Saltwater marsh restoration, Canada

Compendium Volume 2 Number 2 January 2019 r.1

The Atlantic coast of Canada has started seeing damages related to sea-level rise and storm surges, including flooding, landslides, and shoreline recession. Some communities fear dikes will fail. As a result, people are looking to restoration of native coastal ecosystems as a defense against rising waters. When flooded, coastal marshes often receive large sediment loads that raise their elevation, potentially keeping pace with higher ocean levels. A recent study [Schuerch 2018] showed that making space for inland marsh migration can allow marshes even to thrive in the face of sea-level rise, which is expected to be 1 to 2 feet by 2100 on much of the Canadian Atlantic coast.

In 2010, the Canadian government funded a project in the Bay of Fundy on the Atlantic Coast to restore 16 hectares of saltmarsh land, long ago dried for agriculture, back to its original marshy state. Ducks Unlimited Canada, who led the project, initiated the restoration process by breaching a 150 year-old dike to allow the tide to flow back onto the land. The purpose of this project was to preserve agricultural land further inland from the eroding coastline and rising seas, so a new dike was built just behind the restored marsh.[5]

As noted, marshes can adapt to sea level rise by accumulating sediment. These sediment deposits also enable marshes to quickly bury (or sequester) large amounts of carbon. During the six years after the restoration process began, annual carbon accumulation at the site averaged 13.29 Mg/ha [~5.5 t/ac], mainly due to the sediment deposit that would otherwise likely have mineralized and been released as CO2.

If not deposited in marshes, the organic C in the suspended sediments in the upper Bay of Fundy is likely to be deposited in nearby mudflats. Unlike salt marshes, which tend to be stable or accreting, mudflats are highly dynamic systems subject to frequent erosion events, with scouring to depths of 20 cm or more. … Sediment and associated organic C is also more likely to be preserved in marshes compared with mudflats due to the stabilization effect of macrophyte roots and the associated erosion protection [Wollenburg 2018: 10].

In addition to quickly burying large amounts of carbon, the restored marsh showed signs of success when vegetation (cordgrass) re-established itself in 2012. By 2016, although patches of bare mud were still present, cordgrass was covering most of the marsh area.

This success story is likely to be repeated several times over since the Canadian government announced $75 million for coastal restoration as part of a $1.5 billion Coastal Protection Plan. This includes a project to restore another 75 hectares of salt marshes in the same Bay of Fundy. The coastal restoration fund prioritizes coastal watersheds, estuaries, saltgrass marshes, eel-bed marshes, and migratory corridors for salmon and other species.

Salt marsh restoration project launched:

Coastal restoration fund backgrounder: East Coast salt marshes to be restored to battle effects of climate change:

Future response of global coastal wetlands to sea-level rise:

Rapid carbon accumulation following managed realignment on the Bay of Fundy:

Schuerch, Mark,  Tom Spencer, Stijn Temmerman, et al., 2018, Future response of global coastal wetlands to sea-level rise, Nature 561,

[5] A similar project is being undertaken in Northern California: “HUMBOLDT BAY NWR: Living Coastline Project Will Restore Tidal Salt Marsh at Humboldt Bay” -

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 2 Number 2 January 2019 r.1