A source-sink landscape approach to mitigation of agricultural non-point source pollution: Validation and application

Optimizing landscape pattern to reduce the risk of non-point source (NPS) pollution is an effective measure to improve river water quality. The source-sink landscape theory is a recent research tool for landscape pattern analysis that can effectively integrate landscape type, area, spatial location, and topographic features to depict the spatial heterogeneity of NPS pollution. Based on this theory, we quantitatively analyzed the influence of source-sink landscape pattern on the river water quality in one of the most intensive agricultural watersheds in Southeastern China. The results indicated that the proportion of sink landscape (68.59%) was greater than that of source landscape (31.41%) in the study area. In addition, when elevation and slope increased, the source landscape proportion decreased, and the sink landscape proportion increased. Nitrogen (N) and phosphorus (P) pollutants in rivers showed significant seasonal and spatial variations. Farmland was the primary source of nitrate nitrogen (NO3 -N) and total nitrogen (TN) pollution, whereas residential land was the primary source of ammonium nitrogen (NH4+-N) and total phosphorus (TP) pollution. Intensively cultivated areas and densely inhabited areas degraded water quality despite high proportions of forest land. The four source-sink landscape indices (LWLI, LWLI'e, LWLI's, LWLI'd) had significant positive correlations with NO3 -N and TN and weak correlations with NH4+-N and TP. The capacity of LWLI to quantify the NPS pollution was greater in agricultural areas than in residential areas. The source-sink landscape thresholds resulted in abrupt changes in water quality. When LWLI was similar to 0.35, the probability of river water quality degradation increased sharply. The results suggest the importance of optimizing the source-sink landscape pattern for mitigating agricultural NPS pollution and provide policy makers with adequate new information on the agroecosystem-environmental interface in highly developed agricultural watersheds.

Automated summary

Optimizing landscape pattern is crucial for reducing non-point source pollution and improving river water quality. The source-sink landscape theory provides insights for analyzing the spatial heterogeneity of NPS pollution. In Southeastern China, the proportion of sink landscape is greater than that of source landscape, with farmland being the primary source of nitrogen and phosphorus pollution. Intensive farming areas and densely populated areas degrade water quality despite a high proportion of forest land. The source-sink landscape indices have significant correlations with different pollutants. Optimizing the source-sink landscape pattern is important for mitigating agricultural NPS pollution.