The Carbon Sequestration Benefit from Wetlands has Positive Impacts to Help Mitigate Climate Change
Explore our Field Guide addressing the benefits and methodology of wetland restoration.
What are wetlands?
Wetlands are habitats that occupy low, flat places in the land where water naturally slows and pools. Nutrients abound in wetlands, brought in with surface runoff in the form of sediments and organic detritus. These wet, nutrient rich conditions make wetlands the most productive ecosystems in temperate climates, rivaling rain forests and coral reefs for their diversity and shear biomass. 40% of the world's species live and breed in wetlands. 1 billion people depend on wetlands for their livelihoods. But the runoff that carries in nutrients also brings in pollution, making wetlands the most susceptible habits to degradation by chemicals.
There are many types of wetlands. Marshes dominated by reeds and grasses, swamps dominated by trees and shrubs, and bogs and fens dominated by peat. There are fresh and salty versions of each of these, various associations with streams, lakes, and oceans, and wetlands change with latitude and climate.
Before European settlement, wetlands covered 10% to 12% of the continental US. A little more than half of these were lost between the 1790’s and the 1990’s, mostly to agricultural expansion. Farming and horticultural manuals of the 19th century extolled the virtues of draining marshes to mitigate “foul air”. State and federal legislation supported filling wetlands.
The legislative tide did not turn until the 1977 amendment to the Clean Water Act, which created the current practice of protecting wetlands with riparian buffers and cleaning and controlling runoff. The roughly 110 million acres of wetlands that remain in the lower 48 States today (5.5% of total land area) are better protected than in the 19th century, however, since 1977 about ½% of the remaining wetlands, about ½ million acres, have disappeared each decade.
Planting Wetlands
Study the hydrology, soils and endemic vegetation found in wetlands near the site. Mimicking these will yield the most successful and least expensive restoration project.
Remove contaminated soils. Areas where sediments accumulate are likely to be contaminated.
Remove invasive species, with a combination of controlled burns, mechanical removal and herbicides.
Place clean sand as the substrate for the wetland and overlay with rich organic soils to jumpstart the nutrient rich vegetative cycle.
Create a varied ground surface within the wetland – shallows and deeper areas – to support diverse plant communities and promote sediment deposition.
Seed for erosion protection to outcompete and exclude invasives during the grown-in period before planting trees, shrubs, wetland grasses and wildflowers.
Choose plant species with high biomass production and deep root systems to maximize carbon capture and storage. Where feasible, include a peat-rich planting palette, which is especially successful at capturing carbon.
Incorporate a mix of emergent, floating, and submerged vegetation to create a diverse ecosystem.
Maintenance
Have the installation contractor maintain and monitor the wetland for a minimum of 3 years. It is important to have a contractor with the right equipment available for follow up.
Remove invasive species as soon as possible. The longer they remain and produce seeds, the harder they are to eradicate.
Monitor the water level in the wetland carefully, keeping as close to the natural seasonal cycle of inundation as possible. This keeps the wetland naturally sequestering carbon. Oversaturation causes an increase in methane emissions, a potent greenhouse gas. Prolonged low water causes carbon dioxide to be released.
Implement measures to trap sediment in the wetland. Sediments store significant amounts of carbon.
Environmental Benefits
Wetlands are a type of landscape that we have depended on for flood control since the beginning of human history. They are natural sponges that absorb and then slowly release storm water, buffering built up areas against rising waters. They also filter runoff and recharge water tables, ensuring clean drinking water.
Apart from increasing recognition over the 20th century as significant habitats, wetlands have only recently been seen as carbon sinks. Though wetlands occupy only a small fraction of the earth’s total area, about 6% to 7%, they hold 20% to 30% of the world's soil carbon. Their capacity to sequester soil carbon is greater than any other habitat on the planet, about 4 times the Earth’s average land use, more than twice that of temperate forests.
This is because of the waterlogged conditions found in wetlands. As plants shed their summer foliage each year, leaf litter accumulates in slow moving waters. As sediments wash over the organic matter each year, the two mix and sink to the bottom. The wet soils found in wetlands are poor in oxygen, which slows decomposition, keeping vegetation tissue accumulation ahead of decay. The carbon-rich results, initially found at the surface, are slowly pushed down into the soil. This carbon rich soil is sometimes referred to as Blue Carbon.
Wetlands can be beautiful amenities that provide unique opportunities for passive recreation and education, in parks, campuses, natural areas, and along infrastructure corridors. They cool the air in summer. Made accessible by boardwalks and trails, they provide respite from urban stress.
As a rule, carbon sequestration works best in wetlands roughly a half acre in size or more, though this varies considerably by type of wetland and climate. Over the last 30 years, many small artificial wetlands have been constructed in urban and suburban areas across the US in the form of bioretention basin for stormwater control. These now occupy between 2% to 8% of urban lands, roughly 3 million acres in total. To date, these have not been used for carbon sequestration because their small size and rapid wet/dry cycles are too frequent to create the stable soil conditions that facilitate carbon sequestration. This is changing with current research. In the coming decades, stormwater facilities can become a powerful tool for greenhouse gas sequestration.
Download the full Wetlands Field Guide.
Our Commitment to Sustainability
MKSK is committed to designing the change our world needs, discovering new solutions and building new ways of working. Every project is an opportunity to address climate change and loss of biodiversity in the design and planning of communities, landscapes, and cities. MKSK can assist in the design and planning of carbon sequestering landscapes, to help fulfill the environmental stewardship goals of our commercial, institutional, industrial, and public clients.
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