Fred H. Sklar

Modeling coastal landscape dynamics

redicting the way ecological systems respond to human modifications has been a primary goal of ecosystem ecology (Hall and DeAngelis 1985). Ecosystems represent an economic resource whose value to society is only now becoming recognized. Coastal ecosystems in particular provide valuable marketed and nonmarketed services, including fish and wildlife resources, storm protection, and recreation. The average value to society of coastal wetlands has been estimated as

Periphyton-Water Quality Relationships along a Nutrient Gradient in the Northern Florida Everglades

2000-

The ecological–societal underpinnings of Everglades restoration

10,000/acre, even though their market price is only

Methods to evaluate the performance of spatial simulation models

200

Articulation, accuracy and effectiveness of mathematical models: A review of freshwater wetland applications

400/acre (Costanza et al. in press, Farber and Costanza 1987, Turner et al. 1988). Coastal ecosystems are being threatened by a host of human activities, including oil and gas exploration, urban development, and sediment diversion. The potential for sea level rise due to global greenhouseeffect warming is also of concern. Protecting and preserving these ecosystems requires the ability to predict the direct and indirect, temporal, and

Development of a general ecosystem model for a range of scales and ecosystems

We monitored a 14-km nutrient gradient in the northern Everglades to identify statistical relationships between periphyton and water-quality changes caused by canal discharges into the marsh. Water chemistry measurements were taken at 15 sampling stations every 2 wk over a 20-mo period to quantify changes in major ions along the gradient. Standard algal bioassays were conducted using water from each station to identify trends in nutrient limitation and algal growth potential along the gradient. Patterns of periphyton biomass accumulation and taxonomic composition on artificial substrata were determined in situ during 6 sampling events across seasons. Concentrations of most ions decreased by <25% along the gradient, whereas average total phosphorus (TP) decreased from 150 μg/L at peripheral marsh stations (near canal inflows) to ≤10 μg/L at interior stations (>8 km from inflows). Limiting nutrient assays showed a shift from P limitation at interior stations to possible limitation by other nutrients at peripheral stations. Both algal growth potential and biomass accumulation decreased with increasing distance from the canal, and stepwise regression analysis showed that these changes were best explained by changes in TP along the water-quality gradient. Changes in periphyton taxonomic composition, analyzed using principal components analysis, were also related strongly to distance from canal discharges and to TP. In particular, diatom species indicative of low TP (e.g., Anomoeoneis vitrea, Mastogloia smithii) were consistently replaced by eutrophic indicator species (e.g., Gomphonema parvulum, Nitzschia amphibia) at TP concentrations between 10 and 20 μg/L. The Everglades periphyton assemblage is sensitive to phosphorus enrichment and may provide one of the first reliable indications of eutrophication in the marsh.

Maintaining tree islands in the Florida Everglades: nutrient redistribution is the key

The biotic integrity of the Florida Everglades, a wetland of immense international importance, is threatened as a result of decades of human manipulation for drainage and development. Past management of the system only exacerbated the problems associated with nutrient enrichment and disruption of regional hydrology. The Comprehensive Everglades Restoration Plan (CERP) now being implemented by Federal and State governments is an attempt to strike a balance between the needs of the environment with the complex management of water and the seemingly unbridled economic growth of southern Florida. CERP is expected to reverse negative environmental trends by “getting the water right”, but successful Everglades restoration will require both geochemical and hydrologic intervention on a massive scale. This will produce ecological trade-offs and will require new and innovative scientific measures to (1) reduce total phosphorus concentrations within the remaining marsh to 10 µg/L or lower; (2) quantify and link ecolo...

ANALYSIS AND SIMULATIONS OF FRAGMENTATION PATTERNS IN THE EVERGLADES

Turner, M.G., Costanza, R. and Sklar, F.H., 1989. Methods to evaluate the performance of spatial simulation models. EcoL Modelling, 48: 1-18. Quantitative methods are necessary to compare spatial patterns and evaluate the performance of spatial simulation models. We present and review several approaches to the analysis and comparison of spatial patterns. The methods are readily applicable to digital data that are in matrix (i.e., grid cell or raster) format, and include: (a) indices of particular aspects of spatial pattern, including fractal dimension, contagion, and interface; (b) spatial predictability; and (c) a variable resolution approach for measuring the degree of fit between two patterns. Because these methods measure different aspects of spatial patterns, they may be differentially suited to particular modeling and analysis objectives. In this paper, we describe the methods, apply each method to a sample data set, then evaluate the information provided and appropriate situations for its use.

Dynamic spatial simulation modeling of coastal wetland habitat succession

Abstract Eighty-seven mathematical models of freshwater wetlands and shallow water bodies were classified by wetland type, location, and degree of nonlinearity, and rated by three new indices: articulation; accuracy; and effectiveness. Articulation measures the size and complexity of the model in the three modes of components, space, and time. Accuracy combines measures of goodness-of-fit in each mode. Effectiveness measures explanatory power as a combination of articulation and accuracy. For the models reviewed accuracy was seen to fall with increasing articulation, probably as a result of increasing complexity and cost. Effectiveness, however, rose to a maximum at intermediate articulation and then fell, reflecting the fact that highly accurate models tended to be low in articulation (they said much about little), while highly articulate models tended to be low in accuracy (they said little about much). These methods for ranking models may prove useful for further analysis and the results of this analysis may provide a useful guide to model builders concerned with maximizing the effectiveness of their models using limited resources.

Importance of Storm Events in Controlling Ecosystem Structure and Function in a Florida Gulf Coast Estuary

Abstract We have developed a General Ecosystem Model (GEM) that is designed to simulate a variety of ecosystem types using a fixed model structure. Driven largely by hydrologic algorithms for upland, wetland and shallow-water habitats, the model captures the response of macrophyte and algal communities to simulated levels of nutrients, water, and environmental inputs. It explicitly incorporates ecological processes that determine water levels, plant production, nutrient cycling associated with organic matter decomposition, consumer dynamics, and fire. While the model may be used to simulate ecosystem dynamics for a single homogenous habitat, our primary objective is to replicate it as a “unit” model in heterogeneous, grid-based dynamic spatial models using different parameter sets for each habitat. Thus, we constrained the process (i.e., computational) complexity, yet targeted a level of disaggregation that would effectively capture the feedbacks among important ecosystem processes. A basic version was used to simulate the response of sedge and hardwood communities to varying hydrologic regimes and associated water quality. Sensitivity analyses provided examples of the model dynamics, showing the varying response of macrophyte production to different nutrient requirements, with subsequent changes in the sediment water nutrient concentrations and total water head. Changes in the macrophyte canopy structure resulted in differences in transpiration, and thus the total water levels and macrophyte production. The GEMs modular design facilitates understanding the model structure and objectives, inviting variants of the basic version for other research goals. Importantly, we hope that the generic nature of the model will help alleviate the “reinventing-the-wheel” syndrome of model development, and we are implementing it in a variety of systems to help understand their basic dynamics.