| The impact on wetland ecosystem by land use change in urbanization is one of the important topics in wetland ecology. River as one of the important types of wetlands, the quality of the water environment not only determines the quality of the urban landscape in future, but also affects the sustainable development of urban areas. From the perspective of landscape ecology, it has brought an important theoretical and practical significance to explore the relationship between the land use pattern and river water quality of the urban areas in landscape planning and environmental protection of river water. In this context, using the environment quality of river water as a check point, Jiuxiang River Basin was selected as a case study for its rapid urbanization. Based on two remote sensing in2003,2009and water quality monitored in April2010and March2011,this paper stated the characteristics of watershed land use pattern changes and environmental quality of river water, relationship between watershed land use pattern and water quality, and the impact of land use intensity on water quality by means of GIS technology and the RDA analysis. The paper also presented strategies of water quality of the river basin.The main findings of the paper were summarized as the following:1.Identify the features of landuse change of the Jiuxiang River watershed in the rapid urbanization process.(1) From2003to2009, the landuse structure of Jiuxiang River watershed has made significant changes. The arable rapidly reduced from34.86%in2003to19.52%in2009, while construction land rapidly increased from17.80%to25.80%; It also showed a certain gradient feature in space:The farmland reduced140.05hm2,506.15hm2,979.82hm2in the upstream, midstream and downstream respectively, while construction land increased48.86hm2,284.05hm2,515.95hm2; The key reason of arable reduction was that construction land occupied farmland in the process of urbanization.(2) Watershed land use spatial variation presented significant differences: the center of gravity of wetland, farmland, and woodland move to upstream in a whole; Unused land and grassland moved to downstream; Construction area moved to the west of the city.(3) Land use pattern in watershed significantly changed in temporal and spatial. From2003to2009, land use spatial heterogeneity was enhanced, and evenness was increased, however a decline in dominance, watershed land use becomed more complicated; In space level, the land use type tended to be fragmentated in the upstream and midstream, and the land use evenness in the midstream had most obviously increased.(4) From2003to2009, land use intensity in the watershed showed a trend to the strong and weak poles, and the enhancement was the most significant in northeast-southwest direction; The spatial distribution of land use intensity in the Jiuxiang River watershed showed a strong positive correlation,which was closely related with the scale. With increase in the scale, land use intensity autocorrelation reduced.2. Dissect the spatial and temporal variation characteristics of the water quality in the Jiuxiang River.(1)The water quality was generally poor in Jiuxiang river. The annual average water quality was categoried as below â…£ class, and TN, TP and NH3-N reach inferior to â…¤ class. Water quality was mainly contaminated by nitrogen and phosphorus. The water was polluted by nitrogen in the upstream, while the water quality was polluted by nitrogen, phosphorus in the middle and lower catchment.(2)There existed a large spatial and temporal differences in river water quality. The water quality in the upper reaches was better than that in the middle and lower reaches, and the water quality did not make any difference between downstream and middle reaches of the river, but the concentration of NH3-N and Chla varied significantly; The water quality was superior in wet season than the dry season. However, there were some differences among the indicators:the concentration of NH3-N, TP and TDS was lower in the wet season. In the middle and lower reaches of the river, TN was lower in the wet season, and TN concentration was higher in the wet season in the upstream; only CODMn and Cond concentration showed high in the wet season.(3) Differences existed in pollutant sources in different parts of the river. Water quality was mainly affected by agricultural non-point source pollution in the upstream. The rural sewage was the main impacting source of the water quality in the middle reaches of the river. Municipal sewage and waste water from small size industries were the key sources in the downstream. 3.Explore the multi-scale response between the land use pattern and water quality in the Jiuxiang River basin.(1) The impacts of land use and its pattern obviously depended on water quality in different scales. In the small spatial scale, construction land and wetland were the main factors to influence the water quality; In the large spatial scale, woodland and construction land were the main factor; In terms of land use pattern, COHE had a greater impact on water quality in the small spatial scale; In larger spatial scale, SHID was a key factor to determine the water quality; Land use status at the watershed scale had the strongest impact on water quality; The land use pattern had the greatest impact on water quality in the spatial scale along the100m shore.(2) The correlation was differenent between land use pattern and water quality, However, the seasonal difference was not obvious. Woodland and wetland show negative correlation with the indicators of water quality; Construction land, unused land present positive correlation with the indicators of water quality; Arable land in the watershed scale also showed positive correlation with water quality, butnegative correlation presents in other scales; In small scale, grassland was negative correlation with indicators of water quality, and positive correlation in the larg scale. Land use intensity had a significant positive effect on the concentration of the indicators of water quality. But overall, land use intensity in basin-scale had the greatest impact on water quality.4. Develop the regulation countermeasures for the water environment in the context of urbanization. Combined the above analysis results of the development trend of Jiuxiang River watershed in the future, landscapes in watershed were zoned as protected areas(landscape protection, landscape restoration), restricted development areas, key development areas and optimized development areas.Accordingly, some measures were proposed in this paper to control water environmental quality in the context of urbanization including the rational allocation of land use pattern along the100m shore, and control of rural and urban land-based sources pollution. |
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