Abstract
Queensborough mudflat (QM) is 16 ha of shoreline located at the convergence of the north and south arm of the Fraser River, on the northeastern tip of Lulu Island in New Westminster, BC. The QM is a candidate marsh creation site selected by Ducks Unlimited Canada as part of the Process[1]Based Marsh Establishment Pilot Project (ProMEPP). This project will use process-based marsh restoration methods to establish endangered Lyngbye's sedge estuarine marsh (LSEM) at the existing low elevation mudflat. Historically, the region surrounding the QM was a forested flood plain and cranberry bog, seasonally used by the Stó:lō and Kwantlen First Nations prior to colonial settlement. Since then, dyking has facilitated agriculture, industrial activity and residential development. While the hard armouring bordering the site protects the urban landscape from flooding, it has negative effects on sedimentation patterns and shoreline health as seen across many parts of the Fraser River. The QM is impacted by several compounding stressors including urbanization, industrialized river channel activity, invasive species encroachment and sea level rise. Sediment erosion from hard armoring and boat wakes prevents sediment accretion. In addition to the mudflat's low elevation, logging debris and Canada goose herbivory suppress emergent vegetation growth. The present conditions of the QM provide little support for an estuarine marsh habitat to develop naturally and withstand the effects of climate change. Therefore, this project is designed to respond to coastal squeeze by accelerating sediment accretion for marsh development to outpace sea-level rise. Our restoration goal of establishing LSEM through process-based methods will be conducted through an experimental design. This will involve baseline biophysical surveys, installing test sediment accretion structures, protection from geese, and planting. Eight treatment plots will be established on site. With two replicates of each plot which will include three sedimentation structure designs: (1) sandbag wall, (2) triangle fence, and (3) live stake fencing, and a control. These will be installed 5 m from the rip-rap boundary, and a single replicate of each will receive goose exclosure fencing to test grazing pressure. When a desired coverage of emergent vegetation is reached, each treatment plot will be planted with Lyngbye's sedge (Carex lyngbyei) and evaluated for marsh planting success. Long-term monitoring will track sediment changes, goose herbivory and vegetation establishment in all established plots. The experimental design of this project will help identify how these factors influence marsh development and determine the most effective strategies for accelerating sediment accretion and ensuring planting success. Monthly monitoring will also facilitate structure maintenance as needed at the QM. Interpretive signage will be installed along the seawall path, and volunteer opportunities will be offered to learn about process-based marsh restoration. All plots will be statistically analyzed to determine any significant effects for sediment accretion rates and vegetation growth within each structure type. Site activity and grazing pressure will also be summarized over the course of our study. Findings from this project will inform future process-based designs and best practices for restoring Lyngbye's sedge estuarine marsh at the QM and comparable sites within the Fraser River Estuary. By doing so, the project aims to improve long-term restoration success, sustain carbon sequestration and support intertidal primary production, and habitat value over time.