Experimental Study On Community Characteristics Of Zoobenthos In Constructed Wetlands In Subtropical Hilly Area

As a green wastewater treatment technology that uses natural processes to achieve water purification,constructed wetland has been effectively promoted and applied in the treatment of agricultural non-point source pollution.However,most of the researches on sewage purification in constructed wetlands focused on the synergistic effect of matrix-plant-microorganism,while the research on zoobenthos was relatively few.As an important part of constructed wetland ecosystem,zoobenthos can directly remove pollutants from water through feeding and enrichment,and can also indirectly promote the removal of pollutants by plants and microorganisms by changing the physical and chemical effects of sediments through biological disturbance.Therefore,it is of great significance to study the community characteristics and influencing factors of zoobenthos in constructed wetland for further improving the function of constructed wetland and improving the sewage purification efficiency of constructed wetlands,the typical subtropical red soil hilly area located in Changsha,Hunan Province was selected as the experimental area in the study.Constructed wetlands was set up eight treatments:Pontederia cordata,Canna glauca,Iris psudacorus,Myriophyllum elatinoides,P.cordata+M.elatinoides,C.glauca+M.elatinoides,I.psudacorus+M.elatinoides and CK.Through a one-year field experiment,the seasonal characteristics of zoobenthos community and their relationships with water environmental factors,such as COD,nitrogen(N)and phosphorus(P),were studied in the constructed surface flow wetland.The main conclusions were as follows:(1)A total of 34 species of zoobenthos were collected in four seasons,with the smaller arthropods as the main group and the larger molluscs less.Among them,season has a greater impact on the number of zoobenthos species,which is higher in summer and autumn than those in spring and winter.Compared with single emergent plant wetland,the number of zoobenthos species in emergent plant+M.elatinoides wetland is less.(2)The dominant species composition of zoobenthos in different seasons and different plant wetlands were different.In general,except for the CK in spring,M.elatinoides and emergent plant+M.elatinoides in summer,the dominant degree of Limnodrilus hoffmeisteri in other wetland occupied a certain dominant position(Y>0.02),with the highest dominance value of 0.48.It is indicated that L.hoffmeisteri was the main dominant species in constructed wetland.(3)The average annual abundance and biomass of zoobenthos were positively correlated with the degree of eutrophication.The average annual abundance and biomass of zoobenthos in the CK wetland were the highest,reaching 3665 ind/m² and 146 g/m²,respectively,and the average annual abundance and biomass of zoobenthos in the M.elatinoides and emergent plant+M.elatinoides wetland were relatively low.In general,the biodiversity of zoobenthos in constructed wetlands is low,the Shannon-Weiner diversity index(H'),Margalef richness index(d)and Pielou evenness index(J)only ranged from 0.46-1.26?0.26-1.03 and 0.27-0.81.(4)The species number of zoobenthos in constructed wetland was significantly positively correlated with p H and DO,and negatively correlated with Eh.Abundance and biomass were significantly positively correlated with NH₃-N,TN,EC,p H,WT and COD(P<0.05),but negatively correlated with Eh.The influence factors of species abundance of different zoobenthos are also different.The abundance of Gastropoda was positively correlated with DO,and most of them appeared in M.elatinoides and emergent plant+M.elatinoides wetland in summer.Hirudinea and other insects were positively correlated with Eh,which mainly existed in autumn and winter,and existed in almost every wetland.Chironomid larvae were positively correlated with NH₃-N,EC,COD and TN and Oligochaeta showed a great correlation with p H,which mainly appeared in various wetlands in spring and summer.