太湖地区典型降雨水稻田径流污染物输出特点及相关性分析

Analysis of output characteristics and interrelationship of pollutants from typical rainfall runoff of rice fields in Taihu Lake Region

为研究降雨过程中水稻田径流污染物的输出特点及其主要污染物之间的内在关系,在太湖地区何家浜流域划定若干块水稻田作为研究区域,并分别选取单块封闭水稻田沿河岸的直入河点和多块水稻田沿沟渠汇流后的沟渠入河点为采样点,对比封闭小区域和非封闭大区域污染物随降雨径流的输出特点及其相关性。结果表明,降雨引起水田水的扰动,对水田土壤及其污染物只产生间接的扰动或冲刷,而非直接冲刷,因此,不同降雨强度对SS(悬浮态固体)的冲刷并未表现出明显的差异。无论短历时强降雨还是长历时弱降雨,其径流中SS、氮、磷均随降雨历时的延长而降低,其中溶解态氮、磷随降雨历时的变化较小。相比大面积的汇水区域,较小的汇水区域SS峰值点出现的时间更接近降雨峰值点,对降雨的响应时间更短,降雨前期,大汇水区域径流中SS比小汇水区域小很多,而降雨后期要大很多,其主要污染物随降雨历时的延长而降低的规律性更显著,小汇水区域的径流SS和TN(总氮)、TP(总磷)具有很好的线性相关性。

To investigate the output characteristics and interrelationship of main pollutants in rice field＇s runoff during rainfalls,two sampling points representing small enclosed area and large non-enclosed area separately were chosen in several selected rice fields in Hejiabang Creek basin around Taihu Lake. The former was at the confluence of an enclosed paddy field along the bank to flow to river directly. The latter was set at the confluence of the ditch and river to collect water that was from several rice fields and flew together in ditch. Water samples from these two points were studied and compared to figure out the pollutant migration law. Characteristics and interrelationship of main pollutants were analyzed and discussed. Results showed that effects of rainfall intensity on suspended solids（ SS） content of runoff were insignificant in rice field,because rainfall only made indirect flush and disturbance to rice field＇s soil and pollutants inside. The concentrations of SS,nitrogen and phosphorus decreased with time in either short-time heavy rain or long-time weak rain,while the content of dissolved nitrogen and phosphorus declined slightly. The content of SS in small field runoff reached its peak value around the peak time of rainfall intensity,much closer than that in large region. Moreover,its response time was shorter and the amount of main pollutants in the runoff from small field dropped more obviously with time. During the initial period of a rain,the concentration of SS in runoff from large region was much less than that of small field,while in the later period,it increased substantially and was more than that of small field.