Effects of land cover patterns on pond water nitrogen and phosphorus concentrations in a small agricultural watershed in Central China

Seasonal variations in agricultural land cover patterns and their spatial scale effects on surface water nitrogen (N) and phosphorus (P) concentrations in watersheds have been major concerns. Understanding the relationships between land cover metrics and pond nutrients are of great significance to enhance water contamination prediction efficiencies and guide land use planning in agricultural watersheds. In this context, the present study aims to investigate the seasonal variations in the N and P concentrations in 28 ponds in a developed agricultural watershed in central China in 2019. Multivariate statistical analyses were applied to assess the relationships of the pond water N and P concentrations with multi-scale land cover patterns. Besides the pond water ammonium nitrogen (NH4+-N) concentrations, the total nitrogen (TN), nitrate nitrogen (NO3--N), total phosphorus (TP), and dissolved phosphorus (DP) concentrations in the investigated ponds were higher in summer than those observed in other seasons. The hierarchical partitioning model results demonstrated a spatial consistency in scale effects of land cover metrics on the pond hydrochemical parameters in the different seasons. Redundancy analysis (RDA) showed that the land cover patterns better predicted the variations in the pond water N and P concentrations at the 100 m buffer zone scale in spring and summer, as well as at the 50 m buffer zone scale in fall and winter. Among the land cover metrics considered in this study, the orchard area proportion (POR), landscape shape index (LSI), and largest patch index (LPI) showed the highest significant correlations with the pond water N and P concentrations. The results of this study provide valuable information for effective land use management to control pond water pollution and promote sustainable development in agricultural watersheds.