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Biogeochemical Characteristics of the Everglades Sloughs

Duke Wetland Center, Box 90333, Durham, NC 27706.

^* Corresponding author (wetlands{at}gate.net or panchabiv{at}hotmail.com).

ABSTRACT

Everglades sloughs are alkaline hardwater systems. Mean water column dissolved phosphate (5 µg/L) and TP (9 µg/L) concentrations in the sloughs are typical of oligotrophic waters. Molar ratios of dissolved inorganic N and P (DIN:DIP = 28:1) in the surface waters suggest that P may be limiting the aquatic primary productivity in the Everglades sloughs. Variations in water column TP and TN in the sloughs were inversely related to the water depth fluctuations (P <0.0001) suggesting a strong link with hydrology. Periphyton and macrophytes in the sloughs exhibited N/P ratios indicative of depletion in P relative to N. The N/P ratios in the Everglades slough communities were in the upper range of values reported for aquatic plants from other ecosystems. The N/P ratios in periphyton were higher than macrophytes suggesting that P depletion was even greater for periphyton. As a result any introduced inorganic phosphate was taken up rapidly by the periphyton reducing the water column PO₄-P to near background levels. Our results suggest that C/N/P ratios of the periphyton provide a reliable measure of the P-status of the Everglades sloughs whereas the water column P concentration may not truly reflect the P-status of the system. Periphyton mat also plays an important role in oxygenating the water column of the sloughs. Experimental results show that a decline in periphyton mat cover will result in a decrease in the water column dissolved oxygen concentration and may also lead to other ecosystem changes by enhancing the PAR availability to the slough bottom.