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This article is part of the Fall 2019 issue of the Earth Science Matters Newsletter.

The U.S. coast of the Gulf of Mexico stretches about 1,631 miles from southern Florida through Alabama, Mississippi, and Louisiana, ending at the U.S.-Mexico border in Texas. Along this coastline are numerous types of coastal wetlands that provide many societal benefits. Coastal wetlands comprise grassy salt marshes, mangrove forests, freshwater forested swamps, freshwater marshes, and tidal flats. In addition to supporting fish and wildlife habitat, these wetlands improve water quality by filtering out excess nutrients and contaminants, sequester carbon and release oxygen, stabilize the shoreline to control erosion, provide recreation and tourism opportunities, and protect coastal communities from storms. USGS Climate Research and Development Program (Climate R&D) researchers are studying these important ecosystems and communicating with local natural resource managers to better inform their management.

Coastal wetlands have immense economic value, with estimates averaging about $194,000 per hectare per year on a global scale (2007 US$ price level) (Mehvar et al., 2018). For example, almost all the fish and shellfish caught by the fishing industry depend on estuaries and wetlands at some point in their life cycle, and the money brought in annually by the fishing industry in the Gulf region reaches hundreds of millions of dollars. Loss of healthy coastal wetland habitats can have severe impacts not only on fish populations, but on the fishing industry and regional economy as well. Coastal wetlands also incur economic value from their recreational use (fishing, kayaking, hiking, etc.), provisioning of raw materials (food, fiber, wood), and protective nature (prevent erosion, filter pollution, hold excess rain to help control flooding).

succulent and grass-dominated slat marsh
A succulent and grass-dominated salt marsh ecosystem in San Bernard National Wildlife Refuge (Texas). The succulent plants in the foreground of this photo are indicative of dry and hypersaline conditions. However, the high water levels shown in the photo are abnormal and due to very heavy rainfalls from Tropical Storm Imelda (September 2019; one of the wettest tropical cyclones on record in the USA). The photo was taken about two weeks after Imelda’s passage. Two years ago, this marsh was also inundated by very heavy rains associated with Hurricane Harvey (2017).

However, due to their position at the land-sea interface, coastal wetlands are highly dynamic, variable, and vulnerable to major change. Coastal wetlands face pressure directly from natural coastal hazards such as flooding and erosion but also are indirectly threatened from human population growth and economic development. Coastal areas make up 4% of the land area on earth but are home to about a third of the global population, and the population density along the coasts continues to grow each year spurring increased land conversion and development (Mehvar et al., 2018). Additionally, as the planet’s climate changes, the natural hazard events that coastal wetlands are susceptible to, including changes in precipitation and warming temperatures, are expected to increase in probability and severity.

The Gulf Coast is home to many parks, refuges, and other public lands. Managers at those locations have responsibility for managing their lands to preserve natural resources and the services they provide. USGS scientists are collaborating with managers at Apalachicola National Estuarine Research Reserve (ANERR), Florida Forest Service (FFS), Florida Fish and Wildlife Research Institute (FWRI), and Mission Aransas National Estuarine Research Reserve (Mission-Aransas NERR) (among others) with the aim of providing unbiased, robust science to guide and support their environmental management decisions.

map of protected land along the U.S. Gulf Coast
National, state, and locally protected natural areas, forests, parks, and wildlife reserves are located along the Gulf Coast (shown in shades of green). The four red stars on the map indicate the location of the four specific stakeholders surveyed for this piece. (Data Sources: U.S. Fish and Wildlife Service, National Park Service, National Oceanic and Atmospheric Administration NERRS SWMP Boundaries , State of Florida, State of Texas, State of Louisiana)

These resource managers are tasked with monitoring species, providing public use and access to natural lands, managing habitat and restoration efforts, protecting and managing natural resources to ensure their availability for future generations, collecting and analyzing scientific data to inform climate change adaptation, promoting understanding of coastal ecosystems to diverse audiences, and promoting public appreciation and support for stewardship of coastal resources.

Current State of Knowledge

Wetland vulnerability assessments have been used to identify coastal areas that are most susceptible to environmental change or stress. Previous coastal wetland vulnerability assessments have generally focused solely on sea-level rise without considering the effects of other facets of climate change. Across the globe and in all ecosystems, macroclimatic drivers (e.g., temperature and rainfall regimes) greatly influence ecosystem structure and function. In some coastal wetlands, research suggests that changing macroclimatic conditions could result in the replacement of foundation plant species (species that have a strong role in structuring an ecosystem, such as mangrove trees, salt marsh graminoids, and succulents in coastal wetlands).

Foundation plant species are able to withstand and moderate the physically stressful tidal conditions, and they provide primary, tolerable habitat for a wealth of other species. They supply important ecosystem goods and services, such as water filtration, and wave energy absorption, and increase the resilience of the ecosystem under a range of environmental stressors. USGS scientists are working to improve our understanding of the impact of macroclimate drivers and ecosystem dynamics in coastal ecosystems by documenting how changes in temperature and rainfall regimes affect coastal wetland systems.

mangrove forest with prop roots
A mangrove forest in Everglades National Park (Florida, USA). Mangrove forests in this area are greatly influenced by hurricanes and rising sea levels. The arching roots in this photo are called “prop roots” and are growing from red mangrove trees (Rhizophora mangle). Another common mangrove species in this area (the black mangrove- Avicennia germinans) produces roots called “pneumatophores” that extend vertically, perpendicular to the soil surface. High belowground mangrove root production in combination with marine sediments transported into these ecosystems during hurricanes can help some mangrove wetlands build soil elevation and adjust to (i.e., keep pace with) moderate rises in sea level.

USGS Research Benefitting Gulf Coast Stakeholders

We recently began surveying stakeholders for USGS Climate R&D research to evaluate their science needs and potential synergies between them and USGS research efforts in order to maximize the relevance of our efforts to stakeholders in various federal, state, and local agencies.

A common goal of the stakeholders is development of adaptation plans for wildlife and ecosystems that promote long-term protection and management of valuable coastal resources given an uncertain future. Creating these adaptation plans is an important step in preparing and protecting local communities for any effects of change on the natural resources that they depend upon. USGS research on the impacts of macroclimatic changes on coastal foundation species is producing maps and projections of vegetation response to changing temperature and rainfall regimes. These provide important evidence that support management planning by resource managers in coastal wetlands.

Of particular interest to Gulf Coast stakeholders is USGS monitoring and mapping of salt marsh and mangrove extent under various past and future conditions. Maps of potential mangrove range expansion into salt marshes under different climate change scenarios allow stakeholders to identify priority conservation areas and create targeted monitoring programs. Likewise, maps of marsh migration under different growth and development scenarios allow stakeholders to weigh costs and benefits of different management strategies. Correlation of current mangrove forest extent maps with state forest inventory characteristics provides a way for state forest managers to better track and predict the future of mangrove ecosystems. Developing mangrove damage assessments after hurricanes also helps managers track the natural resources, they are responsible for and to identify potential areas for restoration projects.

The network of collaborating scientists and land managers from the USGS and agencies throughout the Southeast and Gulf Coast leverages their collective expertise to examine how changing land management and environmental factors affect coastal ecosystems in a comprehensive way. Local stakeholders and resource managers noted that they are able to spend more time focusing on the “bigger pictures” and regional trends in land management because USGS scientists are supplying rigorous, hypothesis-driven research and science products. Further, they are using USGS research to create targeted restoration projects and environmental resource monitoring programs in their locality.

salt marsh and mangrove trees in coastal wetland
A coastal wetland near Cedar Key National Wildlife Refuge (Florida) that contains a mixture of salt marsh grasses and mangrove trees. This location is near the northern range limit of mangrove forests in Florida. Thus, freeze events in the past have prevented mangrove forests from outcompeting the salt marsh plants. In the absence of freeze events, mangrove forests would dominate this wetland. The last major freeze event in this area occurred in December 1989, and mangroves have been expanding since then. The forests in the background are dominated by the black mangrove (Avicennia germinans) — the most freeze-tolerant mangrove species in North America.

These collaborations also are helping USGS researchers tailor their research to address pressing questions while achieving a core mission of the agency: to provide reliable scientific information to describe and understand the Earth. As a result, scientists and resource managers are more effectively communicating the urgency and importance of environmental change issues in the region to the public, state and local governments, nonprofits, and universities they serve.

We gratefully acknowledge the support of the resource managers and stakeholder institutions who helped in the creation of this piece. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

References Cited

Mehvar, S., Filatova, T., Dastgheib, A., De Ruyter van Steveninck, E., and Ranasinghe, R., 2018, Quantifying economic value of coastal ecosystem services: a review: Journal of Marine Science and Engineering, v. 6, no. 1, doi: 10.3390/ jmse6010005.

mangrove forest adjacent to mudflat
A mangrove forest and adjacent mudflat near Big Sable Creek in Everglades National Park (Florida, USA). In this area, mangrove forest mortality and peat collapse due to a powerful tropical cyclone in 1935 led to the conversion of mangrove forests to mudflats. This area was once covered by more extensive mangrove forests but is now a mosaic of mangrove forest and mudflats.

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