| Session IV: Wetlands |
Abstract #: 97402 |
A CONCEPTUAL MODEL FOR SOIL PHOSPHORUS AVAILABILITY IN HYDROLOGICALLY ALTERED WETLANDS OF THE EVERGLADES
Fred H. Sklar and Sue Newman
ESRD, SFWMD, West Palm Beach, FL
ABSTRACT
A number of ecologicalmodels are being developed to evaluate the impacts associated with Everglades restoration. However, current ecological and water quality models for the Everglades do not include detailed soil physics associated with repeated wetting and drying of hydric soils. As part of the Everglades Landscape Model (ELM), designed to evaluate plant and nutrient structure and function, we hypothesize that the relationship between hydrology and cattail invasions in the Everglades can, at times, be explained by changes in soil nutrient content as a function of bulk density. Low water tables and the concurrent oxidation of Everglades peat, due to fire, water diversions, drought, and flood control, are thought to concentrate nutrients in the upper root zones of sedges and grasses. A STELLA
TM program was developed to evaluate this hypothesis and to establish the merits of a bulk density algorithm for the ELM. The goal was to create a bulk density response parameter that was sensitive to the cumulative impacts of successive dry downs. This was accomplished by calibrating the model against soil and plant data from the Holey Land Wildlife management Area. Observations in the Holey Land suggest a spatial distribution of cattail that has been controlled by a combination of water depth and fire. We duplicated this relationship by developing a cumulative cattail suitability function that was sensitive to water depth, biologically available phosphorus, and the proportion of slough within a region. The Holey Land was divided into five regions according to depth. Each region was initialized with the proportion of sawgrass, cattail, and slough known to exist in 1990. Weekly water depths and inputs of nutrients from agriculture from 1990 to 1995 were the forcing functions. Results are not yet conclusive. However, it is clear that fire has the potential to create both the space (i.e., slough) and soil nutrient conditions required by cattail. Computer experiments continue as we refine the cumulative impact functions. We suspect that these functions, once calibrated, will have significant utility in Water Conservation Area 3A where water tables have been low and therefore, the potential for cattail invasion may be high.
