Measuring sediment accretion in early tidal marsh restoration |
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Authors: | John Y Takekawa Isa Woo Nicole D Athearn Scott Demers Rachel J Gardiner William M Perry Neil K Ganju Gregory G Shellenbarger David H Schoellhamer |
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Institution: | (1) US Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Station, 505 Azuar Drive, Vallejo, CA 94592, USA;(2) Present address: U.S. Fish and Wildlife Service, Arcata Fish and Wildlife Office, 1655 Heindon Road, Arcata, CA 95521, USA;(3) Present address: H. T. Harvey & Associates, 983 University Ave., Bldg D, Los Gatos, CA 95032, USA;(4) Present address: Centre for Wildlife Ecology, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada;(5) US Geological Survey, Western Ecological Research Center, Dixon Field Station, 6924 Tremont Road, Dixon, CA 95620, USA;(6) US Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento, CA 95819, USA;(7) Present address: US Geological Survey, Woods Hole Coastal and Marine Science Center, 384 Woods Hole Road, Woods Hole, MA 02543, USA |
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Abstract: | Sediment accretion is a critical indicator of initial progress in tidal marsh restoration. However, it is often difficult
to measure early deposition rates, because the bottom surface is usually obscured under turbid, tidally-influenced waters.
To accurately measure early sediment deposition in marshes, we developed an echosounder system consisting of a specialized
acoustic profiler, differential global positioning system unit, and laptop computer mounted on a shallow-draft boat. We conducted
a bathymetry survey at the Tubbs Setback tidal restoration site on San Pablo Bay, California, along north–south transects
at 25-m intervals. Horizontal position was recorded within 1 m each second and water depth to 1 cm every 0.05 s. Bottom elevations
were adjusted for tidal height with surveyed tide gages. We created detailed bathymetric maps (grid cell size: 12.5 m × 12.5 m)
by interpolation with inverse distance weighting. During the third year after restoration, sediment accretion averaged 57.1 ± 1.1 cm
and the estimated sediment gain was 132,900 m3. The mean difference between the elevations from the bathymetry system and the 9 sediment pins was 2.0 ± 1.0 cm. The mean
difference of the intersection points of east–west and north–south survey transects was 2.1 ± 0.2 cm, which provided a measure
of repeatability with changing water levels. Our echosounder system provided accurate and repeatable measurements of sediment
accretion of a recently restored tidal wetland, and this system proved to be a viable tool for determining sediment deposition
in marshes and assessing early restoration progress. |
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