滩涂农业垦区排水沟连接度对氮磷输出的影响

沟渠廊道提供了氮磷输送与排放通道,同时还提供氮磷滞留降解的环境,因此排水沟渠及其连通程度与氮磷输移及面源污染排放密切相关。为揭示不同连接度水平对氮磷污染物质扩散功能和净化功能的影响,论文以江苏盐城农业垦区排水沟为研究对象,分别在2015年8月和10月两次降水事件前后对不同等级排水沟进行4次水质（氮磷）监测,研究构建了基于氮磷输移过程关系的沟渠廊道连接度模型,进而利用回归模型分析了垦区排水沟连通度与氮磷输移的关系,结果显示：1）氮磷负荷呈现出10月雨前 < 8月雨前 < 10月雨后 < 8月雨后的时间变化特征,并有从上游到下游先升后降的空间变化特征;2）回归模型分析表明,排水沟TN、TP 输出随沟渠廊道连接度的增大呈先增后减的趋势,且其拐点分别位于沟渠廊道连接度为0.79、0.77时。研究表明,排水沟连接对于农田排水沟的扩散和净化功能的发挥起着重要作用,农业面源污染可以通过提高排水沟连接度来控制。

Effects of Drainage Ditch Connectivity on Nitrogen and Phosphorus Export in Tidal Flat Agricultural Reclamation Area

Ditch corridors not only serve as the nutrient transportation and discharge channel, but also provide retention and purification services for nitrogen and phosphorus removal. Therefore, drainage ditch corridors and their connectivity are closely related to nutrient transportation process critical for non-point source pollution control in agricultural areas. However, a large body of literatures has only quantified the retention and removal of agriculture-driven nitrogen and phosphorus emissions in single drainage ditch. These studies specifically have explored the impacts of different biophysical characteristics (e.g., length, size, sediment, and plant species) of the single drainage ditch on retention and removal of nutrients. Few studies have explicitly addressed the effects of drainage ditch network and connectivity on nutrient transportation and retention from a landscape perspective. This paper built the drainage Ditch Network Connectivity model (DNC) in accordance with the use of “connectivity” in the science of landscape ecology and hydrology for characterizing the degree that nitrogen and phosphorus was expedited or blocked within the drainage ditch network. We applied the DNC model to a typical reclamation area of Yancheng coastal zone, in which the total nitrogen (TN) and total phosphorus (TP) concentrations were measured before and after each rain event in August and October of the year 2015, captured their spatio-temporal dynamics respectively. We further employed the regression model to unravel the relationship of drainage ditch connectivity with nitrogen and phosphorus exports, and ultimately explored the effects of drainage ditch connectivity on diffusion and removal of nitrogen and phosphorus. Our results showed that: 1) TN and TP concentrations showed spatio-temporal variations that October pre-rainfall