest comprehensive score was W1（Wanshan Lake）,and the lowest was S4（Dabeifu perch pond）.Healthy and sub-healthy waters accounted for 18.18%and 54.55%,respectively.The obstacle model revealed the intensity of impact factors,and the results showed that the factor with the greatest contribution was the total nitrogen content in the sediment,and the factor with the smallest contribution was the benthic biodiversity.（3）The study on the release of nitrogen and phosphorus from sediment reveals that the higher the environmental p H,the greater the release intensity of TN and TP from sediment.When DO>6.0mg/L,the release of TN and TP from sediment is inhibited.The release intensity of TN and TP from sediment is positively correlated with disturbance intensity and temperature.In simulated restoration experiments,Ca O₂has a significant impact on overlying water p H,and the removal rates of TN and TP in overlying water are 28.69%and 68.25%,respectively.Ca（NO₃）₂addition causes an increase in NH₃^--N and TN concentration in overlying water.Intermittent aeration increases the dissolved oxygen content in overlying water,and the removal rates of NH₄⁺-N,TN,and TP in overlying water are 45.23%,42.03%,and 50.29%,respectively.Bacillus and Lactobacillus have removal rates of 28.20%and 31.35%for TN in overlying water and 37.52%and 13.33%for TP,respectively.（4）Microbial response results indicate that the microbial richness of sediment in Ca（NO₃）₂and Ca O₂groups is lower than that in the CK group.At the phylum level,the abundance of Proteobacteria,Firmicutes,and Campilobacterota in the Ca O₂group increased by 11.6%,22.35%,and 131.12%,respectively,compared to the CK group.The abundance of Proteobacteria in the Ca（NO₃）₂group increased by 65.54%,while that of Chloroflexi and Firmicutes decreased by 24.8%and 25.75%,respectively.At the genus level,norank＿f＿＿norank＿o＿＿SBR1031 and norank＿f＿＿Anaerolineaceae,which are related to denitrification,were found in the sediment of both Ca（NO₃）₂and Ca O₂groups.Combining with the previous research results,it can be concluded that both CaO₂and Ca（NO₃）₂additions promote denitrification in the system.