Study On Water Environment Characteristics Of Taihu Basin Under The Influence Of Land Use And River Systems

Water quality and quantity have occurred deterioration and shortage,which retard socio-economic development and impede the sustainable development of regional or global ecological and natural environments.Current studies mainly focused on the water resources variation,the evaluation of aquatic health,the water quality variation and influencing factors,based on the perspectives of environmental geography,hydrology and water resources,landscape ecology.Taihu basin has abundant water resources,but the rapid socio-economic development and high population density had damaged the aquatic environment.For example,there are problems such as the reduction of water area,the damage to the natural structure of river systems,the shrinking of rivers,the low compliance rate of water function zones,and severe water pollution.Therefore,we investigated the dynamic changes and influencing factors of lakes and rivers in Taihu Basin.Then,we explored the spatiotemporal changes of water quality and its response to environment factors such as land-use,river systems.Our research provides theoretical and practical references for river basin land-use and water resources planning and management,river systems restoration and protection,and water environment treatment.This paper taked the Taihu basin as the research object.Fristly,we used the JRC global surface water dataset and Landsat remote sensing image data to analyze the water body dynamics and the area changes of important lakes from 1984 to 2018 based on the Google earth engine platform?GEE?.Moreover,we used digital line graphic?DLG?to analyze the structure and connectivity of river systems.Secondly,we employed water chemical characteristic analysis,Mann-Kendall trend test,and principal component analysis,in order to understand the temporal and spatial distribution of water quality in the basin and the source of the pollution.Furthermore,we establish a set of evaluation method for water quality in Taihu basin based on CCME WQI and SOM-Kmeans.Finally,we revealed the relationship between land-use,river systems,hydrological factors and water quality,using Spearman correlation analysis and ridge regression analysis.The main research contents and conclusions of the thesis are as follows:?1?Lakes and river systems variationSignificant changes occurred in the water body of the Taihu basin during 1984 to2018.?1?In terms of water body variation,water area significantly increased and decreased at eastern Shanghai,the region of upper Tiaoxi River and the region of near Changdang and Yangcheng lake,junction area of Nanxun District and Deqing County,Wujiang District,respectively.In terms of water type transitions,2018 compared to1984,41.4%,19.4%and 5.6%were permanent,lost permanent,new seasonal water body.?2?In terms of interannual variation,Yuandang lake and Dianshan lake decreased0.397 km² and 2.013 km²,respectively;Taihu and Dongtaihu increased 45.31 km² and68.61 km²,respectively.?3?The river network structure and connectivity in the Taihu basin were significantly different.Among them,Rd,Rf,D,Wp,?,and?in the eastern plains were generally higher than those in the western hilly;SR in the west part of basin was higher than that in the east;Rc was relatively higher in Shanghai and western Zhejiang than in other regions.?2?Spatiotemporal variation of water qualityWe demonstrated comprehensive spatio-temporal analysis of the water quality of the Taihu basin from 2013 to 2017.The main conclusions are as follows:?1?In terms of time,most water quality parameters have obvious seasonality,and the concentration decreases year by year.Among them,DO,NH₃-N,TN and petroleum were higher in spring and winter then summer and autumn;BOD5 was higher in spring;CODMn,TP,COD_cr and As were higher in summer;Cu and Zn were higher in winter.Because agriculture,industry,transportation,and urban pollution were controlled,water quality in the basin was effectively improved from 2013 to 2017.In terms of spatial,the water quality of each water function zone was significantly different.The water quality in order was conservation zones>drinking water source zones>agricultural water zones>landscape recreation water zones>industrial water zones>transition zones>buffer zones.?2?Watershed pollution had diversity and complexity.Phosphorus and biochemical factors were universal and persistent pollution sources in the basin from2013 to 2017.Ammonia nitrogen nutrients and heavy metals were potential and occasional pollution sources,respectively.?3?According to the classification of CCME WQI,water quality of the basin was generally at“medium”level.According to the SOM-Kmeans evaluation method,the water quality in the western region,the central Taihu basin,the inter-provincial junctions and the eastern plains region were class I?best?,class II^IV?general?,and class V^VII?worst?,respectively.The SOM-Kmeans qualitative evaluation results are highly consistent with the quantitative CCME WQI,which illustrated that the CCME WQI was accurate and suitable for water quality evaluation in Taihu basin.?3?Impact of environment factors on water qualityWe took catchment as a research unit to explore the relationship between land-use,river systems,hydrological factors and water quality.The main conclusions are as follows:?1?Land-use of Taihu basin was classified into three patterns:woodland,build-up land,and cropland catchements.The water quality was as follows:woodland catchements>cropland catchements>build-up land catchements.The seasonal characteristics of water quality in natural region and urban region were opposite.Water quality during non-flood season was better than flood season within build-up land catchement,but that was opposite within woodland catchement.?2?Water quality was strongly correlation with land-use,river systems and hydrological factors.Water quality was positive and negative correlated with woodland area and buid-up land,cropland area,respectively.Water quality was positively correlated with flow velocity and flow discharge.Water quality was negatively correlated with?,?,Rd,Wp,Rf,and D.Our study showed that strong human disturbance weakened the impact of natural characteristics of the basin on water quality.?3?We employed ridge regression analysis to establish a quantitative prediction model between macro factors?land-use,river systems,hydrological factor?and water quality parameters.It showed that the ridge regression model is an effective tool for the analysis of water quality driving factors at catchemnts scale and provided a scientific reference for water environment management in the basin.