农业流域“汇”型景观结构对径流调控及磷污染物截留作用的研究

Control of runoff and retention of diffuse P-pollutants by sink landscape structures of agricultural watershed

选取天津于桥水库北岸桃花寺流域作为实验流域 ,进行了流域景观格局对生态水文及磷污染物迁移转化过程影响的野外实验研究 .研究结果表明 ,流域中广泛分布于季节性河流附近的汇型景观结构 (石坝、植草水道、植被过滤带、干塘、缓冲区等 ) ,通过滞留 /缓冲功能 ,对地表径流的流速及流量具有双重调控作用 ,延长了养分物质在流域内部的滞留时间 ,对产生于不同源区的面源污染径流具有截留、吸纳、贮存作用 ,使径流中泥沙和磷素浓度逐渐得到降低 ,减少了养分对下游水体的负荷输出 .多次降雨径流的监测结果表明 ,无论在大暴雨下的连续流事件还是在小雨下的间断流事件中 ,汇型景观结构均能表现出良好的养分持留功能 .在 2 0 0 3年 6月 2 2日连续径流事件中 ,地表径流的流速可由系统入口处的 3 7 2cm·s- 1 降至系统出口处的 11 1cm·s- 1 ,污染径流体积可削减 5 0 2 % ,TSS、TP、TDP、DRP的持留率分别可达 72 7% ,69 3 % ,5 9 8%和 5 7 9% .在间断径流事件中 ,污染径流全部为汇型景观结构所截留 ,泥沙和磷素的持留率更高 .对 2 1场降雨 径流事件的统计分析结果表明 。

Experiments were conducted in Taohuasi agricultural watershed in Northern China to study the interactions between landscapes and diffuse P-pollutants during 2001 to 2003. Watershed investigation, rainfall-runoff events monitoring, sampling activities and simulation experiments were carried out all along. Agricultural landscape in North of China was different from the landscape in humid area in South of China. The contrast of the heterogeneity landscape was obvious, and the dependence of water source was high. Stability of watershed ecosystem was low and sensitive to natural or human interference. Heterogeneity of landscape in agricultural watershed was high. Channels, valleys, plains and ephemeral streams were intermixed. Artificial or natural sink landscape structures for buffer and detention were distributed broadly. It was found that a series of artificial or natural sink landscape structures as stone dams, grassed ditch, grassed filter strip, dry ponds and buffer zone distributed along the ephemeral stream in the watershed could effectively control the flow velocity and volume of surface runoff with their detention and buffering function. Hydrological control by these structures could not only decrease the kinetic energy of the runoff, but also provide a good opportunity for sand sediment as well as P-pollutants maintenance and transform due to prolong the detention time. The retaining efficiency of sediment and P was high during both continuous and discontinuous runoff events. During the continuous runoff event on June 22nd, 2003, surface flow velocity could be reduced from 37.2cm·s^(-1) to 11.1cm·s^(-1) after passing through these structures. And the volume of the polluted runoff could be cut down to 50.2%. The sink structures greatly influenced the concentration of the pollutants along the transporting pathway. Usually, high concentration appeared in the middle part of the watershed where the village and orchard were located, and decreased gradually after passing through these structures. During the continuous runoff event on June 22nd, 2003, the concentration of TSS,TP,TDP,DRP in surface runoff from village area were 3.68g·L^(-1), 3.56mg·L^(-1), 0.48mg·L^(-1), 0.33mg·L^(-1), and the concentration decreased to 0.39g·L^(-1), 0.26mg·L^(-1), 0.08mg·L^(-1), 0.06mg·L^(-1) in the outflow of the watershed after it had passed through a series of sink structures. The retention rates of TSS,TP,TDP,DRP were 72.7%、69.3%、59.8% and 57.9%, respectively. During the discontinuous runoff event, the reduction of the flow velocity and volume was obvious, and the retention efficiency of pollutants was higher due to the relative small runoff volume and the intermitted transportation of the polluted runoff in the stream channel. The control mechanisms of the sink landscape structures included many factors in which hydrological control was significant. The adsorption by landscape matrix could retain and adsorb pollutants, especial for phosphorus, during they transported in the flow pathway. Furthermore, the vegetation growing in these sink landscape areas could also adsorb large quantity of nutrients. The statistical analysis of 21 rainfall-runoff events indicated that dry pond and grassed filter strip were reliable structures for controlling the effluent of the pollutants from this watershed. The sink landscape fragments could be connected, repaired and conformed to control the production and transportation of the non-point source pollutants in agricultural watershed.