Is groundwater discharge an overlooked source of methane in restored coastal wetlands?

By 01/03/2024Current Projects
HSF 22034 | Amount: $75,706 | Project Leader: M Sadat-Noori | Project Period: 0

A project undertaken at The University of New South Wales, and supervised by Dr Mahmood Sadat-Noori.

Coastal wetlands including saltmarsh and mangroves (known as blue carbon ecosystems) can accumulate carbon and act as a natural sink for atmospheric carbon dioxide (CO2). They, therefore, have a potential to mitigate climate change. However, the CO2 captured by wetlands may be counteracted by emissions of methane (CH4) from the wetland, which is a stronger greenhouse gas (GHG).

Figure 1. UNSW researchers Associate Professor Martin S. Andersen and Dr. Mahmood Sadat-Noori sampling groundwater quality, including dissolved carbon dioxide and methane, in a restored coastal wetland.

The Australian Government has recently created a blue carbon accounting system that encourages low-lying land be converted to blue carbon ecosystems by reintroducing tides to areas that were drained for grazing and settlement. However, effective restoration for carbon storage requires a better quantitative understanding of the fate of carbon following restoration.

For example, it is currently unknown how much CH4 export will occur and whether the GHG impact of this flux is larger (or smaller) than the benefit of the overall carbon sequestration following wetland restoration. Dissolved gasses including CH4 are often orders of magnitude higher in groundwaters than surface waters, suggesting groundwater seepage or discharge within restored wetlands may be a significant, but an unaccounted source of CH4 export from coastal wetlands. 

Figure 2. Geochemical processes in anoxic (depleted of oxygen) sediments of a coastal wetland forming gas bubbles.

This project aims to investigate the groundwater export of carbon and greenhouse gases (carbon dioxide and methane) from restored coastal wetlands. The project will make a significant contribution to our understanding of the fate of carbon, following restoration by utilizing a combination of innovative field measurements and tracer experiment approaches to estimate the contribution of groundwater to CH4 emissions in coastal wetlands at varying stages of restoration. This research will significantly benefit Australia’s climate change mitigation efforts and ensure evidence supported carbon trading market via restored wetlands.