Comparative Analysis Of Correlation Between Water Quality And Land Use Pattern Of Different River Hierarchies

Water is one of the most important material foundations of human survival and development. Nowadays, water resource shortage and water environmental problem have gone from bad to worse all over the world. Exploring the cause and solution to the dilemma has become a major issue faced by all human beings to be solved.Human activities, mainly including land use and change, was considered to be the principal cause for water environmental problem, and its effect is significantly influenced by natural and geographical conditions. The mechanism between water quality and its adjacent land use in rivers of different hierarchies or in different parts of river may differ from each other. Therefore, it should be of great importance to study the relationship between water quality and its adjacent land use over certain scales in rivers of different hierarchies.Water quality always differs from each other in different rivers or in different parts of rivers. Besides the differences in pollution sources, the geometry shape, hydrodynamic conditions and ecological characteristics also impact the transition and conversion process. The river can absorb and transit nutrient elements such as N and T through process such as sediment adsorption, microorganisms, plant uptake and sedimentation. Big differences always exist in the shape of river channels, hydrodynamic processes and ecological characteristics between rivers of different hierarchies in agricultural landscape. So correspondingly, the mechanism between water quality and the adjacent land use should also differ from each other. The comparative study of the relationship between water quality and land use within certain scale in rivers of different hierarchies should help a lot in non-source pollution control. Meanwhile, we paid much attention to the sewage production process in farmland and the transition mechanism in big rivers and lakes, ignoring the intermediate process in which non-point source pollution can be absorbed or transited by drainage and other tributaries.Based on the monitoring data of water quality in2006-2007and related Landsat TM images, we investigated the different responses of water quality on their adjacent land use compositions between main streams and branches in Guan River basin in north Jiangsu Province at scales ranged from0.1-0.5km in width and0.25-10km in length along the river channels, with a multiple linear regression model. The results showed that:(1) From2006-2007, river water quality of the24invertebrate sites involved in the research presented an overall poor status, with most of the water quality of the sites in grade V and grade IV. The indicators with concentration exceeding the national standard included total nitrogen(TN), total phosphorus (TP), ammonia nitrogen (AN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD).(2) The nutrient concentrations in the branches were significantly higher than that in the main streams, while those of organic matters in branches were significantly lower. The water in main stream was significant better than that in the branches in dry season while the difference was small in wet period.(3) Comparing the explanatory power of land use composition on the variance of water quality across different study scales, we found that, with certain buffering width, water quality of main streams had significant correlations with land use composition within relatively smaller (i.e.0.25-4km) buffering lengths; for the branches, in contrast, significant correlations were observed between water quality and land use across all observation length scales. Comparatively, with certain buffering length, the largest variance in water quality was explained by the land use within0.3km of the river channels for all the main streams and branches. (4) The concentrations of TN and TP were mostly related to land use on larger scales, while those of organic matters were primarily influenced on smaller scales. There are some differences between different water quality indicators in their responding scales to land use.Generally speaking, the water quality in branches in Guan basin was more related to its adjacent land use than that in main stream. Responses of water quality to land use composition was different between main streams and branches over different spatial scales.The result indicates that differential treatment tactics should be developed for rivers of different hierarchies and different water quality indicators but increasing proportion of forest and natural wetland has a universal meaning for improving the water environment. Further research may focus on the cooperation of the landscape factors and the spatially nested mechanism, while enhancing the connection between results of theoretical research and practical applications is also needed.