David Walters, Longwood University

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Abstract:

Wetlands have been diminishing throughout the world due to poor management practices and sea-level rise. It is important to study the wetlands' ability to rebound from this, and accumulate sediment in order to keep up with sea-level rise. Research on freshwater tidal wetlands is much less cohesive in this area. This study seeks to determine what factors affect sedimentation rates in freshwater tidal wetlands both spatially and temporally. The wetlands studied in this research project are located in Dyke Marsh Preserve in Alexandria, VA. We hypothesized that sedimentation rates would be higher at sites with lower elevation, as well as over monthly time scales in comparison to decadal time scales. To analyze these nested time scales, ceramic tiles were placed in the sediment so they could collect sediment over a monthly scale. Decadal scale rates were determined by analyzing sediment cores for ²¹⁰Pb activity, and plotting the rates using linear regression. Sites at lower elevations did prove to have higher rates than the sites in the high marsh area. However, the monthly scale rates were actually lower than the decadal scale rates in most cases. This is likely because the sampling period did not include the prime depositional period of the year during the growing season. The major conclusion of this paper is that sedimentation rates are highest at sites in low elevation, located close to their sediment source, because they receive regular delivery of sediment through tidal flooding events.