HR: 0800h
AN: H51E-0810    [Abstracts]
TI: Constraining the Timescales of Sediment Sequestration Associated With Large Woody Debris Using Cosmogenic Beryllium-7
AU: * Fisher, G B
EM: gbf@umail.ucsb.edu
AF: Dartmouth College, Department of Earth Sciences 6105 Fairchild Hall, Hanover, NH 03755,
AU: Magilligan, F J
EM: fjm@dartmouth.edu
AF: Dartmouth College, Department of Geography 6017 Fairchild Hall, Hanover, NH 03755,
AU: Kaste, J M
EM: kaste@dartmouth.edu
AF: Dartmouth College, Department of Earth Sciences 6105 Fairchild Hall, Hanover, NH 03755,
AU: Nislow, K H
EM: nislow@dartmouth.edu
AF: U.S. Department of Agriculture, U.S. Forest Service, Northern Research Station, University of Massachusetts, Amherst, MA 01003,
AB: The overabundance of fine sediment (<2 mm) in fluvial environments engenders various detrimental impacts on aquatic ecosystems, such as embedded spawning gravels. Conversely, large woody debris (LWD) has been shown to provide an array of positive geomorphic and ecogeomorphic functions at multiple scales in the fluvial environment. In this study along a 9 km stretch of the Ducktrap River of coastal Maine we use a novel application of cosmogenic 7Be to calculate the storage times of fine-grain sediment sequestration by in-channel obstructions (LWD and boulders). Using a constant initial activity (CIA) sediment storage aging model, the majority of in-channel sediment bars associated with channel obstructions in the transport dominated reach were found to be young (< 106 days), while those in the transport limited reach were found to be older (> 200 days) as evidenced by the lack of detectable 7Be activity in the majority of samples. Emergent channel margin bar sediment storage times indicate longer-term storage on the order of one year to several years, as evidenced by stratigraphic and geochemical data. These findings underscore the importance of wood frequency and size in offsetting relatively short residence times of sediment sequestration and have implications for assessing the benefits of wood in channel restoration efforts and the potential impacts of wood removal to sediment regimes in disturbed landscapes.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
SC: Hydrology [H]
MN: 2007 Fall Meeting