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 (CH 4 ). 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 CH 4 emissions (3,633 AE 812 μg CH 4 m À2 hour À1 ) than mangroves (27 AE 8 μg CH 4 m À2 hour À1 ) and saltmarsh (13 AE 8 μg CH 4 m À2 hour À1 ). Soil redox, moisture, carbon, nitrogen, and bulk density were all significantly correlated to methane emissions. Conversely, freshwater impounded wetlands had significantly lower nitrous oxide (N 2 O) emissions (À0.72 AE 0.18 μg N 2 O m À2 hour À1 ) than mangroves and saltmarsh (0.35 AE 0.29 and 1.32 AE 0.52 μg N 2 O m À2 hour À1 respectively). Nevertheless, when converting to CO 2 equivalents (CO 2-eq ), freshwater impounded wetlands emitted 91 AE 20 g CO 2-eq m À2 hour À1 , compared to the much lower 0.8 AE 0.2 and 0.7 AE 0.2 g CO 2-eq m À2 hour À1 emission rates for mangroves and saltmarsh. In conclusion, restoration of freshwater impounded wetlands through tidal restoration is likely to result in reduced GHG emissions.

Synthesis of special feature —Tailored Restoration Response: Predictions And Guidelines For Wetland Renewal

“…Study site locations (A) of the field‐based study examining greenhouse gas emissions from) (B) freshwater‐impounded wetland, and (C) tidally connected wetland comprised of saltmarsh and mangroves (reproduced from Cadier et al 2023). …”

“…(P8): The study by Cadier et al (2023) provides baseline data needed for estimating the potential of restored tidal wetlands in mitigating climate change due to the increasing concentration of greenhouse gasses. The researcher measured the fluxes of the greenhouse gasses, such as CO 2 , CH 4 , and N 2 O, at two types of wetlands: freshwater-impounded wetlands with restricted tidal regime and at the natural wetlands, including mangroves and saltmarshes, which are tidally connected.…”