California wetland restoration study: some restored wetlands still emit greenhouse gases years later

A new study in Global Change Biology examined 44 site-years of continuous greenhouse gas measurements from six restored wetlands in California's Sacramento-San Joaquin Delta. Researchers found that restoration does not automatically turn former farmland into a consistent carbon sink. Some wetlands remained sources of methane and carbon dioxide years after reflooding, especially where vegetation establishment was delayed by unstable water levels. The study highlights that methane emissions can offset carbon dioxide uptake, making climate benefits slower and more variable than expected. The researchers recommend long-term monitoring and site-specific water and vegetation management to improve outcomes. For carbon project developers, this is a reminder that nature-based offsets need careful validation before assuming net climate gains.