城郊居民农田混合区田间沟渠水质空间变异特征研究

Spatial Variability of Field Ditches Water Quality in the Mixed Area of Suburban Residents and Farmland

选择滇池北岸大清河流域下游46.7 hm^2韭菜田与花卉地田间26条沟渠为对象,通过网格法布点采集沟渠水样结合化学分析,研究了其水质空间变异特征,并解析了其污染源汇关系。结果表明,调查区沟渠水TN为2.3～172.7（40.5±31.7）mg/L,NH3-N为0～34.4（7.5±7.7）mg/L,NO3^--N为0～7.4（1.1±0.1.0）mg/L,TP为0.2～9.5（1.5±1.8）mg/L,H2PO4^--P为0.1～5.6（0.9±1.1）mg/L,CODMn为1.4～62.3（17.8±10.4）mg/L。污水来源差异导致不同区域沟渠水质空间变异明显,B区（养殖废水＋生活污水＋韭菜田侧渗水）〉A区（生活污水＋韭菜田侧渗水）〉C区（花卉地侧渗水）、D区（韭菜田侧渗水）。A,B区污水流经沟渠其水中磷浓度逐渐降低,表明沟渠对高浓度磷具有自净作用。但是,所有沟渠出水氮磷浓度均大于Ⅳ、Ⅴ类水质标准。因此,为了减少农业面源污染风险,滇池北岸居民农田混合区排水应采取净化措施。

Water quality was investigated in total 26 field ditches at 46.7hm^2 farmland located at the lower of Daqinghe of the northern bank of Dianchi lake to study spatial variability of ditch water quality, and also to analyze pollution sources. Ditch water samples were collected in 40 m× 80-90 meters on Aug. 8-14, 2006. Result show concentrations of TN in water samples were 2.3-172.7 （40.5±31.7） mg/L, 0-34.4 （7. 5± 7.7） mg/L for NH3-N, 0-7.4 （1.1±0.1.0） mg/L for NO3^- -N, 0.2-9.5 （1.5±1.8） mg/L for TP, 0.1-5.6（0.9±1.1）mg/L for H2PO4^--P, and 1.4-62.3 （17.8±10.4） mg/L for CODMn, respectively. Spatial variability of water quality was determined in dependence on sub-cell, concentrations of water quality follows decrease order as bellow. B（hoggery sewage ＋ domestic sewage ＋ leek field leakage） 〉 A （domestic sewage ＋ leek field leakage） 〉 C （flower field leakage）, and D （leek field leakage）, this reason could be ascribed to differences of pollution sources among sub-cell. Concentration of P in ditches received domestic sewage and/or hoggery sewage decreased with along water-stream direction, viz far from pollution sources, implying that ditches could purify P in waster water. The water quality of outlet in all ditch exceeded critical values of Ⅳ, Ⅴstandard. Therefore, ditches water should be purified in order to decrease risk of agricultural non-point source pollution in the investigated area.