US Coastal Wetlands Drowning in Rising Seas

The Cliff News | 9 August 2026

A stark reality is emerging for the United States' coastlines: the vital ecosystems of salt marshes and mangroves are engaged in a losing battle against rising sea levels. A comprehensive first national assessment has quantified this alarming trend, finding that a significant majority of these coastal wetlands are now succumbing to the encroaching tides.

These wetlands are more than just ecological havens; they serve as critical natural defenses against storm surges, protect infrastructure like roads and buildings, and provide essential habitats for migratory birds and endangered species. Their continued inundation poses a direct threat to coastal communities and biodiversity.

Wetlands Struggling to Keep Pace

The new study indicates that while 89 percent of American coastal wetlands are still attempting to build elevation by accreting sediment and through plant growth, a devastatingly low 16 percent are succeeding fast enough to outpace the rising waters. The remaining wetlands are steadily losing ground, a phenomenon researchers term submergence.

Submergence manifests subtly from shore, characterized by increasingly frequent and prolonged flooding, a thinning of vegetation, and eventually, the transformation of marshland into bare mudflats and open water. This gradual loss erodes the protective capabilities of these crucial natural barriers.

Plant Physiology Under Pressure

Coastal wetland plants have evolved to tolerate certain levels of tidal inundation. In fact, up to a point, increased flooding can stimulate plant growth and soil development, which has historically allowed marshes to persist. However, this resilience has its limits.

"All coastal plants have optimum ranges," explained Glenn Guntenspergen, a coastal wetland ecologist with the U.S. Geological Survey (USGS) and senior author of the study. "But if they get flooded too much, then the system shuts down. The plants decrease production and eventually die."

Accelerating Sea Level Rise

Adding to the pressure is the accelerating rate of sea-level rise. While global sea levels rose at an average of approximately 0.07 inches (1.7 millimeters) per year throughout the 20th century, that rate has nearly doubled, climbing to about 0.15 inches (3.8 millimeters) per year between 2006 and 2018.

This faster influx of water overwhelms the natural accretion processes of the wetlands, pushing them beyond their adaptive capacity. The assessment highlights the urgent need for strategies to mitigate sea-level rise and bolster the resilience of these invaluable coastal ecosystems.