DYNAMICS OF METABOLIC GASES IN GROUNDWATER AND THE VADOSE ZONE OF SOILS ON DELMARVA
| dc.contributor.advisor | Fisher, Thomas R | en_US |
| dc.contributor.author | Fox, Rebecca Jane | en_US |
| dc.contributor.department | Marine-Estuarine-Environmental Sciences | en_US |
| dc.contributor.publisher | Digital Repository at the University of Maryland | en_US |
| dc.contributor.publisher | University of Maryland (College Park, Md.) | en_US |
| dc.date.accessioned | 2012-02-17T06:52:00Z | |
| dc.date.available | 2012-02-17T06:52:00Z | |
| dc.date.issued | 2011 | en_US |
| dc.description.abstract | Denitrification removes nitrogen from watersheds under reducing conditions, but N<sub>2</sub>O and CH<sub>4</sub>, both greenhouse gases, can also be produced. The overarching hypothesis of my thesis was that hydric environments accumulate N<sub>2</sub>O and CH<sub>4</sub> in groundwater and the vadose zone. To test the hypothesis, groundwater samples were taken monthly during 2007-2009 at 64 piezometers in 10 wetlands for analysis of excess N<sub>2</sub>, N<sub>2</sub>O, CH<sub>4</sub>, and CO<sub>2</sub>. Vadose zone gas and groundwater samples were taken during 2008-2010 at two riparian buffers and a hydrologically restored wetland. The hydrology of the 10 locations was complex. A hydrologic connection across a transect was determined at one location where NO<sub>3</sub><super>-</super> significantly decreased, excess N<sub>2</sub> significantly increased, and moderate concentrations of N<sub>2</sub>O and CH<sub>4</sub> accumulated. Within these 10 locations, three N<sub>2</sub>O and four CH<sub>4</sub> hot spots were identified, and hot moments accounted for a large percentage of total accumulated N<sub>2</sub>O and CH<sub>4</sub>. I found evidence of CH<sub>4</sub> ebullition, the production of CH<sub>4</sub> bubbles in the vadose zone that strip other dissolved gases. The locations that accumulated the most dissolved CH<sub>4</sub> and N<sub>2</sub>O were natural wetlands and riparian areas, respectively. I measured both positive and negative excess N<sub>2</sub> concentrations in the vadose zone. Flux estimates ranged from -600 to 880 kg N ha<super>-1</super> yr<super>-1</super>, which brackets missing N estimates at the watershed scale. These concentrations were calculated using N<sub>2</sub>/Ar, and both gases are affected by physical processes. These calculated excess N<sub>2</sub> profiles could have been produced through either biological and/or physical mechanisms, and these processes currently cannot be distinguished. Less than 1% of the missing N on the transect scale, measured as the difference in N concentration between two piezometers, was accounted for by calculated diffusional fluxes from groundwater to the vadose zone. The primary mechanism transporting gases from the vadose zone to the atmosphere was diffusion, but convection transported 20% of the calculated median CO<sub>2</sub> yearly flux. Increased production of N<sub>2</sub>O and CO<sub>2</sub> was observed in the vadose zone after rainfall events. Overall, large concentrations of N<sub>2</sub>O, CH<sub>4</sub>, CO<sub>2</sub>, and excess N<sub>2</sub> accumulated in the groundwater and vadose zone of these locations, supporting the overarching hypothesis. | en_US |
| dc.identifier.uri | http://hdl.handle.net/1903/12291 | |
| dc.subject.pqcontrolled | Biogeochemistry | en_US |
| dc.subject.pqcontrolled | Environmental science | en_US |
| dc.subject.pquncontrolled | Carbon Dioxide | en_US |
| dc.subject.pquncontrolled | Denitrification | en_US |
| dc.subject.pquncontrolled | Greenhouse Gases | en_US |
| dc.subject.pquncontrolled | Methane | en_US |
| dc.subject.pquncontrolled | Nitrous Oxide | en_US |
| dc.subject.pquncontrolled | Wetlands | en_US |
| dc.title | DYNAMICS OF METABOLIC GASES IN GROUNDWATER AND THE VADOSE ZONE OF SOILS ON DELMARVA | en_US |
| dc.type | Dissertation | en_US |
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