Spatial and temporal distribution of soil nitrogen and phosphorus and ecological risk assessment in Yanhe river riparian zone on the Loess Plateau of China

The riparian zone is a transition zone between terrestrial and aquatic ecosystems and is vulnerable to human activities. Pollution sources are scattered, pollutants are diverse, and pollution loads vary greatly over time and space, leading to ecological fragility in riparian areas and difficulties in pollution management. In order to understand the distribution characteristics of N and P in soils and their ecological and environmental risks in the riparian zone of the Yanhe River Basin in northern Shaanxi Province, this study investigated the characteristics of N and P in the surface sediments of the riparian zone and their spatial and temporal distributions by means of on-site testing, spatial analysis, and mathematical statistics, and made a preliminary assessment of their environmental risks by using the risk assessment index method in order to explore the ecological and environmental risks in the riparian zone of the Yanhe River Basin. The results showed that total nitrogen (TN) had a certain pooling effect at the basin scale. TN content was higher in dry water period, smaller in rich water period and flat water period, and the trend of Total phosphorus (TP) content was not obvious in both space and time scale. The surface sediments in the riparian zone of the Yanhe River Basin are mildly to moderately polluted, and the nitrogen and phosphorus contents of the sediments are easily affected by soil water content (SWC), soil bulk density (BD) and land use (LULC) on the bank. These results provide a certain basis for watershed management and ecological environmental protection in northern Shaanxi, and are of great significance in promoting ecological restoration and sustainable development in the Yanhe River basin.