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Time-varying drivers of tidal wetland sediment accumulation over the last century measured using biogeochemical proxies

 

Project Description: Over the last century (~1900 – present), tidal wetland sediments have recorded the histories of sea level rise and sediment input along the Oregon coast. Along-coast comparisons of sediment accretion have revealed the coupled importance of both sea level rise and fluvial sediment input in controlling average vertical high marsh growth; however, the influence of changes in these drivers over the last century is unclear. Using sediment cores collected from seven Oregon estuaries with varying relative sea level rise rates, mean annual fluvial sediment loads, and land-use histories, we analyze relative contributions of changing sediment supply and accommodation space on high marsh accretion. We couple records of sediment accumulation, estimated by excess 210Pb, with physical characteristics, including downcore dry bulk density derived from X-ray computed tomography (CT) scans, and various geochemical proxies, including organic carbon and nitrogen contents; stable carbon and nitrogen isotopes (δ13C and δ15N); and element ratios derived from X-ray fluorescence (XRF). We will compare these records to climate oscillations in the Pacific Northwest (e.g., Pacific Decadal Oscillation, El Niño-Southern Oscillation); large precipitation and flood events; and land-use changes within each watershed (e.g., timber harvest, fire history, dike construction and removal, urbanization) to determine possible controls on sediment accumulation. Preliminary results using mass accumulation rates and XRF-derived element ratios from a high marsh core collected within Alsea Bay, OR suggest a correlation between high mass accumulation rates, terrestrially-delivered sediment, and the record of timber harvest. Clarifying the relative importance of these drivers of coastal morphodynamics will ultimately contribute to the accuracy of future predictions of resiliency under climate and land-use change.

Co-PIs: Rob Wheatcroft & Laura Brophy

Funding: Oregon Sea Grant Omnibus Award

Status: in prep. 

Related Conference Abstracts:

CERF 25th Biennial Conference, Mobile, AL (November 2019)

Poster – Time-varying drivers of tidal wetland sediment accumulation over the last century measured using biogeochemical proxies