A disappearing resource
My childhood summers were spent along the banks of the Chesapeake Bay, specifically around the lower reaches of the Rappahannock River. In this estuarine environment, the daily rhythm of life marched in beat with the tide’s rise and fall. Fresh water delivered by inland rivers mingled with the salty ocean water, creating a rich brackish-water ecosystem filled with aquatic life of all sorts. Ospreys and other animals of prey connected the forested shores with the teaming life below the water’s surface. What I couldn’t see, or didn’t understand, was the vast network of carbon storage perched precariously within the ecological interface where water and land met.
Along the Rappahannock river’s shores, both east and west of our cabin, freshwater streams flowed onto a flood plain carved through the ages into the surrounding landscape. In these locations, grassy wetlands took hold, giving way to swamps and islands of razor grasses. Walking through these odd landscapes was a constant adventure for young boys. At times you would sink thigh-deep in mud and muck. You could press your arm deep into the mud and pull out handfuls of rich black clay and silt, which smelled of sulfur and rotting plants. This organic goo is an important part of the carbon storage provided by wetlands.
Wetlands
Today, three and a half thousand miles west of the Chesapeake Bay, along the southern California coast, scientists from the conservation organization Wildcoast and Scripps Institution of Oceanography are studying the role of salt marshes and seagrass in buffering climate change through carbon capture. Today only about ten percent of California’s original wetlands have survived a century of development, as urban sprawl captured coastal lands for growing cities and their suburban satellites.
The shallow, marshy waters around the edges of our oceans, rivers, and estuaries are vital habitats for the biosphere. In these coastal wetlands lie the spawning grounds for many species of fish and other sea life. Birds and mammals also call wetland ecosystems home. The mix of water and grassy marshes provides both food and shelter for the wetland inhabitants. The very characteristics making them desirable habitats for many plants and animals also make them valuable carbon storage environments.
The current southern California research by Wildcoast and Scripps scientists follows up on a Wildcoast project in Baja, Mexico where 19.5 million metric tons of carbon were determined to be stored in a single project area. Putting this volume of carbon in perspective, it is equal to the annual carbon emissions of a million U.S residents.
Coastal wetlands account for only two percent of the Earth’s ocean surface, but they capture more than 50 percent of the carbon absorbed by the oceans each year. Once captured, the carbon is then efficiently sequestered in the wetland sediments. Wetlands are 10 to 100 times more efficient at carbon sequestration than inland forests.
What makes a good carbon sink?
An essential part of Earth’s carbon cycle revolves around the needs of plants. Trees, grasses, and shrubs all derived their energy from photosynthesis — extracting carbon dioxide (CO2) from the atmosphere and using the carbon to build new plant mass. So as plants grow, they remove greenhouse gases from the atmosphere and store the carbon. Unfortunately, when the plants die, they decay and are consumed by bacteria that eat the carbon and convert it back to atmospheric CO2. Therefore, a mature forest might reach a balance where annual new-growth equals the annual accumulation of dead plant material. In this case, there is no more carbon storage, and the forest emits as much CO2 as it absorbs.
Long-term carbon storage requires removing atmospheric carbon and a mechanism for permanently storing it, thus keeping it from reentering the atmosphere. One of the ways this happens is by preventing bacteria from eating the dead plant material. The bacteria chewing up dead wood and leaves require oxygen to metabolize organic carbon. Remove the oxygen, and the decay process stops. This is where wetlands come into their own as efficient carbon stores.They provide an environment with high organic growth above the mudline, and low oxygen storage below.
The stinky, rotting, sulfurous-smelling muds I walked around in as a boy were rich in organic carbon and very low in oxygen. As plants die in the swamps and marshes, they are quickly buried below rapidly accumulating mud and clay layers. In this boggy environment, oxygen is quickly depleted, and the bacteria stop eating. The carbon is not returned to the atmosphere.
Dynamic change
Part of the elegance of wetlands is their dynamic adaptation to a changing environment. As sea levels rise, the wetlands either keep pace or migrate inland. I either case, they continue their role as a sustainable habitat for many species. The wetlands will also continue serving as valuable carbon storage areas, helping to remove carbon dioxide from the atmosphere and oceans.
The wetlands act as a damper on the build-up of greenhouse gases and global warming. They can’t stop rising levels of CO2 in our atmosphere, but they can slow down the process.
The fact that wetlands organically build and often keep pace with sea-level rise is critical. As the marshes grow, they thicken, and the volume of carbon in long term storage grows. But, the success of these dynamic systems depends on the conservation and protection of these fragile habitats.
Protect the wetlands
Overdevelopment and uncontrolled commercial /agricultural activity adjacent to the wetlands often create significant damage. When dikes and other structures for water flow control are built, they alter the entire system’s hydrodynamics and make it less effective. Likewise, too much agricultural runoff into the wetlands leads to damaging nitrogen pollution and loss of efficiency. Lastly, the infill of the marshes to create new land permanently destroys wetland areas.
Pessimistic assessments of climate change sometimes overlook the things humans can do to protect Earth’s environment during a period of rapid climate change. Conserving, protecting, and restoring wetland habitats is a positive step within reach of local, state, and federal government policies. It is a step that is also within reach of individuals who are looking for positive solutions.
Sources:
Wetlands will keep up with sea level rise to offset climate change (Emily Greenhalgh) – https://eurekalert.org/pub_releases/2019-12/mbl-wwk121919.php
Researchers exploring how San Diego County wetlands can be part of climate-saving strategies (By Deborah Sullivan Brennan; The San Diego Union-Tribune) – https://www.sandiegouniontribune.com/news/environment/story/2021-01-11/blue-carbon
Feature Image: Wetlands (Modified by ArcheanWeb) — Original Credit: Photo by Kevin Ortiz on Unsplash
