Climate change creates paradox for wetlands

While higher CO₂ levels drive sea levels to rise, they also stimulate wetland-sustaining plant growth.

By Noreen Parks

From the Daily Planet

Publication Date (Web): April 22, 2009

Coastlines are already bearing the brunt of rising sea levels, and a recent government report warns that the mid-Atlantic seaboard, with its bountiful wetlands, is particularly vulnerable. However, new research published in the March 23 issue of the Proceedings of the National Academy of Sciences U.S.A. (2009, DOI 10.1073/pnas.0807695106) suggests that the escalating CO₂ concentrations driving climate change also stimulate plant growth that counteracts the inevitable erosion from higher seas.

SAMANTHA CHAPMAN

Researchers investigated CO₂’s effects on wetlands in the Chesapeake Bay watershed, where they manipulated conditions in experimental chambers.

Coastal wetlands must continuously build upward to “keep their heads above water”, or they would wash out with the tides. Plant growth and the accumulation of soil-building organic litter normally preserve this equilibrium, but the pace of sea-level rise threatens to upset the balance. Ecologist Adam Langley, at the Smithsonian Environmental Research Center in Edgewater, Md., and his colleagues investigated how changes in plant productivity influence soil elevation in Chesapeake Bay tidelands. They enclosed marshland plots in chambers, half of which received a constant supplement of CO₂ to simulate atmospheric levels predicted for 2100. CO₂ in the other chambers was maintained at present levels. The team also added soil nitrogen to some chambers in both groups to mimic polluted estuaries. From 2006 to 2007, they measured total plant growth and tracked changes in soil height.

The results revealed that by the end of the experimental period, exposure to elevated CO₂ alone had increased the rate of elevation gain by 3.9 millimeters per year. To explain the pattern, the authors looked belowground. Root growth had doubled, pushing the soil surface upward. “This also explains why nitrogen-fertilized enclosures didn’t boast the same gains,” Langley says. “With added nitrogen, the plants didn’t have to produce as many roots to obtain nutrients.” In companion greenhouse experiments that simulated salinity and flooding conditions likely to accompany rising sea levels, the CO₂ effect was even more pronounced.

The findings sound a hopeful note that mounting CO₂ concentrations may boost the capacity of wetlands to weather advancing seas, at least in the short term. However, “it’s important to remember that by warming the planet and accelerating sea-level rise, increasing CO₂ is precisely what threatens marshes the most,” Langley warns.

Simulating Sea Level Rise

From: Underwatertimes.com

April 22, 2009 17:09 EST

WASHINGTON, D.C. -- The U.S. Fish and Wildlife Service today released a new user-friendly internet tool that allows the public to view simulations of sea level rise. Released in honor of Earth Day, this program is designed to help people understand the potential impacts of climate change on sea levels.

The Sea Level Affecting Marshes Model (SLAMM)-View is a web browser-based application that displays map pairs of the same area, each at different sea levels. The strength of this tool is its ability to visually show the modeling of sea level rise predictions, allowing people to see the impacts in a more intuitive way.

“Sea level rise is certainly one of the most pressing issues facing many coastal communities, as well as national wildlife refuges,” said Chincoteague National Wildlife Refuge Manager Lou Hinds. “SLAMM will be used by many coastal refuge managers to involve the public in discussions concerning sea level rise as part of the Comprehensive Conservation Planning process. This planning process must be undertaken every 15 years and unless something changes dramatically coastal refuges will be dealing with this issue over the next 100 years,” Hinds added.

Most sea level rise models examine inundation patterns and do not take into account the biological impacts. SLAMM also looks at sediment and organic matter accumulation on the marshes as well as erosion from tides and storms that can overtake coastal barrier beaches. In addition, SLAMM depicts how these relationships will remain coupled as sea levels rise.

The SLAMM also predicts changes in coastal wetlands and shorelines. These simulations are based on the best available science and technology. Users can select different scenarios by combining time, in 25-year intervals, at different severities, e.g., 0.5 meters to 1 meter increase in sea level.

“This new web-mapping tool can be used to educate communities on the potential effects of sea level increases,” said Leopoldo Miranda, Supervisor, Chesapeake Bay Field Office. “For nearly 20 years, the information provided by SLAMM was available only in table or static map form. SLAMM-View now provides this in a visually dynamic way that more organizations and individuals will be able to use.”

One unique aspect of SLAMM is that the dual maps are geographically-linked: zooming or panning in one map causes an identical alteration in the other map. Regional simulations have been posted on SLAMM-View for a number of important estuaries, including Delaware Bay, coastal South Carolina, coastal Georgia, Puget Sound and Chesapeake Bay. As data becomes available, more map layers and simulations will be made available to the public, including site-specific SLAMM simulations for Chincoteague National Wildlife Refuge. The Viewer shows 45 possible fine-scale combinations of sea level rise scenarios with over a dozen contextual layers you can turn on or off. The visual impact of this map modeling tool makes it a reality to everyone.

The SLAMM view tool could be accessed at http://www.fws.gov/chesapeakebay/slamm and http://www.slammview.org.