Muddy Waters: Monitoring of Sediment Properties on Bay of Fundy Mudflats Post Causeway Modification

摘要

The Petitcodiac River causeway, situated in New Brunswick between the cities of Moncton and Riverview, was constructed in 1968, stopping the flow of sediment-laden tidal water and halting access for spawning fish. A complex process has begun to remove the causeway to restore the Petitcodiac River bringing it closer to its pre-causeway condition; the first stage was to open the causeway gates to allow free-flow of tidal water. The effects of the change in hydraulics have been hypothesized, but due to the nature of the cohesive sediment there is still some uncertainty about the fate of the flushed sediment, and the impacts it may have on downstream mudflat ecosystems in the upper Bay of Fundy. Two mudflats downstream of the Petitcodiac River causeway, Grande-Anse (NB) and Daniel's Flats (NB), were monitored, as well as two reference sites, Peck's Cove (NB) and Minudie (NS). Over the course of one year, transects were repeatedly visited and the erosion threshold and erosion rate of the mud surface was measured using the Benthic Environment Assessment Sediment Tool (BEAST), as well as several other measures of sediment and biological properties such as diatom concentration, Corophium volutator density, mud penetrability, average particle size, and moisture and organic content at several depths. A total of eight field visits were made, spanning from pre-causeway gate opening to one year post gate opening. Preliminary results suggest that there were no detectable changes in the measured mudflat properties at the potentially impacted sites, though monitoring continues.