Wetland desiccation promotes carbon dioxide emissions from air-exposed sediments

Abstract

High primary production in wetlands, together with the anaerobic conditions prevailing in their flooded or waterlogged sediments, make these ecosystems sinks of atmospheric carbon on a global scale. Water shrinking exposes previously flooded sediments to the atmosphere, enhancing microbial aerobic respiration and remobilizing organic carbon stored for long periods. In agreement, the wetland becomes a source of CO₂ to the atmosphere. Here, CO₂ fluxes from the air-exposed sediments during a water shrinking event in a restored wetland were measured. Only waterlogged sediments remained as a carbon sink. All other air-exposed sediments became a CO₂ source to the atmosphere. Emissions were related to sediment moisture through a polynomial trend. CO₂ fluxes were positively correlated with air-exposed sediment temperature, and inversely related to sediment pH. Implications for restored wetland management are pointed out.