西溪湿地底泥氮、磷和有机质含量竖向分布规律

Contents of nitrogen,phosphorus and organic materials in sediments and theirs distribution along depth at Xixi Wetland

利用特制的取样器从西溪湿地钻取连续完整的底泥试样,对不同深度底泥中总氮(TN)、总磷(TP)和有机质(OM)含量进行测试;通过TN、TP、OM在表层底泥、底泥孔隙水和上覆水体中含量变化的分析结果,并运用有机指数法对该湿地底泥的污染程度进行了评价.结果表明,该湿地60cm深度以内的底泥为轻度～中度污染,属于活性层;埋深大于60cm的底泥未受污染或者污染较轻,属于相对稳定层;TN、TP、OM在垂向上的变化呈显著相关关系.TN、TP在底泥孔隙水中的含量显著高于在上覆水体中的含量;由于存在浓度梯度,底泥孔隙水中的氮、磷及其他有机污染物会释放到上覆水体中去,只实施换水处理难以根除湿地水体富营养化的问题.对作为内污染源的底泥,疏浚应是一种更有效的治理措施,60cm活性层深度可作为该湿地疏浚参考深度.

A special sampler was made to take continous specimens of sediment （up to 2m long） from Xixi Wetland. The contents of total nitrogen （TN）,total phosphorous （TP） and organic matter （OM） were measured on the sediment specimens taken from different depths,and their distributions along depth in this wetland were determined. Concentrations of TN,TP and OM in the pore-water of sediments and the upper water body were also measured. On the base of the measurements,the eutrophication pollution degree in the sediments was evaluated by using the organic index method. It was found that the active zone of pollution was extended to a depth of 60cm below the river bed. Sediments in the active zone were slightly-moderately polluted,and no pollution was observed at the depth greater than 60cm （i.e.,relatively stable zone）. The distributions of TN,TP and OM along depth showed a consistent trend. The amounts of TN and TP in the pore water of shallow sediments were found to be much more than those in the above water body. So nitrogen and phosphorous in the pore water was likely released into the above water due to the concentration gradient. The test results indicate that the water quality in the wetland could not be completely recovered only by replacing the polluted water with clean water. It is also needed to dredge the contaminated sediments in the wetland. The depth of active zone （i.e.,60cm） provides an implication for a proper dredging depth.