Fractionation of Phosphorus in the Sediment of a Wetland after a Decade of Receiving Sewage Effluent

Abstract

AbstractSediment deposited in traps positioned along a pollution gradient in a wetland receiving sewage effluent was fractionated with respect to phosphorus (P) to understand the processes of P removal. Significant differences in P fractions were found between sites. Close to the point of effluent discharge, virtually all of the P deposited was in organic form; whereas downstream of a confluence with a wetland not impacted by the sewage, inorganic P constituted 50 to 80% of the total P. More than 80% of the inorganic P occurred in forms extractable by 0.1 M NaOH. This form of P was highly correlated (r2 ≃0.5–0.8) with oxalate‐extractable Fe. Natural wetlands unimpacted by sewage effluent were shown to be the main source of the Fe. Hydrologic conditions regulating the delivery of Fe to the sewage‐impacted wetland were implicated as the main factors determining the relative concentrations of inorganic P within the impacted wetland system. While it is not clear whether adsorption or precipitation reactions were responsible for the P deposition, we conclude that the present rate of P removal is sustainable. Our results may explain why, in some cases, the P removal achieved in wastewater wetland systems is much greater than can be predicted solely from soil adsorption maxima.