Abstract:
BACKGROUNDThe 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.
OBJECTIVESIn 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.
METHODSSRP, 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.
RESULTSThe 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.
CONCLUSIONSThe 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.
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