Insights into nutrient export from dryland to receiving waters using synchronous data observed along the transport pathway in a coastal plain river network region

In plain river networks, high river density enhances hydrological connectivity, accelerating non-point pollution transport and threatening aquatic ecosystems. However, assessing farm nutrient impacts on water quality remains challenging. In the current study, a continuous 2-year study was conducted in Chongming Island, Shanghai, China. Synchronous sampling of wet deposition, soil solution, runoff, and adjacent water bodies was conducted within a 1.5 ha catchment area under a cauliflower-corn rotation. An electrical conductivity (EC) meter and an OBS turbidity (TURB) meter were installed at the field outlet to provide data with a 5-min resolution for elucidating hysteresis between dissolved/particulate nutrients and discharge (Q). The majority of runoff events demonstrated significant source limitation transport and anti-clockwise hysteresis in the EC-Q relationship, while exhibiting transport-limited mobilization and clockwise hysteresis in the TURB-Q relationship. The maximum EC values for each runoff event decreased due to the degradation of nitrogenous ions, and the maximum concentrations of TN in runoff were significantly correlated with those in soil solutions (R² = 0.945, P < 0.001). The maximum EC values under runoff events, along with the assessment of nitrogen in soil solution, could be used as indicators of nitrogen loss potential. Additionally, monitoring NH₄⁺ in wet deposition is critical as it dominates field-to-water transport pathways.