29 years of carbon sequestration in two constructed riverine wetlands

The International Panel on Climate Change (IPCC) has made it clear that a reduction in carbon emissions and a promotion in carbon sequestration are necessary in order to prevent the planet from reaching catastrophic warming levels of 1.5 °C globally. The IPCC identifies the investment in “high‑carbon ecosystems” as a potential mitigation strategy, with one such ecosystem being wetlands. Historically, the majority of the world's wetlands have been destroyed due to human activities, with the midwestern U.S. being one of the most affected regions. Only in recent history has the U.S. sought to remedy this by mandating the construction of wetlands to replace those that are drained. While long-term carbon sequestration rates for natural wetlands are well-documented, it is unknown how constructed wetlands sequester carbon long-term. The Olentangy River Wetland Research Park (ORWRP) in Columbus, Ohio, USA is an ideal location to research this due to its extensive datasets collected over 29 years of biogeochemical and ecological monitoring. We used soil core samples taken across two constructed freshwater wetlands to quantify carbon storages and paired this data with similar studies at 18-month, 10-year, and 15-year milestones to create a timeline of carbon sequestration across 29 years. Our findings suggest that both wetlands have sequestered relatively equal amounts of carbon since construction and neither have shown a net gain or loss since year 15. At year 29, the average carbon storage between both wetlands is 3.58 ± 2.21 kg C m⁻² which equates to 0.12 ± 0.08 kg C m⁻² yr⁻¹, which is similar to other constructed wetlands. Results indicate that these wetlands likely have reached stability and are not expected to exhibit future carbon gains or losses under current conditions. Because these and other constructed wetlands have greater carbon sequestration rates than other options for conversion of croplands, they represent a successful climate change mitigation strategy.