太湖五里湖表层沉积物中不同形态磷的分布特征

DISTRIBUTION CHARACTERISTICS OF DIFFERENT FORMS OF PHOSPHORUS IN SURFICIAL SEDIMENTS FROM WULI,TAIHU LAKE,CHINA

利用连续提取法(SEDEX)详细调查了太湖五里湖表层沉积物中不同形态磷的组成和分布特征。结果显示:其中磷的含量较高,受人为污染输入的影响较大,并且已经有了一定的释放。总磷的变化范围为2 05～4 05mg/g,平均约为2 80mg/g。总磷主要由无机磷组成(70%～90%),大多数无机磷为CDB溶液提取的铁结合态磷(75%～85%)。CDB溶液的n(Fe)/n(P)都较小(2 0～5 3),说明CDB溶液提取的铁主要是以无定形态存在的,并且铁与磷酸盐之间的吸附可能已经达到了平衡状态。除底部个别样品以外,多数样品n(Corg)/n(Norg)较小(8 8～10 6),所有样品的n(Corg)/n(Porg)都较大(135～320),表明沉积物在早期成岩作用过程中,湖泊内源自生有机质降解时有机磷优先释放。无机磷,特别是铁结合态磷,在氧化还原条件变化的情况下,能够通过沉积物—水体界面被再次释放到水体中去,这可能对湖泊的水体质量和营养状况有一定的影响。

In order to investigate the cycling and burial of phosphorus in Taihu Lake, the SEDEX method, a sequential extraction method for separating different forms of phosphorus was used in measuring phosphorus in surficial sediments. The sediments were sequentially extracted for loosely bound + exchangeable P, Fe-bound P, authigenic + biogenic + CaCO_(3)-bound P, and detrital apatite + other inorganic P, and non-sequential total P and inorganic P, where the difference between total and inorganic P was assumed to be organic P. The results suggest the anthropogenic inputs can have very high impact on nutrients of the lake, and the release of phosphorus could have occurred in surface sediments. The concentrations of total P are very high in dry sediments, with an average value of ～2.80 mg/g, and a variation between 4.02 mg/g and 2.05 mg/g. Total P is composed mainly of inorganic P (70%-90%), and most of inorganic phosphorus (75%-85%) is the CDB-extractable iron oxide phase. The low Fe/P atomic ratios (2.0-5.3) indicate that the Fe compounds extracted with CDB have a lower proportion of relatively crystalline phases in all samples, and the absorption between iron and phosphorus could have apparently reached certain equilibrium. Except few bottom samples, organic C/N atomic ratios are lower (8.8-10.6), suggesting a lacustrine authigenic source of organic matter in the sediments. Moreover, organic C/P atomic ratios in all samples are usually higher than those of the particles of lacustrine living organisms (100∶1), which indicate that the organic phosphorus had been preferentially released via organic matter degradation during the early diagenesis process. Fe-bound phosphorus can be removed through the sediment-water interface by a variety of the redox conditions in the sediments, which could be have a distinct impact on water quality and trophic condition of the lake.