Our coastal wetlands absorb CO2 — but environmental changes alter that
A few years ago, I spent the spring exploring coastal wetlands up and down the Mid-Atlantic coast, looking for a new place to start an experiment to study how landscapes “breathe.” After driving a thousand miles and talking with outdoor enthusiasts, environmental managers, scientists and farmers, I found the perfect place: a tidal marsh, a stunning place where the land and the coastal ocean meet.
If you love bird watching or waterfowl hunting, you know what I am talking about. Tidal marshes are peaceful places, with amazing sunrises and sunsets — and a breeze. I love that coastal breeze. But there is much more to these places than meets the eye. Something is always happening: right in front of us, under our feet, and always — invisibly — are processes that are critical to the health of our local communities, the planet and each one of us.
I am talking about the positive benefits that coastal ecosystems provide to people. We call these benefits ecosystem services. Tidal marshes provide a place to live for aquatic and terrestrial animals and plants. They provide protection against storms making safer coastal neighborhoods. They also help maintain healthy water quality and to regulate the climate.
This brings me back to my journey and the experiment. All ecosystems “breath” as part of a delicate balance of the uptake (or “inhalation”) of carbon dioxide gas (CO2) from the atmosphere via plant photosynthesis, and the eventual release (or “exhalation”) of CO2 as part of a natural process. In most cases, the inhalations are greater than the exhalations, resulting in a net gain and storage of carbon by the marsh ecosystem.
The carbon stored in coastal wetlands, including tidal marshes, mangroves and seagrass meadows, is referred to as “blue carbon.” But if these ecosystems are degraded or damaged, their capacity to capture and store carbon can be reduced — or even lost — resulting in CO2 (and other greenhouse gases) being released back to the atmosphere and contributing to global environmental change.
As an analogy, consider a bank account where carbon is represented by dollars. An account with income higher than expenses will increase savings and build wealth. But if expenses and losses increase, or income is reduced, the account will lose value and (if these conditions persist) will result in debt — or even bankruptcy.
What is the monetary value of the capacity to capture and store carbon of tidal marshes? Scientists have estimated that the present carbon sequestration value of current tidal marshes around the Delaware Estuary is nearly $3.7 billion. Losing these ecosystems could have enormous costs.
Tidal marshes are among the most productive (and protective) ecosystems on Earth. Just around the Chesapeake Bay these ecosystems can capture over 2 teragrams of carbon per year via photosynthesis. How much carbon is that? If one African elephant weighs about 12,000 pounds, and one teragram is about 2,205,000,000 pounds, then 2 teragrams are equivalent to more than 365,000 elephants.
Not all of this carbon stays within the ecosystem, and there is an urgent need to understand what can happen to it. A national report recently concluded that ecosystems and the benefits they provide are being altered by climate change. Furthermore, sea-level rise is contributing to the declining health of tidal marshes, and the degradation is expected to occur faster in the U.S. East Coast than in the West Coast due to expected higher sea-level rise along the East Coast. Consequently, we must try to understand how changing environmental conditions are going to affect ecosystem services such as the potential carbon sink of tidal marshes.
Multiple scientists across the U.S. are studying how tidal marshes “breath,” where the carbon goes and what could happen under different climate scenarios. These efforts seek to support restoration and conservation projects across the nation and serve as outdoor laboratories to train the next generation of environmental scientists. They also contribute to state and national environmental assessments and promise to provide insights that help to ensure the health of these ecosystems and the services that they provide.
So next time you visit a tidal marsh, close your eyes, feel the breeze, and listen how the ecosystem “breathes.” It is that breath that protects all of us.
Rodrigo Vargas is a professor of ecosystem ecology and environmental change at the University of Delaware. His research has been supported by the National Science Foundation. Follow him on Twitter @vargaslab.
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