Wetlands comprise only 9% of the Earth’s surface and contain a significant proportion of the terrestrial carbon (C) pool. Wetlands provide a number of ecosystem services, in addition to maintaining biodiversity. Moreover, wetlands play an important role in landscape function, including cycling of carbon, water, and nutrients, food, and fiber production, water purification, regulation of flows, habitat provision, as well as tourism and recreation services. Soils comprise the most extensive terrestrial C pool, and wetlands have the most crucial component, estimated to range between 18-30 % of the total soil C (global terrestrial carbon). Wetlands are an essential part of the global C budget but typically are omitted from large-scale assessments. The reasons for wetlands being excluded are inadequate models and limited knowledge and information of C turnover and temporal dynamics.
What Is the Carbon Cycle?
Carbon is the primary building block of all life on Earth. Plants and animals use carbon to build their cell structures. Stored carbon can be released or emitted through the process of respiration or when cell structures decompose, are burnt, or in the case of soil carbon, disturbed. The more straightforward definition of the carbon cycle is a multitude of processes by which natural systems absorb and emit carbon.
From the formation of Earth and the first living organisms, the processes of emitting and sequestering carbon were generally balanced prior to the Industrial Revolution. For millennia, vast amounts of carbon have been trapped in highly condensed forms such as coal, oil, and natural gas; also known as fossil fuels.
Since the industrial expansion, fossil fuels are burned for energy in the manufacturing process, thus the carbon content of fossil fuels are released into the environment. Additionally, human activities, like land clearing, have disrupted the natural sequestering processes. Consequently, carbon emissions are one of the primary causes of the greenhouse effect and climate change.
Wetlands and the Carbon Cycle
The dynamic and crucial role of wetlands in carbon sequestration and storage has generally been underestimated. According to the Ramsar Scientific and Technical Review Panel, despite the minor wetland coverage of the planet’s land surface, they store approximately 35% of terrestrial carbon. Since wetlands have the capacity of high productivity in the landscape, they also have an increased ability to sequester and store carbon. Additionally, wetlands are depositional areas. Therefore, these areas have the capability to store carbon-rich organic sediments. Under anaerobic conditions, wetlands produce greenhouse gases (GHGs) that contribute substantially to global warming.
Loss of wetlands, through land clearing or draining, can lead to significant losses of stored organic carbon to the atmosphere. Wetlands need an adequate evaluation of their contribution to climate change mitigation and adaptation. Scientists can use the collected data to create protection, restoration, and enhancement programs.
It is essential to mention that wetlands’ ability to absorb and sequester carbon varies and depends on several factors, including the wetland type, temperature, and water availability. Undisturbed or intact wetlands with dense vegetation, algal activity, and soils act as natural carbon sinks.
Carbon Sequestration in Wetlands
There are many different types of wetlands; ranging from mineral to organic soils and forested to non-forested systems. They are further differentiated by the type of biome in which they are found. All of which have one thing in common: all wetlands sequester carbon from the atmosphere and act as sediment traps for runoff. Vegetation clutches the carbon in organic litter, peats, organic soils, and sediments, which may be built up for thousands of years.
The U.S. Global Change Research Program estimates that freshwater wetlands store up to 13.5 billion metric tons of carbon. Non-tidal wetlands can hold nearly ten times more carbon than tidal wetlands due to the substantial acreage. Moreover, this study also discovered that peatlands in forested regions store the most carbon, accounting for approximately half of the wetland carbon in the U.S.
Protecting and Restoring Wetlands
With wetlands holding large amounts of carbon, the protection and restoration of wetlands is an opportunity to mitigate greenhouse gas emissions globally. Loss of an existing wetland is detrimental from two aspects: the loss of a carbon sink, and the carbon stored in that wetland, when lost, can be released into the atmosphere.
Scientists from all around the globe are working on this topic and are developing methodologies for restoring and managing wetlands. Some of the best practices to protect the carbon stores in wetlands include reduced wetland drainage and other land management practices. Natural re-vegetation is one of the options that will help wetlands restore their natural capability, along with restoration of diverse vegetation to prevent the proliferation of invasive species, which may destroy wetlands.