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<p> Reports an investigation of the effects of chemical and physical weathering on submerged karst surfaces that pairs laboratory studies with computer modeling studies. The first study attempts to quantify the production of carbonate fines; soluble sediments produced by the incomplete dissolution of karst minerals during chemical weathering. Results show carbonate fine production in relation to dissolutional action; <i>Chalk:</i> 42.8%; <i>Coquina:</i> 2.6%; <i>Dolomite:</i> 3.1%; <i>Gray Limestone:</i> 4.8%; <i> Ocala Limestone:</i> 3.1%; <i>Shell Limestone:</i> 6.1%; <i> Travertine:</i> 8.6%. Due to the use of hydrochloric acid as opposed to carbonic acid these results may not be fully valid for application to natural speleogenic processes. The Limestone Weathering Model, a numerical-computer model, was developed using these experimental findings as minimal values compared with published rates. Reported as the actual volume of rock mass lost to both dissolution and to carbonate fine production, the rates for carbonate fine production ranged from 5.8% to 10.9% (year 1-5.8%, year 2-8.5%, year 3-9.7%, year 4-10.3%, year 5-10.9%), with a mean value for carbonate fine production of 9%, but a continuing rate after five years approaching 11%. The second study uses metrological laser scanning to measure the erosive loss due hydraulic shearing force and corrasion on submerged limestone surfaces. The rates for material removed using increasing velocity values (0.3m/s, 0.5m/s, 1.0m/s, 1.5m/s, 2.0 m/s, 2.5m/s) during flow durations of less than 6 minutes duration were : 1) Hydraulic shearing force- 0.3&micro;m/s, 0.5&micro;m/s, 0.4-1.7&micro;m/s, 2.5 &micro;m/s, 5.5 &micro;m/s, 2) Corrasion- 0.3 &micro;m/s, 0.7 &micro;m/s, 1.5 &micro;m/s, 1.5-1.8 &micro;m/s, 8.9 &micro;m/s, 8.1 &micro;m/s. The study model was modified to return these rates for hydraulic shearing force limited by the depth of the chemical corrosion of the surface. The model returns % rock volume lost to hydraulic shearing force compared to dissolutional rate (1mm/y) for 3 flow velocities (0.03m/s&lt;, 1.0m/s&lt;, 2.5m/s&lt;) on 4 timing schedules: Annual- 7.8,14.3,19.6, Semiannual- 21.1,21.1,69.7, Quarterly- 32.8,43.6, 70.9, Monthly- 80.0, 109.3, 200.3. Model demonstrates significant effect (7.8% to 200% over dissolutional rate) on speleogenic rates from even infrequent, moderate changes in flow velocities due to storm events. Investigation&rsquo;s results support the significance of chemical weathering by disaggregation and physical weathering by hydraulic shearing force as major factors in the processes of karst speleogenesis.</p>

<p> Accurate projections of future sea level rise require detailed modeling of the relevant processes affecting glacier and ice sheet dynamics. Although sophisticated high-resolution ice sheet models have been developed in recent years, some processes are still not well understood. Through a combination of field experiments, numerical modeling, and theoretical analyses, this research explores several processes affecting dynamics of the Greenland ice sheet, particularly in a changing climate as melt increases further inland: a) A novel, low-cost in-situ method of inferring firn permeability is presented, which is especially useful in regions of the ice sheet experiencing increased melt and refrozen solid ice layers in the firn. b) Thermo-mechanically coupled flow line modeling of the Greenland ice sheet interior reveals insights about the distribution of temperate ice and sensitivity to different modeling parameters. c) A subglacial hydrology model is introduced (SHAKTI: Subglacial Hydrology and Kinetic, Transient Interactions) that allows for the coexistence of laminar and turbulent flow regimes and flexible geometry configurations that include both sheetlike and channelized drainage systems, while including melt from viscous dissipation. Application of the SHAKTI model to marine-terminating Store Glacier in west Greenland suggests a channelized system develops near the terminus with high meltwater input and collapses to a sheetlike system with low input, with some residual channel structure extending inland from the front. d) Heat transfer coefficients are obtained through modeling of internal viscous and turbulent dissipation (appropriate for subglacial and englacial hydrology) compared to the case of heated walls (the classical experimental case upon which most heat transfer coefficients are based). A difference of about a factor of two is found between the heat transfer coefficients for heated walls and the internal dissipation case.</p><p>

This thesis defines a physically based model describing the kinetic energy of throughfall from any vegetation canopy. Empirical measurements of the drop-size distribution of rainfall and sub-canopy throughfall were used to develop the model which was tested in the context of splash erosion. Comparisons are made for individual storms between rain falling in the open and through a canopy. Three canopies were used, one oak and two tropical rain forest differing in height. Through each storm raindrop sizes were frequently measured using the paper-staining technique. Kinetic energy/mm/m2 was calculated from the drop sizes, their velocities and amount of rain or throughfall. The velocities were assumed to depend on the height of fall. In the rain forest sites splash cups surrounded by uniform areas of sand were used to measure the material splashed. The oak canopy data was used to examine the validity of a working hypothesis relating qualitatively the size of throughfall drops to the saturation of the canopy. It was confirmed that the canopy changed the drop-size distribution of the rain and consequently changed the kinetic energy/mm/m2. The sequences of drop-size distribution change proposed by the hypothesis were related to the cumulated canopy storage. The tropical rain forest results confirmed these findings and extended them. Although rainfall kinetic energy/mm/m2 may be predicted from rainfall intensity, throughfall kinetic energy/mm/m2 was independent of intensity and the frequency distribution of the energy of throughfall samples was bimodal, with a high energy group which was commonly higher than that of the rainfall. The probability of a thoroughfall sample being in either energy group depended on the cumulated canopy storage or the percentage storm duration elapsed. The relative magnitude of rainfall and throughfall total kinetic energy depended on the saturation of the canopy and on the canopy height and for some storms the throughfall energy was higher than the rainfall. Soil splash increased with increasing kinetic energy. The model predicting throughfall energy requires inputs of canopy height, rainfall intensity and the frequency distribution of energy of discrete samples of throughfall. The model is most sensitive to canopy height.

The purpose of the study was to undertake a quantitative assessment of the proportions of river sediment derived from the various rock types within the catchment.b) to determine the rate of removal of sediment from the catchment. The former purpose involved the determination of the mineralogy of source rocks, soils, alluvium and sediment by X.R.D. and heavy mineral analysis. The data indicate that each source rock has a characteristic mineralogy, but that this is not sufficiently variable for a quantitative assessment of proportions of sediment from each source rock to be determined. Certain conclusions, however, are drawn from the data, including a tentative formation, by sorting on a basis of specific gravity, of heavy mineral assemblage zones in channel sediment, that are probably indicative of areas of aggradation and degradation. To determine the rate of sediment loss from the catchment, the dissolved load, the suspended load and thebed load were investigated. The dissolved load includes Ca2+ and HCO3 formed from the solution of Chalk, anderosion rates of CaCO3 have been estimated at approximately 39.8 tonnes/km. 2/year. Suspended sediment concentrations were determined for samples collected from a variety of stations during a variety of flow conditions. An estimated 2,182 tonnes of suspended sediment was lost from the catchment in 1972 , of which 1,720 tonnes was non-organic. The data indicate that the frequency and duration of storm events is a major controlling factor for suspended sediment concentration. Pates of bed load movement were determined using fluorescent sand tracers for two stretches of the Pother and a relationship between grain size, river discharge and sediment loss is presented for each. Modifications of techniques and methodology for use of fluorescent tracers are suggested and the data indicate the probability of aggradation of sizes of medium sand and larger between the two experimental stretches.

<p> Altered waters impacted by serpentinization of Coast Range Ophiolite (CRO) ultramafic units have been reacting with trapped Cretaceous seawaters, meteoric waters, and other surface derived waters since tectonic emplacement of this ophiolite. In 2011, groundwater monitoring wells of various depths were established near Lower Lake, CA, USA in the McLaughlin Natural Reserve, administered by the University of California-Davis, in order to understand ongoing low temperature alterations and biogeochemical interactions taking place. Wells were installed at two sites in the Reserve. There are three Quarry Valley area wells (QV1-1 [23m depth], QV1-2 [14.9m], QV1-3 [34.6m]) and five Core Shed area wells (CSW1-1 [19.5m], CSW1-2 [19.2m], CSW1-3 [23.2m], CSW1-4 [8.8m], CSW1-5 [27.4m]). Water samples were collected from all installed wells, as well as from an older well drilled near the historic core shed (Old Core Shed Well, or OCSW [82m]), and an upper (TC1) and lower (TC2) site sampling a nearby groundwater-fed alkaline seep, at Temptation Creek. Key environmental parameters (temperature, pH, conductivity, oxidation-reduction potential, and dissolved oxygen) were collected in the field using YSI-556 multiprobe meter, and total concentrations for major cations (Ca⁺², Na⁺, Mg⁺², K⁺) were analyzed using Thermo Scientific iCAP 7400 Inductively Coupled Plasma-Atomic Emission Spectrometry, and anions (F^&ndash;, Cl^&ndash;, SO₄^&ndash;2, NO₃^&ndash;) on Dionex Modular DX 500 Ion Chromatography. </p><p> Principal component analysis was conducted to determine key factors and processes controlling water chemistries at CRO. Geochemist&rsquo;s Workbench software was used to model the low temperature alteration of a serpentinization-influenced model water volume passing through serpentinite over a period of 100 million years. Modeling provided insight into the changing pH, Eh, evolving water chemistries, stepwise mineral assemblages, appearance of marker minerals at geochemical transitions in the system, and supported evidence of pervasive impacts of low temperature, oxidative weathering of serpentinites. This work supports the case of incremental dilution and transformation of a deeply sourced Ca²⁺-OH^&ndash; Type II water in this environment, and constrains reaction status of present day CRO waters and those of similar sites, in terms of the progress of serpentinite weathering reactions. Further, the study informs our understanding of serpentinization-related geological environments present on other celestial bodies (<i>e.g.</i>, Mars, Europa, Enceladus) in our Solar System and beyond.</p><p>

<p> Streams and rivers are an integral component of the freshwater carbon cycle as they provide the lateral transport of carbon from terrestrial environments to the ocean. Urbanization is one of the fastest growing land uses and it has major impacts on streams and rivers. This study examined twenty-eight watersheds varying in land uses from pre-restoration forested to urban in Charlotte, North Carolina. Their impervious cover ranged from 0.5&ndash;55%. The objective of this study was to examine alterations to freshwater carbon processes among watersheds of various land uses in multiple streams in Mecklenburg County, Charlotte, NC. </p><p> Surface water was collected at each site in addition to discharge measurements. Water quality parameters were analyzed including: DOC concentration, Specific UV Absorbance of DOC, DIC concentration, alkalinity concentration, &delta;¹³C-DIC, major cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺), and anions (F^&ndash;, Cl^&ndash;, PO₄^3&ndash;, NO^3&ndash;and SO₄^2&ndash;). DOC concentration ranged from 1.1&ndash;18 mg/L and SUVA values ranged from 0.2&ndash;18 L/mg*m. Alkalinity concentrations ranged from 0.1&ndash;3.8 meq/L and DIC concentrations ranged from 0.2&ndash;3.8 mM. &delta;¹³C-DIC values ranged from &ndash;18.0&permil; to &ndash;7.4&permil;. Overall, DOC concentrations and SUVA values had weak negative relationships with percent impervious cover. DIC concentrations, alkalinity concentrations, &delta;¹³C-DIC values, all cations, and F^&ndash;, Cl^&ndash; , and SO₄^2&ndash; had strong positive relationships with percent impervious cover. PO₄^3&ndash; and NO^3&ndash; had weak correlations with percent impervious cover. The increase in DIC, alkalinity, &delta;¹³C-DIC, and cations with high impervious cover was largely due to the increased chemical weathering of concrete materials in urban areas.</p><p>

<p> Human interventions in the hydrologic cycle have intensified to the extent that water resources cannot be managed and understood in isolation from anthropogenic influences. New approaches are needed to understand the effects of humans on hydrology, especially in regions of the world with limited hydrologic records. This dissertation focuses on a case study of the Arkavathy watershed adjacent to Bangalore, India, which has been transformed by rapid urbanization, intensification of agriculture, and over-exploitation of water resources over the last 50 years. During this time, the disappearance of streamflow in the watershed was largely overlooked as Bangalore shifted from Arkavathy-sourced water supply to imported water and farmers from surface water to groundwater irrigation. With Bangalore continuing to expand its water footprint and local groundwater resources drying up, moving towards sustainable water resources management in the Arkavathy requires overcoming the general absence of local hydrological records to develop an understanding of the changing hydrology of the watershed. To this end, a multifaceted research approach is developed and applied to the Arkavathy watershed to identify the dominant hydrologic dynamics within the watershed and understand the conditions under which hydrologic change occurred. This research reveals a number of important findings. First, humans are the primary drivers of change in this watershed, as neither precipitation variability nor increases in temperature can explain the observed changes in hydrology. Second, hydrologic change within the watershed is spatially heterogeneous, with drying occurring in the northern part of the watershed and increased surface water availability downstream of Bangalore. Third, streamflow decline in the northern Arkavathy has most likely been caused by extensive groundwater depletion driven by groundwater irrigated agriculture. And finally, management strategies designed to reverse groundwater depletion by constructing check dams within the surface water network are unlikely to succeed on the scales pertinent to watershed management. In addition to understanding water resources within the Arkavathy, this work serves as a foundation for understanding the trajectory of water resources in the region. This research also presents an approach for investigating historical hydrologic change in a poorly monitored watershed, understanding human-water interactions, and supporting long-term predictions for sustainable water management.</p><p>

<p> Years of conflict, political instability, and national emergencies have left behind very little information on water resources in Liberia, West Africa. This research leverages major ion and trace element analysis, <i> Escherichia coli</i> (<i>E. coli</i>) field tests, and high-throughput sequencing of microbial 16S rRNA genes to address these gaps and develop a comprehensive snapshot of groundwater quality in the region surrounding Monrovia, the capital city. A novel protocol to collect and preserve microbial DNA from groundwater under tropical field conditions lacking a constant source of electricity was employed and yielded high quality DNA sequences of bacterial and archaeal phylogenetic marker genes. </p><p> Multivariate compositional data analysis methods were used to investigate geochemical processes impacting groundwater quality throughout the study area. Low conductivity, low pH groundwaters were found to dominate the system with the majority of geochemical variability in the water samples attributed to surficial inputs both natural and anthropogenic. The implicated low buffering capacity of the groundwater system suggests a high risk associated with mining operations in Liberia. From a public health perspective, nitrate contamination, attributed to widespread but localized infiltration of human and or animal waste/fertilizer(s), was identified as the most important chemical water quality issue. Sulfate was found to be indicative of urban water cycling processes. </p><p> Although nitrate, arsenic, and lead concentrations exceeded WHO guidelines in several wells, <i>E. coli</i> was identified in 39% of all groundwaters analyzed, suggesting fecal contamination as the most significant regional water quality risk to human health. Deeper wells had significantly (p &lt; 0.05) lower probability of <i>E. coli</i> contamination, with no <i> E. coli</i> encountered in any well greater than 22 meters deep. Sequencing of 16S rRNA genes revealed highly variable microbial community compositions. Surficial inputs are suggested as the major drivers of microbial diversity and community composition. Groundwaters that tested positive for <i> E. coli</i> in the field were found to have significantly higher estimates of microbial alpha diversity (p &lt; 0.05) than groundwaters that tested negative. Additionally, nitrate, silica, pH, and several other geochemical constituents were found to be strongly correlated with shifts in microbial community structure. </p><p> The identification of a wide diversity of pathogen-associated bacteria to the genus and species level suggests that microbial contamination is more widespread than indicated by the <i>E. coli</i> field test alone. Results highlight the vulnerability of aquifers in Liberia to contamination and call for an increased investment in the water supply infrastructure and enhanced monitoring of chemical and microbial constituents throughout the country. This work will help the government of Liberia establish baseline water-quality conditions and provides an initial set of water resource databases to improve water-quality monitoring capacity.</p><p>

<p>A better understanding of groundwater flow through bedrock fractures is critical to applications involving heat and solute transport. Pumping tests performed to characterize these systems are often ill-suited because the radius of penetration quickly expands beyond the inter-well distance, gaining information beyond the well pair of interest. Periodic hydraulic tests allow the radius of penetration to be controlled by the frequency of oscillation, and testing at multiple frequencies gives parameter estimates for a range of spatial scales. Periodic pumping tests were performed at the Mirror Lake experimental fractured rock hydrology field site in New Hampshire. Results suggest a more complex, 3D network of connectivity than previously indicated by constant rate pumping tests. The relative degree of connectivity, given by diffusivity, corresponds to early-time response seen in the constant rate test. This confirms that the periodic tests investigated at a smaller penetration radius than the steady response from constant pumping.