Why Canada's protected wetlands are washing away despite conservation laws

Vanishing lines in the mud

Even drawn lines on official maps cannot keep coastal mud in place. Canada holds the world's second largest area of tidal marsh, coastal wetlands flooded and drained by ocean tides. Yet rates of tidal marsh loss across the nation have quietly tripled since 1988.

By 2023, these coastal ecosystems were disappearing at about 150 hectares each year. Oddly, this retreat was not concentrated along built-up city shores. Instead, net losses appeared mostly in remote, minimally modified areas.

What the satellites uncovered

To measure changes across four decades, researchers examined 41,563 Landsat satellite images using a tide-informed tracking system. This produced the first unified yearly record of Atlantic and Pacific marshes. Previous surveys had relied on fragmented local reports that often contradicted each other.

The satellite data revealed an unexpected trend. More than a quarter of Canada's tidal marshes lie inside protected conservation areas, or PCAs. Yet marsh area within these static spatial protections, fixed zones drawn on maps, still shrank after legal designation.

Protecting a shifting coast with a fixed fence is like drawing a chalk box on the pavement to protect a puddle. As the water evaporates or shifts, the box stays put, but the puddle disappears anyway.

The hidden carbon debt

Marshes lock away massive amounts of blue carbon, which is carbon stored naturally by ocean ecosystems. While some new marshes do sprout elsewhere, a newly formed mud flat cannot suddenly replace an old, mature marsh. It lacks the deep, carbon-rich soil built up over decades, giving humans a false sense of security.

What we still don't know

Satellite photos confirmed losses along the Atlantic and Pacific coasts, but they did not track Canada's other remote shorelines. We also do not know how many years new marshes need to match the carbon storage of mature wetlands. Finally, scientists are still trying to determine which dynamic management tools can save shifting coastlines when stationary fences fail.