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Phosphorus Sorption by Sediments in a Southeastern Coastal Plain In-Stream Wetland

USDA-ARS-Coastal Plains Soil, Water and Plant Research Center, 2611 West Lucas St., Florence, SC 29501

^* Corresponding author (novak{at}florence.ars.usda.gov)

Received for publication February 21, 2006. A close relationship has been reported between sediment organic C (SedOC) content and its P sorption capacity (P_max) and total P (TP) concentration. Phosphorus sorbed to organically complexed cations is a proposed explanation for this relationship. The objectives of this study were (i) to determine relationships between in-stream wetland SedOC content and both the sediment's P_max and TP concentrations, and (ii) to ascertain the role of both organically complexed and oxalate-extractable cations on the sediment P_max and TP values. The sediment's oxalate-extractable Fe (Fe_ox) and Al (Al_ox) contents were determined using acidified ammonium oxalate, while sodium pyrophosphate was used to extract organically complexed cations (Al_pryo, Ca_pyro, Fe_pyro, Mg_pyro, and Mn_pyro). Both the sediment's P_max and TP contents were strongly correlated with its SedOC concentration (r² > 0.90, P < 0.001). Only the Al_ox contents were significantly correlated with TP and P_max, suggesting that amorphous Al forms have an important role in P sorption. All five pyrophosphate-extracted cations were significantly correlated with SedOC contents. Regression analyses showed that the Al_pyro accounted for 88% of the variation in sediment P_max values, whereas a combination of Al_pyro and Ca_pyro accounted for 98% of the variation in sediment TP concentrations. Additionally, Al and Ca chelated by SedOC compounds also have an important role in P binding and indicate that a linkage exists between the wetlands SedOC and P_max content and its ability to accumulate TP. This study identified that two different mechanisms have significant roles in regulating P sorption by sediments in a southeastern Coastal Plain in-stream wetland.

Abbreviations: Al_ox, oxalate-extractable aluminum • Fe_ox, oxalate-extractable iron • OC, organic carbon • P_max, phosphorus sorption maxima • SedOC, sediment organic carbon • TP, total phosphorus