The geochemistry of phosphorus in peat soils of a semiarid altered wetland

An understanding of P transformations in altered wetlands has mainly developed from temperate and humid regions with neutral to acidic soils. Little is known regarding downstream water quality impact of P transformations in semiarid wetlands that undergone repeated cycles of drying and rewetting. The P geochemistry was studied using the Hedley fractionation scheme in the altered peat soils of the Hula Valley, Israel. The peat soils were sampled according to the peat depth and redox potential characteristics. The mean total P concentration (P_t) in the surface peat horizons (1190 ± 300 mg kg^-1) was significantly higher than in the anaerobic (E_H < -220 mV) peat layers (650 ± 260 mg kg^-1). The concentrations of P in all fractions except the most labile P were significantly higher in the aerobic (E_H = 400 mV) peat layers. The predominant extractable fractions in the surface peat horizons were Ca-P extracted by 1M HCl (21-60% of P_t), Iron-P extracted by 0.5 M NaOH (11-41% of P _t), and residual P extracted by H₂SO₄ (20-40% of P_t). The source of the Ca in the Ca-P fraction was mainly from gypsum dissolution following the rewetting cycles. The results clearly showed that the drainage of these wetlands facilitated rapid organic matter (OM) oxidation, release of organically bound metals and P followed by sesquioxides and gypsum precipitation. These geochemical transformations enhanced the P _t concentration per mass of altered peat soil and changed the P distribution among the different pools. Most of the P is currently associated with Fe oxides and hydroxides and/or coprecipitated with Ca.