State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, 92 Weijin Road, Nankai District, Tianjin, 300072, China.
Department of water conservancy engineering, Tianjin Agriculture University, Tianjin, 300384, China.
Environ Sci Pollut Res Int. 2017 Mar;24(9):8336-8351. doi: 10.1007/s11356-017-8470-2. Epub 2017 Feb 6.
Nonpoint storm runoff remains a major threat to surface water quality in China. As a paddy matures, numerous fertilizers are needed, especially in the rainy seasons; the concentration of nitrogen and phosphorus in rainfall runoff from farmland is much higher than at other times, and this poses a great threat to water bodies and is the main reason for water eutrophication, especially in high concentration drainages. To date, most studies regarding the characteristics of pollutants in rainfall runoff have mainly been concentrated on urban runoff and watershed runoff; therefore, it is particularly important to investigate the characteristics of nitrogen and phosphorus loss in rainfall runoff from paddy fields. To study the characteristics of nitrogen and phosphorus loss and whether the first flush effect exists, continuous monitoring of the rainfall runoff process of six rainfall events was conducted in 2013, of which four rainfall events during storm, high, middle, and low intensity rainfalls were analyzed, and runoff and quality parameters, such as suspended solids (SS), total nitrogen (TN), ammonium nitrogen (NH-N), nitrate nitrogen (NO-N), total phosphorus (TP), and phosphate (PO-P), were analyzed to determine the relationship between runoff and water quality. The paddy field is located north of Wuxi Lake Basin along the Hejia River upstream in Zhoutie town, Yixing city. An analysis of the load distribution during rainfall runoff was conducted. Event mean concentration (EMC) was used to evaluate the pollution situation of the paddy field's rainfall runoff. A curve of the dimensionless normalized cumulative load (L) vs. normalized cumulative flow (F) (L-F curve), the probability of the mass first flush (MFFn), and the pollutants carried by the initial 25% of runoff (FF) were used to analyze the first flush effect of the paddy field runoff, and different contaminants show different results: the concentration of nitrogen and phosphorus fluctuate and follow a similar trend as runoff changes, NO-N concentration is lower in the early part of runoff and higher in the later, and TP mainly occurs in the particle state in storm runoff and mainly in the dissolved state when the rainfall intensity is smaller. Nitrogen and phosphorus losses from paddy fields are closely related to the average rainfall intensity and the max rainfall intensity, and the runoff loss of nitrogen and phosphorus is more severe when the rainfall intensity is large. Based on an analysis of multiple methodologies, TN and NH-N show a certain degree of a first flush effect, whereas the first flush effect of TP is not obvious. The first flush effect of SS is obvious in larger intensity rainfall and shows a slight secondary flush effect in smaller rainfall events.
非点源暴雨径流仍然是中国地表水水质的主要威胁。随着稻田的成熟，需要大量的肥料，特别是在雨季；农田降雨径流水体中氮、磷的浓度远高于其他时期，这对水体构成了巨大威胁，也是水体富营养化的主要原因，特别是在高浓度排水沟中。迄今为止，关于降雨径流中污染物特征的研究主要集中在城市径流和流域径流上；因此，研究稻田降雨径流中氮、磷流失的特征尤为重要。为了研究氮、磷流失的特征以及是否存在初期冲刷效应，对 2013 年 6 次降雨过程的降雨径流进行了连续监测，其中分析了 4 次暴雨、高强度、中强度和低强度降雨事件，对径流水质参数如悬浮物（SS）、总氮（TN）、铵氮（NH-N）、硝酸盐氮（NO-N）、总磷（TP）和磷酸盐（PO-P）进行了分析，以确定径流量与水质之间的关系。稻田位于宜兴市周铁镇河家浜上游的无锡湖流域以北。对降雨径流过程中的负荷分布进行了分析。采用事件平均浓度（EMC）来评价稻田降雨径流的污染状况。采用无量纲归一化累积负荷（L）与归一化累积流量（F）的曲线（L-F 曲线）、质量初期冲刷概率（MFFn）和初始 25%径流量携带的污染物（FF）来分析稻田径流的初期冲刷效应，不同污染物表现出不同的结果：氮、磷浓度随径流变化而波动，呈相似趋势，NO-N浓度在径流初期较低，后期较高，TP 主要以颗粒态存在于暴雨径流中，当降雨强度较小时主要以溶解态存在。稻田氮、磷的流失与平均降雨强度和最大降雨强度密切相关，当降雨强度较大时，氮、磷的径流损失更为严重。基于多种方法的分析，TN 和 NH-N 表现出一定程度的初期冲刷效应，而 TP 的初期冲刷效应不明显。SS 的初期冲刷效应在较大强度降雨中较为明显，在较小降雨事件中表现出轻微的二次冲刷效应。
