香溪河沉积物、间隙水的磷分布特征及释放通量估算

采集香溪河沿程5个样点不同季节、不同深度的沉积物,用Hedley分级方法分析磷形态及垂向变化特征,同时研究上覆水和间隙水理化性质对沉积物中磷释放的影响.香溪河上覆水及间隙水pH值范围为4.72~8.55,夏季呈弱酸性,秋季、冬季及次年春季pH值呈弱碱性;沉积物处于较强还原性环境;上覆水及间隙水总磷质量浓度(TP)年变化范围为0.02~0.48mg·L~(-1),沉积物TP含量为0.48~1.45 g·kg~(-1);沉积物中磷形态的含量为HCl-P(HCl提取态)Res-P(残余磷)NaOH-P(NaOH提取态磷)NaHCO_3-P(NaHCO_3提取态磷)H_2O-P(水提取态磷).沉积物-上覆水体交界面还原性环境有利于沉积物中磷向上覆水中释放;春季水体的弱碱性、夏季的弱酸性有利于沉积物向上覆水释磷,从而增加了上覆水体富营养化的风险;间隙水TP与沉积物TP含量密切相关;5个样点中有4个样点的PO_4~(3-)-P由间隙水向上覆水扩散,释放通量为0.01~0.04mg·(m~2·d)~(-1).沉积物是底层水体营养盐的重要来源.

Distribution and Emission Flux Estimation of Phosphorus in the Sediment and Interstitial Water of Xiangxi River

The distribution and vertical variation of phosphorus forms in sediments along Xiangxi River were analyzed with Hedley classification method, meanwhile the influences of physical and chemical properties of overlying and interstitial water on the release of phosphorus in sediment were discussed. The major findings showed that the pH values in the overlying and interstitial water increased from 4.72 to 8.55, and were slightly acidic in summer, while weak alkaline in other seasons. The redox potential of sediment was in the reduction state overall. The annual variation range of total phosphorus (TP) content in the overlying and interstitial water, and that in the sediment was 0.02-0.48 mg·L^-1 and 0.48-1.45 g·kg^-1, respectively. The distribution features of TP content in the sediment were the same with those in the interstitial water along the Xiangxi River. It was interesting that the content of TP in the interstitial water in spring and summer was higher than that in autumn and winter, but that in the sediment of Xiangxi River was opposite. The content of different phosphorus (P) forms decreased successively:HCl-P (HCl extracted phosphorus)> Res-P (residual phosphorus)> NaOH-P (NaOH extracted phosphorus)> NaHCO₃-P (NaHCO₃ extracted phosphorus)> H₂O-P (water-soluable phosphorus). The reductive environment of the interface between sediment and overlying water, and pH of water in spring (weak alkaline) and summer (slightly acidic), were conducive to phosphorus release from sediment into overlying water, increasing the eutrophication risk. TP content in the interstitial water was closely related to that in sediment. The PO₄^3--P in 4 sampling areas diffused from the interstitial water into the overlying water with diffusive fluxes in the range of 0.01-0.04 mg·(m²·d)^-1. All of these findings indicated that sediments is an important source of nutrient for the overlying water.