Abstract：
The significant impacts of total nitrogen (TN) and total phosphorus (TP) on riverine ecosystems underscores the critical need to identify the primary nutrient source areas in watersheds. This study aims to unravel the influences of terrain and land use types on mean monthly TN (TNM) and mean monthly TP (TPM) export across varying catchment resolutions in the Qiantang River Watershed of China. The findings of this study illuminated the critical role of topography in understanding nutrient dynamics, wielding a profound influence over water flow patterns and nutrient dispersion. Both land slope and Stream Power Index (SPI) displayed substantial negative correlations (r < -0.6) with TNM and TPM concentrations, whereas the Topographic Wetness Index (TWI) showed positive correlations with the nutrient indexes. In addition to terrain characteristics, impervious land surfaces had a positive correlation with nutrient concentrations, while grassland and forest areas exhibited negative correlations. Results further underscored the substantial influence of catchment resolution on correlations between watershed properties and riverine nutrient concentrations. It was imperative to choose an effective catchment resolution in watershed delineation - not too coarse, nor too fine - to accurately capture the topographic and land use impacts on nutrient dynamics. With the most appropriate catchment size (Catchment 700 km2), the critical pollution source areas for TN and TP pollution were identified, and thus could be used to guide future pollution reduction efforts. The study not only highlights the importance of identifying an appropriate catchment size for water pollution, but also emphasizes the necessity of effectively extracting critical pollution source areas to mitigate water nutrient pollution and increase the ecological integrity of the Qiantang River Watershed.
摘要：
总氮（TN）和总磷（TP）对河流生态系统的重大影响强调了确定流域主要养分来源区域的迫切需要。这项研究旨在揭示地形和土地利用类型对中国钱塘江流域不同流域分辨率的平均每月TN（TNM）和平均每月TP（TPM）出口的影响。这项研究的结果阐明了地形在理解养分动力学方面的关键作用，对水流模式和养分分散产生深远影响。土地坡度和河流功率指数（SPI）与TNM和TPM浓度均表现出明显的负相关（r<-0.6）。而地形湿度指数（TWI）与营养指数呈正相关。除了地形特征,不透水地表与养分浓度呈正相关，草地和森林面积呈负相关。结果进一步强调了流域分辨率对流域特性与河流养分浓度之间相关性的重大影响。必须在流域划分中选择有效的集水分辨率-不要太粗糙，也不太精细-准确捕捉地形和土地利用对养分动态的影响。在最合适的集水区大小(集水区700km2)的情况下，确定了TN和TP污染的关键污染源区，因此可以用来指导未来的污染减排工作。这项研究不仅强调了确定水污染的适当集水区大小的重要性，但也强调了有效提取关键污染源区域以减轻水养分污染并增加钱塘江流域生态完整性的必要性。
