Exploring the Impact of Landscape Ecological Risk on Water Quality in the Danjiangkou Reservoir, China

Evaluating the spatial-temporal dynamics in ecological risk and understanding its impact on water quality in reservoirs could optimize watershed land use and protect reservoir water quality. However, this impact remains elusive due to the lack of long-term field data, the heterogeneity of land use, and scale effects. Therefore, Danjiangkou Reservoir area was selected as the study area, where rapid urban expansion and ecological conservation and restoration measures have significantly changed the ecological environment, altering the water quality. We investigated the spatial-temporal changes of land use from 1990 to 2020 and evaluated how landscape ecological risk changed, as well as explored the impact of landscape ecological risk changes on water quality. The landscape ecological risk was calculated by landscape vulnerability and landscape disturbance (based on fragmentation, separation, and fractal dimension). The results indicated that the growth rate of water bodies surged (7.65 km(2)/a) and cropland experienced an apparent reduction (14.39%) over the past 30 years. These landscape changes decreased ecological risk, especially after the water transfer. The results revealed that the impacts of ecological risk on water quality were better explained at the riparian scale than at the reach and catchment scales. Specifically, the ecological risk was strongly relevant to dissolved oxygen, Turbidity, Cl- and NO3-, and moderately correlated to Ca2+ and pH. While it was not correlated with total nitrogen, total phosphorus, and F-, possibly due to the irregular reservoir operations, occasional excessive use of fertilizers, and rock weathering. This study preliminarily discloses the impact of landscape ecological risk on water quality in a basin reservoir and provides a theoretical basis to take measures in advance for the sustainable development of a reservoir basin. Plain Language Summary Assessing the spatial and temporal dynamics of ecological conditions (denoted by ecological risk) and understanding their impact on reservoir water quality is not only important for optimizing land use in the basin, but also for protecting reservoir water quality. However, this impact remains elusive due to the limitations of existing studies and data. Therefore, the Danjiangkou Reservoir area was selected as the study area, where rapid urban expansion and major ecological conservation and restoration measures around the reservoir have significantly altered the ecological environment and water quality. We evaluated the changes in landscape ecological risk based on an investigation of spatial and temporal changes in land use between 1990 and 2020, and explored the impact of changes in landscape ecological risk on water quality. The results show that the rate of growth of water bodies has increased dramatically and the area of cropland has decreased significantly following the implementation of the dam raising project and water transfer. These landscape changes reduced ecological risk, improved ecological conditions and ultimately improved water quality. This study provides preliminary insights into the effects of landscape ecological risk on water quality and provides a theoretical basis for sustainable development of reservoir basins.