Decomposition of Desiccated Submersed Aquatic Vegetation and Bioavailability of Released Phosphorus

In-situ decomposition and P release (litter bags) in Lake Okeechobee for Vallisneria, Hydrilla, and Potamogeton followed a simple exponential decay model. Vallisneria and Hydrilla decomposed at rapid rates (k = 32–42/yr) so that only 9–14% of initial dry wt remained after 3 weeks; Potamogeton decomposed at a rate of 9.9/yr with 57% of the dry wt remaining during this period. Phosphorus was readily mobilized from decomposing plants: rates of phosphorus loss were 37.2, 25.2, and 9.1/yr for Hydrilla, Vallisneria, and Potamogeton, respectively (>75% of initial phosphorus was lost after 3 weeks for Hydrilla and Vallisneria). Laboratory experiments confirmed that the loss of phosphorus from desiccated submersed aquatic vegetation is fast (within 4 hr) and readily bioavailable. Yield coefficients of 564–665 mg dry wt of algal cells (Selenastrum) or 1.4–5.6 mg chlorophyll a per mg P released were obtained.