Elevating water table reduces net ecosystem carbon losses from global drained wetlands

Area of Science:

• Environmental Science
• Climate Change Research
• Ecosystem Ecology

Background:

• Drained wetlands are often carbon (C) sources, contributing to climate change.
• Current C balance assessments primarily consider vertical fluxes, ignoring lateral C movement and land-use impacts.
• Wetland rewetting is proposed for climate change mitigation through enhanced C storage.

Purpose of the Study:

• To synthesize global data on wetland net ecosystem C balance (NECB) across various statuses and land uses.
• To evaluate the impact of water table changes on C fluxes in wetlands.
• To inform policy decisions for wetland management and C sequestration.

Main Methods:

• Global synthesis of 893 annual NECB measurements.
• Inclusion of CO2 exchange, manure fertilization, biomass harvest, and hydrological C exports.
• Analysis across drained, natural, and rewetted wetlands with diverse land-use histories.

Main Results:

• Elevating water tables substantially reduces net ecosystem C losses globally.
• Drained wetlands lose 2579 kg C ha⁻¹ year⁻¹, natural wetlands gain -422 kg C ha⁻¹ year⁻¹, and rewetted wetlands gain -934 kg C ha⁻¹ year⁻¹.
• Drainage for agriculture/forestry, especially in (sub)tropics, leads to high C losses, persisting for decades.

Conclusions:

• Rewetting all drained wetlands is crucial for mitigating C losses and enhancing C sequestration.
• Rewetting former agricultural wetlands in (sub)tropical regions offers significant potential for C loss reduction.
• Elevating water tables is a key strategy for restoring C storage in degraded wetlands.