Humans Threaten Wetlands' Ability to Cope with Sea Level Rise

Wetlands can usually cope when it comes to sea level rise. They can move further inland over time, adapting to changing conditions. Despite this resiliency, though, it seems as if wetlands may be in danger. Scientists have revealed that humans may be sabotaging some of their best defenses against sea level rise.

Wetlands are crucial to coastlines. They can buffer coastal cities from floods and storms, filter out pollution and offer other protections. Over time, wetlands can build up their soils and outpace sea level rise. Yet humans can impact this process by creating dams and seawalls.

"Tidal marsh plants are amazing ecosystem engineers that can raise themselves upward if they remain healthy, and especially if there is sediment in the water," said Patrick Megonigal, one of the researchers, in a news release. "They would either build vertically at faster rates or else move inland to slightly higher elevations. But now we have to decide whether we'll let them."

Tidal marshes build up their soils when water floods the marshes during high tide. This water brings sediment with it, which then is trapped by the plants and adds new soil to the ground. This means that when sea level rise accelerates and flooding occurs more often, more soil can be added more quickly. Yet everything has a threshold; if a wetland becomes so flooded that vegetation dies off, then the positive feedback loops are lost.

Human activities in particular have the potential to cause this type of harm to wetlands. Groundwater withdrawal and artificial drainage can cause the land to sink--something that's happening right now in Chesapeake Bay. In fact 8 of the world's 20 largest coast cities are experiencing relative sea level rise that's greater than projections due to this. Dams and reservoirs can also cause issues for wetlands, keeping sediment from reaching the coast. In addition, seawalls and dykes can prevent marshes from moving further inland to cope with sea level rise.

The findings reveal how human impact could greatly affect how wetlands cope with rising sea levels. This could be a major issue in the future since wetlands provide beneficial resources for the coastline and help prevent erosion. As the climate changes, it's more important than ever to protect natural ecosystems, like wetlands, that can help curtail environmental impacts.

The findings are published in the journal Nature.