A marsh is a type of wetland found along coastlines, rivers, and estuaries, defined by the dominance of herbaceous plants such as grasses, rushes, and sedges rather than woody trees. These low-lying areas are frequently or continuously saturated with water, creating a unique, productive ecosystem that acts as a transition zone between land and aquatic environments. Marshes perform functions that benefit human communities and the broader natural world. When these habitats are destroyed, the consequences are immediate and severe, removing natural protections and disrupting fundamental ecological cycles.
Loss of Natural Coastal Defense
The destruction of a marsh immediately removes a powerful, natural buffer against the physical forces of the ocean and weather events. Marsh vegetation and the underlying soil structure function together to absorb and dissipate wave energy. The dense network of roots and rhizomes anchors the sediment, stabilizing the shoreline and making it highly resistant to erosion from tides and currents.
This stabilizing effect is pronounced during major weather events like hurricanes and tropical storms. The shallow, gently sloping bathymetry of a marsh forces incoming storm waves to break further offshore, which significantly reduces their energy before they reach the mainland. Salt marshes can reduce the height of damaging waves in storm surge conditions by nearly 20 percent over a relatively short distance. The marsh’s surface vegetation and organic-rich soil act like a massive sponge, absorbing and slowing the flow of floodwater.
The loss of this natural infrastructure translates into increased vulnerability for inland communities and coastal development. Without the marsh to dampen wave action and absorb surges, the full force of a storm impacts artificial structures and infrastructure. The economic value of this physical protection is substantial, with tidal marshes in the United States alone estimated to provide over $23 billion in annual storm protection services. Removing this barrier leaves residential areas, roads, and commercial properties exposed to the destructive power of flooding and accelerated erosion.
Degradation of Local Water Quality
Marshes serve as highly effective natural filtration systems, intercepting runoff from the land before it can pollute larger bodies of water. The movement of water through the marsh is slowed by the dense vegetation, allowing suspended solids, sediments, and attached pollutants to settle out of the water column. The marsh plants, along with the bacteria and microorganisms in the soil, actively take up and transform dissolved contaminants.
This function involves the removal of excess nutrients, specifically nitrogen and phosphorus, which often enter waterways from agricultural runoff and wastewater discharge. Marsh plants incorporate these nutrients into their biomass for growth, preventing them from flowing downstream. Specialized chemical reactions within the marsh’s anoxic (oxygen-poor) soils convert forms of nitrogen into harmless nitrogen gas through denitrification, removing the nutrient permanently from the ecosystem.
When a marsh is destroyed, this filtration capacity is lost, allowing pollutants to flow unimpeded into adjacent estuaries, rivers, and oceans. The resulting influx of excess nutrients can trigger massive algal blooms in coastal waters. As these blooms die and decompose, they consume large amounts of dissolved oxygen, creating hypoxic conditions, or “dead zones,” that suffocate marine life. Heavy metals and other chemical pollutants trapped in the marsh sediment can be remobilized, potentially contaminating shellfish beds and making them unsafe for human consumption.
Collapse of Essential Wildlife Nurseries
Marshes provide an extraordinarily productive and sheltered habitat, particularly important for the early life stages of many aquatic species. The complex structure of the vegetation and the shallow tidal creeks create a refuge where juvenile fish and shellfish can avoid larger predators that inhabit deeper offshore waters. This physical protection is coupled with a rich food supply derived from the marsh’s high biological productivity.
The detritus, or decaying organic matter from the marsh grasses, forms the base of an intricate food web that supports a vast array of invertebrates, which feed young fish and crustaceans. Many commercially and recreationally important species, including shrimp, blue crabs, oysters, salmon, and sea trout, rely on marshes as primary nursery grounds. These species spend their vulnerable juvenile phases feeding and growing in the marsh before migrating to the open ocean as adults.
The destruction of a marsh eliminates this refuge, leading to a sudden, localized loss of biodiversity. Young organisms are exposed to higher rates of predation and competition in less suitable habitats, disrupting the entire estuarine food chain. This ecological collapse has significant economic repercussions, as the health and sustainability of local commercial and recreational fisheries are linked to the marsh-dependent species.
Release of Stored Carbon
Marshes are recognized globally as significant “blue carbon” ecosystems, meaning they are exceptionally efficient at capturing and storing carbon dioxide from the atmosphere. Unlike terrestrial forests, which store most carbon in above-ground biomass, marshes store up to 99 percent of their carbon in the waterlogged soil beneath the surface. The constant saturation of the soil creates an anoxic environment that dramatically slows the decomposition of organic matter, allowing carbon to accumulate and remain buried for thousands of years.
Salt marshes sequester carbon at a rate up to 10 times greater than that of mature tropical forests and store three to five times more carbon per acre. When a marsh is drained, dredged, or otherwise destroyed, the carbon-rich soil is exposed to oxygen. This exposure reverses the natural process, causing the rapid decomposition of the stored organic material.
The destruction shifts the marsh from a long-term carbon sink to a source of greenhouse gas emissions. Significant amounts of carbon dioxide (CO2) and methane, a potent greenhouse gas, are released back into the atmosphere. This release contributes to the increase in atmospheric greenhouse gas concentrations, accelerating global climate change.