Landscape Heterogeneity Of Urbanized Watershed And Its Impact On Wetland Water Environment

Urban wetland is an important part of urban ecosystem,which plays an important role in maintaining the health of urban ecological environment and biological diversity and other aspects. With the rapid urbanization, urban land continues to be exploited, the original landscape structure and pattern has been changed. So the landscape heterogeneity has been changed significantly. The water environment of urban wetland is also faced with the threat of pollution. Taking the rapid urbanization of Nanjing JiuXiang River as a case study, from the perspective of landscape ecology, this study uses the method of GIS and geostatistical analysis to systematically analyse the temporal changes of landscape structure and pattern, spatial differentiation characteristics of landscape heterogeneity and the impact on the water quality of the environment in JiuXiang River. The results as follows:(1)Great changes have taken place in landscape structure of the study areaAffected by urbanization, the landscape structure of JiuXiang River changed significantly. At the beginning of the regional development in 2003,the natural woodland and arable in JiuXiang River basin account for 38.22% and 34.69%. By 2013, the most significant change is arable land, from 3684.06 hm2 reduced to 1931.74 hm2, the proportions declined to 18.19%. Natural forest area decreased 164.21 hm2, but plantations increased 272.31 hm2; wetland area decreased 14.68 hm2; and grassland increased 674.91 hm2; except residential land decrease 183.09 hm2, industrial buildings, and science and education sites, roads and other construction land increased 606.34 hm2, construction land area ratio increased from 16.86% to 26.39%.(2)Landscape pattern changes are very obvious in the study areaAffected by urbanization, the landscape pattern in JiuXiang River also changed significantly. Lake Wetlands are numerous and widely distributed. But during the decade of 2003-2013, the number of North basin showed a decreasing trend and a total reduction of 146. The amount of cultivated land did not change significantly, but the area has a significant reduction. Grass scattered in the city, which the number and area of irregular shapes both increase. The types of construction land are numerous.And the number and area of construction land continuce to increase.From the whole landscape level of the stydy area, the diversity index increases from 1.58 of 2003 to 1.99 of 2013. Basin landscape evenness increased from 0.64 of 2003 to 0.8 of 2013. Basin landscape dominance decreases, the dominance index in 2003 and 2013 is 0.90 and 0.50 respectively.(3)Landscape heterogeneity of study area has clear differentiationThe results showed that:under the influence of urbanization, the landscape heterogeneity of JiuXiang River has obvious spatial differentiation. To 2013, low heterogeneity is mainly distributed in the southern region of the study area, the area accounts for 7.08% and 18.79% respectively, the area of medium heterogeneity account for 36.69%, which is mainly distributed in the central and southeastern part of the study area. The area of high heterogeneity accounted for 28.59%, which locates in the northern part of the study area and are affected by urbanization significantly.(4)The characteristics and seasonal differences in urban wetland water environmentThis study selects representatives 17 different wetlands to conduct a one-year investigation of water quality monitoring, the results showed that:the whole water quality of each wetland is poor.Except NH3-N and DO index, other chemical indicators are poor, basically in the Grade Ⅲ-Ⅳ standard, The degree of eutrophication is serious. In addition, the changes in urban wetland water quality are significant.(5) The impact of landscape heterogeneity on wetland water environment has obvious response relationshipFrom two aspects of best scale landscape heterogeneity (1500m grid scale) and wetland catchment scale,the research conducts statistics and regression analysis on the surrounding landscape heterogeneity of wetlands and each index of water environmental. The results showed that:from the perspective of the impact of landscape types, relations catchment scale landscape types and quality of wetland buffers than 1500m significant scale; Wetlands, woodlands, construction land is the main factor affecting the wetland water quality. Where wetlands, woodlands and water quality indicators showed a negative correlation was positively related to construction land. From the point of view of the impact of landscape pattern,1500m buffer scale landscape pattern and water quality index correlated significantly compared with the catchment area, patch density, average patch area, diversity, evenness, dominance is the main factor affecting the wetland water quality. Patch density, dominance was positively correlated with the water quality, the average patch area, diversity, evenness and water quality negatively.