<p> Groundwater plays an important role in runoff generation in the humid tropics, both as subsurface stormflow during rain events and sustaining baseflow during dry periods. Yet groundwater fluxes in tropical areas, particularly groundwater/surface-water (GW-SW) interactions, are not very well characterized at regional scales, thus preventing us from estimating how climate change and anthropogenic activities will affect future groundwater availability. In the case of Panama, abundance of water resources has caused its misuse and thus groundwater is exploited without previous knowledge of its distribution and availability. However, regions of the country such as the Central Pacific Region suffer from water scarcity during periods of extended drought, when streamflow reduces significantly and shallow wells get dry. Understanding groundwater dynamics, especially GW-SW interactions, is crucial for government authorities to make informed decisions in order to secure water availability for current and future generations. This thesis presents advances on the characterization of the La Villa groundwater basin, located in the Central Pacific Region of Panama. By building a groundwater conceptual and numerical model, and a surface water model, potential recharge areas and groundwater flow patterns were identified. Also, the model reveals that groundwater feeds the rivers, not only during dry periods, but throughout the year. Although this preliminary model is not yet capable of predicting the total amount of groundwater stored, and neither can be used to inform management decision, it can inform us of which features have the greatest influence on groundwater flow and it can tell us what types of data are necessary to improve the results of the simulation. The development of these models is the first step towards the development of an integrated hydrologic simulation that can be used to test different climate change and/or management scenarios.</p><p>

<p> The midcontinent of the U.S. is heavily karstified containing well developed subsurface drainage systems that are covered by beds of coarse-grained, poorly sorted fluvial sediments, resembling those found in upland surface streams. The movement of coarse sediment as bed load within karst streams has been considered negligible in the past as it was assumed that all karst is developed through dissolution rather than mechanical abrasion. The frequency and magnitude of sediment transporting events in karst streams has implications for models of fluviokarst landscape development and the stability of aquatic ecosystems. </p><p> Within Tumbling Creek Cave (TCC) in the Ozark Plateau of south-central Missouri, and Bear Cave Hollow (BCH), one of TCC&#129;es surface drainage streams, bed load entrainment and transport dynamics of coarse-grained (16-180 mm), mainly siliciclastic material, was evaluated using hydrological measurements and 670 painted tracer particles. Tracers are used in this research for the first time in a karst stream. Tracers are well suited for studying the stochastic and spatially variable nature of bed load transport because they reflect the movement of individual particles of known characteristics, and they are also inexpensive and simple to employ.</p><p> Median surficial sediment grain size in the study reaches ranged from 39 to 71 mm in TCC, and from 24 to 37 mm in BCH with bed and/or water slopes ranging from 0.006 to 0.077 in TCC and from 0.002 to 0.009 in BCH. TCC is classified as a pool-riffle channel morphology type and BCH is classified as a plane-bed channel. Preliminary data from surveys of the longitudinal (downstream) movement of tracers over a 10-month period indicate that minor amounts (0-13.2%) of coarse bed material in TCC are mobilized by relatively low flows (5-28% of bankfull) that recur somewhat frequently (less than 3.1 years). BCH transports a higher percentage of material (0-59.1%) during similar flows (2-29% of bankfull) and frequencies (less than 3.59 years). Bed load transport was observed to be in a state of partial transport for any one grain size class in TCC during the study, while the complete mobilization of tracer size classes was observed in BCH at the highest observed flow, indicating &ldquo;phase 2&rdquo; transport and the break-up of the armor layer. The differences are attributed to the wider observed range of grain sizes covering the bed in TCC compared to BCH.</p><p> The use of the Shields (1936) criteria tends to over predict the critical shear stress required for entrainment of the largest mobilized grain size of individual tracers, while the empirical equation of Bagnold (1980) performs much better. Thus, the Shields equation may be better suited as a gage for complete mobilization of a grain size class across a reach, while the Bagnold (1980) equation may be better suited for estimating entrainment of grains from patches of the bed.</p><p>

<p>The Peruvian/Bolivian Altiplano is an important hydrologic system for paleoclimate reconstruction because it is unique in its ability to record climate variability associated with the near-continental scale South American summer monsoon (SASM), which is responsible for much of the precipitation over the Amazon basin and the southern subtropics. Over long timescales moisture on the Altiplano fluctuates in intensity due to changes in precessional insolation forcing as well as teleconnections to decadal-to-millennial scale abrupt temperature shifts in the Northern hemisphere Atlantic. These long-term changes in moisture transport to the Altiplano have been observed in multiple paleoclimate records, including drill core records and paleo-lake level records, as apparent advances and retreats of large lakes in the terminal basin occupied by the Salar de Uyuni and the Salar de Coipasa. </p><p>Presented here are the results from three studies that utilize different methods to create a refined reconstruction of paleohydrology, as well as paleoclimate, on the Altiplano. A major goal of this research is a more detailed understanding of millennial scale climate variability as it relates to insolation changes and abrupt warming and cooling in the north Atlantic. The first study discusses the creation of a paleohydrologic profile to reconstruct north-south hydrological history using previously reported lake core sediment records the northern and southern basins of the Altiplano, and a new 14 m core from the Salar de Coipasa representing the last ~45 ka. The second study uses a terrestrial hydrology model to simulate lake level changes through time given changes in precipitation and temperature. The third study uses strontium isotopic measurements of carbonates and halites in a 220-m core from the Salar de Uyuni to determine how source waters to the southern basin have changed through time. </p><p>The paleohydrologic profile in the first study is constructed using records from three major basins within the Altiplano: Lake Titicaca in the north, and Salar de Coipasa and Salar de Uyuni in the south. The new continuous sediment core from Salar de Coipasa indicates a lake that has fluctuated between deep and shallow phases for the last 45 ka. Lacking sufficient calcium carbonate, we instead take advantage of the general correlation between d18O and d13C in closed basin lakes to approximate water balance using d13C from organic carbon. This reconstruction is validated with diatom paleoecological records. The isotope measurements and diatom records indicate that from 45-36 ka Coipasa was moderately deep, consistent with paleoshoreline evidence of paleolake Minchin (46-36 ka). From 36-26 ka a shallow lake <10 m deep occupied the Coipasa basin. During the LGM (26-21 ka) the lake varied from moderate to shallow and during the Holocene (< 10 ka) the lake evolved from a shallow lake to a salt flat. </p><p>The hydrologic model in the second study was run through many scenarios including increases in precipitation, decreases in temperature, and combinations of the two. During the LGM southern Altiplano lakes fluctuated between 3,660 - 3,700 masl. Model results suggest that during this period basin wide precipitation increased up to 250 mm/yr compared to modern values dependent on a temperature decrease of 5 °C relative to modern values. To create a lake at elevation 3,760 masl consistent with the highest paleolake phase (Tauca, ~16 ka) the model requires an increase of 350 mm/yr compared to modern values dependent on a 5 °C decrease in temperature (relative to modern values). An increase in temperature alone of 2 °C above modern values causes Lake Titicaca water level to decrease ~30 m, creating a closed basin lake. Results indicate that Lake Titicaca outflow is necessary to sustain large lakes in the southern basin, providing ~40-60% of total input via the Rio Desaguadero. </p><p>Analysis of a 220 m core from the Salar de Uyuni suggests periods of alternating wet and dry phases (indicated by alternating mud and salt units respectively) at the salar. Evident in the record is a transition at ~60 ka from sediments consistent with dry conditions ("playa lakes") to sediments consistent with deep lakes ("great lakes"). It has been shown that rivers and lakes in the Bolivian and Peruvian Altiplano display a range of Sr isotopic ratios that can be connected to the lithologies of specific drainage basins. Measurements of Sr ratios of the alternating halites and carbonate sediments are used to determine when paleolakes in the Salar were supplied by flow from the northern and central basins of the Altiplano, and when they were more a product of increased precipitation in the Uyuni basin. The results from Sr isotope analysis suggest that prior to ~60 ka the primary source of Sr to the Uyuni was local runoff and direct precipitation. Following the state change from the "play lakes" phase to the "great lakes" phase Sr isotope measurements suggest a significant influence from more radiogenic waters originating in the central and northern Altiplano basins. The reason for this state change is attributed to a combination of a general increase in precipitation following the onset of the MIS-4 (~70 ka) glacial period and downcutting of the Laka Jahuira hydrologic divide, which connects Lago Poopó in the central basin to the Salar de Coipasa. </p><p>This approach of reconstructing hydrology using the combination of multiple paleolake records, hydrological modeling, and isotopic tracers allows for a better understanding of how precipitation and temperature changes affect the advance and retreat of large lakes on the Altiplano, and ultimately a more accurate understanding of how decadal-to-millennial forcings influence the climate of the subtropical Andes.</p> / Dissertation

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains ix, 149 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 60-63).

<p> The transport of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) from land to coastal environments strongly influences coastal ecosystems. The presence of first flush phenomena due to rainwater runoff traveling from land into waterways can greatly affect carbon fluxes to coastal areas. This research utilizes sensors, autosamplers, and standard watershed sampling in order to assess for the presence of first flush and its significance. </p><p> A rainfall simulator was built in order to collect runoff on two land use types. Time series data suggest that first flush of dissolved organic carbon was present for all rainfall intensities simulated on an impervious surface. At this location, approximately 40% to 51% of DOC flux occurred within the first 20% of runoff. At the permeable sampling location, first flush was observed in surface runoff collected during 12.7 and 25.4 mm hr^-1 simulated storms, with 31% and 26% of DOC flux occurring within the first 22% of runoff. </p><p> Seven storm events at two locations in the Neponset River Watershed, Massachusetts, USA were monitored to study the impact of storm events on DOC export from an urban watershed. Real-time CDOM fluorescence sensor measurements were better able to capture the variability present in riverine DOC and CDOM concentrations due to runoff influxes. Using modeled flow data, estimates of total DOC export fluxes during storms were compared to estimated total annual export. Based on these calculations, the seven sampled storm events account for 7 to 10 percent of the calculated yearly flux during 4 to 5 percent of the year. Additional work is needed to collect consistent year round data using sensors at these locations. </p><p> DOC was sampled throughout the Neponset River Watershed monthly for seven years. Increased concentrations were observed following storm events and snowmelt, and were an average of 28% greater than concentrations observed during dry periods. Based on daily sampling data in September 2011, monthly fluxes may be underestimated by 38% or overestimated by 35%. More frequent sampling allows for better certainty in estimations of monthly and yearly fluxes from the watershed, but must be balanced with logistical and cost constraints.</p>

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No description available.

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 135-142).

Thesis (M.S.)--Ohio University, June, 1987. / Title from PDF t.p.