沱江沉积物-水界面磷形态垂向分布及时空变化特征

水体中富营养化水平与磷元素的赋存形态密切相关。目前围绕引起富营养化关键因子之一的磷形态的垂向分布特征、各磷形态间的迁移转化行为及其影响因素取得了比较明确的研究进展。为进一步揭示不同磷形态在沉积物-水体系中迁移转化行为随时空的变化特征,本文采用磷钼蓝分光光度法对沱江流域简阳段间隙水中可溶性活性磷(SRP)、可溶性非活性磷(SUP)及总溶解性磷(TDP)进行测定;采用SMT法和改进的沉积物无机磷形态连续提取法对沉积物中总无机磷(TIP)、总磷(TP)、难提取磷(Res-P)、可交换态磷(Exc-P)、铁结合态磷(Fe-P)、铝结合态磷(Al-P)、钙结合态磷(Ca-P)进行提取,磷钼蓝分光光度法进行测定,以揭示沉积物-水体系中磷的赋存形态垂向分布行为特征,并将实验数据与十年前该地区磷的赋存形态结果进行对比,探讨磷赋存形态的变化趋势及影响因素。结果表明:间隙水中SRP、SUP和TDP的含量分别为0.004～0.36mg/L、0.080～3.19mg/L和0.056～3.28mg/L;沉积物中TP、TIP、Res-P、Exc-P、Al-P、Ca-P含量分别为1235.40～1646.94mg/kg、860.00～1318.59mg/kg、130.31～537.13mg/kg、1.35～14.10mg/kg、0.007～0.12mg/kg、743.13～1109.91mg/kg,Fe-P未检出。对比十年前后沉积物-水体系中磷赋存形态的变化可知,由于受到外源磷输入的影响,间隙水中SRP、SUP以及TDP含量虽然在-10cm以上变化不明显,但在-10cm以下明显增大,且导致沉积物中TP、TIP含量增加;偏碱性的沉积环境导致Al-P的释放,其含量明显减小;Exc-P含量的减小与其转化为稳定的Ca-P或Res-P形态有关。研究认为:随着时空的变化,沱江简阳段沉积物呈现外源磷输入和内源磷释放的综合污染。总体而言,由于输入的磷形态大部分以稳定的Ca-P和Res-P形态存在于沉积物中,使得表层间隙水中生物可直接利用的磷含量总体变化不大,该地区富营养化程度不会加重。维持沉积环境的弱碱性,有利于Al-P、Exc-P等向Ca-P的有效转换,抑制河流富营养化。

Vertical Distribution of Phosphorus Species at the Sediment-Water Interface of the Tuojiang River and Its Spatial and Temporal Characteristics

BACKGROUND: The eutrophication level in water is related to the phosphorus species in porewater and sediment closely. At present, as the one of the eutrophic elements, the vertical distribution characteristics of phosphorus species, the transfer and transformation behavior among phosphorus species and its influencing factors have made clear research progress.
OBJECTIVES: In order to further reveal the temporal and spatial characteristics of the transfer and transformation of different forms of phosphorus in porewaters and sediments, and assess the ecological restoration in the area by analyzing the soluble reactive phosphorus (SRP), soluble unreactive phosphorus (SUP) and total dissolved phosphorus (TDP) in porewaters, and by analyzing total inorganic phosphorus (TIP), total phosphorus (TP), residual phosphorus (Res-P), exchangeable phosphorus (Exc-P), Fe-bound phosphorus(Fe-P), Al-bound phosphorus (Al-P) and Ca-bound phosphorus (Ca-P) in sediments in Jianyang section of Tuojiang River. And the results were compared with the records of phosphorus species in the same place ten years ago to discuss the change trend and influencing factors of phosphorus occurrence.
METHODS: SRP, SUP and TDP in porewaters were determined by phosphomolybdate blue spectrophotometry. TIP, TP, Res-P, Exc-P, Fe-P, Al-P and Ca-P in sediments were extracted by SMT method and the improved sequential extraction method. The concentration of the phosphorus species were determined by phosphomolybdate blue spectrophotometry.
RESULTS: The content of SRP, SUP and TDP in porewaters ranged from 0.004 to 0.36mg/L, 0.080 to 3.19mg/L and 0.056 to 3.28mg/L, respectively. The content of TP, TIP, Res-P, Exc-P, Al-P and Ca-P in sediment ranged from 1235.40 to 1646.94mg/kg, 860.00 to 1318.59mg/kg, 130.31 to 537.13mg/kg, 1.35 to 14.10mg/kg, 0.007 to 0.12mg/kg and 743.13 to 1109.91mg/kg, respectively. However, Fe-P in the sediment samples were not detected. Compared with the results of phosphorus species in sediment-water system ten years ago, it was found that although the content of SRP, SUP and TDP in porewaters were not significantly changed above -10cm, but they increased below -10cm due to the influence of exogenous phosphorus input, which also led to the increase of TP and TIP in sediments. The weak alkaline environment resulted in the release of Al-P, and the decrease of Exc-P was related to its transformation into stable forms of Ca-P or Res-P.
CONCLUSIONS: The sediment in Jianyang section of Tuojiang River presents the comprehensive pollution of exogenous input and endogenous release. Generally speaking, because most of the input phosphorus exist in the forms of stable Ca-P and Res-P in sediments finally, the part of phosphorus which can be directly used by organisms in the sediment-water interface has little changed. So the eutrophication degree in this area has not increased with the change of time and space. To maintain the weak alkalinity of the sedimentary environment is conducive to the effective conversion of Al-P and Exc-P to Ca-P, and to inhibit the river eutrophication.