Sorption Characteristics of Phosphorus in Peat Soils of a Semiarid Altered Wetland

Abstract

We studied the adsorption characteristics of P in altered peat soils of the Hula Valley, Israel, which has undergone repeated drying and rewetting cycles. As a result, the water quality of Lake Kinneret, the only freshwater lake in Israel, may have been adversely affected. Peat sample collection was based on pedogenic evaluation of the wetland's history and on the redox potential of aerobic (Eh = 450 mV) and anaerobic (Eh < −220 mV) conditions. Extractable citrate–bicarbonate–dithionite iron (FeCBD) was a dominant mineral phase in the aerobic layers (29 ± 5 g kg−1). Mössbauer spectra suggested that hematite, goethite, ferrihydrite, and magnetite are the main Fe minerals in these peat soils. The sorption maximum (Smax) of the aerobic layers ranged from 670 to 1750 mg P kg−1, with a mean value of 1250 mg P kg−1, whereas the anaerobic layers ranged from 625 to 975 mg P kg−1, with a mean value of 775 mg P kg−1 The equilibrium phosphorus concentration (EPC0) values in the most anaerobic peat layers were several orders of magnitude higher (0.31 mg L−1) than in the aerobic layers (0.01 mg L−1). Only a weak to moderate correlation was found between the sorption attributes and the Fe content due to precipitation of Ca‐P phases. The main source of Ca in these soils is gypsum. Rewetting of the peat soils leads to a decrease in Smax and the buffer capacity, and an increase in EPC0, which could lead to higher P mobility. The increased potential of P mobility declined with a concurrent increase in Ca‐P precipitation due to enhanced dissolution of gypsum.