<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>

<p> I examined flow-ecology relationships among stream communities in the Ozark Highlands, USA. I sampled fish, crayfish, and benthic macroinvertebrates during two consecutive summers, including a drought year (2012) and a flood year (2013). Biological response variables related to community structure were assessed via two different statistical methods: an Information Theoretic approach relating response variables to <i>a priori</i> selected predictor variables incorporating hydrology, habitat, geomorphology, and water quality, and canonical ordination using forward selection to relate these same response variables to a large assortment of hydrologic metrics. In addition to assessing metrics related to predicted natural flow, flow alteration at gaged sites was also quantified and community metrics were assessed with respect to flow alteration. Additionally, I conducted a manipulative laboratory greenhouse experiment to examine the effects of stream drying, one of the major components of the natural hydrologic disturbance regime in the region, on stream fishes as well as benthic community structure. Hydrologic variation was often less important than other environmental variables and substantial temporal variation existed in flow-ecology relationships. Stream flow magnitude was the most important category of hydrologic metric overall, but there were key differences in which metrics were important for each assemblage and how those assemblages responded to those metrics. Flow alteration has a strong effect on Ozark riverine communities, and the most important categories of flow alteration affecting these communities are magnitude of average flows, and frequency, magnitude, and duration of high flows. The large number of important high flow metrics suggests that flood events may play a particularly crucial role in structuring aquatic assemblages in the region. I found that seasonal stream drying had strong species-specific effects on organisms in pool refuges, and that type of drying specifically affected periphyton growth. Overall, I found that the elucidation of flow-ecology relationships and management decisions that are based on those relationships face a variety of challenges: the complex interaction of hydrology with other kinds of environmental variables, temporal variation in the aquatic community, and the differential effects of flow metrics on different assemblages.</p>

<p> The effective impervious area (EIA) is the portion of the total impervious area (TIA) that is hydraulically connected to the storm drainage network; thus, it is responsible for a majority of the runoff and its adverse effects in watersheds. Empirical equations for determining EIA are frequently used since they are quick and easy to use, but their accuracy has been untested in the Southern California region. The goals of this study are to: (1) test the accuracy of empirical equations on watersheds within the Southern California region (2) develop an EIA equation for the region based on the EIA vs. TIA relationships (3) Calibrate a stormwater management model using the TIA and EIA values from the equations and see how they perform compared to the measured hydrograph. The results will help inform planners and engineers of the effectiveness of utilizing EIA empirical equations for Best Management Practices (BMP) structures and stormwater conveyance system sizing in the region. </p><p>

<p> Geochemical mixing methods utilizing ²²²Rn and chloride and statistical hydrograph separation techniques were carried out in an attempt to understand baseflow dynamics in a section of the Kern River in the Sierra Nevada of Southern California. ²²²Rn has become a valuable tool for evaluating groundwater inflow to a river, particularly when groundwater and surface water have similar major ion geochemistry. When using geochemical methods it is important to minimize uncertainty through comparison with separate tracers and techniques, though this is complicated in this setting. Snow melt discharge and regulation of natural river flow cause hydrograph-based techniques to suffer from inaccuracies. Geochemical mixing using major ions and stable isotopes are complicated by the chemical similarity between surface water and groundwater. ²²²Rn is a powerful tool to elucidate this relationship in this setting if major uncertainties, like rate of radon degassing and parafluvial and hyporheic radon production can be constrained.</p><p>

<p> The Chico Aquifer System is a sole source aquifer located in the southwest region of Louisiana. A comprehensive study of the groundwater level of the Upper, Massive, and &ldquo;200-foot&rdquo; sands was undertaken to produce potentiometric surfaces for every five years from 1940 to 2015. The historical surfaces were produced for two different periods of the year; peak water-level months (non-irrigation season from January to March) and trough water-level months (irrigation season from May to July). ESRI ArcGIS extensions Arc Hydro Groundwater and Geostatistical Analyst were used to evaluate the spatial variability of the potentiometric surfaces, and ordinary kriging interpolation models were used to produce the surfaces. The cross-validation process indicated that the models were unbiased with satisfactory accuracy. From 1945 to 2015, Acadia Parish had the highest overall groundwater level decline (44.4 feet), followed by Evangeline Parish (32.6 feet), and Jefferson Davis Parish (29.63 feet). After high declines from 1945 to 1980 (33.2 feet), Calcasieu Parish showed signs of recovery since 1980 (+16.3 feet). The rate of change of the potentiometric surface for all parishes in the Chicot Aquifer System was higher from 1945 to 1980 than from 1980 to 2015. The grand average of the change in the potentiometric surface for the Chicot Aquifer System since 1945 was a decline of 23.3 feet. As society continues to improve water resource management, the results and methods presented here demonstrate an improvement in historical hindcasting that could create better plans for water management in the future.</p><p>

<p> Wood dynamics that store, transport, break down, and ultimately export wood pieces through watershed networks are key elements of stream complexity and ecosystem health. Efforts to quantify wood processes are advancing rapidly as technological innovations in field data collection, remotely sensed data acquisition, and data analyses become increasingly sophisticated. The ability to extend the temporal and spatial scales of wood data acquisition has been particularly useful to the investigations presented herein. The primary contributions of this dissertation are focused on two aspects of wood dynamics: watershed-scale wood export processes as identified using the depositional environment of a mountain reservoir, and wood deposition mechanisms in a bedrock-dominated mountain river. Three chapters present this work: </p><p> In Chapter 1, continuous video monitoring of wood in transport revealed seasonal and diurnal hydrologic cycle influences on the variable rates at which wood transports. This effort supports the efficacy of utilizing continuous data collection methods for wood transport studies. Annual wood export data were collected via field efforts and aerial image analyses from New Bullards Bar Reservoir on the North Yuba River, Sierra Nevada, California. Examination of data revealed linkages between decadal-scale climatic patterns, large flood events, and episodic wood export quantities. A watershed-specific relation between wood export quantities and annual peak discharge contributes to the notion that peak discharge is a primary control on wood export, and yielded prediction of annual wood export quantities where no data were available. Linkages between seasonality, climatic components, and hydrologic events that exert variable control on watershed scale wood responses are presented as a functional framework. An accompanying conceptual model supports the framework presumption that wood responses are influenced by seasonal variations in Mediterranean-montane climate conditions and accompanying hydrologic responses. </p><p> Chapter 2 contains development of new theory in support of the introduction of multiplicative coefficients, categorized by water year type, that were used to predict wood export quantities via utilization of an existing discharge-based theoretical equation. This new theory was the product of continued investigations into watershed-scale factors in search of explanation of observed variation of wood export rates into New Bullards Bar Reservoir. The gap between known variability and the attribution of wood export to one hydrologic relation continues to be a persistent issue, as the hierarchical and stochastic temporal and spatial nature of wood budget components remain difficult to quantify. The development of &ldquo;watershed processes&rdquo; coefficients was specifically focused on a generalized, parsimonious approach using water year type categories, with validation exercises supporting the approach. In dry years, predictions more closely represented observed wood export quantities, whereas the previously derived annual peak discharge relation yielded large over-predictions. Additional data are needed to continue development of these watershed-specific coefficients. This new approach to wood export prediction may be beneficial in regulated river systems for planning purposes, and its efficacy could be tested in other watersheds. </p><p> Chapter 3 presents the results of an investigation into wood deposition mechanisms in a 12.2 km segment of the confined, bedrock-dominated South Yuba River watershed. Inclusion of coarse wood particles in the analyses was essential in recognizing depositional patterns, thus supporting the value of utilizing a wider wood-size range. A near-census data collection effort yielded myriad data, of which topographic wetted width and bed elevation data, developed for an observed 4.5-year flood event, were standardized in 10-m intervals and then univariate and linked values were ordered into landform classifications using decision tree analyses. Digital imagery collected via kite-blimp was mosaicked into a geographic information system and all resolvable wood pieces greater then 2.5 cm in one dimension were delineated and categorized into piece count density classes. Visual imagery was also key in identifying two river corridor terrains: bedrock outcrops and cobble-boulder-vegetation patches. A conceptual model framed an investigation into how topographic variability and structural elements might influence observed wood deposition dynamics. Forage ratio test results that quantified wood piece utilization versus interval availability revealed that high-density wood deposition patterns were most significantly co-located with five discrete bedrock outcrops that dominated small portions of the river corridor in high flow conditions. Topographic variations and cobble-boulder-vegetation patches were found to be subordinate factors in wood deposition patterns. Bedrock outcrops with specific structural components were the primary depositional environments that acted as floodplain extents for coarse wood deposition, with mechanisms such as topographic steering, eddying, trapping, stranding, backwater effects, and lateral roughness features inferred to be responsible for observed wood deposition patterns.</p><p>

<p> In this study, we take a numerical modeling approach to investigate crustal-scale fluid flow in areas of crustal extension subjected to normal and/or detachment faulting. In areas subjected to continental extension, brittle normal faulting of the upper crust leads to steep topographic gradients that provide the driving force (head gradient) and pathways (fractures) to groundwater flow. Ductile extension in the lower crust is characterized by high heat fluxes, granitic intrusion, and migmatitic gneiss domes. When downward fluid flow reaches the detachment shear zone that separates the upper and lower crust, high heat flux combined with magmatic/metamorphic fluids cause density inversions leading to buoyancy-driven upward flow. Therefore, mid-crustal shear zones represent crustal-scale hydrothermal systems characterized by buoyancy-driven fluids convection. Several geochemical studies of North American core complexes show that circulation of meteoric fluids during the development of the detachment shear zone is ubiquitous. The circulation of fluids at lower crustal levels is the result of the interplay between rock type, temperature, porosity and permeability, and fluid pathways. </p><p> We present the results of finite-element numerical models using ABAQUS/Standard that simulate groundwater flow in an idealized cross-section of a metamorphic core complex. The simulations investigate the effects of (1) crust and fault permeability and porosity, (2) width of the faults, (3) depth of the faults and shear zone, and (4) topography (head gradient) on groundwater flow. Our results show that fluid migration to mid- to lower-crustal levels is significantly fault-controlled and depends primarily on the permeability contrast between the fault zone and the crustal rock as well as the presence of a permeable shear zone, and additionally, our simulations reveal that higher fault/crust permeability contrast leads to channelized flow in the fault zone and shear zone, while lower contrast allow leakage of the fluids in the crust. </p><p>

No description available.

No description available.

Valley Creek, an urbanized stream in Southeastern Pennsylvania, has undergone changes typical of streams in urbanized areas, such as bank erosion, channel redirection, and habitat disruption. One area of disruption that has been little studied is the hyporheic zone, the top layer of the streambed where stream water exchanges with subsurface water and chemical transformations occur. The hyporheic zone of an 18 m reach of Valley Creek in Ecology Park was characterized using a tracer test coupled with a hydrogeophysical survey. Nested wells screened at depths of 20, 35, 50, and 65 cm were placed at four locations along the center of the stream to monitor the passage of the salt tracer through the hyporheic zone. Results from well sampling were compared with time-lapse Electrical Resistivity Tomography (ERT) monitoring of the stream tracer. The streambed was also characterized using temperature probes to calculate the stream water-groundwater flux and freeze core samples to characterize heterogeneities in streambed sediment. Models were created using MODFLOW, MATLAB, and EARTH IMAGER 2-D to understand differences between Ecology Park and Crabby Creek, a tributary within the Valley Creek watershed, where similar studies were performed in 2009 and 2010. Hyporheic exchange and ERT applicability differed between the two study sites. At Ecology Park, tracer was detected only in the 20 cm wells at nests 2 and 4 during the injection period. Noise in the falling limbs of the tracer test breakthrough curves made it difficult to determine whether tracer lingered in the hyporheic zone using well data. ERT surveys were unable to detect tracer lingering after the injection period. At Crabby Creek, tracer was present in all shallow wells, and lingering tracer was detected in the hyporheic zone using ERT during the post-injection period. ERT surveys at Ecology Park were less effective than at Crabby Creek for two reasons: the presence of groundwater discharge (which inhibited hyporheic exchange) and increased stream water depth at Ecology Park. Temperature modeling of heat flux data revealed groundwater discharge at three locations. MODFLOW models predicted that this discharge would diminish the length and residence time of subsurface flow paths. Groundwater discharge likely increased along the contact between the hydraulically conductive Elbrook Formation and the less conductive Ledger Formation. Models created with MATLAB and Earth-Imager 2-D showed ERT sensitivity to tracer in the hyporheic zone depended on stream thickness. With increased water depth, more current propagated through the stream, which reduced sensitivity to changes in the hyporheic zone. A sensitivity analysis showed that the resistivity change in the hyporheic zone at Ecology Park (average water depth 0.36 m) would have to exceed 30% to be detectable, which was greater than the induced change during the tracer test. Deeper water also amplified the confounding effect of changes in the background conductivity of the stream water, though time-lapse ERT detected no lingering tracer even after correcting for this drift. Studies performed at Crabby Creek were able to map lingering tracer in the hyporheic zone because the site had a thin water layer (0.1 m), a large percentage increase of conductivity during the tracer test, and no groundwater discharge. Conversely, at Ecology Park groundwater discharge inhibited hyporheic exchange, and imaging sensitivity was reduced by the thicker water layer, demonstrating the limitations of ERT for hyporheic zone characterization. The modified inversion routines used here demonstrated that, with accurate stream conductivity and depth measurements, ERT can be used in some streams as a method for hyporheic characterization by incorporating site-specific conditions. / Geology