Type of Presentation

Oral

Session Title

Challenges and opportunities related to habitat enhancement, restoration, and ecosystem productivity in the Salish Sea

Description

Large areas of tidal marsh on the Fraser River estuary, B.C. have disappeared in recent decades. The leading edge of the bulrush zone on Sturgeon Banks (Lulu Island, Richmond) receded by 350-400 m between 1989 and 2011, equivalent to a mean annual loss of 16-18 m. Measurements at other locations indicate lower but still significant losses over the same period. These losses are cause for concern given the importance of marsh primary production to the ecology of the estuary. For decades the Steveston North Jetty and dredging of the Fraser River diverted sediments away from Sturgeon Banks, and this probably altered substrate accretion rates on the banks. The jetty has also been diverting fresh water away from Sturgeon Banks and this must have altered the salinity regime there. In addition, the Pacific decadal oscillation combined with strong storm event(s) may have been important driving factors behind the marsh losses. The slope of the tidal platform is shallow, so even minor changes in substrate elevation, salinity, or some other abiotic factor could have negatively impacted marsh plant growth and survival, resulting in large (horizontal) losses of marsh area. We used high quality GPS units to map the marsh leading edge on Sturgeon Banks and at Westham Island (our control site) in 2011 and again in 2015 to determine more recent rates of change. On average, the leading edge at Westham Island advanced by 0.8 m between 2011 and 2015. In contrast, there was no change on Sturgeon Banks, suggesting that marsh recession there has slowed or has halted completely. We are evaluating air/satellite photos and LIDAR maps of the tidal platform, and measuring marsh elevation, sediment accretion, and salinity to determine which factor(s) were responsible for the marsh recession between 1989 and 2011.

Comments

Key words: bulrush, marsh, recession, Fraser River, estuary, salinity, sediments

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Why have tidal marshes in the Fraser River estuary receded?

2016SSEC

Large areas of tidal marsh on the Fraser River estuary, B.C. have disappeared in recent decades. The leading edge of the bulrush zone on Sturgeon Banks (Lulu Island, Richmond) receded by 350-400 m between 1989 and 2011, equivalent to a mean annual loss of 16-18 m. Measurements at other locations indicate lower but still significant losses over the same period. These losses are cause for concern given the importance of marsh primary production to the ecology of the estuary. For decades the Steveston North Jetty and dredging of the Fraser River diverted sediments away from Sturgeon Banks, and this probably altered substrate accretion rates on the banks. The jetty has also been diverting fresh water away from Sturgeon Banks and this must have altered the salinity regime there. In addition, the Pacific decadal oscillation combined with strong storm event(s) may have been important driving factors behind the marsh losses. The slope of the tidal platform is shallow, so even minor changes in substrate elevation, salinity, or some other abiotic factor could have negatively impacted marsh plant growth and survival, resulting in large (horizontal) losses of marsh area. We used high quality GPS units to map the marsh leading edge on Sturgeon Banks and at Westham Island (our control site) in 2011 and again in 2015 to determine more recent rates of change. On average, the leading edge at Westham Island advanced by 0.8 m between 2011 and 2015. In contrast, there was no change on Sturgeon Banks, suggesting that marsh recession there has slowed or has halted completely. We are evaluating air/satellite photos and LIDAR maps of the tidal platform, and measuring marsh elevation, sediment accretion, and salinity to determine which factor(s) were responsible for the marsh recession between 1989 and 2011.