三峡库区澎溪河底泥及消落区土壤磷的形态及吸附特性研究

沉积物是自然水域的重要生态组成部分,是形成湖泊、水库富营养化的关键因素之一.为研究三峡库区澎溪河流域沉积物中磷的赋存形态特征及迁移转化规律,采用连续提取法对澎溪河底泥3个断面及消落区3种土壤类型中磷赋存形态进行分析,并通过等温吸附实验研究了磷的吸附规律,确定了零净吸附磷浓度(EPC0).结果表明,澎溪河底泥中的总磷含量在0.80～1.45 g·kg-1之间,赋存形态以无机磷为主,其中钙结合磷和蓄闭态磷比例在80%以上,铁铝结合磷含量较低,该流域底泥受自然岩石状态及沉积环境的影响较大,而人为活动对其影响较小;消落区土壤总磷含量在0.65～1.16 g·kg-1之间,磷的赋存形态也以无机磷为主,冲积土和紫色土也以钙结合态磷和蓄闭态磷为主,水稻土中则以蓄闭态磷含量最高.澎溪河高阳、黄石和双江3个断面底泥的EPC0分别为0.08、0.13和0.11 mg·L-1,消落区冲积土、紫色土和水稻土的EPC0分别为0.08、0.09和0.04 mg·L-1.EPC0值与沉积物中总磷、pH、Ca-P、黏粒含量呈正相关性,其中与pH和Ca-P相关性显著.根据澎溪河上覆水中磷浓度的季节变化,初步判定底泥及消落区土壤在夏秋季节为磷的"汇",在冬春季节则成为其"源".EPC0高于水体富营养化临界值,底泥及消落区土壤中磷的释放依然是不可忽视的潜在问题.

Fractions and Adsorption Characteristics of Phosphorus on Sediments and Soils in Water Level Fluctuating Zone of the Pengxi River, a Tributary of the Three Gorges Reservoir

The sediment,one of the key factors leading to the eutrophication of water bodies,is an important ecological component of natural water body. In order to investigate the morphological characteristics and moving-transiting rule of phosphorus in the sediments of the Pengxi River, a tributary of the Three Gorges Reservoir,the distributions of different phosphorus forms on the three cross-section in the sediments and three soil types of riparian zone were investigated using the sequential extraction method. The characteristics of phosphorus adsorption on the sediments were also investigated by batch experiments. The equilibrium phosphorus concentrations at zero adsorption (EPC₀) on those sediments were estimated using the Henry linear models. The results show that the total phosphorus (TP) contents of these sediments and soils of riparian zone were 0.80-1.45g·kg^-1 and 0.65-1.16g·kg^-1, respectively. Phosphorus in sediments and soils were divided into inorganic phosphorus (IP) and organic phosphorus (Or-P), and the inorganic phosphorus was the dominant component of TP. Of the inorganic phosphorus fractions, the percentages of phosphorus bounded to calcium (Ca-P) and occluded phosphorus(O-P) from sediments were higher than 80%, implying that the contents of phosphorus were mainly influenced by their bedrocks and the sedimentary environmental conditions, not by the activities of human beings. The fractions of Ca-P and O-P were the dominant components of inorganic phosphorus in alluvial soil and purple soil, while the fraction of O-P was the highest in the paddy soil. The EPC₀ values of the sediments from the sections of Huangshi, Shuangjiang and Gaoyang were 0.08, 0.13 and 0.11mg·L^-1, respectively, but the EPC₀ values of the alluvial soil, purple soil and paddy soil located in riparian zone were 0.08, 0.09 and 0.04mg·L^-1, respectively. Correlation analysis shows that the values of EPC₀ positively related to the contents of total phosphorus and clay content, and significantly related to the content of Ca-P and pH values. According to the phosphorus concentration in the water of Pengxi River, it concludes that sediments and soils in the zone of fluctuating water level of the Pengxi river can be the sink of phosphorus in summer and autumn, while can be the source of phosphorus in the spring and winter. Therefore, the inherent phosphorus present in sediments and soils would be a major threat to the water quality and ecosystem reservation in the watershed of the Pengxi River.