| With the rapid development of urbanization,the urban land use structure change was caused.Rapid expansion of urban land strongly affected the regional water cycle process,accelerated the attenuation of river network,and caused a series of water environment problems.Therefore,exploring the response of landscape pattern change and the rivers water quality under the urbanization,calculating and analyzing the river water environmental capacity on the basis of understanding the present situation of regional water environment,can provide theoretical basis for reasonable planning of urban land,the determination of pollutant reduction degree and the improvement of water environment quality.Suzhou city is located in the abdominal area of Taihu lake basin and is a typical area for plain river network.The paper chosed Suzhou city as the research object,based on a multidisciplinary perspective,with the integrated application of remote sensing,geographical information system,the numerical simulation method,studying the underlying surface changes and its relationship with water environment from different spatial scales.The paper also calculated water environment capacity from the perspective of the point source discharge,analyzed pollutant reduction combined with non-point source pollutants emissions data,revealed "urbanization-human activities-land use-water environment"effect finally,and explored the urban land planning and water environment protection issues.The main research content includes the following three aspects:1.Analysis of the changes of urban river water quality and river landscape patternCombined with single factor evaluation and comprehensive evaluation method of water quality,water quality change of Suzhou city in 2004-2014 was analyzed.The results showed that the proportion of water quality monitoring section which the water quality was ?-worse V decreased generally in 2004-2014,but its proportin still reached 52.38%in 2014.Overall condition of water quality was poorer,but showed a trend of certain improvement.TN and NH3-N were the main pollutants,meanwhile,pollution share rate of TN was the highest.Based on three phase of the interpretation data of land use in 1991,2001 and 2010,the land use type structure and spatial structure of landscape pattern of Suzhou city were analyzed,and the transfer rule of all land use type was determined.The results showed that the main land use types of the Suzhou city was paddy field and waters,their proportion in different periods was all above 60%.Urban land and the dry land which were in a growing state were the next.The amount of forest was the least,while the proportion had been below 4%with a trend of fluctuated change.Underlying surface changes gave priority to the increase of urban construction land and the dry land and the decrease of paddy field and forest land area,water area also increased.Transfer of land use characteristics in paddy field into urban land,dry land and waters,led to a decrease of paddy field area.Landscape spatial structure showed a growth trend in fragmentation,land use type richness and landscape diversity.2.Landscape pattern change and its response to the water quality under the urbanizationIn order to explore the response of landscape pattern change and the rivers water quality under the urbanization,landscape pattern and structure information of different spatial scales were obtained by the use of ArcGIS at first.Then pattern indexes of different spatial scales buffer was calculated by the landscape pattern analysis software,response analysis of landscape pattern and river water quality was carried on combined with the actual monitoring value of water quality monitoring sites.The results showed that:(1)from the perspective of landscape pattern,the water quality in the study area was closely related to urban area,paddy field,dry land,and the correlation changed with the change of buffer size.The existence of the obvious scale correlation reflected the complex influence mechanism of land use pattern to water quality.With the increase of buffer scale,the correlation between land use type and water quality index enhanced generally,and its influence was more significant within the buffer of 700-1000m.(2)In terms of the spatial structure of landscape pattern,the river water quality showed a negative correlation with CONTAG and LPI which represented patches aggregation degree and the dominant landscape type,and a positive correlated with NP,PD,SHEI and SHDI which represented landscape fragmentation,the correlation was more significant in the 1000m buffer.The influence of landscape pattern on the water quality indicators was more significant across a wide range of buffer compared with smaller buffer.3.The analysis of urban water environment capacity and pollutant reductionBased on the condition of river network of Suzhou,through the analysis of hydrological conditions,calculation of pollution emissions and river pollution load from industry,life,agriculture,livestock and poultry breeding,river network generalization,determination of the channel parameters,water quality situation and its target,water environmental capacity and quantity of pollutant reduction of Suzhou city and its major rivers were calculated respectively on the basis of water quality target of each function in 2010 and 2020,According to comprehensive analysis of emissions and river pollution load of various kinds of pollutant,the proportion of urban pollution in the total pollution of river basin was the largest,the second one was industrial pollution emissions,and non-point source pollution produced by livestock farming proportion was higher as well.In addition,the statistical results showed that the pollutant emissions of basin-wide rivers was more than that of regional rivers in the study area.The water environmental capacity which was calculated by water quality target of each function of 2010 showed that water environmental capacity of COD was 102007.18 t/a,and that of NH3-N was 4954.6 t/a.Pollutant reduction of COD was 59160.7 t/a,and NH3-N cut was 16784.57 t/a.The water environmental capacity which was calculated by water quality target of each function of 2020 showed that the environmental capacity of COD was 89143.75 t/a,and that of NH3-N was 3613.44 t/a.Pollutant reduction of COD was 79024.4 t/a,while NH3-N cut was 19023.02 t/a.Compared with 2010,water environment capacity and residual water environmental capacity were in a trend of decrease,while the pollutants cut increased.According to the results of environmental capacity of COD,only Xujiang river,Qiputang river,the Jiangnan canal and Changhuhe river had certain surplus environmental capacity,while the rest of the river all required emissions cuts.In terms of NH3-N,only the Jiangnan canal had residual water environmental capacity,the remaining water all needed to reduce NH3-N emissions.Furthermore,the amount of reduction calculated by water quality target of 2020 was higher than that of 2010. |
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