Landscape ecological risk assessment and driving factor analysis in Dongjiang river watershed.

The ecological and environmental quality of Dongjiang river watershed has great influence on Guangdong, Hong Kong and Macao. The landscape ecological risk assessment model could effectively monitor and assess environmental quality. In this study, spatial autocorrelation and geographic detector methods were used to explore the spatial characteristics of landscape ecological risk and their driving factors in the Dongjiang river watershed for four decades. The results showed that the ecological risks of Dongjiang River Source Watershed are mainly classified as low and intermediate, which are distributed in the hilly regions and the marginal mountainous regions at the junction of the Xunwu and Dingnan counties. From 1980 to 2018, the area of regions with the low ecological risk increased by 587.01 km 2. The size of regions with moderate, high and severe ecological risk decreased by 165.6 km 2, 258.82 km2 and 162.58 km2, respectively. Moreover, landscape ecological risk values exhibited an apparent spatial dependency, and high-risk areas cluster together. Among influencing factors, population density has the most significant impact on the change of landscape ecological risk in the Dongjiang river watershed, followed by elevation (DEM), human interface, vegetation index (NDVI), and urbanization level. However, the interaction of driving factors has a greater impact on the ecological risk of the Dongjiang river watershed than a single driving factor. The research provides good knowledge for environmental quality management, and the proposed methods can be used for other regions.

[Scale Effects of Landscape Pattern on Water Quality in Dongjiang River Source Watershed].

Based on water quality monitoring data and land use data, Dongjiang River source watershed water quality variation characteristics from 2017 to 2019 and the relationships between the landscape pattern of the Dongjiang River source watershed and water quality were analyzed using spatial analysis, correlation analysis, and redundancy analysis. The results showed that:① the water quality of the Dongjiang River source watershed improved overall, but the total nitrogen pollution was still severe. As of 2019, the annual average concentration of total nitrogen in all sampling points exceeded the type Ⅲ water quality standard. ② At the landscape level, water quality was positively correlated with landscape shape index, number of patches, and Shannon's diversity index but negatively correlated with largest patch index and aggregation index. Considering the land use type, construction land was the primary source of total nitrogen and total phosphorus. Landscape shape index and number of forest patches were positively correlated with NH4+-N. The number of forest patches was positively correlated with total phosphorus. However, the largest patch index and aggregation index of the forest were negatively correlated with total phosphorus. The number of patches of grassland was positively correlated with total phosphorus. The aggregation index of grassland was negatively correlated with total phosphorus. ③ It is suggested that management departments should focus on the optimization of the landscape pattern within the 2000 m buffer zone of monitoring points. The reasonable allocation of urban sewage-centralized treatment facilities, strengthening management of abandoned mining areas, improvement of intensive treatment of cultivated land, and construction of shelterbelt in areas where cultivated land is concentrated are beneficial for the water quality of Dongjiang River source watershed.