Abstract
Landscape patterns in a watershed potentially have significant influence on the occurrence, migration, and transformation of pollutants, such as nitrogen (N) and phosphorus (P) in rivers. Human activities can accelerate the pollution and complicate the problem especially in a peri-urban watershed with different types of land use. To characterize the heterogeneous correlations between landscape patterns and seasonal variations of N and P in a peri-urban watershed located upstream of Tianjin metropolis, China, observations of total nitrogen (TN) and total phosphorus (TP) at 33 locations were performed in the wet and dry seasons from 2013 to 2016. The data from individual locations were averaged for the wet and dry seasons and analyzed with geographical detector to identify influential landscape indices on seasonal water quality variations. The geographically weighted regression method, capable of analyzing heterogeneous correlations, was used to evaluate the integrated effects from different landscape indices. The results demonstrated that the location-weighted landscape contrast index (LWLI), the ratio of urban areas, and the ratio of forest areas were major influential indicators that affected TN and TP in river water. These indices also had integrated effects on variations of TN and TP together with other indices such as Shannon diversity index, landscape shape index, largest patch index, and contagion index. The integrated effects were different in the wet and dry seasons because of different effects of flushing and dilution by rainwater and the heterogeneity in landscape patterns. The LWLI had a positive relationship to water quality in the areas with high ratio of urban areas, indicating that domestic wastewater can be a major source of N and P pollution. The approaches and findings of this study may provide a reference for characterizing the major factors and integrated effects that control nonpoint source pollution in a watershed.
Highlights
A wide range of human activities may cause discharge of nitrogen (N) and phosphorus (P) into water environments, Responsible editor: Alexandros StefanakisEnviron Sci Pollut Res (2020) 27:34067–34077 be used to control and manage water quality in a watershed (Uuemaa et al 2007; Xu et al 2019a)
A positive t value obtained from the t test corresponds to positive effects, and the value of p obtained from the t test can be used to evaluate the significance of the effects of a landscape pattern indicator on river water quality
We examined the effects of different kinds of landscape indicators, the types of land use and landscape indices capable of describing the landscape structure, on total nitrogen (TN) and total phosphorus (TP) in the rivers in Yuqiao watershed at Tianjin, China, using the methods of geographical detector and geographically weighted regression
Summary
A wide range of human activities may cause discharge of nitrogen (N) and phosphorus (P) into water environments, Responsible editor: Alexandros StefanakisEnviron Sci Pollut Res (2020) 27:34067–34077 be used to control and manage water quality in a watershed (Uuemaa et al 2007; Xu et al 2019a). The objectives of this study were twofold: 1) to identify influential landscape indices that may affect seasonal variations of water quality in rivers and 2) to evaluate heterogeneous correlations between landscape patterns and water quality in rivers caused by the integrated effects of different landscape indices To realize these objectives, the geographical detector method, a novel method based on spatial variance analysis (Wang et al 2010, 2016), and the geographically weighted regression method (Fotheringham et al 2002; Robinson et al 2013; Chu et al 2018), which can evaluate spatial variations in the relationships between dependent and independent variables, were adopted for the first and second objectives, respectively.
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