Salt Marshes

Intertidal zones 

Salt marshes cover an estimated 9 per cent of Canada’s coastline. Data from 2022 place the area of Canada’s salt marshes at 3,602 square kilometres. However, there are more than 1,000 kilometres of further coastline that are classified as salt marsh but not yet assigned an area value. In addition, there are significant stretches of Canada’s coastline that are not yet classified.

Mapped salt marsh extent:

Arctic coast (mainly Hudson’s Bay) . . . .  63%

Atlantic coast . . . . . . . . . . . . . . . . . . . . . . . 21%

Pacific coast . . . . . . . . . . . . . . . . . . . . . . . . 17%

Prepared with information from Salt Marshes: A Crucial Ecosystem Component (Statistics Canada) 

Formation of a Salt Marsh

Salt marshes can form in shallow inlets where tidal flooding and streams deposit sediments gradually forming the base soil of the marsh. Salt marsh plants grow and help hold the soil in place. The roots and stems slow and trap more sediment. As the plants die and become partially decomposed, they form a bed of peat. Peat is formed by the lack of oxygen and saltiness of the soil which prevents complete decay of the plant from occurring. The peat layer continues to support plant growth.

Vegetation in Salt Marshes

Plants in the marsh are regularly flooded by saltwater tides and must withstand high levels of salinity. Plants adapted to salinity excrete salt from their leaves and roots, trap fresh water in their cells, and have narrow leaves which prevent water loss.

• The plants in salt marshes play a critical role in stabilizing marsh soils to prevent erosion and facilitating establishment and growth of the marsh.
• Many salt marsh plants are perennial and die in the winter. Their root structure is strong and fibrous which holds them in place during severe storms or allows them to grow again after ice cakes have scraped off the top of the soil.
• Few animals eat the plants on the salt marsh; however, the plants contribute to the ecosystem when they die and become detritus which is a food source for many salt marsh inhabitants.

Threats to Salt Water Marshes

The salt marsh can be destroyed by the removal of plant root material which causes the tides to erode the soil and displace the sediment elsewhere. Interference with tidal action by dykes and causeways may also destroy or substantially alter salt marsh ecosystems. 

Major causes of salt marsh loss: 

• Sea-level rise 
• Climate change 
• Invasive species 
• Coastal development 
• Hurricane-fueled storm surges 

Coastal squeeze:  

As oceans creep higher and cause erosion, salt marshes are migrating inland. But when roads, dikes and buildings block their path of retreat, these ecosystems can be lost to “coastal squeeze”—caught between sea-level rise and built infrastructure. 

• Learn about rising pressures on Canada’s coasts: A tale of two coasts 

Adapted from Salt Marshes: Interactions & Ecosystems. Wetland Ecosystems, Grades 7-9. Ducks Unlimited Canada.