Final Report: Assessment of the Consequences of Climate Change on the South Florida Environment

EPA Grant Number: R827453
Title: Assessment of the Consequences of Climate Change on the South Florida Environment
Investigators: Harwell, Mark A. , Ault, Jerald S. , Cropper, Wendell P. , Gentile, John H. , Letson, David , Lirman, Diego , Luo, Jiangang , Wang, John
Institution: University of Miami
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002 (Extended to September 30, 2003)
Project Amount: $889,579
RFA: Integrated Assessment of the Consequences of Climate Change (1999) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Ecological Indicators/Assessment/Restoration , Water , Ecosystems , Climate Change

Objective:

A team of scientists from the University of Miami, in collaboration with the South Florida Water Management District (SFWMD) and the U.S Geological Survey (USGS), conducted multidisciplinary research to evaluate the potential effects of changes in precipitation and freshwater deliveries caused by climate change and by the Comprehensive Everglades Restoration Plan (CERP) on ecological systems of the South Florida landscape. The objective of this research was to develop a suite of linked simulation models to simulate and evaluate potential impacts on: (1) the regional surface and groundwater hydrology; (2) the abundance and distribution of wading birds within the Florida Everglades; (3) freshwater inputs into Biscayne Bay and associated salinity fields; (4) seagrass and hardbottom community productivity and distribution; and (5) population dynamics and stock abundance of estuarine fish. In a final step, the impacts of these changes on the regional economy were evaluated by using economics models to estimate the value of changes in fisheries stock abundance to recreational users.

Summary/Accomplishments (Outputs/Outcomes):

The focal system of our research was Biscayne Bay, a shallow (< 4 m) subtropical, coastal, marine, lagoonal system adjacent to the City of Miami on the southeastern coast of Florida. Biscayne Bay is a few kilometers to the east of the northern boundary of the Florida Keys coral reef tract. The benthos of the 750-km2 lagoonal system is composed of a wide variety of substrates (e.g., rocky outcrops, sand, and silt-clay) that provide a mosaic of habitats for associated floral and faunal assemblages (such as seagrasses, sponges, soft corals, and mangroves) and more than 150 species of fishes and macroinvertebrates. Along the bay's western shore is an extensive network of water management canals that regulate freshwater discharges. Canals facilitate agriculture and provide flood control; however, episodic, human-controlled, freshwater releases contribute to the development of ephemeral salinity gradients that range from freshwater on the bay's western side to undiluted seawater to the east.

Water exchange with the ocean is by way of numerous passes between the eastern barrier islands or Keys, and typical residence times range between weeks and months. Salinity patterns fluctuate seasonally between wet (June to November) and dry (December to May) seasons. Freshwater exchanges in the bay are driven by canal inputs, overland runoff, rainfall, and evaporation. Timing (seasonality), intensity, and duration of precipitation events are critical to the dynamics of the regional environment. Restoration of freshwater flows to Biscayne Bay has become a regional water supply allocation issue closely linked to similar issues facing the major coastal environments of the modern day modified drainage basin, which includes metropolitan Miami and Everglades National Park. Salinity variations and the hydrodynamic regime, established by the freshwater runoff and precipitation and evaporation patterns, have been important controls on the type and health of biota and flora found in the bay. Substantial changes in the volume and timing of freshwater outflows into coastal bays undoubtedly will affect key benthic communities, recreational and commercial inshore and coral-reef fish populations directly and indirectly through environmental changes and food-web interactions.

The hydrology of South Florida is controlled by an extensive system of canals, levies, and water control structures that regulate freshwater flows across the landscape. Direct links were created from outputs of the hydrological model, the South Florida Water Management Model (SFWMM) (developed by the SFWMD to describe overland and groundwater flow dynamics for the region), and the Biscayne Bay hydrodynamic model developed at the Center for Marine and Environmental Analyses (CMEA). Similarly, the Biscayne Bay hydrodynamic model was linked to a series of ecological models developed at CMEA that describe the population dynamics of seagrasses, sponges, and fisheries resources. In addition, the outputs from the SFWMM were used as inputs to the Across-Trophic Level System Simulation, developed by the USGS, to simulate the effects on the long-legged and short-legged wading birds of the Everglades. The seamless modeling framework, developed with the support of the National Oceanic and Atmospheric Adminstration's Coastal Ocean Program and the U.S. Environmental Protection Agency's (EPA) Global Change Research Program, enables us to directly simulate the effects of water management scenarios, as well as different climate change scenarios, on the hydrology of South Florida, and to evaluate the potential effects of these scenarios on important ecological and economic endpoints of Biscayne Bay and the Everglades.

The basis for our approach was the ecological risk assessment framework developed for the U.S. EPA. A scenario-consequence analysis approach was used. Paired scenarios were developed to characterize the effects on selected ecological endpoints from changes in precipitation caused by climate variability, from implementation of the CERP project, or from both. Our assessment was conducted as a sensitivity analysis, wherein a realistic, plausible range of climatic conditions was explicitly simulated and tested. The following simulation scenarios were developed using historical precipitation and temperature data, based on the 1965-1995 record available for South Florida, and modified by a set of global climate-change scenarios developed at a climate-change scenario workshop:

• 2050 BASE / D13R (CERP water management scenario, no climate change)

• 2050 BASE / D13R and 25 percent increase in rainfall (CERP plus climate change)

• 2050 BASE / D13R and 25 percent decrease in rainfall (CERP plus climate change)

• 2050 BASE / D13R and 2°C increase (CERP plus climate change).

Results

Precipitation values were changed uniformly within each cell of the SFWMM. Similarly, the temperature scenario was used to modify the evapo-transpiration (ET) values of each cell. The output from the SFWMM, expressed as daily freshwater flows into Biscayne Bay from canal, overland, and groundwater sources, provided input for the Biscayne Bay hydrodynamic model. The hydrodynamic model provided input, expressed as daily salinity values, for the SEASCAPE model of benthic communities of Biscayne Bay. The SEASCAPE model (100,000 grid cells, 100 x 100 m) was used to simulate the impacts of the scenarios on seagrasses and sponges of Biscayne Bay. A Fish Trophodynamics Model, a spatial-age structured, predator-prey model, was developed to assess seatrout (Cynoscion nebulosus) population risks from exploitation and environmental changes. Travel Cost models were used to estimate the value of changes in fisheries stock abundance to recreational users. The impacts of the scenarios were simulated by predicting habitat suitability for wading birds across the Everglades landscape using the ATLSS model.

The results from the simulations indicate that interannual variability in precipitation is a dominant driver in South Florida, significantly affecting many of the ecological endpoints for Biscayne Bay and the Everglades. Major changes in canal, overland, and groundwater flows into coastal bays can result from climate change-induced modifications in precipitation. These changes in freshwater flows can lead to significant differences in the salinity fields within Biscayne Bay as simulated in this project. Areas where canal influences are prevalent (i.e., central bay) can experience significant reductions in mean salinities for extended periods of time under "wet" scenarios, whereas areas with restricted circulation (i.e., southern bay) can experience periods of hypersalinity (> 40 ppt) under "dry" conditions. In contrast, minor changes in salinity patterns were simulated for those areas in eastern Biscayne Bay where oceanic influences prevail.

When changes in salinity patterns are translated into changes in seagrass biomass, location within Biscayne Bay becomes the most influential factor. This is clearly shown by seagrass biomass patterns (e.g., value and variability) simulated for cells from eastern Biscayne Bay, which were unaffected by interannual variability or water management. The large influence of freshwater inputs from canal, overland, and groundwater sources produces fluctuations in salinity that result in the simulated differences in biomass patterns.

Seagrass species vary in their response to changes in salinity, and these differences in susceptibility are captured in our simulations. For Halodule wrightii, the seagrass species with the widest salinity tolerance, the largest difference found between scenarios was only 13 g/m2 (< 10 percent of the maximum biomass obtained for that cell) when biomass values for a wet and a dry year were compared. For Thalassia testudinum and Syringodium filiforme, two species with narrower tolerance limits, large differences in biomass patterns were detected when interannual variability and drastic changes in precipitation (from –25 percent to +25 percent) were simulated for cells within the nearshore region of Biscayne Bay. As is the case for the other biological components of our assessment, interannual climate variability was found to have a large impact on seagrass biomass. For T. testudinum, with an optimum growth-salinity near oceanic values (35-40 ppt), higher biomass was simulated under drier conditions (e.g., a dry year or a reduction in precipitation during a wet year). Although T. testudinum thrives under oceanic salinity, a 25 percent reduction in precipitation from a dry baseline can result in detrimental hypersaline conditions and reduced productivity.

When changes in salinity patterns are translated into patterns of sponge abundance, populations from eastern Biscayne Bay were largely unaffected by the restoration scenario (D13R), whereas populations from western Biscayne Bay were negatively impacted. Sponges in western Biscayne Bay are susceptible to increases in precipitation that reduce mean salinity and increase the frequency of low-salinity events. The restoration scenario (D13R), which increases freshwater flows, can have negative impacts on sponge population abundance. Similar results are observed when increases in precipitation (+25 percent) are simulated under both restoration scenarios. A 25 percent increase in precipitation can result in a 15-50 percent reduction in sponge population size. In contrast, decreases in precipitation will benefit marine sponges by increasing mean salinity and reducing the frequency of low-salinity peaks.

For wading birds in the Everglades, an increase of 25 percent in precipitation during a dry year increases the number of cells with high Foraging Condition Index (FCI) values as well as the spatial extent of suitable habitat for short-legged birds (SLWB), such as white ibis and great blue herons, and long-legged birds (LLWB), such as wood storks and snowy egrets, under both the 2,050 Base and D13R scenarios. A decrease of 25 percent in precipitation during a wet year also is beneficial for both types of wading birds under both water management scenarios within the deeper areas of the landscape that are not suitable for wading birds during wet years.

For fisheries resources, we found that those scenarios that increased freshwater inflows into Biscayne Bay (D13R and + 25 percent precipitation) favor seatrout population production, resulting, on average, in bigger fish and more abundant fish stocks. The salinity patterns that prevailed under these wetter scenarios resulted in decreased average salinities (more favorable) over the middle portion of the bay and reduced the real extent of hyper-saline waters (i.e., > 36.6 ppt). Scenarios that increased freshwater inflows into Biscayne Bay, through management or climate change-induced increases in precipitation, resulted in increased areas of suitable habitats and promoted expansion of areas with higher fish growth-rate potentials, because changes in freshwater regime expanded the range and duration of favorable salinity environments over favorable physical habitats for shrimp. These expanded salinity ranges also were more favorable for seatrout.

A key finding for economic/policy analyses is our estimated welfare of an increase in the catch-and-keep rate per trip by one additional fish, which we found to be $2.66. Multiplying this number by the additional fish that might be caught and kept will yield an aggregate benefit estimate. For example, the simulated seatrout abundance for the ages 5 through 8 cohort groups was 36 million higher in the D13R restoration scenario as compared to 95Base scenario. If 10 percent of the additional fish could be caught and kept by recreational anglers, the aggregate benefit would be $9.6 million/year.

In conclusion, the results from our simulations are consistent at showing that interannual variability in precipitation is a dominant driver in South Florida, significantly affecting ecological and economic endpoints of Biscayne Bay and the Everglades. The potential reduction in precipitation from climate change could have as significant an effect on the ecosystems as the present difference between very wet and very dry years. The risk assessment of the CERP restoration scenario indicates that the incremental effects of implementing CERP would be significantly less than present interannual variability; however, the implementation of CERP would significantly reduce the adverse ecological effects of dry years, reducing the vulnerability of the system to extremely dry conditions.


Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 17 publications 9 publications in selected types All 9 journal articles
Type Citation Project Document Sources
Journal Article Biber PD, Harwell MA, Cropper, Jr. WP. Modeling the dynamics of three functional groups of macroalgae in tropical seagrass habitats. Ecological Modeling (accepted, 2003). R827453 (2002)
R827453 (Final)
R828677C004 (2003)
not available
Journal Article Cropper WP, Lirman D, Tosini SC, DiResta D, Luo J, Wang J. Population dynamics of a commercial sponge in Biscayne Bay, Florida. Estuarine Coastal and Shelf Science 2001;53(1):13-23. R827453 (2001)
R827453 (2002)
R827453 (Final)
  • Full-text: sciencedirect
    Exit
  • Abstract: sciencedirect
    Exit
  • Journal Article Gentile JH, Harwell MA, Cropper W, Harwell CC, DeAngelis D, Davis S, Ogden JC, Lirman D. Ecological conceptual models: a framework and case study on ecosystem management for South Florida sustainability. Science of the Total Environment 2001;274(1-3):231-253. R827453 (2001)
    R827453 (2002)
    R827453 (Final)
  • Abstract from PubMed
  • Full-text: sciencedirect
    Exit
  • Journal Article Irlandi E, Orlando B, Macia S, Biber P, Jones T, Kaufman L, Lirman D, Patterson E. The influence of freshwater runoff on biomass, morphometrics, and production of Thalassia testudinum. Aquatic Botany 2001;72(1):67-78. R827453 (2001)
    R827453 (2002)
    R827453 (Final)
  • Full-text: sciencedirect
    Exit
  • Abstract: sciencedirect
    Exit
  • Journal Article Lirman D, Manzello D, Macia S. Back from the dead: the resilience of Siderastrea radians to severe stress. Coral Reefs 2002;21(3):291-292. R827453 (2002)
    R827453 (Final)
    not available
    Journal Article Lirman D, Orlando B, Macia S, Manzello D, Kaufman L, Biber P, Jones T. Coral communities of Biscayne Bay, Florida and adjacent offshore areas: diversity, abundance, distribution, and environmental correlates. Aquatic Conservation-Marine and Freshwater Ecosystems 2003;13(2):121-135. R827453 (2001)
    R827453 (2002)
    R827453 (Final)
  • Abstract: interscience
    Exit
  • Journal Article Lirman D, Cropper WP. The influence of salinity on seagrass growth, survivorship, and distribution within Biscayne Bay, Florida: Field, experimental, and modeling studies. Estuaries 2003;26(1):131-141. R827453 (2001)
    R827453 (2002)
    R827453 (Final)
  • Full-text: springerlink
    Exit
  • Abstract: springerlink
    Exit
  • Journal Article Manzello D, Lirman D. The photosynthetic resilience of Porites furcata to salinity disturbance. Coral Reefs 2003;22(4):537-540. R827453 (2002)
    R827453 (Final)
    not available
    Journal Article Wang JD, Luo JG, Ault JS. Flows, salinity, and some implications for larval transport in South Biscayne Bay, Florida. Bulletin of Marine Science 2003;72(3):695-723. R827453 (2001)
    R827453 (2002)
    R827453 (Final)
  • Full-text: ingentaconnect
    Exit
  • Abstract: ingentaconnect
    Exit
  • Supplemental Keywords:

    watershed, regional hydrology, canal discharge, groundwater, overland flow, precipitation, marine, estuarine, coastal lagoon, seagrasses, sponges, fishes, shrimp, fisheries resources, stressor, exposure, ecological endpoints, ecological effects, ecosystem vulnerability, ecosystem, indicator, restoration, aquatic, habitat, integrated assessment, simulation modeling, management decision support, conservation, socioeconomic models, fisheries, aquatic ecology, benthic ecology, ecological modeling, population models, GIS, hydrodynamics models, regional hydrological models, Southeastern United States, Florida, FL, Everglades, Biscayne Bay, Miami., RFA, Scientific Discipline, Air, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Ecology, Ecosystem/Assessment/Indicators, climate change, State, Ecological Risk Assessment, Ecology and Ecosystems, risk assessment, South Florida, Florida Everglades, recreational fisheries, environmental monitoring, flood control, human activities, watershed, hydrologic models, agriculture, water quality, coastal ecosystems, estuarine ecosystem, fuel spills, Florida, climate variability, FLA

    Relevant Websites:

    http://www.atlss.org Exit

    Progress and Final Reports:

    Original Abstract
  • 2000 Progress Report
  • 2001 Progress Report
  • 2002 Progress Report