Nutrient dynamics and seasonal vegetation growth were examined in a newly formed floating marsh dominated by Panicum virgatum in the Mississippi River delta. The floating marsh formed in a shallow aquatic environment receiving secondarily treated municipal effluent. Net Areal Primary Productivity (NAPP), total belowground biomass, NO3, and plant-tissue δ15N ratios varied significantly (P < 0.05) along a 75-m marsh transect, while mean plant-tissue δ13C values differed between the dominant species. The area nearest the effluent discharge had the highest NAPP (3876 g m−2 y−1), total belowground biomass (4079.0 ± 298.5 g m−2), and mean NO3 (5.4 ± 2.9 mg l−1). The mean δ15N of Hydrocotyle umbellata floating marsh was less enriched at 0–75 m (9.7 ± 1.9‰) compared to 100–200 m (21.0 ± 3.8‰). The δ13C of the belowground peat mat of the floating marsh was similar to P. virgatum but not H. umbellata, indicating that P. virgatum was forming the mat. Nutrient availability affected NAPP and δ15N. NAPP was greater than most reported values for floating marsh from 0–45 m then decreased along with NO3 concentrations and δ15N further from the effluent source. These results suggest that nutrient rich freshwater can promote restoration of some floating marshes.
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Vol. 29 • No. 3