不同降雨特征下缓冲带水分及TN分配规律

以3种典型植被缓冲带为研究对象,基于现场监测、质量平衡、相关分析等方法,探明缓冲带水分分配与降雨、土壤因子的关联性,确定水分及总氮(TN)污染负荷去除分配系数.结果表明,径流与降雨量呈高度正相关(0.980~0.987,P<0.01),渗流与降雨量、降雨历时呈显著正相关(0.595~0.828,P<0.01).植被缓冲带在14.3mm以下降雨不产流,中雨、大雨、暴雨平均产流系数为0.10、0.36和0.72,TN负荷平均截留系数分别为11.0、8.2和4.5mg/(m²·mm),径流及TN负荷去除效果随雨量增大而降低.中大雨、暴雨下植被缓冲带水分分配分别以土壤渗透(0.48~0.71)、末端出流(0.69~0.74)为主,TN负荷去除以土壤渗透为主(中雨56%、大雨44%、暴雨20%).茎叶覆盖地表、根系细密发达的植被去除效果更好,其中百慕大缓冲带对水分、白花三叶草缓冲带对TN负荷的去除效果最优,分别达60%和61%.即使在高地下水位的平原河网地区,缓冲带对径流与TN负荷削减仍发挥重要作用,特别是在50mm以下降雨发生频率较高的区域.研究结果为降雨、植被多因素影响下的径流污染削减差异化评估提供数据支撑,为不同降雨特征下缓冲带径流污染控制提供重要的参考价值.

Distribution of water and TN loads in buffer strips under different rainfall characteristics

On-site monitoring, mass balance, correlation analysis and other tools were adopted to investigate the correlation between water distribution and rainfall/soil factors, and then determine the partition coefficients between water and TN pollution load removal at three typical vegetation buffers. The results showed that runoff at outlet of strips was highly positively correlated with rainfall depth (0.980~0.987, P<0.01), and seepage was significantly positively correlated with rainfall depth and rainfall duration (0.595~0.828, P<0.01). The average runoff coefficients under moderate rain, heavy rain and storm were 0.10, 0.36 and 0.72, and the average interception coefficients of TN load were 11.0, 8.2 and 4.5mg/(m²·mm) respectively. The removal effects of runoff and TN load decreased with the increase of rainfall depth. Under moderate-heavy rain and storm, the water distribution of vegetation buffer strips was mainly characterized with seepage (coefficient: 0.48~0.71) and runoff at outlet (coefficient: 0.69~0.74). The TN load removal by vegetation buffer strips under moderate rain, heavy rain and rainstorm was mainly characterized with soil infiltration, accounting for 56%, 44% and 20% of the inflow-load respectively. The vegetation with stems and leaves covering the ground and fine roots had better effect on water and pollution removal for Farmland Runoff and its pollution. The buffer strips planted with Cynodon dactylon had the best removal effect on water and Trifolium repens L had the best removal effect on TN load, up to 60% and 61% respectively. Even in the plain river network area with high groundwater level, the soil infiltration of vegetation buffer strips still greatly contributes to the runoff and TN load reduction, especially in the areas with high frequency of rainfall less than 50mm. The results provided data support for the differential evaluation of runoff pollution reduction under the influence of rainfall and vegetation, and worth referencing for the control of runoff pollution by buffer strips under different rainfall characteristics.