Phosphorus status and retention capacity of wetlands in south region of Taihu Basin, China

Abstract

选取太湖流域南区29个典型湿地采样点进行土-水磷素状况调查,并采集杭州西湖茅家埠、湖州德清下渚湖、湖州长兴包漾河等泥样进行静态柱和稳流水槽模拟实验.研究区域湿地底泥含TP 0.169-1.200g/kg,Olsen-P 7.08-67.08mg/kg,最大吸附量为269.5-824.5mg/kg.NaOH+EDTA-P占底泥TP的52.%±11.6%,且伴随其积累会提高Olsen-P含量.相应上覆水含TP 0.036-0.944mg/L,总颗粒态磷占TP含量的70.9%±13.2%,DRP相对较低.静态柱实验中的DRP初始阶段缓慢下降,之后快速下降并维持在稳定水平.稳流水槽实验的DRP动态表现出准U型曲线特征.经验证,底泥的磷素吸附能力在Langmuir吸附实验及室内模拟实验中表现一致.;The South Lake Taihu region is increasingly threatened by water eutrophication, so it is important to understand phosphorus status in sediments and water of the riparian wetlands in this region and develop sound technologies for optimizing wetlands'ecological values. 29 typical sampling sites in this region were chosen for the investigation, and the sites located at Hangzhou West Lake, Deqing Xiazhuohu Wetland, and Changxing Baoyanghe River were selected for static column simulation experiments and steady-flow flume simulation experiments. According to the investigation, total phosphorus (TP) and NaHCO₃(pH=8.5) extractable phosphorus (Olsen-P) in sediments of the region reached 0.169-1.200g/kg and 7.08-67.08mg/kg, respecially, and the adsorption capacity (Q_max) of sediments varied from 269.5 to 824.5mg/kg. NaOH+EDTA extractable phosphorus (NaOH+EDTA-P) constituted 52.0%±11.6% of TP, while Olsen-P was increased as organic phosphorus accumulated. TP in overlying water was 0.036-0.944mg/L, while dissolved reactive phosphorus (DRP) was relatively and 34.5% of the total sites was below detective limits. Total particle phosphorus (TPP) contributed 70.9%±13.2% of TP in water samples. There was no significant relationship between TP, DRP in overlying water and TP, NaOH+EDTA-P, Olsen-P in sediments, implying that phosphorus status in sediments was not the only factor restricting phosphorus in overlying water. In the static column simulation experiments, DRP in overlying water decreased slowly at the beginning, then decreased fastly later on. A quasi U-pattern curve was found in the steady-flow flume simulation experiments, i.e. DRP in the overlying water decreased at first and then turned to be increasing. It indicated that the role of the sediments might be changed from phosphorus sink to source when high phosphorus water flow over a wetland in rain season. It was also proved in the simulation experiments that organic matter accelerated the adsorption rates of phosphorus by sediments.