A carbon sink is any natural or engineered system that absorbs and stores more carbon than it releases over a given period of time. Carbon sinks remove carbon dioxide (CO₂) from the atmosphere through biological, chemical, or physical processes and retain it in vegetation, soils, sediments, oceans, or geological formations. By reducing the amount of atmospheric carbon dioxide, carbon sinks help slow the accumulation of greenhouse gases that contribute to climate change.
In the context of stormwater management, green infrastructure, and watershed restoration, carbon sinks are typically natural landscapes or engineered systems that incorporate vegetation and healthy soils. Trees, wetlands, forests, riparian buffers, rain gardens, bioswales, and other green infrastructure practices can all function as carbon sinks while simultaneously providing stormwater management, water quality improvement, habitat, and flood reduction.
Plants absorb carbon dioxide from the atmosphere during photosynthesis. Using sunlight, water, and nutrients, they convert carbon dioxide into sugars and other organic compounds that become part of their roots, stems, leaves, branches, and trunks. As vegetation grows, carbon accumulates within plant tissues. When leaves, roots, and other organic materials decompose, a portion of that carbon becomes incorporated into the soil as organic matter. Healthy soils rich in microorganisms and fungi can store significant amounts of carbon below ground for decades or even centuries, depending on environmental conditions. As long as a landscape stores more carbon than it releases through decomposition, disturbance, or land use changes, it functions as a carbon sink.
The Earth's largest natural carbon sinks include forests, wetlands, grasslands, oceans, soils, and peatlands.
Forests are among the most effective terrestrial carbon sinks because trees store carbon in wood, bark, roots, and leaves while continuously absorbing carbon dioxide throughout their lives.
Wetlands store carbon both in vegetation and in waterlogged soils where decomposition occurs slowly. These saturated conditions allow organic material to accumulate over long periods, making wetlands some of the most efficient natural carbon storage systems.
Healthy soils contain organic matter derived from decaying plants and microorganisms. Well-managed soils can store enormous quantities of carbon below the surface while improving soil structure, infiltration, and water-holding capacity.
Grasslands and prairies also function as important carbon sinks because much of their biomass is stored underground in extensive root systems.
Many green infrastructure practices create or enhance carbon sinks while managing stormwater. Examples include:
These systems remove carbon dioxide from the atmosphere while reducing stormwater runoff, filtering pollutants, increasing infiltration, lowering urban temperatures, and supporting biodiversity. For municipalities, investing in green infrastructure often produces multiple environmental benefits from a single project.
Although the terms are closely related, they are not identical.
A carbon sink is the system or reservoir that stores carbon, such as a forest, wetland, or healthy soil.
Carbon sequestration is the process by which carbon is captured and stored within that system.
For example, a riparian forest is a carbon sink because it stores carbon in its trees and soils. The continual uptake and storage of atmospheric carbon dioxide by those trees is carbon sequestration.
The amount of carbon a carbon sink can store depends on several factors, including:
Protecting mature forests and preserving healthy soils generally results in greater carbon storage than repeatedly clearing and replanting vegetation.
Carbon sinks provide many environmental benefits in addition to climate change mitigation. They often:
These co-benefits make carbon sinks an important component of sustainable watershed management and green infrastructure planning.
As communities adapt to changing weather patterns and increasing storm intensity, preserving and expanding carbon sinks has become an important component of climate resilience planning. Restoring wetlands, planting urban trees, protecting riparian corridors, and improving soil health not only increase carbon storage but also reduce flooding, improve ecosystem health, and strengthen natural stormwater management systems.
Rather than serving only as environmental assets, carbon sinks are increasingly recognized as critical infrastructure that provides measurable ecological, economic, and public health benefits.
A carbon sink is any natural or engineered system that absorbs and stores more carbon than it releases. Forests, wetlands, healthy soils, grasslands, and many green infrastructure practices function as carbon sinks by capturing atmospheric carbon dioxide and storing it in vegetation and soils. In stormwater management, carbon sinks provide the added benefit of reducing runoff, improving water quality, supporting biodiversity, and helping communities become more resilient to climate change.