Northern permafrost regions contain vast stores of organic carbon (OC) and rapidly rising temperatures make these frozen soil OC stores increasingly vulnerable to thaw and mobilization. While considerable attention has been given to carbon export from large Arctic river systems and lowland areas, significant gaps remain in characterizing OC quality and export in headwater catchments and in alpine regions. Northern wetlands and lakes have been highlighted as critical areas for OC storage and processing, and while ubiquitous in alpine regions, there have been few studies to examine their integrated role in DOM dynamics at the watershed scale. This study examines controls on DOM quality and concentration in Wolf Creek Research Basin (WCRB), Yukon, over four years using repeat spatial sampling. Optical indices were used to assess changes in DOM quality from different landscape types including permafrost influenced alpine headwater streams, lake and wetland complexes, and the catchment outlet in a low elevation boreal forest. Results indicate that DOM export in WCRB is transport-limited with greater exports during years with greater snowpack and higher spring discharge. Principal component analysis revealed that the predominant driver of DOM quality was seasonality, but landscape type was also an important control during the open water season. High SUVA254 /HIX in headwater streams indicated primarily humic, terrestrially derived DOM while high BIX and comparatively lower SUVA254 /HIX in a mid-catchment lake indicated autotrophic production of new DOM. DOM quality at the catchment outlet reflected a mixture of upstream sources and increased influence of groundwater. The results of this study highlight the importance of evaluating DOM quality in all seasons and provide insight into the diverse nature of DOM at a watershed scale. These characterizations help to elucidate potential DOM response in a rapidly changing and understudied environment. / Thesis / Master of Science (MSc)

No description available.

No description available.

Subsurface fluids may travel along paths having a minimum permeabilility greater than the effective permeability of the rock. This may have an important impact on contaminant migration. A stochastic approach related to percolation theory is advanced to address the question of what is the probability that a high permeability path extends across a given volume of the subsurface. The answer is sought numerically through subdividing the volume of interest into a three-dimensional grid of elements and assigning a random permeability to each element. Four permeability processes are considered: 1) Stationary with independence between grid elements; 2) Stationary and autocorrelated; 3) Nonstationary due to conditioning on measured values; and 4) Random rock volume included in grid. The results utilizing data from fractured granites suggest that in large grids, at least one path having a minimum permeability in excess of the "effective" rock permeability will cross the grid. Inclusion of autocorrelation causes an increase in the expected value of the minimum permeability of such a path. It also results in a significantly increased variance of this permeability. Conditioning on field permeabilities reduces the variance of this value over that obtained by unconditional, correlated simulation, but still produces a variance greater than that obtained when independence was assumed. When conditioning is performed, the mean of the minimum permeabilities along these paths is dependent on the principal axis of the path. Finally, including a random rock volume by allowing the length of the grid to be random increases the variance of the minimum permeability.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1983. / Includes bibliographical references (leaves 98-101).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

<p>Disturbed peatlands may undergo a dramatic alteration in ecohydrological conditions, potentially limiting the recolonisation of peat-forming species like <em>Sphagnum</em>. A poor fen was experimentally drained in 1984, both the drained and undrained portion of the peatland burned in 2001, providing an unique opportunity to examine the ecohydrological response to ‘double disturbance’.</p> <p>The undrained site<em> </em>was characterized by a healthy recovery of<em> </em>peatland microform <em>Sphagnum</em> species, low soil water pressure (Ψ), high volumetric soil moisture (θ) content and high and stable water table position. However, the drained site showed no recolonization of <em>Sphagnum</em> with <em>Brome</em> grasses representing the dominant surface cover nine years post-wildfire.</p> <p>While the study period was generally wet and as such Ψ did not exceed thresholds limiting <em>Sphagnum</em> growth (≥ -100 mb) during the study period, a series of ecohydrological influences were found to be operating, limiting <em>Sphagnum</em> recolonisation at the drained site. The physical peat structure following drainage and wildfire has been considerably altered, changing the moisture retention and water storage properties of the peat, largely through substantive increases in bulk density (ρ_b). Moreover, specific yield (<em>Sy</em>) has also decreased the drained peat having become more humified, increasing unstable water table fluctuations. As such, this has lowered the resilience to drought. Only smaller decreases in θ are required to reach Ψ ≥ -100 mb at the drained and impose ecophysiological stress on <em>Sphagnum</em> growth. Dense canopy cover (<em>Betula</em> and <em>Sali</em>x) has limited available radiation at the surface to recolonisation, shading out the surface, further limiting <em>Sphagnum</em> recolonisation.</p> / Master of Science (MSc)

Thesis (M.S.)--Mississippi State University. Department of Geosciences. / Title from title screen. Includes bibliographical references.

As the population on the island of Maui drastically increases, water resource demands continue to rise. In order to match water demands and to manage water resources, it is important to understand streamflow and drainage basin interactions. If relationships between a drainage basin’s hydrologic and geomorphologic characteristics can be quantified, then streamflow conditions of ungaged streams can potentially be estimated. The baseflow recession constant is an important variable to analyze for water management, yet until this study, recession constants were not calculated for the island of Maui, or Hawai‘i as a whole. Recession constants of currently gaged streams on Maui correlated to the permeability and flow conditions of the watersheds. Streams with recession constants >0.95 were generally placed in areas of the island with dike-impounded groundwater and streams with recession constants

A chemical-isotopic equilibrium model was developed for adjustment of radiocarbon ages of groundwater from the arid Tucson basin for dilution of the initial groundwater C-14 activity by the solution of soil calcite having a C-14 of 25 ± 19% modern. Input to the model consisted of the laboratory chemical analyses for Ca⁺⁺, Mg⁺⁺, Na⁺, H₄SiO₄, SO₄⁼, HCO₃⁻, CO₃⁼, NO₃⁻, and pH, and δ C-13 for the total dissolved carbon in the groundwater. Output consisted of the equilibrium chemical composition of the groundwater, the ratio of soil CO₂ derived to total dissolved carbon, Q, and δ C-13 of total dissolved carbon, H₂CO₃, HCO₃⁻, and CO₃⁼, and δ C-13 for the soil CO₂ and calcite that initially dissolved in the surface water as it equilibrated with soil minerals. Radiocarbon age of the groundwater is computed from the equation T = 8270 ln [(Q + (1-Q) A(CaCO₃)/Am] where T is the age in years before A.D. 1950, A(CaCO₃) is the soil calcite activity and Am is the measured activity for the dissolved carbonate in the groundwater, both with respect to modern wood. The validity of the model was tested by comparing the predicted values for δ C-13 (CO₂), δ C-13 (CaCO₃) with measured values for samples from the Tucson basin. δ C-13 (CO 2) calculated = (-12.9 ± 1.9) per mil PDB. δ C-13 (CO2) measured = (-15.1 ± 2.8) per mil PDB. δ C-13 (CaCO3) calculated = (-3.9 ± 1.7) per nil PDB. δ C-13 (CaCO3) measured = (-3.6 ± 1.7) per mil PDB. On the basis of these results, the model adequately describes the natural system and may prove useful in future radiocarbon dating work in desert regions.