Salt Marshes: Ecosystem Powerhouses in Climate Regulation and Biodiversity

The Vital Role of WetlandsWetlands are critical ecosystems that play a fundamental role in maintaining the stability and well-being of both local and global environments.  Coastal salt marshes, flooded and drained by tides, and often composed of deep mud and peat, provide a wide range of ecosystem services that contribute to biodiversity, water quality, carbon storage, and climate regulation. Biodiversity and Habitat ConnectivitySalt marshes are incredibly diverse habitats and serve as breeding grounds, nurseries, and foraging areas for a wide range of aquatic and terrestrial species. This biodiversity helps maintain ecosystem resilience and adaptability in the face of environmental changes. Wetlands also provide essential habitat connectivity by serving as corridors for the movement of species between different ecosystems and supporting genetic diversity and species’ adaptation to changing environmental conditions. Natural Water RegulationSalt marshes act as natural water regulators, storing excess water during periods of heavy rainfall, reducing the risk of floods in downstream areas. During dry periods, wetlands slowly release stored water, helping to maintain steady streamflow and prevent water shortages. Wetlands are natural filters that improve water quality by trapping sediment, nutrients, and pollutants from runoff and wastewater. Further, coastal wetlands act as natural buffers against sea-level rise and storm surges. They stabilize shorelines, protect coastal communities from erosion, and reduce the impacts of extreme weather events.Greenhouse Gas SequestrationSalt marshes are among the most efficient ecosystems in terms of carbon sequestration. The plants in salt marshes, including grasses and other vegetation, absorb carbon dioxide and convert it into organic matter. This organic matter is then stored in the soil, where it can remain for long periods, effectively acting as a carbon sink. In fact, tidal marshes can sequester carbon at a rate 10 times higher than tropical rainforests. Salt marshes also play a role in regulating methane emissions. Some wetlands, known as "methane sinks," actively consume methane from the atmosphere through specialized microbial processes, effectively reducing its impact as a greenhouse gas. Methane gas has significant atmospheric heating qualities, and in turn excess emissions have negative environmental impacts. The carbon storage and methane regulation services provided by salt marshes have a direct impact on the global climate. “ Because methane is “both a powerful greenhouse gas and short-lived compared to carbon dioxide, achieving significant reductions would have a rapid and significant effect on atmospheric warming potential” the EPA states. By storing carbon and reducing methane emissions, wetlands help to mitigate the greenhouse effect.The Nitrogen Cycle and Coastal WatersSalt marshes are a key component in the nitrogen cycle as well. These ecosystems filter and process excess nutrients that can enter coastal waters. Excess nitrogen runoff from agricultural activities and urban areas can lead to harmful algal blooms and dead zones in coastal waters. Salt marshes act as natural filters, trapping and transforming nutrients, which helps maintain water quality and support marine ecosystems. Conserving and restoring these ecosystems is crucial for both mitigating the impacts of climate change and maintaining the overall health of coastal and marine environments.Human BenefitsSalt marshes and tidal wetlands provide critical services to humans as well, including protection of infrastructure from coastal hazards, and habitat protection for economically important species. A large majority of U.S. wetlands today have been lost or degraded due to human activities, primarily related to development of coastal wetlands. NASA scientists conducted an analysis of salt marsh ecosystems changes and degradation from 2000 to 2019, and they found the loss of these ecosystems resulted in an “estimated net global emissions of 16.3 Teragrams of carbon dioxide across the study period, an annual equivalent of emissions from approximately 3.5 million motor vehicles.” Feedback and interactions among natural and anthropogenic drivers have altered the stability and persistence of coastal wetlands, and continue to accelerate carbon emissions and atmospheric warming.Restoration Efforts and ChallengesDr. Kroeger and his team’s latest salt marsh restoration project occurred at Cape Cod National Seashore (CCNS), which encompasses a diverse range of ecosystems, including coastal dunes, salt marshes, woodlands, and freshwater ponds. Salt marsh restoration efforts within CCNS focus on restoring tidal flow to marshes that have been affected by human alterations. This involves removing or modifying structures that impede natural water movement, allowing marshes to recover and thrive. The CCNS ecosystem restoration project also used numerous tools such as prescribed fire and construction of new culverts constructed in Hatches Harbor to allow for greater tidal exchange. To date, twenty culverts have been replaced, restoring natural tidal exchange to more than 300 acres of coastal wetland habitat. Currently, plans are underway for additional tidal restoration throughout Cape Cod, including the Herring River Restoration Project in Wellfleet. Involving almost 1,000 acres of former salt marsh, the Herring River is the most ambitious and largest tidal restoration project in New England.Wetland restoration faces many challenges including sediment starvation by dams and dikes, land subsidence from oil drilling and river channelization. River sediments often dumped into gulfs instead of marshes deteriorating the foundations of these wetlands. Excessive agricultural run-off containing high quantities of nitrogen are also damaging these ecosystems by crippling root growth and causing algae blooms and dead zones. Increased frequency and force of natural disasters, such as hurricanes and sea level rise, due to climate change exacerbate restoration efforts too. Another barrier is the high costs associated with restoration. The U.S. Department of Agriculture estimates restoring and preserving wetlands costs between $170-$6,100 per acre, with lower costs in rural midwestern areas and higher costs in populated coastal regions.Who is our Guest?Dr. Kevin Kroeger has studied coastal ecosystems since 1990, with focus on a range of topics including fluxes and biogeochemistry of nitrogen in groundwater discharge to estuaries and wetlands, estuarine water quality, and carbon and greenhouse gas cycling and fluxes in coastal wetlands. Dr. Kroeger is currently the lead of the Biogeochemical Processes group at Woods Hole Coastal and Marine Science Center in Massachusetts. Dr. Kroeger also received his PhD in Biogeochemistry from Boston University’s marine program, an M.S. in Marine Sciences from the University of Connecticut, and a B.A. in ecology from the University of Tennessee.  For a transcript of this episode, please visit https://climatebreak.org/salt-marshes-ecosystem-powerhouses-in-climate-regulation-and-biodiversity/