Browsing by Author "Dr. John Fountain, Committee Member"

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Effects of interbasin groundwater transfer on water and chemical budgets in lowland tropical watersheds- La Selva, Costa Rica
(2003-11-13) Jordan, Michael Terence; Dr. David Genereux, Committee Chair; Dr. Edward Stoddard, Committee Member; Dr. John Fountain, Committee Member
Small watershed budget studies are a major research tool in hydrology, ecology, and geochemistry. Most watershed hydrology and geochemistry studies attempt to avoid sites with groundwater seepage beneath topographic divides, known as interbasin groundwater transfer (IGT), due to the difficulty in quantifying it. However, IGT is an important and relatively common hydrological process that merits study. This project identified and quantified IGT by making detailed physical and chemical measurements in two adjacent lowland rainforest watersheds in Costa Rica: the Arboleda watershed, which receives IGT, and the Taconazo watershed, which is not affected by IGT. Physical hydrologic data allowed total IGT (mm/year) to be quantified in the context of water budgets for the watersheds, and the combination of physical and chemical data together allowed the IGT to be quantitatively separated into two components (high-solute bedrock groundwater and low-solute local water). Physical measurements of change in groundwater storage using piezometers, rainfall using a tipping bucket rain gauge, and stream discharge using V-notch weirs were made for four consecutive budget years. Major ion concentrations were measured in bulk rainfall samples, streamwater samples, and groundwater samples. The physical and chemical data were used to calculate annual water and chemical (Cl, SO4, Na, K, Mg, Ca) budgets for the two study watersheds. The watersheds had equal annual rainfall and ET (averaging 4,973 mm/yr and 2,107 mm/yr, respectively), but the Arboleda also had additional large water inputs by IGT (averaging about 4,367 mm/yr from bedrock groundwater and 5,590 mm/yr from local water). IGT to the Taconazo (all local water) was negligible (328 mm/yr). IGT of bedrock groundwater was mainly responsible for the Arboleda watershed receiving 18 times more Cl, 11 times more SO4, 36 times more Na, 54 times more K, 220 times more Mg, and 71 times more Ca input than the Taconazo watershed. Total solute input to the Arboleda watershed is dominated by bedrock groundwater, which accounts for an average of 84 percent (SO4) to 99 percent (Mg) of total solute input as compared with the Taconazo watershed where total solute input is controlled by rainfall accounting for on average of 77 percent (Mg) to 91 percent (SO4) of total solute input. The Arboleda watershed was in a steady state condition (i.e., the difference between inputs and outputs was within the range of uncertainty) for each solute during the 12/00-11/01 and 12/02-11/02 budget years, as was the Taconazo for Na and Ca in both budget years and Cl in the second budget year. The Taconazo chemical budgets showed an excess of SO4 inputs over outputs (+88 mol/ha and +115 mol/ha), a net loss of K (-165 mol/ha and -162 mol/ha), and a net loss of Mg (-256 mol/ha and -330 mol/ha). Traditionally, most watershed budget studies are conducted on the assumption that the watershed is 'tight'; however, the results of this study clearly indicate that caution should be used in making such an assumption. Results also suggest a linkage between deep groundwater systems and lowland rainforest may be important to watershed science, water quantity and quality, water management, and conservation of lowland rainforest ecosystems.
The Neoproterozoic-Early Paleozoic Tectonic Evolution of the Peri-Gondwanan Margin of the Appalachian orogen: An Integrated Geochronological, Geochemical and Isotopic Study from North Carolina and Newfoundland
(2008-02-27) Pollock, Jeffrey Charles; Dr. Brent Miller, Committee Member; Dr. James Hibbard, Committee Chair; Dr. John Fountain, Committee Member; Dr. Kevin Stewart, Committee Member
LAM-ICP-MS U-Pb dates are reported from more than 1000 detrital zircons from the Neoproterozoic-early Paleozoic clastic sequences of Carolinia and Avalonia. The majority of analyzed zircon grains from Carolinia are late Neoproterozoic with minor amounts of Mesoproterozoic⁄Paleozoic and accessory Archean grains. The overall distribution of age populations of detrital zircons is consistent with derivation from the Amazonian craton and its peripheral orogenic belts on the margin of west Gondwana. The dominance of Ediacaran-early Paleozoic zircons in the Albemarle sequence suggests an underlying local protosource and deposition occurring synchronously with arc magmatism. Neoproterozoic rocks of the type area of Avalonia are dominated by Ediacaran zircons. Early Paleozoic platform units contain an abundance of grains that have ages between 1.0-1.6 Ga, with lesser Paleoproterozoic and Archean zircons. These ages are inconsistent with recycling from underlying Neoproterozoic rocks and indicate that Avalonia's provenance is a Gondwanan craton that contains Archean, Paleo-, Meso- and Neoproterozoic rocks. These data are inconsistent with a West African provenance and suggest that Avalonia originated along the margin of the Amazonian craton. The prominent change in provenance is interpreted to be related to separation of Avalonia from Gondwana during the Early Ordovician opening of the Rheic Ocean. In central North Carolina, mafic rocks of the Stony Mountain gabbro are characterized by variable LREE enrichment, prominent negative Nb anomalies and low Nb⁄Th ratios; features of tholeiitic basalts in modern island-arc, subduction related lavas. Nd isotope data indicate juvenile magmas consistent with derivation from lithospheric and asthenospheric sources during decompression melting of the mantle. The Stony Mountain gabbro can be modeled as the product of 10–15% hydrous partial melting of variable mixtures of MORB- and OIB-like mantle sources overprinted by a minor subducted-slab derived hydrous fluid component. By analogy with modern settings the Stony Mountain gabbro are comparable to MORB-like to OIB-type enriched rocks from the Lau Island and Sumisu Rift and are interpreted to have formed within an evolving early Paleozoic island arc–back arc rift-basin system. The presence of an Early Cambrian arc-back arc rift system in Carolinia is broadly coeval with arc-back arc volcanism in other peri-Gondwanan blocks of the Appalachians and may be related to the Early Paleozoic opening of the Rheic Ocean.
Quantification of Nitrate Export from a Biosolid Application Field to the Neuse River.
(2008-06-12) Harris, Jonathan Ian; Dr. Del Bohnenstiehl, Committee Member; Dr. John Fountain, Committee Member; Dr. William Showers, Committee Chair