Effects of Land Use Patterns on Pond Water Nitrogen and Phosphorus Concentrations in a Central Chinese Small Agricultural Watershed

Seasonal variation in intensive agricultural land use patterns and its spatial scale effects on water nitrogen (N) and phosphorus (P) concentrations in watersheds have always been major concerns. However, the relationships and contributions of the important land use metrics to the pond water N and P concentrations remain uncertain. In this context, the present study aims to investigate the seasonal variation in the N and P concentrations in 28 ponds of a developed agricultural watershed in central China in 2019. Multivariate statistical analyses were applied to reveal the relationships between the multi-scale land use patterns and pond water N and P concentrations. The obtained results showed substantial seasonal variations in total nitrogen (TN), nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), and total phosphorus (TP). The highest average concentrations of TN, NO3−-N, TP, and DP in ponds were observed in summer. Redundancy analysis (RDA) showed that the land use patterns predicted better the variations in the pond N and P concentrations at the buffer zone scales than at the catchment scale. Land use patterns showed the greatest effects on the pond N and P concentrations at the 100 m buffer zone scale in spring and summer, and at the 50 m buffer zone scale in fall and winter. In addition, the importance of the land use metrics showed seasonal differences. The most contributions to the pond N and P concentrations were made by the orchard area proportion (POR) in spring and summer and the landscape shape index (LSI) in fall and winter. Stepwise multiple linear regression (SMLR) also indicated spatial consistency in the scale effects on the N and P variables. The results of the this study provide valuable information for effective land use management to control pond water pollution and promote sustainable development in agricultural watersheds