Bioavailable Phosphorus Export by Surface Runoff from Agricultural Field Plots in Guanting Watershed,Beijing

Abstract

Bioavailable P (BAP) in agricultural runoff represents P potentially available for algal uptake and consists of soluble P (SP) and a variable portion of particulate P (PP). Runoff and soil losses from agricultural fields were investigated as major nonpoint sources of phosphorus(P) entering Guanting Reservoir, Beijing. There is relatively little information on bioavailable P transport from cropland of Guanting watershed. Soil and bioavailable P in surface runoff from a series of plots in the waershed were evaluated under simulated rainfall conditions. The objectives of this study were to evaluate the effects of rainfall intensity, slope, crop cover, and fertilizer application on bioavailable P concentrations in surface runoff and eroded soil. Accumulated sediment yields varied from 305.1 to 24933.4g/10m2, depending on rainfall intensity, slope, crop cover, and fertilizer application. Weighted average concentrations of soluble P(SP) and particulate bioavailable P (BPP) were much higher than 0.02mg/L,the limiting concentration for lake (reservoir) water. This result showed the potential contamination of reservoir water from agricultural surface runoff. Accumulated BAP losses were 0.08-4.804g/10m2 for croplands. The estimated annual loss of BAP was more than 0.49kg/hm2 per year for croplands in Guanting watershed. Most of BAP loss was in the PP form, which accounted for more 79.7% of BAP loss from cropland. The large amount of BPP may constitute a long-term source of potentially bioavailable P in Guanting Reservoir.