Dep. of Soil and Water, Faculty of Agronomy, UdelaR, Garzón 780, Montevideo, Uruguay.
J Environ Qual. 2010 Nov-Dec;39(6):2121-9.
The Water Erosion Prediction Project (WEPP) model has been tested for its ability to predict soil erosion, runoff, and sediment delivery over a wide range of conditions and scales for both hillslopes and watersheds. Since its release in 1995, there has been considerable interest in adding a chemical transport element to it. Total phosphorus (TP) loss at the watershed outlet was simulated as the product of TP in the soil, amount of sediment at the watershed outlet, and an enrichment ratio (ER) factor. WEPP can be coupled with a simple algorithm to simulate phosphorus transport bound to sediment at the watershed outlet. The objective of this work was to incorporate and test the ability of WEPP in estimatingTP loss with sediment at the small watershed scale. Two approaches were examined. One approach (P-EER) estimated ER according to an empirical relationship; the other approach used the ER calculated by WEPP (P-WER).The data used for model performance test were obtained from two side-by-side watersheds monitored between 1976 and 1980. The watershed sizes were 5.05 and 6.37 ha, and each was in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Measured and simulated results were compared for the period April to October in each year. There was no statistical difference between the mean measured and simulated TP loss. The Nash-Sutcliffe coefficient was 0.80 and 0.78 for the P-EER and P-WER methods, respectively. It was critical for both methods that WEPP adequately represent the biggest sediment yield events because sediment is the main driver for TP loss so that the model can adequately simulate TP losses bound to sediment. The P-WER method is recommended because it does not require use of empirical parameters to estimate TP loss at the watershed outlet.
水蚀预测项目（WEPP）模型已经过测试，以验证其在广泛的条件和尺度下预测土壤侵蚀、径流量和泥沙输送的能力，包括山坡和流域。自 1995 年发布以来，人们一直有兴趣在其中添加化学输运元素。流域出口处的总磷（TP）损失模拟为土壤中的 TP、流域出口处的泥沙量和富集比（ER）因子的乘积。WEPP 可以与简单的算法耦合，以模拟流域出口处与泥沙结合的磷输运。本工作的目的是将 WEPP 纳入并测试其在小流域尺度上估算 TP 与泥沙损失的能力。考察了两种方法。一种方法（P-EER）根据经验关系估算 ER；另一种方法使用 WEPP 计算的 ER（P-WER）。模型性能测试数据来自 1976 年至 1980 年监测的两个并排流域。流域面积分别为 5.05 和 6.37 公顷，每个流域都种植玉米（Zea mays L.）-大豆[Glycine max（L.）Merr.]轮作。每年 4 月至 10 月对实测和模拟结果进行了比较。实测和模拟的 TP 损失平均值之间没有统计学差异。纳什-苏特克里夫系数分别为 0.80 和 0.78，用于 P-EER 和 P-WER 方法。对于这两种方法，WEPP 充分代表最大泥沙产量事件都是至关重要的，因为泥沙是 TP 损失的主要驱动因素，因此模型能够充分模拟与泥沙结合的 TP 损失。建议使用 P-WER 方法，因为它不需要使用经验参数来估算流域出口处的 TP 损失。
