| Session IV: Wetlands |
Abstract #: 97401 |
SAWCAT PROBABILITY MODEL AND THE EFFECTS OF A DELAYED EVERGLADES RESTORATION PROGRAM ON THE DISTRIBUTION OF SAWGRASS
Wu, Yegang, Fred Sklar, Ken Rutchey, Tom Fontaine
Everglades Systems Research Division, South Florida Water Management District, West Palm Beach, FL 33414
ABSTRACT
In the last two decades sawgrass (
Cladium jamaicense) communities of Water Conservation Area 2A (WCA 2A) in the northern Everglades have been invaded by cattail (
Typha spp.) communities. A spatially explicit Markov chain probability model (SAWCAT) was developed to simulate the fragmentation processes of cattail invasion (Wu et al. 1997). The model combines the effects of agricultural phosphorus (P) runoff and water depth (D) into a probability function for cattail invasion where: Prob_pw = 1 / (1 + a * exp(-b * P)) + c * D / P; sawgrass cells are 20 x 20 m; invasion is based on the number of 1-8 adjacent cattail cells; and probabilities are expressed as, Prob_a = [0.049, 0.052, 0.061, 0.065, 0.069, 0.072, 0.076, 0.094]. We used Jensen et al.'s 1973 vegetation map and a cattail coverage of 4.7% (2,054 ha) as the initial condition. A spatial distribution of soil total phosphorus was simulated in the SAWCAT. Rutchey and Vilchek's 1991 and 1995 cattail distribution maps were used to calibrate the model. The simulated cattail distributions for 1991 and 1995 (15.7% and 21.0%, respectively), were very similar to actual cattail maps (13.02% and 22.17%, respectively). The model assumes that Stormwater Treatment Area-2 (STA-2) built in 1999 will reduce TP runoff to 50 ppb. However, STA construction could be delayed by two years. What could be the impacts of such a delay? SAWCAT predicted that by the year 2006 cattail will occupy about 34.8% (mean = 15,074 ha, standard deviation = 9.1 ha) of WCA-2A if STA-2 is finished by 1999. If STA-2 is finished by 2001, the model predicts a total cattail expansion of 15,387 ha by the year 2006. The delay would cause a net increase of 55 ha of cattail, 133 ha of cattail mix, and 125 ha of mixed cattail. The model also predicted that water depth might have an impact on cattail invasion but not significantly.
