Browsing by Author "Michael Burchell, Committee Member"

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    Denitrification and Molecular Detection in Riparian Buffer Soils.
    (2010-06-25) Wu, Lin; Deanna Osmond, Committee Chair; Owen Duckworth, Committee Chair; Michael Burchell, Committee Member; Alexandria Graves, Committee Member; Michael Hyman, Committee Member
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    Riparian Buffer Effectiveness at Removal of NO3-N from Groundwater in the Middle Coastal Plain of North Carolina
    (2009-12-04) Knies, Sara Victoria; Deanna Osmond, Committee Chair; Owen Duckworth, Committee Member; Michael Burchell, Committee Member
    Non-point source pollution from agriculture is one of the causes of surface water quality degradation in the Coastal Plain of North Carolina. Riparian buffers are an important best management practice for reducing NO3 concentrations in natural waters, predominantly by vegetation uptake and denitrification. However, there continues to be debate over the optimal design of buffers, specifically buffer width, and vegetation type. This project was designed to investigate the effects of vegetation type, groundwater depth, and buffer width on NO3 removal from groundwater. Four buffers have been established at a research farm in the Middle Coastal Plain of North Carolina to investigate these factors; individual buffers are comprised of five vegetation types, two buffer widths, and two well depths. The influence of vegetation type on NO3-N groundwater decreases were as follows: revegetation had a decrease of 14% (5.75 mg N/L to 4.97 mg N/L); switchgrass had a decrease of 40% (9.19 mg N/L to 5.48 mg N/L); trees had a decrease of 32% (9.18 mg N/L to 6.20 mg N/L); native vegetation had a decrease of 35% (8.36 mg N/L to 5.41 mg N/L); fescue had a decrease of 23% (7.34 mg N/L to 5.67 mg N/L); the control had a decrease of 0% (5.85 mg N/L to 5.86 mg N/L). Influence of width and depth on NO3-N decreases were as follows: deep wells in 15 m buffers had a NO3-N decrease of 77% (5.76 mg N/L to 1.34 mg N/L), deep wells in 8 m buffers had a decrease of 53% (4.55 mg N/L to 2.13 mg N/L), intermediate wells in 15 m buffers had a decrease of 47% (7.51 mg N/L to 4.00 mg N/L), and intermediate wells in 8 m buffers had a decrease of 14% (8.38 mg N/L to 7.19 mg N/L) There was a significant three-way interaction (p = 0.001) between vegetation type, buffer width, and well depth. This interaction was desegregated by depth: at the deep depth, the effect of switchgrass was significant (p=0.0120) in removal of NO3-N in both the narrow and wide buffer widths. The effect of the revegetation treatment was significant (p=0.0093) at removal of NO3-N in the narrow width. The ratio of NO3-N/Cl was evaluated to determine if dilution of groundwater was responsible for observed NO3-N concentration decreases. Dilution was slight and did not significantly account for any observed NO3-N decreases. Reduction potential (Eh) values indicated reducing conditions at the deep well depth in three of the four buffers, suggesting denitrification was most likely responsible for observed NO3-N decreases in groundwater. Inhibition of denitrification rates could be occurring in buffers due to low levels of organic C (≈3.4 ± 0.6 mg C/L). To test this hypothesis, a laboratory study was designed to complement the field study. Flow-thru soil columns were constructed to determine the effect of dissolved organic carbon (DOC) concentration on denitrification rates and products in buffer soils. Three DOC concentrations (2.0 mg DOC/L, 4.0 mg DOC/L, 8.0 mg DOC/L, and 16.0 mg DOC/L) and a control (0.0 mg DOC/L) were utilized to study this relationship between DOC and denitrification. There was no trend between DOC concentration and rate of NO3-N loss. DOC concentrations > 4.0 mg DOC/L increased up until 12.0 mg DOC/L, after which rates leveled off. There was a linear relationship between DOC concentration and rate of N2O-N production with the exception of 12.0 mg DOC/L, with the rate of N2O-N production increased with increasing concentrations of DOC.
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    Surface Shading, Soil Temperature, and Soil Moisture Effects on C Loss in a Temperate Peatland
    (2010-04-20) Taggart, Matthew J.; Michael Burchell, Committee Member; Joshua Heitman, Committee Chair; Michael Vepraskas, Committee Member
    TAGGART, MATTHEW. Surface Shading, Soil Temperature, and Soil Moisture Effects on Soil C Loss in a Temperate Peatland. (Under the direction of Joshua Heitman). Histosols are a huge reservoir for C, covering < 1% of the world‟s land surface but holding up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from peatlands is critical for proper management of these C sinks. Three experiments evaluated how formerly cultivated, warm climate Histosols undergoing restoration efforts might respond to increasing water content via water table re-establishment and decreases in soil temperatures via vegetative shading. We compared temperature and soil CO2 efflux differences from intact soil cores, collected from Juniper bay, under three levels of light reduction in a greenhouse: 0%, 70%, and 90%. Soil in full sun was consistently warmer and showed higher efflux rates than 70% and 90% shade treatments: 4.132, 3.438, and 2.054 μmol CO2 m-2 s-1, respectively. Shade treatments reached peak efflux rates at similar water potential, -2 to -4 kPa. A field experiment at Juniper bay subjected in-situ soil to full sun, 70% light reduction, and light reduction from naturally occurring herbaceous vegetation. Shade treatment effects on soil temperature and C mineralization were evident throughout the growing season. Vegetation shade effects on soil temperature were greatest in August and September when soil under vegetation was 5°-11°C cooler than unshaded soil. Soil CO2 efflux was correlated strongly with soil temperature; daily efflux rates were consistently highest from unshaded soil. Efflux across treatments showed a strong seasonal correlation to soil moisture, increasing as soil dried in response to water table decline. Soil water potential was unaffected by shade treatment, suggesting temperature effects were solely responsible for efflux differences between treatments. C mineralization response to temperature and moisture was verified with lab incubations of soil material at 25° and 37°C for three moisture ranges. Incubation showed a temperature/moisture interaction where Q10 was 2.55 under wet soil conditions (0.40 m3 m-3) and 1.64 when soil was driest (0.15-0.16 m3 m-3). All results confirm surface shading has a strong influence on soil temperatures and C mineralization rates. Thoughtful management of vegetation in mitigated peatlands may be an effective strategy for slowing soil C losses and promoting soil C sequestration.