Research Progress on Nitrogen and Phosphorus Loss in Small Watersheds: A Regional Review

As an ecological subsystem, a small watershed is mainly located upstream from lakes, rivers, or other water bodies. The characteristics of non-point source (NPS) pollution in a small watershed are random and complex. Rainfall is the direct driving force of NPS pollution, and different land-use types are the main factors affecting NPS output in small watersheds. At present, the NPS pollution of small watersheds is serious, and the problem of eutrophication of watershed water is prominent. Nitrogen (N) and phosphorus (P) are essential nutrients for aquatic organisms, but excessive amounts can lead to water pollution and ecological imbalances. The study of N and P loss in small watersheds can provide a decision-making basis for NPS pollution control in small watersheds. This paper introduces the research progress on small watersheds in detail, focusing on the main influencing factors of N and P output in small watersheds, including rainfall, different land-use types, N and P loss prevention, and control measures; it also provides a prospective view of the current problems, hoping to provide references for the study of NPS pollution in small watersheds.