Simulation of periphyton phosphorus dynamics in Everglades National Park

Mathematical modelling is a useful tool to investigate potential ecological responses to variations in hydrodynamic and nutrient inputs in managed aqu atic landscapes. The objective of this study was to develop a periphyton gr owth model and use it to identify critical factors in ecosystem phosphorus dynamics in pristine freshwater wetlands of Everglades National Park (ENP). We simulated changes in periphyton biomass under increased total phosphoru s (TP) input for comparison to an ongoing manipulative field experiment. Th e field experiment analyzes the responses of periphyton, macrophytes, soils , and fauna to increased TP concentrations in replicated flow-through flume channels built within ENP. Both field and model experiments introduce TP e nrichments of 5, 15, and 30 mu g l(-1) above ambient concentrations (typica lly 5-10 mu g l(-1)). The model domain was an individual flume channel (3 m wide x 85 m long) with incident light, water temperature, and volume flux at the head as forcing functions. Base case model periphyton biomass increa sed with incoming TP during the wet season (June-November) and reached a ma ximum of 70 g C m(-2) in late August. There was strong evidence of P-limite d primary production as water column TP accounted for 95.5% of the variabil ity in average daily carbon biomass. In addition to positive responses in b iomass, water column TP and net production also increased under increased T P input. TP enrichment led to lower recycling within and increased export f rom the model flume channel. Although our simplified model was not structur ed to simulate shifts in periphyton composition frequently observed as a co nsequence of P enrichment, the processes and ramifications of community str ucture are complicated and are not well understood. We suggest a two or mor e component formulation that can account for a continuum of oligotrophic to eutrophic conditions in order to model periphyton biogeochemical relations hips in the Everglades. Refined versions of this model will be used to bett er simulate observed changes during the course of the field experiment in o rder to generate new hypotheses for further investigations. (C) 2000 Elsevi er Science B.V. All rights reserved.