New research creates model for measuring CO2 uptake

Given the pivotal role coastal wetlands play in erosion control, habitat provision, and water purification, restoration projects are unquestionably a valuable investment. But now, new work that emphasizes their role as major global carbon sinks may help provide a novel funding source for restoration — carbon markets.

Flanked by ocean and land, salt marshes serve as a buffer, filtering pollutants and nutrients, and reducing the human footprint on marine ecosystems as native and invasive grasses take up carbon dioxide (CO₂) and sequester the greenhouse gas in their roots.

The research published by University of Rhode Island (URI) scientists in the November 2016 issue of the journal Ecosphere provides data and a preliminary greenhouse gas model that ultimately may help offset the cost of restoration efforts by qualifying these projects for carbon credits. If this happens, then communities and government agencies can recoup some of their project costs.

“For the first time in the world, it is now possible to restore tidal wetlands and also get carbon credit financing through the carbon markets to help pay for the restoration activity,” explains lead author Assistant Professor Serena Moseman-Valtierra, URI College of the Environment and Life Sciences (CELS), Department of Biological Sciences. “This is drawn out of the explicit recognition that salt marshes serve as strong carbon sinks. And, by restoring salt marshes and promoting vegetation regrowth or altering hydrology back to original conditions, we can maximize the strength of those sinks.”

Moseman-Valtierra’s work was part of a collaborative research project funded by the National Oceanic and Atmospheric Administration (NOAA) and supported by Rhode Island NSF EPSCoR undergraduate and graduate fellowships.

“This is one of the first really detailed studies of greenhouse gases in coastal wetlands — it’s received a lot of attention,” Moseman-Valtierra notes, putting the relevance of the research into context.

She says the questions posed by stakeholders conducting coastal wetlands restoration work was whether the plants could serve as an indicator or proxy for carbon dioxide uptake and if differences existed between the major plant zones in the salt marshes.

“One of the hardest things they have to do as wetlands managers, in getting carbon funding for their restoration project, is actually demonstrating that their activities have increased the uptake of carbon dioxide. That is not an easy thing for a non-biogeochemist to do.”

The researchers set out to test whether there might be a simpler substitute, says Moseman-Valtierra, such as taking a measurement of plant growth to gauge the activity. They also hoped to generate a model where managers could insert basic data like salinity or temperature, measurements easily taken in the field, and get an estimate of what the net CO₂ uptake would be.

“This is exciting for coastal managers. The roots are an easy, cheap thing to measure while CO₂ fluxes are not.”

Moseman-Valtierra says one of her collaborators, Omar Abdul-Aziz, Ph.D., an environmental engineer at West Virginia University, generated a new type of model — one of the first of its kind — that is intended for non-scientists to use in calculating how greenhouse gas fluxes may change with a planned restoration project. He  took a subset of the project’s data and found that the below-ground biomass (the weight of the roots of a plant) could partially predict the amount of CO₂ uptake; the more root development, the greater the absorption of carbon dioxide from the atmosphere.

“People can input basic environmental data to predict what greenhouse gas fluxes will look like,” she explains.

Using an online spreadsheet, coastal wetlands managers can generate predictions of what the greenhouse gas flux, or movement of gases between reservoirs, will look like under a restoration scenario. Essentially, they can pose the question, if the environment is altered in ‘x’ way, how will that change the flux?

“This is exciting for coastal managers,” Moseman-Valtierra notes. “The roots are an easy, cheap thing to measure while CO₂ fluxes are not. Also, they can gather baseline information before the project starts, such as what does the system look like before restoration, plant the grasses and let them grow, and take another sample and measure the change. By measuring the change in plant growth, they can potentially use a model like this to predict the change in the biogeochemistry.”

RI EPSCoR funding at work

The groundbreaking project also provided the framework for the research of Rhode Island NSF EPSCoR graduate fellow Rose Martin, a recent URI Ph.D, now in a postdoctoral position with the U.S. Environmental Protection Agency (EPA) in Narragansett, funded by Oak Ridge Institute for Science and Education. The work is continuing now and funding URI master’s student Katelyn Szura, who is testing how greenhouse gas emissions vary in marshes under a wide range of nitrogen loads in Narragansett Bay.

Martin, one of the paper’s co-authors, says she was proud to participate in the research and resulting publication: “The paper is an important contribution to our understanding of carbon cycling in coastal wetlands, a collection of processes that drive marshes’ ecosystem service of sequestering carbon that could otherwise enter that atmosphere in the form of heat-trapping greenhouse gases.”

Her major contribution to the paper was collecting greenhouse gas flux data from portions of the study site invaded by the grass Phragmites australis, which aligned with the major aims of her dissertation work. Martin sought to understand the impacts of the invasive Phragmites on the biogeochemistry of coastal wetlands, particularly with regard to the greenhouse gas fluxes that define the role these systems play in global climate.

“As was the case for much of my dissertation work, RI EPSCoR funding supported equipment purchases such as those that allowed me to develop the large flux chambers we used for the Phragmites research,” Martin says. “In addition, RI EPSCoR funding released me from teaching assistant obligations and allowed me the freedom to engage in side projects such as the one that led to this publication.”

Another co-author, Elizabeth Brannon, helped with many of the data analyses and some of the effort to measure gas fluxes with a Picarro analyzer, an instrument capable of measuring greenhouse gases in the field. Brannon is a URI Ph.D. student in Moseman-Valtierra’s lab, about to defend her thesis.

In other research, Moseman-Valtierra says she is conducting a time series related to efforts by the U.S. Fish and Wildlife Service to restore Narrow River marshland. This is now part of a graduate thesis by Danielle Perry, in the lab of CELS Interim Associate Dean of Research Carol Thornber. The hope is that the installation of hand dug ditches will drain water off the marsh surface and allow plants to flourish.

“We’re taking preliminary measurements to see whether there is a big change over time in carbon fluxes as the plants regrow,” she explains. “The marshland has been very waterlogged, in association with sea level rise. The restoration of hydrology is one of the biggest opportunities for restoration.”

Typically, these projects mean opening up the connection between coastal marshes and the ocean, returning them to full marine or saline conditions. Doing so, Moseman-Valtierra says, reduces the level of methane brought on by human activity.

“What’s been most exciting is that I have been able to participate in research early on in my career at URI that can translate into action for the conservation and restoration community,” she adds. “I felt like were were answering a question that was actually helpful. We work in these systems, we care about them and we like them. We want them to be here for our grandchildren to enjoy. So, this work is very rewarding.”

Story by Amy Dunkle|Courtesy photos