Methane and carbon dioxide flux in a tidal freshwater marsh recovering from three years of experimental seawater additions and following the Hurricane Irma storm surge

Methane (CH4) and carbon dioxide (CO2) flux rates were measured in a tidal freshwater marsh using static flux chambers. The experimental field site, SALTEx (Seawater Addition Long-Term Experiment) is part of the Georgia Coastal Ecosystems (GCE) LTER and is located on the Altamaha River, GA. The marsh was experimentally dosed with brackish water additions for 3 years, from 2014 – 2017. There are three treatments groups (Press, Pulse, and Fresh) and two control groups (with and without siding on the plots), each with six replicates. Press treatment plots received brackish water throughout the year, Pulse plots received brackish water in September and October and fresh water the rest of the year, Fresh plots received fresh river water throughout the year. The two control groups, one with siding on the plots and one without, received no water addition manipulations. All dosing ceased in January 2018, at which point we began to study the recovery of the marsh. In this study, the Hurricane Irma Rapid Grant evaluated additional effects of the Hurricane Irma storm surge that occurred in October 2017. Greenhouse gas measurements were taken seasonally beginning in March 2018 and ending in March 2019.