Portions of the northern Everglades of Florida, USA have become enriched with phosphorous and have responded with increased plant productivity and increased litter decomposition rates. Many lakes respond to eutrophication with decreased redox potential in sediments. The objective of this study was to determine if there were differences in soil redox potential along a nutrient-enrichment gradient in the Everglades marshes. We measured redox potential, the depth at which iron reduction occurs as determined by steel rod oxidation, and the oxidation state of exchangeable iron along the gradient. The results of redox potentials at fixed depths, redox-potential profiles, and rusting of steel rods all suggest that iron-reducing conditions exist beneath the surface of the sediment in both the unenriched and enriched areas and that differences between the enriched, cattail-invaded area and the unenriched sawgrass areas are either not significant or, in the case of the redox profiles from 20- to 40-cm depth in the soil, of borderline significance and small magnitude (< about 50 mV). The lack of large differences also suggests that reduction of the soil redox potential by eutrophication is not a significant factor influencing the competition between sawgrass and the invading cattail or other biogeochemical differences that have been observed along this gradient.
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Vol. 21 • No. 3