Event Title

Some tidal marshes on the Fraser River delta are disappearing…fast

Presentation Abstract

Large areas of intertidal marsh on the Fraser River delta, B.C. have disappeared in recent decades. The monotypic bulrush zone off Lulu Island has receded by 350-400 m between 1989 and 2011, equivalent to a mean annual loss of 16-18 m. Measurements at other locations suggest relatively high losses at Brunswick Point but lower losses at Westham Island. The loss of primary production is cause for concern given the importance of marshes to the ecology of the Fraser River estuary, both directly to herbivores and indirectly via the detrital food chain. Two potential factors contributing to the losses, especially at Lulu Island, might be: 1) rising sea levels and 2) sediment diversion. Sea levels are rising at a rate of ca. 0.6 cm y-1 and the resulting increases in inundation/exposure ratios and higher salinity levels may be causing higher than normal mortality rates at the leading edge of the marsh. In addition to the Steveston North Jetty that for decades has been diverting sediments from the main arm of the Fraser River directly into the Salish Sea, ca. 2.5 million m3 y-1 of sand are being dredged out of the system every year; hence, it is highly unlikely that the tidal platform is being “fed” with sediments at the same rate as in historical times. Finally, some other factor such as the Pacific decadal oscillation may be acting in concert with the above to enhance marsh losses. The slope of the marsh platform is very shallow so only small changes in some important vertical component can result in a large differences in the horizontal (area).

Session Title

Session S-05F: Ecosystem Restoration: Geomorphic Context, Design Considerations, and Success Stories

Conference Track

Restoration

Conference Name

Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)

Document Type

Event

Start Date

1-5-2014 10:30 AM

End Date

1-5-2014 12:00 PM

Location

Room 602-603

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

Text

Language

English

Format

application/pdf

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May 1st, 10:30 AM May 1st, 12:00 PM

Some tidal marshes on the Fraser River delta are disappearing…fast

Room 602-603

Large areas of intertidal marsh on the Fraser River delta, B.C. have disappeared in recent decades. The monotypic bulrush zone off Lulu Island has receded by 350-400 m between 1989 and 2011, equivalent to a mean annual loss of 16-18 m. Measurements at other locations suggest relatively high losses at Brunswick Point but lower losses at Westham Island. The loss of primary production is cause for concern given the importance of marshes to the ecology of the Fraser River estuary, both directly to herbivores and indirectly via the detrital food chain. Two potential factors contributing to the losses, especially at Lulu Island, might be: 1) rising sea levels and 2) sediment diversion. Sea levels are rising at a rate of ca. 0.6 cm y-1 and the resulting increases in inundation/exposure ratios and higher salinity levels may be causing higher than normal mortality rates at the leading edge of the marsh. In addition to the Steveston North Jetty that for decades has been diverting sediments from the main arm of the Fraser River directly into the Salish Sea, ca. 2.5 million m3 y-1 of sand are being dredged out of the system every year; hence, it is highly unlikely that the tidal platform is being “fed” with sediments at the same rate as in historical times. Finally, some other factor such as the Pacific decadal oscillation may be acting in concert with the above to enhance marsh losses. The slope of the marsh platform is very shallow so only small changes in some important vertical component can result in a large differences in the horizontal (area).