官厅流域农田地表径流磷流失初探

农田径流和侵蚀泥沙是磷进入官厅水库的主要非点污染源。针对该流域夏季农田暴雨径流发生的典型情景进行模拟降雨径流试验，对该流域农田地表径流泥沙和磷流失进行了初步的研究，结果表明，本降雨过程径流累积泥沙产量为30．5l～2493．34g／m^2，受雨强、坡度和作物覆盖的影响明显；径流溶解态磷(DP)中绝大部分是生物可利用性磷(DRP)，径流平均DP、DRP浓度都远大于水体允许临界值0．02mg／L，对官厅水体存在直接污染危害。径流累积全磷(TP)流失达O．0439～2．0798g/m^2；估算的流域农田径流全磷(TP)流失水平达2．67kg／(hm^2．a)以上，其颗粒态占969，0以上，可能成为官厅水库浮游生物长期丰富的潜在可利用磷源。降低农田土壤速效磷水平、减少水土侵蚀，是控制库区水华季节性发生和复原库区水体富营养化状态的关键。

Phosphorus export by surface runoff from agricultural field plots in Guanting watershed

Runoff and soil losses from agricultural fields were investigated as the major non-point sources of phosphorus (P) entering Guanting Reservoir. There was relatively little information on P transportation from cropland of Guanting watershed. Soil and P in surface runoff from a series of plots in the watershed 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 P concentrations in surface runoff and eroded soil. Accumulated sediment yields varied from 30.51~2493.34 g/m2, depending on rainfall intensity, slope, crop cover, and fertilizer application. Weighted average concentrations of total-P, dissolved P (DP) are much higher than 0.02 mg/L, the limiting concentration for lake (reservoir) water. This result showed the potential contamination of reservoir water from agricultural surface runoff. Accumulated TP losses were 0.0439~2.0798 g/m2 for cropland. The estimated annual loss of TP was more than 2.67 kg/(hm2a) for cropland in Guanting watershed. Most of P loss is in the PP form, which accounts for more 96% of TP loss for cropland. The large amount of PP may constitute a long-term source of potentially bioavailable P in Guanting Reservoir.