Climate Change Vulnerability Assessment and Adaptation Opportunities for Salt Marsh Types in Southwest Florida James Beever III, Principal Planner IV, Southwest Florida Regional Planning Council 239-338-2550, ext., 224 jbeever@swfrpc.org Whitney Gray, Senior Environmental Planner, Southwest Florida Regional Planning Council Currently at Florida SeaGrant wgray@ufl.edu Lisa B. Beever, Ph.D., Director, Charlotte Harbor National Estuary Program 239-338-2556, ext., 235 lbeever@swfrpc.org Dan Cobb, GIS Analyst, Southwest Florida Regional Planning Council Currently at City of Tampa mapmaker13@hotmal.com Tim Walker, GIS Analyst, Southwest Florida Regional Planning Council 239-338-2550, ext. 212,twalker@swfrpc.org June 30,2012
Executive Summary The salt marsh community of the Southwest Florida Ecosystem is one of the most unique salt marsh systems in the United States. The subtropical climate of Florida supports a combination of temperate salt marsh vegetation and tropical mangroves that intermix to form an important transitional ecotone that is subject to extremes of temperature, salinity, winds, evaporation, and storm. Ecosystem services of salt marshes include a base of the estuarine detrital food pathway, nurseries and escape from predation habitat for many species of aquatic life including the early life stages of game fish and commercial fish, recreational fishing, commercial fishing and harvesting, hunting, migratory bird habitat, bird watching, other forms of ecotourism such as kayaking, carbon sequestration, storm protection, water quality treatment, stabilization of sediment and shorelines, increases in market-based property appraisal values and aesthetic values. From existing scientific literature, southwest Florida salt marsh provides habitat to a variety of resident and transient organisms including 301 plant species, 422 invertebrate species, 217 fish species, 11 amphibians, 31 reptiles, and 15 mammals; including 6 federally listed and 27 state listed animal species. Mangroves primarily dominate the CHNEP shoreline (Drew and Schomer 1984). Monotypic stands of black needlerush (Juncus roemerianus) are more common in slightly elevated areas with lower ranges of tidal inundation and dominate salt marsh communities around the midestuarine transition zones at the mouths of rivers (e.g., Myakka and Peace Rivers) and creeks (Hancock). Parts of the interior habitat of Sanibel Island have bands of salt marsh dominated by Baker s cordgrass (Spartina bakeri) and leather fern (Acrostichum aureum and danaeifolium). Although almost 74 percent of salt marsh habitat is protected in the CHNEP, habitat continues to be lost to human-induced impacts including development, alterations of hydrology, and pollution. Salt marshes in Charlotte Harbor Estuary have been directly destroyed or impacted from construction activities for residential and commercial purposes including construction for seawalls, drainage ditches for agriculture and mosquito control, boat facilities, and navigation channels. Man-made hydrological alterations have reduced the amount of freshwater flow from some rivers (e.g., Peace, Myakka), while artificially increasing the flow through others (e.g., Caloosahatchee). The primary focus of this project is the extent and nature of salt marshes and the adaptation of salt marshes to climate change. This report includes the results of a new study to inventory and determine the areal extent of salt marsh types throughout the Charlotte Harbor National Estuary Program (CHNEP) study area; determine the vulnerability of those marshes to climate change; identify the need and opportunities for avoidance, minimization, mitigation, and adaptation (AMMA) to climate change, and recommend strategies to implement alternate AMMA. This report is designed for local for use by governments, stakeholder groups and the public at large in developing coastal and land use planning, and avoidance, minimization, mitigation and adaptation of climate change impacts to salt marshes throughout the CHNEP study area.
This is the first salt marsh mapping in the CHNEP that includes a mapping of the salt marshes by type. There are 12 different types of salt marsh in the CHNEP. Seventy percent of the salt marshes of the CHNEP are high marsh and 30% of the salt marshes are fringing marsh. The fringing marsh is found on major rivers and tributaries. The salt marshes are moving landward where there is opportunity to do so. The current pace of sea level rise appears to be at pace that allows marsh migration on mainland shores. In contrast, in other locations salt marshes are drowning where there is no location to move to such as the center of islands in Pine Island Sound. Elsewhere areas of former salt marsh have been replaced by: deeper water salt marsh types, mangrove forest, or open water. Leather fern marshes have been significantly impacted by freeze events associated with recent extremes in winter climate. Recovery appears to be occurring very slowly. Barriers to the movement of salt marshes have already contributed to the disappearance of salt marshes from areas of former shoreline extents. These barriers include the standard model example of sea walls, and bulkheads, but also include spreader canals, road beds, rip rap revetments, borrow pits, stormwater treatment beam barriers, and even golf course bunkers. The best solution to maintain salt marsh habitats in the CHNEP is planned relocation and adaptations allowing the salt marshes to maintain themselves at the elevations of sea level that occur through time. There are adaptations that can be undertaken to assist in salt marsh migration and in some locations this has been occurring. These adaptations include; 1) Maintaining the existing marsh migration corridors that have been established on Cape Haze, the Eastern Charlotte Harbor shoreline, and Estero Bay Preserve State park and identify the highest priority marsh migration corridors so that they can protect these areas from future development. 2) Acquisition/Protection of inland/landward buffer zones to provide an opportunity for salt marsh habitats and wildlife to migrate inland. 3) Support the restoration of existing salt marshes by removal of exotic vegetation, backfilling ditches, removal of barriers to tidal connection, and degradation of exotic dominated uplands to make the salt marsh more resilient and capable of self-sustaining substrate building and migration. 4) Stop shoreline hardening including seawalls, bulkheads, rip-rap, and "living shorelines" backed by rip-rap. Use natural shoreline vegetation for shoreline stabilization instead 5) Re-engineer existing vertical shoreline infrastructure to a sloped soil based shoreline with GeoWeb or other permeable stabilization. 6) Restore impaired water flows to enhance sediment supply for salt marsh deposition. Restoration of natural hydrology could facilitate sediment accretion and building of deltaic salt marsh wetlands 7) Make roadway berms permeable to marsh migration and hydrology by bridging and culverting or abandon coastal road corridors with associated bermed road beds. 8) Back-fill mosquito control ditches to reduce depth and sediment loss.
9) Backfill or reslope shores of borrow pits, agricultural pits, and spreader waterways to allow salt marsh establishment and establishment of marsh migration corridors 10) Sediment-slurry addition to assist in marsh sediment building processes For some watersheds of the CHNEP it is unlikely these adaptations will be employed because there is no physical space remaining for salt marshes to move into and because of competing human interests for maintaining higher elevation uplands in direct proximity to open waters and wetlands and navigation channels to access deeper waters. It is necessary to refine the CHNEP salt marsh environmental indicators and targets related to quantities and qualities, as appropriate, to the future distribution of salt marshes in a world with higher sea levels and a changed climate. It is possible utilizing the tools developed in this study to do so provide the CHNEP conference proceeds to this decision.
Climate Change Vulnerability Assessment and Adaptation Opportunities For Salt Marsh Types in Southwest Florida Jim Beever, Whitney Gray, Dan Cobb, Tim Walker, SWFRPC and Lisa Beever, CHNEP: June 30, 2012 AMMA: Avoidance Minimization Mitigation Adaptation Inventory and determine the areal extent of twelve types of salt marsh in the study area. Determine the vulnerability of the salt marsh types to climate change. Identify opportunities/needs for AMMA. Develop strategies to implement AMMA options. 9 of sea level rise locally since 1910
Salt Marsh Locations CHNEP 2012 Watershed Acres Charlotte Harbor Salt Marshes Caloosahatchee 389.3 Charlotte Harbor 4,222.7 Dona & Roberts Bay 35.7 Estero Bay 2,773.9 Lemon Bay 162.2 Mapped by Type Ground- Truthed Caloosahatchee Charlotte Harbor Dona & Roberts Bay 9% 3% Matlacha Pass 2,332.7 Myakka River 1,291.7 Peace River 2,301.6 Pine Island Sound 1,346.2 Total 14,846.2 Estero Bay 15% 28% Lemon Bay Matlacha Pass Myaka River 9% 16% 19% 0% Peace River Pine Island Sound 1%
Salt Marshes Mapped to 12 Types First Salt Marsh Map of the 12 Types Atlas of Maps By Section Species Lists Water Quality
Observed Effects of Climate Change on Salt Marsh in the CHNEP Migration Landward (on average the length of a football field) Conversion to Another Marsh Type Drowning in Place Freezing (Leather Fern Marshes) Expansion of Invasive Plants and Animals
Potential adaptations and recommended strategies to implement the AMMA options Maintain the existing marsh migration corridors that have been established on Cape Haze, Eastern Charlotte Harbor shoreline, and Estero Bay Buffer. Identify the highest priority marsh migration corridors so that they can protect these areas from future development. Followed by acquisition of inland buffer zones to provide an opportunity for habitats and wildlife to migrate inland. Support restoration of existing salt marshes by removal of exotic vegetation, removal of barriers to tidal connection, and degradation of exotic dominated adjacent uplands Discourage or stop shoreline hardening including seawalls, bulkheads, rip-rap, and "living shorelines" backed by rip-rap. Re-engineer existing vertical shoreline infrastructure to a sloped soil based shoreline with GeoWeb or other permeable stabilization. Restore impaired water flows to enhance sediment supply for marsh deposition Elevate roadway berms by bridging and culver ting or abandon coastal road corridors with associated beamed road beds.. Back-fill mosquito control ditches to reduce depth and sediment loss Back fill borrow pits, agricultural pits, and spreader waterways to allow salt marsh establishment and establishment of marsh migration corridors Sediment-slurry addition to assist in marsh building processes http://www.swfrpc.org/content/natural_resources/climate_change/salt%20m arsh%20study%20draft%20reduced.pdf