Influence of spatial variation in land-use patterns and topography on water quality of the rivers inflowing to Fuxian Lake, a large deep lake in the plateau of southwestern China

- Water quality degradation results from irrational land use in Fuxian Lake catchment.
- A land-use type can exert different effects on water quality in plains and mountains.
- Regions within 200 m of river banks are the key regions affecting water quality.
- A pollution control zoning was established for subarea-level environment management.

With the development of agriculture, industry and urbanization, land-use and land-cover (LULC) change has resulted in significant deterioration of water quality and severe eutrophication in most of the lakes in China. Plateau lake ecosystem in China is very vulnerable and especially sensitive to environmental change and human disturbance, due to its strong closeness, species simplification, oligotrophy and simple food chain. This research focuses on evaluating the quantitative and spatial relationships of land use pattern and water quality of rivers inflowing to Fuxian Lake, China's largest deep freshwater lake in plateau. To investigate the influence of spatial variation in land-use structures and topography on rivers water quality, the distributions of land-use types in the lake's drainage basin were obtained from satellite images, and the correlations between land-use types and inflow water quality indicators were examined by applying statistical analysis and spatial analytical function of Geographic Information System. Subarea-level analysis reveals that a land-use type could exert different effects on water quality in plains and mountains, and the effects had a connection with topographic and hydrologic factors, its mixture with other land-use types, weather conditions during field measurements, as well as its scale. In addition, a comparison of correlation coefficient data for buffer regions of different scales indicated that the effect of land-use type on inflow water quality peaked in buffer regions with a radius between 100 and 200 m. On the whole, the regions within 200 m of river banks were the key regions that affected river water quality, and thus the construction and preservation of a riparian buffer zone in these regions can provide considerable protection from the inputs of non-point source pollutants and nutrients, and important function such as water and soil conservation. Based on these, a pollution control zoning was constructed from two key pollution control zones in the north and south, a phosphate rock pollution control zone in the northeast, a water loss and soil erosion control zone in the east, and a tourism pollution control zone in the west. This research also offers valuable insights into how to carry out subarea-level prevention and control of water pollution and regional development, according to natural environment, land use pattern and characteristics of pollution sources in different pollution control zones.