Abstract
A numerical model has been developed to study the temporal and spatial variations of Phosphorus mass and fluxes around the tree islands of Shark River Slough in the Everglades. The developed model is based on a conceptualization of physical, chemical and biological processes that consider advective and diffusive transport of dissolved Phosphorus, adsorption on to soil, input from rainfall and external sources, and Phosphorus cycling in biomass. The biomass related processes are Phosphorus uptake, release as litter, transport as suspended litter and release from the decomposition of the deposited litter. The water flow and transport of dissolved Phosphorus in the numerical model are implemented originally in the simulator MODHMS. However, the transport equations for dissolved Phosphorus were also coded separately, as well as the balance equation for suspended litter particles and deposited litter. The parameterization of the model was conducted by using the data collected by Ross et al. [2004] in three tree islands of Shark River Slough, as well as other parameters reported among the literature. The model was calibrated in three phases. Initially, Manning coefficients were adjusted from surface water velocity data collected by Bazante et al. [2004]. Then the calibration of several groundwater flow parameters was performed from water table data collected at wells by Ross et al. [2004]. In the third phase, the Phosphorus input rate from external sources and the initial concentration of Phosphorus were calibrated by assuming that the average surveyed Phosphorus concentration in soil pore water remains approximately constant over a 10 year period. The quantitative assessment of the spatial distribution and temporal variations of Phosphorus mass and fluxes around tree islands obtained from the developed model corroborate the negative effect of the rainfall events on Phosphorus accumulation in the head of the tree island. However, the possible positive effect of the ET driven water flows on Phosphorous accumulation was found not as relevant as hypothesed by other authors in the literature. According to the model results, most of the Phosphorus transport in the tree islands occurs as suspended particles in surface water, even though the transport of dissolved Phosphorus in pore water cannot be neglected around the head of the island. The model results also suggest that an input of Phosphorus from external sources (e.g., animal activity such as bird guano and other sources) is needed to preserve the average Phosphorus levels in the head and in the whole tree island. Finally, Phosphorus accumulation and losses in certain areas of the tree island suggest changes in vegetation that need to be investigated in future work. The developed model can be used as a predicting tool to gain insight into the potential effects of restoration scenarios in tree islands environments. The model could be run for hypothetical future conditions and contribute to provide quantitative information for conservation and restoration efforts in the Everglades and similar wetlands.