DUC Study: Factors Influencing the Persistence of Created Tidal Marshes in the Fraser River Estuary

Over the past 40 years, more than 100 tidal marsh restoration projects have been constructed in the Fraser River Estuary to mitigate the loss of habitats from human activities and to maintain the ecological integrity of the area. More projects continue to be proposed. However, reports have shown that the success of these restoration projects varies.

An in-depth report by DUC—the most comprehensive analysis of tidal marsh creation projects in the Fraser River Estuary to date—sheds light on factors that lead to some projects being more successful than others. Among the findings detailed in the report, entitled Factors Influencing the Persistence of Created Tidal Marshes in the Fraser River Estuary:

• Marsh recession was observed in 40 of the 78 surveyed created marshes (51 per cent), resulting in an estimated loss of 23,553 square metres, or 9.3 per cent of the total created marsh area sampled.
• There is no one factor that can determine the loss of marsh recession. Site design, boat wake, and the impact of grazing by Canada geese feeding are emphasized; however, altered sediment processes, sea-level rise, shading, and monitoring effectiveness are all possible causes, and warrant further investigation.
• While protective infrastructure, specifically debris fencing and offshore structures such as marina docks and log storage booms possibly mitigate recession, sites built in the North Arm of the Fraser River Estuary averaged 12 per cent more recession, and recession increased at an average rate of 1 per cent per kilometre upstream among sites.
• The dominance of native vegetation declined at an average rate of one per cent per kilometre upriver in created marshes. This reflects an eastward increase in the dominance of non-native plants, including invasive species such as yellow flag iris, purple loosestrife, and reed canary grass.
• Contrary to this trend, invasive cattail dominates several outer estuary sites. When present, cattails often outcompete native vegetation.

The Factors Influencing the Persistence of Created Tidal Marshes in the Fraser River Estuary report is the start of a longer investment by DUC over the next two years to restore tidal marshes throughout the estuary to support carbon sequestration and restore salmon habitat. DUC will use the findings from the report to inform restoration works and identify some unsuccessful compensation sites to restore.

The study was funded by the B.C. Wildlife Federation Wetlands Workforce project and supported through the provincial Healthy Watersheds Initiative delivered by the Real Estate Foundation of B.C. and Watersheds B.C. with the financial support from the Province of B.C. as part of its $10 billion COVID-19 response.

Ducks Unlimited Canada releases comprehensive report to guide future restoration efforts in the Fraser River Estuary