• Coastal wetlands store large amounts of carbon and are sensitive to chemical interactions driven by salinity and tidal fluctuations • We coupled a land surface model to a reactive transport model to simulate biogeochemical cycling in saline and fresh tidal wetlands • Sulfate availability in saline wetlands lowered simulated methane emissions, which compared well with site measurements Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes.