Abstract Rainfall characteristics can be a major factor influencing the ability of best management practices to reduce nutrient loss from agricultural lands to receiving waterbodies. The goal of this study was to examine how rainfall characteristics impacted NO3 – N concentrations in a tailwater recovery (TWR) ditch implemented at a farm within the Porter Bayou watershed in Mississippi, USA. We used a methodology that correlates rainfall characteristics (i.e., a combination of variables such as depth, intensity, frequency, duration, and antecedent hydrological conditions before water sampling) and NO3 – N levels measured in the ditch. Subsequently, a hierarchical clustering approach was implemented to classify rainfall events in the context of the NO3 – N concentrations. Results indicate that NO3 – N concentrations observed in the ditch were strongly dependent on antecedent hydrological conditions within the study area, specifically on the (1) duration of rainfall events before sampling and (2) characteristics of next-to-last rainfall events that occurred prior to sampling. Combined variables of total rainfall depth and frequency showed that rainfall classes I and III were likely to have the most impact on in-ditch NO3 – N concentration. Effects of class I rainfall events on NO3 – N levels appear to be magnified under higher depth, intensity, duration, and a shorter time before next-to-last rainfall events. Also, the influence of class III rainfall events on NO3 – N concentrations in the ditch was driven mainly by high-frequency, low magnitude, and dry antecedent conditions. Results suggest that during periods with frequent, consecutive rainfall events, the nutrient reduction potential of TWR ditches may be reduced. Data can be used to improve management of TWR ditches with more frequent pumping when possible, to increase retention times, particularly during the spring and late fall periods.

中文翻译：

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降雨特征对尾水回收沟中NO3-N浓度的影响

摘要 降雨特征可能是影响最佳管理实践能力的主要因素，以减少从农田到接收水体的养分流失。本研究的目的是检查降雨特征如何影响美国密西西比州波特河口流域内一个农场实施的尾水回收 (TWR) 沟中的 NO3 – N 浓度。我们使用了一种将降雨特征（即，水采样前的深度、强度、频率、持续时间和前期水文条件等变量的组合）与沟渠中测量的 NO3 – N 水平相关联的方法。随后，采用分层聚类方法对 NO3 – N 浓度背景下的降雨事件进行分类。结果表明，在沟渠中观察到的 NO3-N 浓度强烈依赖于研究区域内的前期水文条件，特别是 (1) 采样前降雨事件的持续时间和 (2) 发生的倒数第二个降雨事件的特征采样前。总降雨深度和频率的组合变量表明，降雨等级 I 和 III 可能对沟内 NO3 – N 浓度的影响最大。I 类降雨事件对 NO3-N 水平的影响似乎在更高的深度、强度、持续时间和倒数第二个降雨事件之前的更短时间下被放大。此外，III 类降雨事件对沟渠中 NO3-N 浓度的影响主要是由高频、低强度和干燥的前因条件驱动的。结果表明，在频繁、连续降雨事件期间，行波水沟的养分减少潜力可能会降低。数据可用于在可能的情况下通过更频繁的抽水来改善行波水沟的管理，以增加保留时间，尤其是在春季和晚秋时期。