Effects Of Riparian Zone Structure And Land Use On Water Quality And Benthic Macroinvertebrates In River Network Area

With global climate change,local differences in hydrological situations and continued human disturbance of the water environment,river ecosystems have been suffering from varying degrees of interference and damage.Problems such as river flow reduction,water quality deterioration and habitat degradation are particularly prominent.The regulatory function of the river ecosystem is becoming increasingly weak and seriously threatening river health.With the low terrain,dense river networks and numerous systems in the plain river network areas,the conflict between rapid economic development and the maintenance of river ecosystems has been intensifying.Globally,human activities pose a serious danger to the stability of river ecosystems.Therefore,exploring the relationship between land use around rivers,riparian zone structure and river ecosystems can help provide a theoretical basis for regional river ecosystem biodiversity conservation and water ecosystem restoration.The thesis investigated the riparian zone,water quality and water ecology of 21 rivers in the western part of Qingpu District,Shanghai（Qingxi region）,exploring the temporal and spatial distribution characteristics of water quality and macrozoobenthic communities and then evaluated them by using a variety of methods.Based on the data,Spearman was used to analyze the relationship between water quality,benthic macroinvertebrates and riparian zone structure,land use.The main research contents and results are as follows:（1）Riparian zone structure and land use evaluationThe results of the comprehensive evaluation of the riparian zone structure of 21rivers in Qingxi region showed that most of the riparian zones were in grade III-IV,with the riparian zone structure of the backbone rivers being better than that of the secondary rivers.Among them,81.00%of the riverine riparian structures had some problems,the main problems were poor stability and insufficient riparian zone width.The land use types in Qingxi were mainly cultivated land and construction land.The proportion of the area of each land use type at different buffer scales in the monitoring section was in the order of cultivated land,construction land,water area,forest land,unused land and grassland.The proportion of cultivated land exceeded 50%of the total area at all buffer scales and increased as the buffer scale increased.（2）Effects of riparian zone structure and land use on water qualityIn order to explore the characteristics of the regional water environment quality,a comprehensive spatial and temporal analysis of the water quality in the Qingxi region in 2021 was conducted using various analytical methods such as the characteristics analysis of physicochemical factor,principal component analysis and comprehensive water quality identification index method,and its correlation with riparian zone structure and land use was explored.The main conclusions are as follows:（1）The physicochemical characteristics of water varied significantly throughout both time and space in the Qingxi region.Temporally,the average concentrations of NH₃-N,TN and DO in the non-flood period were significantly higher than the average concentrations in the flood period;the average concentrations of COD and TP in the flood period were higher than those in the non-flood period;the difference between the values of BOD₅in the flood and non-flood periods was small.Spatially,the water quality of the rivers in the south of Qingxi was better than that in the north.Principal component analysis showed that the main pollution factors in the region were organic matter pollution and nitrogen and phosphorus pollution.（2）The single-factor evaluation method showed that the main pollutants exceeding the standard in the study area were DO,BOD₅ and COD.The improved comprehensive water quality labeling index method based on the excess multiple method showed that the rivers in Qingxi region were Class II.-III.water,and the comprehensive water quality labeling index of each monitoring section in the non-flood period was better than that in the flood period.（3）The land use type in the Qingxi region had a greater influence on the physicochemical factors of water.Among all of the land use types,cultivated land and construction land had the most significant impact on water quality;the percentage of cultivated land and forest land was negatively correlated with the physicochemical factors of water,the percentage of construction land was positively correlated with the physicochemical factors of water,the percentage of water area was positively correlated with DO and negatively correlated with TP and TN,etc.The stability of river banks was highly significantly and positively correlated with TN and NH₃-N.（3）Effects of riparian zone structure and land use on benthic macroinvertebratesBased on the investigation of benthic macroinvertebrates and using various analytical methods,a comprehensive spatiotemporal analysis of macrozoobenthic communities in the Qingxi region in 2021 was conducted,and the correlation between benthic macroinvertebrate and riparian zone structure and land use was explored.The main conclusions are as follows:（1）The identified macroinvertebrates belonged to 3phyla,23 families,35 genera,and 42 species.The number of species was November>May>March>August,with Limnodrilus hoffmeisteri,Bellamya purificata and Bellamya aeruginosa being all the dominant species in the four months.The average biological density was May>March>August>November,and the average biomass was May>November>August>March.（2）Based on RDA analysis,the main physicochemical factors of water affecting macrozoobenthic communities of the Qingxi region were temperature,TP,and NH₃-N.The water quality of rivers in the Qingxi region was evaluated based on the Shannon-Wiener diversity index,Margalef richness index,BI index and Goodnight correction index.The evaluation results showed that the river water quality in the Qingxi region was generally light to moderate pollution.（3）The riparian zone structure of rivers in Qingxi had a greater influence on benthic macroinvertebrates.The stability of river banks had a highly significant positive correlation with the specie,biomass,and diversity index of macrozoobenthic communities,as well as with the biological density of benthic macroinvertebrates.The percentage of cultivated land was negatively correlated with benthic macroinvertebrate species,biological density and diversity index.The percentage of water area at a small scale was significantly positively correlated with the number of benthic macroinvertebrate species.