Phosphorus Dynamics of a Florida Freshwater Marsh Receiving Treated Wastewater

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Abstract
A study was made of the effect of secondarily treated effluent of the P budget of a central Florida freshwater marsh. The marsh was chiefly composed of Sagittaria lancifolia, Pontederia cordata, Panicum spp. and Hibiscus sp. Three 2000 m2 plots received effluent at the rates of 1.3, 3.8 and 10.2 cm wk-1; a 2000 m2 control plot received 3.8 cm wk-1 of freshwater. In the 1st yr the plot receiving the high rate of effluent showed increased net production of plant shoots, increased litter production, increased root and rhizome production and higher P concentrations in living and dead plant tissue compared with the control plot. Effluent treatments did not significantly increase the P concentrations measured in the groundwater draining from the experimental plots. All the wells within the effluent plots had P concentrations .apprx. 97% less than the P concentration of the applied effluent. P budgets were constructed for the control plot and the plot receiving the high effluent treatment. Over the course of the study 38.03 g p m-2 were applied to the high effluent plot. Of the total input 26.31, 8.81 and 1.97 g p m-2 were stored in the soil, roots and rhizomes, and litter, respectively. Outflow of P from the plot amounted to only 0.94 g P m-2. The freshwater control plot received a total of 0.38 g P m-2. Storage in the litter accounted for 0.21 g P m-2 and outflow accounted for the remaining 0.17 g P m-2. There was no evidence of a spring flush of P from the control of the effluent plot. The marsh successfully removed P from the effluent during the 1st yr of application. Long-term use of the marsh for P removal may be contingent upon the P adsorption capacity of the soil and the rate of peat production.

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