Hydrological connectivity in multi-pond systems and its impact on phosphorus transport: research progress and perspectives

Multi-pond systems are common small-scale water conservancy projects in agricultural watersheds. The spatially interlaced structure of pond-ditches leads to complex and variable processes of hydrological connectivity, which is of great importance to source reduction and pollution control for watershed nutrients. To better understand the impact of hydrological connectivity on phosphorus transport in multi-pond systems, we summarize assessment methods of hydrological connectivity index in multi-pond systems based on the definition and connotation of multi-pond systems and hydrological connectivity. Landscape patterns, hydrological processes, and biogeochemical processes play an important role in regulating phosphorus transport in multi-pond systems. The impacts of hydrological connectivity on phosphorus transport environment through driving drying-wetting cycles and on phosphorus transport flux by changing water residence time are illustrated. We point out that the driving mechanism of hydrological connectivity changes, scale extension of nutrient retention efficiency, quantitative simulation, and optimal regulation are important directions for future research on the environmental effects of multi-pond systems. This review will provide a theoretical basis for ensuring the water quality improvement function of multi-pond systems.