Research Highlights

Nature Reports Climate Change
Published online: 9 April 2009 | doi:10.1038/climate.2009.32

Marsh attacks

Anna Barnett

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0807695106 (2009)

J. Ecology 97, 67–77 (2009)

KAREN MCKEE/US GEOLOGICAL SURVEY

Climatic warming by greenhouse gases is causing sea levels to rise, but two new studies find that elevated CO₂ might also help protect coastal marshes from going under. Sea level rise will destroy a marsh only if it outpaces the build-up of land, and CO₂ can encourage plant growth that swells the soil.

Patrick Megonigal of the Smithsonian Environmental Research Center in Edgewater, Maryland, and colleagues studied how fast soils gained elevation under increased CO₂ by exposing plots in a Chesapeake Bay wetland to concentrations of the greenhouse gas that were raised by 340 parts per million above ambient levels over two years. Whereas control plots lost 0.9 millimetres per year on average, the high-CO₂ plots gained 3 millimetres per year, driven by the amplified growth of plant roots, which added volume and mass to the soil. The boost was diminished, however, if nitrogen was added to the plots, a likely effect of pollution from expanding cities and fertilizer use.

In a companion study, Julia Cherry of the University of Alabama and co-workers transferred plots of marsh to the lab, where they mimicked the effect of an encroaching ocean. They found that high CO₂ stimulated plant growth and land build-up even when marshes were flooded with saltwater.