Tidal restoration to reduce greenhouse gas emissions from freshwater impounded coastal wetlands

Abstract

Freshwater impounded wetlands are created by artificially restricting coastal wetlands connection to tides. The decrease in salinity and altered hydrology can significantly increase greenhouse gas (GHG) emissions, specifically methane (CH4). Restoration of freshwater impounded wetlands through tidal reintroduction can potentially reduce GHG emissions; however, studies in tropical regions are scare. This study investigates the potential for tidal restoration of impounded freshwater coastal wetlands by comparing their GHG emissions with tidally connected mangrove and saltmarshes in the Burdekin catchment in Queensland, Australia. We found that freshwater impounded wetlands had significantly higher CH4 emissions (3,633 ± 812 μg CH4 m−2 hour−1) than mangroves (27 ± 8 μg CH4 m−2 hour−1) and saltmarsh (13 ± 8 μg CH4 m−2 hour−1). Soil redox, moisture, carbon, nitrogen, and bulk density were all significantly correlated to methane emissions. Conversely, freshwater impounded wetlands had significantly lower nitrous oxide (N2O) emissions (−0.72 ± 0.18 μg N2O m−2 hour−1) than mangroves and saltmarsh (0.35 ± 0.29 and 1.32 ± 0.52 μg N2O m−2 hour−1 respectively). Nevertheless, when converting to CO2 equivalents (CO2‐eq), freshwater impounded wetlands emitted 91 ± 20 g CO2‐eq m−2 hour−1, compared to the much lower 0.8 ± 0.2 and 0.7 ± 0.2 g CO2‐eq m−2 hour−1 emission rates for mangroves and saltmarsh. In conclusion, restoration of freshwater impounded wetlands through tidal restoration is likely to result in reduced GHG emissions.