Non-point source pollution is an important source of ecological risk in karst lakes. The process of source–sink landscapes is the main pathway of pollution migration and plays an important role in water quality. In this study, the ecological risk evolution in the past 30 years was studied in a karst lake watershed with 495 sub-basins as the basic evaluation unit, and the risk assessment model of non-point source pollution was improved by using rainfall and fertilizer application. The results show that (1) the area of cultivated land shrank significantly, with forest land and construction land showing an upward trend in general; (2) the layout of the sink landscape continuously shrank, while the source landscape gradually expanded, and the space of high load values further increased and shifted from a flower-like layout distribution to concentrated contiguity, with some values exceeding 0.5; (3) the 252 sub-watersheds of the sink landscape migrated from very low risk to low risk, while the risk of the source landscape changed from medium risk to high and very high risk in 48 sub-watersheds; and (4) in terms of the overall trend of ecological risk transformation of the source–sink landscape, the transformation of sink landscapes to source landscapes was greater than that of source landscapes to sink landscapes, and the overall ecological risk showed an increasing trend.

Studying the temporal and spatial evolution pattern and transformation rule of urban–rural construction land in karst mountainous areas has important guiding significance for urban development boundary planning, red lines for ecological protection, and cultivated land protection. The present study took 46 townships (streets) in Qixingguan District of Guizhou Province, southwest China, as the research area; collected the current status of four-phase land use data in 2009, 2013, 2017, and 2020; and used GIS spatial analysis models and geographical detectors to analyze the temporal and spatial evolution pattern characteristics and influencing factors of urban–rural construction. The results showed the following: (1) Since 2009, the total area of urban–rural construction land has continued to increase; the largest area is rural residential land, followed by urban land and transportation land, with relatively little urban industrial and mining land, scenic spots, and special land. The growth rate of land used for transport increased rapidly, and urban land grew faster than rural residential land. (2) More than 57.72% of the newly increased urban–rural construction land came from cultivated land, but the transformation of cultivated land for construction gradually slowed down; 57.48% of urban–rural construction land was transferred for reclamation as cultivated land. During the study period, the transformation of cultivated land to construction land was more intense (the transfer out of cultivated land was greater than the transfer in by 9541.94 hm2). (3) There are strong spatial differences in the density of urban–rural construction land, showing scattered agglomeration distribution, and the degree of aggregation in medium-high- and high- density areas is further strengthened, expanding to the east and southwest. (4) The growth of urban–rural construction land has been controlled by a variety of complex factors, the most influential of which are the completion of fixed asset investment in society as a whole and the total fiscal revenue, with explanatory power (PD) values of 0.819 and 0.607, respectively. Interactions between detection factors have a greater impact on the spatial differentiation of urban–rural construction land than single factors. The results of this study can provide basic research data and support the control and high-quality development of urban–rural construction land in Qixingguan District and karst mountain areas.