Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.h33d0914o&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #H33D-0914
Mathematics
Logic
[0428] Biogeosciences / Carbon Cycling, [0438] Biogeosciences / Diel, Seasonal, And Annual Cycles, [0497] Biogeosciences / Wetlands
Scientific paper
The Bay of Fundy, primarily situated between the provinces of New Brunswick and Nova Scotia in Canada is known have tides among the highest in the world, where tidal amplitudes have reached 17 m, and regularly exceed 12-13m. The reason for these extremely high tides has been attributed to basin morphology and tidal resonance. Along the margin of the Bay of Fundy, salt marshes are exposed to these high tidal ranges. These salt marshes have unknown greenhouse gas (CO2, CH4 specifically) and mercury trace gas budgets. Tides here exert significant pressure on salt marsh sediments, to the point where gases are visibly seen escaping around the waters edge. This pressure-driven gas transport phenomena is markedly different than most greenhouse gas releases from other sediments, which occurs primarily by diffusion. Our study site in Kingsport, NS, Canada also provides a unique opportunity to examine pressure-driven emissions using differential pressure measurements. This work is significant in determining the role of salt marshes in the carbon and mercury emission budgets in the maritime region, and their sensitivity to environmental forcings. For our study, mercury fluxes were measured using Teflon flux chamber technique with Tekran gaseous mercury analysis, while CO2 and CH4 fluxes were measured at 60 second intervals using a new technique called continuous timeseries-forced diffusion (CT-FD). A portable meteorological station was located on site, with soil temperature, solar radiation, soil O2, and soil-atmosphere differential pressure measurements logged continuously for 10 days and 19 tidal cycles. After the field deployment, the CO2 and CH4 instrumentation was moved to soil plots in mesocosm tidal-simulation benches to conduct experiments that would allow us to separate the difference between tidal forcings and thermally-driven microbial greenhouse gas production in sediments. In the field, differential pressure varied according to tidal cycles and was surprising in that rebound to atmospheric pressure rarely occurred. Instead, pressure gradients were sustained in the sediments during high (excess pressure) and low (pressure deficit) tides. While no compelling relationship appears evident between mercury, CO2, or CH4 flux and tidal height, ratios of flux to solar radiation suggest that tidal inundation and gas release does at least facilitate mercury release from sediments during peak flux times. Low gas diffusivity sediments (very fine, impermeable, compact) are potentially very important at these sites, potentially damping transport rates across the soil surface. Gas bubbles, which can be observed at the incoming waterline, may be preferentially emitted through more permeable sediment layers and subsurface sand channels rather than the surface. The Bay of Fundy setting provides a rather unique and challenging opportunity to study extreme examples of trace gas flux and gas transport dynamics.
Beltrami Hugo
Dalziel J.
McArthur G. S.
O'Driscoll N.
Risk D. A.
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