Moore A, Reddy K R
USDA-ARS, Agronomy Dep., Plant Sciences 115, Univ. of Arkansas, Fayetteville, AR, 72701.
Soil Science Dep., 106 Newell Hall, Univ. of Florida, Gainesville, FL, 32611.
J Environ Qual. 1994 Sep;23(5):955-964. doi: 10.2134/jeq1994.00472425002300050016x.
Increases in total P levels in Lake Okeechobee, Florida, have given rise to concern over eutrophication. The objective of this study was to evaluate the effects of redox potential and pH on the solubility of P in lake sediments. Bulk sediment samples were obtained from the mud zone of Lake Okeecbobee and were equilibrated under controlled conditions at fixed Eh and pH levels. The pH levels evaluated were 5.5, 6.5, 7.5, and 8.5; the Eh levels studied were 500, 250, 0, and -250 mV. Redox reactions were very important in the regulation of P in Lake Okeechobee sediments. Under oxidized conditions, soluble reactive P (SRP) concentrations were low (≈ 0.1 mg P L ), whereas under reducing conditions SRP increased to over 1 mg P L . Soluble reactive P was extremely high (18 mg P L ) under acidic (pH 5.5), reducing (Eh < 0 mV) conditions. Water soluble Fe was highly correlated to water soluble P, implicating it as a possible agent governing P behavior. Sodium hydroxide-extractable P (Fe and Al bound) increased with increases in Eh, which indicated Fe phosphate precipitation or adsorption of P by Fe oxides or hydroxides. This was supported by mineral equilibria calculations, which showed porewaters were supersaturated with respect to strengite under oxidized conditions. Calcium-bound P was higher under reducing conditions. The results suggest that Fe phosphate precipitation controls the behavior of P in Lake Okeechobee sediments under oxidizing conditions, whereas Ca phosphate mineral precipitation governs P solubility under reducing conditions. These results also suggest that large fluxes of P from the sediment could occur if the lake water column were to experience low dissolved O levels, due to the reduction and subsequent solubilization of ferric phosphate minerals in surficial sediments. Measurements of P fluxes from intact sediment cores and porewater SRP profiles taken in situ supported this hypothesis.
佛罗里达州奥基乔比湖的总磷水平升高引发了对富营养化的担忧。本研究的目的是评估氧化还原电位和pH值对湖泊沉积物中磷溶解度的影响。从奥基乔比湖的泥区采集了大量沉积物样本，并在固定的氧化还原电位（Eh）和pH值水平的受控条件下进行平衡。评估的pH值水平为5.5、6.5、7.5和8.5；研究的Eh水平为500、250、0和 -250 mV。氧化还原反应在奥基乔比湖沉积物中磷的调节中非常重要。在氧化条件下，可溶性活性磷（SRP）浓度较低（约0.1 mg P/L），而在还原条件下，SRP增加到超过1 mg P/L。在酸性（pH 5.5）、还原（Eh < 0 mV）条件下，可溶性活性磷极高（18 mg P/L）。水溶性铁与水溶性磷高度相关，表明它可能是控制磷行为的一个因素。氢氧化钠可提取磷（与铁和铝结合）随Eh的增加而增加，这表明磷酸铁沉淀或磷被铁氧化物或氢氧化物吸附。矿物平衡计算支持了这一点，计算表明在氧化条件下孔隙水相对于磷铁矿过饱和。在还原条件下，钙结合磷较高。结果表明，在氧化条件下，磷酸铁沉淀控制了奥基乔比湖沉积物中磷的行为，而在还原条件下，磷酸钙矿物沉淀控制了磷的溶解度。这些结果还表明，如果湖水柱因表层沉积物中磷酸铁矿物的还原和随后的溶解而经历低溶解氧水平，沉积物中可能会有大量的磷通量。对完整沉积物岩芯的磷通量测量和现场采集的孔隙水SRP剖面支持了这一假设。
