Student Research

The research abstracts presented below highlight the scientific discoveries being made by our graduate students.

2013 Exit Seminars

Christina Buck- This research explores the benefits of conjunctively managed surface and groundwater resources in a volcanic aquifer system to reduce stream temperatures while valuing agricultural deliveries.  The study involves advancing the understanding of flows, stream temperature, and groundwater dynamics in the Shasta Valley of Northern California.  Three levels of interaction are explored from field data, to regional simulation, to regional management optimization.  Stream temperature processes are explored using Distributed Temperature Sensing (DTS) data from the Shasta River and recalibrating an existing physically-based heat balance flow and temperature model of the Shasta River.  Second, development and calibration of a numerical groundwater model of the Pluto’s Cave basalt aquifer and Parks Creek valley area in the eastern portion of Shasta Valley helps quantify and organize the current conceptual model of this Cascade fracture flow dominated aquifer.  Model development provides insight on system dynamics, helps identify important and influential components of the system, and highlights additional data needs.  The objective of this model development is to reasonably represent regional groundwater flow and to explore the interaction between Mount Shasta recharge, pumping, and Big Springs flow.  Finally, this work uses optimization to explore coordinated hourly surface and groundwater operations to benefit Shasta River stream temperatures upstream of its confluence with Parks Creek.  The management strategy coordinates reservoir releases and diversions to irrigated pasture adjacent to the river and it supplements river flows with pumped cool groundwater from a nearby well.  The problem is formulated for a basic problem and for the Shasta River application.  Optimized results for a week in July suggest daily maximum and minimum stream temperatures can be reduced with strategic operation of the water supply portfolio.  These temperature benefits nevertheless have significant costs from reduced irrigation diversions.

Catherine Fong ("Hydrodynamics of Hydropeaking Flows on the Upper Tuolumne River")- Hydropeaking flows are sudden discharges of water to meet fluctuating electricity demands. These flows have been linked to many detrimental effects on downstream biological communities, including stranding of aquatic species, harm to overall species health, and decreases in richness and diversity of benthic macroinvertebrates. This study focuses on hydropeaking events on the upper Tuolumne River on the western slope of the Sierra Nevada. Hydropeaking events on the river since 1988 were classified using Principal Component Analysis and bulk flow indices to find representative events. Attenuation of hydropeaking events as they flowed down 42km of river was then modeled using a 1D hydraulic model prepared in HEC-RAS. Duration and shape factors highly influence the behavior of events as they move downriver. Results indicate that the rates of change between discharge levels of the vast majority of events, even after maximum attenuation, do not meet ramping rate recommendations to protect aquatic ecosystems.

Armen Malazian ("Soil Moisture Dynamics in Southern Sierra Nevada Soils")- The main purpose of the this study was to quantify soil moisture dynamics in the vadose zone  and generate a water balance for a white fir tree, Critical Zone Tree-1 (CZT-1) located in the Kings River Experimental Watershed (KREW) as part of the Southern Sierra Critical Zone Observatory (SSCZO).  The chosen site is at an elevation of about 6,500 feet in the rain-snow transition zone just outside of Shaver Lake, CA.  Soil texture data at CZT-1 has mean sand contents greater than 80% between 100 and 250 cm underlain by saprock.  An extensive network of the soil water status instrumentation was installed at depths of 150, 200, and 250 cm to determine soil water fluxes, infiltration rates and times, in-situ retention curves, and degree of soil water depletion.  The installed instrumentation includes measurements of temperature and volumetric water content (VWC) using the 5-TM (Decagon Devices, Inc.) and soil matric potential using tensiometers and MPS-1 (Decagon Devices, Inc.) sensors that were all co-located in a single hole at the aforementioned depths.  The tensiometers can only yield data for soil matric suctions less than 60 kPa, where the MPS-1 sensors can measure suctions in excess of 500 kPa.  Using a sensor specific calibration more accurate trends in soil matric potential can be achieved well into late summer and early fall prior to initial precipitation events.  The data was then used to show temporal changes in VWC, soil water storage, soil temperature, and soil matric potential.  As snowmelt and rainfall infiltrate the soil surface the soil profile reaches field capacity with the excess water replenishing groundwater resources.  Soil water resources are increasingly utilized as the shallower subsurface moisture is depleted leading to a more negative soil matric suction causing an upward movement of water during the summer months.  Upward movement of water is typically seen anywhere from late July to early August depending on the profile.  The data collected from all sensors allows for the generation of in-situ soil water retention curves and more importantly soil water fluxes to a depth of 250 cm.  The in-situ retention curves were also used to generate fits in RetC using the van Genuchten retention function yielding parameters to calculate hydraulic conductivities for more accurate determination of soil water fluxes.

Jason Emmons- The Sierra Nevada Mountains provide over 66% of California’s water supply, with meadows dispersed throughout the range like natural reservoirs, as they are accustomed to seasonally flood from snowmelt. The attenuation of snowmelt by a meadow provides ecosystem services like wildlife habitat, water filtration, and water storage. Despite the important role of meadows in the Sierra Nevada, a large proportion is degraded from stream incision, which increases the outflow of the channel to an extent that the meadow no longer floods, and cannot provide storage of water. However, restoration to decrease the outflow by filling-in the channel can be used to resume seasonal flooding of the meadow. Restoration of meadow streams would therefore provide water storage for the California water system, yet their potential capacity to hold water has not been quantified. This research seeks to address this knowledge gap by calculation of the restorable water volume, the volume of water absent from Sierran meadows, due to dry conditions linked to stream incision.

Michelle Lent ("Assessing vulnerability and opportunity in Bay Area’s water supply system:  The potential for regional groundwater banking and water reuse")- The San Francisco Bay Area obtains two-thirds of its water supply from imported surface water and only 5% from groundwater.  In part due to limited surface water storage, the supply is vulnerable to fluctuations in runoff, as well as reductions and disruptions in imports. This study investigates the potential for local groundwater banking and artificial recharge using recycled water to decrease supply vulnerability and system costs. Groundwater banking with surface water and recycled water was modeled in CALVIN, a hydro-economic model of the California water system. Water-scarce conditions were induced by restricting imports into the Bay Area. Preliminary results suggest groundwater banking can lower system costs and reduce scarcity (measured in economic loss) by tens to hundreds of millions of dollars by allowing agencies to pool resources under water-scarce conditions. Additionally, artificial recharge with recycled water may be economically feasible for the groundwater bank host agency, but is generally cost-prohibitive for other agencies due to conveyance infrastructure costs. Agencies with access to small aquifers may still benefit from investing in local recharge projects with reclaimed water.

Sandrine Matiasek ("Dissolved organic matter sources and dynamics in an agricultural watershed: contribution from sediment and insights from an amino acids time series")- Riverine dissolved organic matter (DOM) fuels aquatic ecosystems, but also transports contaminants and constitutes a precursor for carcinogenic by-products during drinking water disinfection.  Understanding the seasonal variability of DOM sources, reactivity, and fate is especially needed in irrigated agricultural landscapes, where hydrologic and sediment regimes are heavily modified.  First, this work assessed whether suspended sediment can be a significant source of DOM in agricultural streams. The extent and controls of sediment-bound organic matter (OM) release were evaluated with desorption experiments using sediments and soils from the Willow Slough watershed, an agricultural catchment of the Sacramento Valley.  Second, the composition and reactivity of desorbed DOM were investigated using optical and molecular tools.  Finally, the seasonal variability of dissolved amino acids was studied at the watershed outlet to obtain one of the most detailed time series for these biomolecules and to characterize DOM origin and reactivity in agricultural surface waters.

2012 AGU Abstracts

Rocko Brown et al. ("Multi-scale and Stage Dependent Geometric Organization in Mountain and Lowland Rivers")- In linking flow and form fluvial geomorphologists have established that alluvial river topography can have specific geometric configurations related to processes that shape these landforms. For lowland alluvial rivers where the flow depth associated with channel changing events is greater than the median particle size it is common that topographic high points have a tendency to be located in wider areas within the stream corridor, while topographic low points such as pools tend to be found in narrower locations. In mountain rivers that have bedrock controls or boulders there can be obvious exceptions to this, especially when large particles lock in constrictions, as the channel boundaries often have a resistance greater than that provided by flow. However, many of these observations are limited in that they are either based on detailed morphologic unit scale (e.g. several channel widths) observations or reach and segment scale observations that have considerably less detail and resolution. We hypothesize that mountain and lowland rivers show contrasting covariance and coherence of stage dependent width and bed elevation. To assess this hypothesis we present preliminary results from the analysis of the longitudinal bed elevation and stage dependent flow width spatial series extracted from a highly detailed 36-km stretch of the Lower Yuba River and 12-km of one of its tributaries of the South Fork Yuba River. These rivers represent contrasting physiographic environments with variations in flow hydrology and boundary materials making up the channel bed and bank resulting in varying stream morphologies. Spatial covariance between the thalweg series and width series at various water stages in both rivers along with power spectral density and coherence estimates are used to show that in alluvial and mountain rivers patterns of flow width and bed elevation can emerge but vary in there spatial consistency and frequency that they are engaged by the flow record. Preliminary results suggest that channel form can manifest varying degrees of geometric organization due to varying environmental controls and subsequent fluvial processes that operate in these settings.

Nick Engdahl et al. ("Mixing measures in non-conservative transport systems")- Predictions of the fate of reactive solutes in porous media are often made by using the mixing state of the system to determine effective reaction rates. This approach can be useful when the mixing measure accurately characterizes the behavior of the solutes, but, in many cases, the behavior of the mixing measure depends on the reaction system itself. Quantifying mixing is further complicated because the mixing measures often require complete knowledge of the concentration field which is never available in practice. Here we investigate the behavior of the scalar dissipation rate, the dilution index, the variance, and total solute mass in non-conservative transport systems for three component kinetic reactions in large, but finite, monitoring areas. The effects of different reaction rates, mass transfer, mobility, and different initial conditions are considered for these mixing measures. Mass transfer can cause a delay in the time required for the reaction system to reach an equilibrium state, and the magnitude of the delay depends on the mass transfer rate. The effects of this multi-step equilibrium process can manifest contrarily for different mixing measures, and these effects are amplified when the reaction product is immobile. For precipitation-dissolution reactions, the mass transfer rate may depend on the concentration of an immobile precipitate. This process causes sharp transitions in the mixing measures that are the result of a lingering chemical disequilibrium, caused by the concentration dependent mass transfer rates. The immobile domain and the initial conditions can have strong effects on the mixing state for long times, and, without knowledge of immobile concentrations, these effects could easily be attributed to measurement errors.

Robert Gonzalez et al. ("Landforms Affect Gravel-Cobble Bed River Hydraulics at Different Spatial Scales and Discharges")- River hydraulics are generally modeled to predict inundation extents, assess aquatic species habitat, understand sediment transport regimes, and describe geomorphic processes. These metrics are in turn used to guide floodplain development, instream flow requirements, river rehabilitation projects, reservoir management, and further research. Consequently, the emergence of 2D hydraulic modeling is usually a means to some end other than characterizing and discussing the fundamental aspects of fluvial hydraulics. The purpose of this study was to ascertain the role of different components of multi-scalar, heterogeneous fluvial landforms in controlling the spatial pattern of river hydraulics at 28 different flows ranging from 0.06 to 22 times bankfull discharge. The testbed data for the study consisted of 1-m resolution rasters of depth, velocity, and Shields stress over 37.5 km of the regulated gravel-cobble bed Lower Yuba River (LYR) located in the Sacramento River Valley of California. Each variable was analyzed for its discharge-dependent power function (i.e. at-a-station hydraulic geometry) at segment, reach, and morphologic spatial scales, with data stratified by 8 reaches, 4 inundation zones, two vegetation regions, and 31 morphological units. This was done using all points, not just at cross-sections. At each spatial scale, trend lines were statistically compared to determine if they were differentiated. Mean velocity and Shields stress as a function of discharge vary by reach, including several velocity and Shields stress reversals. The range of mean velocity and Shields stress between reaches increases with discharge. There are several reach-scale velocity reversals that take place among the reaches, especially at 0.3 and 2 times bankfull discharge, whereas there is only one major Shields stress reversal at 6 times bankfull discharge. Stage-dependent cross sectional area and substrate size govern these interactions. The two most downstream reaches had the highest average shields stress for all flows above baseflow, due to downstream fining and increased shear stress at higher discharge caused by flow constriction induced by vegetation and levees. Among the in-channel bed morphological units, the range of mean velocity decreases with discharge, while that for Shields stress remains large. There are many Shields stress reversals between morphological units. The results show that at each scale landforms topographically steer hydraulics and the steering changes with discharge.

Andy Gray et al. ("Effects of hydrologic event history on suspended-sediment behavior")- The suspended-sediment yields of many developed watersheds have decreased with time, and increased urbanization and hydrologic modifications are often identified as contributing mechanisms. Examination of a river system that did not experience these alterations during the period of record, yet displayed high variability in suspended-sediment behavior and a decreasing trend in sediment yield provided an opportunity to evaluate the effects of hydrologic event history. The objectives of this study were to identify the time-dependent behavior of suspended-sediment concentrations at the terminus of the Salinas River, California since the initiation of monitoring in the late 1960’s, and determine the hydrologic factors that influenced this behavior. The Salinas is a seasonally active river of moderate size that may be particularly susceptible to the effects of hydrologic event history on suspended-sediment behavior due to the high variability of discharge in this system. Sediment and hydrologic data were obtained from samples collected by the USGS from 1967-2010 and the authors from 2008-2011. Comparisons of chronologically stratified rating relationships between fine suspended-sediment concentration (CSSf) and instantaneous water discharge using ANCOVA revealed that changes in rating curve offset and slope had occurred over time. Suspended-sediment yield from the Salinas had decreased, despite little change in the proportion of urbanized land area and no major dam emplacement during the period of record. To evaluate the potential effects of hydrologic and landscape forcing factors on suspended-sediment behavior, sediment concentration residuals about the rating curves were compared with sample attributes including: hydrograph position and hydrologic routing history, seasonality, basin aridity, major and moderate hydrologic event proximity and effective wildfire burn area. The following hydrologic factors were found to have significant positive effects on discharge corrected CSSf: the ratio of mean daily discharges between the date of the sample and the previous day, and elapsed time between sample date and the last major hydrologic event. Elapsed time between sample date and the last moderate discharge event, and effective burn area were found to have significant, negative effects. Only effective burn area possessed a significant temporal trend, which was positive. As increased burn area is generally associated with an increase in suspended-sediment delivery, the apparent negative response of CSSf to effective burn area and the positive temporal trend of this factor indicate that other temporally trending factors not identified by this study are affecting a negative trend in CSSf over time. The positive effect of daily discharge ratio on discharge corrected CSSf implied that fine suspended sediment in the lower Salinas displayed a generally positive hysteretic behavior, which was supported by the prevalence of positive hysteresis in events with sufficient data density for analysis. Identification of the preferential mobilization of sediment on the rising limb of the hydrograph as the major mechanism of the overall hysteretic pattern is forensically supported by the annual occurrence of in-channel suspended-sediment deposition by early season, channel terminating flows, and the flushing function of major hydrologic events found in this study.

Leah Kammel et al. ("Strong Predictability Of Spatially Distributed Physical Habitat Preferences For O. Mykiss Spawning Across Three Spatial Scales")- Currently accepted perception assumes Oncorhynchus mykiss prefer different ranges of similar physical habitat elements for spawning than Chinook salmon (Oncorhynchus tshawytscha), taking into account their difference in size. While there is increasing research interest regarding O. mykiss habitat use and migratory behavior, research conducted to date distinguishing the physical habitat conditions utilized for O. mykiss spawning has not provided quantified understanding of their spawning habitat preferences. The purpose of this study was to use electivity indices and other measures to assess the physical habitat characteristics preferred for O. mykiss spawning in terms of both 1-m scale microhabitat attributes, and landforms at different spatial scales from 0.1-100 times channel width. The testbed for this study was the 37.5-km regulated gravel-cobble Lower Yuba River (LYR). Using spatially distributed 2D hydrodynamic model results, substrate mapping, and a census of O. mykiss redds from two years of observation, micro- and meso-scale representations of physical habitat were tested for their ability to predict spawning habitat preference and avoidance. Overall there was strong stratification of O. mykiss redd occurrence for all representation types of physical habitat. A strong preference of hydraulic conditions was shown for mean water column velocities of 1.18-2.25 ft/s, and water depths of 1.25-2.76 ft. There was a marked preference for the two most upstream alluvial reaches of the LYR (out of 8 total reaches), accounting for 92% of all redds observed. The preferred morphological units (MUs) for O. mykiss spawning were more variable than for Chinook salmon and changed with increasing discharge, demonstrating that O. mykiss shift spawning to different MUs in order to utilize their preferred hydraulic conditions. The substrate range preferred for O. mykiss spawning was within 32-90 mm. Overall, O. mykiss spawning behavior was highly predictable and required a holistic blend of hydraulic and geomorphic representations to explain.

Maziar Kandelous et al. ("Coupled experimental-modeling approach for estimation of root zone leaching of applied irrigation water and fertilizers")- Micro-irrigation methods have proven to be highly effective in achieving the desired crop yields, but there is increasing evidence suggesting the need for the optimization of irrigation scheduling and management, thereby achieving sustainable agricultural practices, while minimizing losses of applied water and fertilizers at the field scale. Moreover, sustainable irrigation systems must maintain a long-term salt balance that minimizes both salinity impacts on crop production and salt leaching to the groundwater. To optimize cropping system efficiency and irrigation/fertigation practices, irrigation and fertilizers must be applied at the right concentration, place, and time to ensure maximum root uptake. However, the applied irrigation water and dissolved fertilizer, as well as root growth and associated nutrient and water uptake, interact with soil properties and nutrient sources in a complex manner that cannot easily be resolved with ‘experience’ and field experimentation alone. Therefore, a coupling of experimentation and modeling is required to unravel the complexities resulting from spatial variations of soil texture and layering often found in agricultural fields. We present experimental approaches that provide the necessary data on soil moisture, water potential, and nitrate concentration and multi-dimensional modeling of unsaturated water flow and solute transport to evaluate and optimize irrigation and fertility management practices for multiple locations, crop types, and irrigation systems.

Armen Malazian et al. ("Soil Moisture Dynamics in Deep Southern Sierra Nevada Soils")- As part of the Southern Sierra Critical Zone Observatory, the soil surrounding a white fir tree has been instrumented with volumetric water content (VWC), temperature, and soil matric potential sensors. The VWC (5-TM (Decagon Devices, Inc.) and neutron probe) and temperature (5-TM) associated with the deep vadose zone monitoring are being measured by 5-TM sensors. The soil matric potential is measured using tensiometers and MPS-1 sensors (Decagon Devices, Inc.). This instrumentation has been installed at depths of 150, 200, and 250 cm, so as to quantify subsurface soil moisture dynamics. The soil is quite sandy to varying depths after which a saprolyte layer exists moving into a more coarse textured subsurface. As snowmelt and rainfall infiltrate the soil at the surface it wets the soil profile to field capacity with the excess water replenishing deep water resources. The deep water resources are utilized as the shallower subsurface moisture is depleted leading to a more negative soil matric suction causing an upward movement of water for the latter part of the summer. This upward movement of water is assumed to occur via total soil water potential gradients. The tensiometers can only yield data for soil matric suctions less than 600 cm of water, where the MPS-1 sensors can reach suctions up 500 kPa. Thus, since the deep vadose zone instrument installation in summer 2011, it was seen that water started moving upward in late July to early August depending on the profile and winter precipitation.

Rashid Owlia et al. ("Modeling of Groundwater Quantity and Quality Management, Nile Valley, Egypt")- Groundwater levels have been rising in the Luxor area of Egypt due to increased agricultural irrigation following the construction of the Aswan High Dam (AHD) in 1970. This has led to soil and groundwater salinity problems caused by increasing evapotranspiration from shallower water table, as well as the degradation of historical monuments whose foundations are weakening by capillary rise of water into the columns and stonework. While similar salinity problems exist elsewhere in the world (e.g., San Joaquin Valley of California), we hypothesize that as long as groundwater discharge to the Nile River continues and serves as a sink for the salt, the regional salt balance will be manageable and will not lead to irreversible salinization of soils. Further, we hypothesize that if a groundwater system such as this one becomes overdrafted, thereby cutting off groundwater discharge to the River, the system salt balance will be less manageable and possibly non-sustainable. With groundwater flow modeling we are investigating approaches for managing the irrigation and groundwater levels so as to eliminate water stresses on Egyptian monuments and antiquities. Consequences of possible actions for managing the water table through groundwater pumping and alternative irrigation practices will be presented. Moreover, through the use of high resolution modeling of system heterogeneity, we will simulate the long term salt balance of the system under various scenarios, including the overdraft case. The salt source will be a function of groundwater discharge to the surface via bare-soil evaporation and crop transpiration. The built-in heterogeneity will account for dispersion, fast transport in connected media and slow mass transfer between aquifer and aquitard materials. Key Words: Groundwater, modeling, water quality, sustainability, salinity, irrigated agriculture, Nile aquifer.

Anne Senter et al. ("A Near-Census Of Streamwood Pieces Reveals Abundance and Distribution Patterns That Would Not Be Otherwise Recognized In A Mountain River, Sierra Nevada, California")- A detailed streamwood (i.e. wood of all sizes geomorphically or ecologically relevant to river processes) survey was conducted along 12.1-km of a mountain river using remotely sensed digital imagery obtained via a helium-filled kite-blimp. The purpose of the study was to assess the abundance and distribution of streamwood along a continuous river corridor as a function of wood size class and river corridor attributes. Questions explored include: What is the relative significance of streamwood pieces smaller than the common lower bound of large wood 1 m in length and 10 cm in diameter? Is streamwood distribution random or organized? What river corridor attributes are associated with observed distributions? What role does streamwood size class play in abundance and distribution patterns? A total of 10,002 streamwood pieces ranging from .0005-m2 to 10-m2 in area were digitized in ArcGIS, providing a lower size-range limit typically not analyzed in wood studies. Pieces < 0.1 m2, considered analogous to the lower limit of large wood, comprised over 85% of total pieces and almost 20% of piece area. Streamwood distribution exhibited distinctive patterns, with concentrated, high-density reaches containing an average 2.5 pieces/m compared to low-density reaches averaging 0.3 pieces/m. Streamwood area in high-density reaches averaged 0.05 m2 and in low-density reaches averaged 0.16 m2, showing that small pieces predominated in high-density reaches. Mann-Whitney U and correlation tests produced a set of significant associations with p-values < 0.05 and 95% confidence levels. In high-density reaches, streamwood pieces were associated with forest land cover in the outer corridor and correlated moderately (r2 > 0.4) with alluvium in the channel and with bedrock in the outer corridor, whereas streamwood area was associated with forest land cover in the outer corridor and correlated strongly (r 2 > 0.7) with bedrock in the outer corridor and moderately with channel slope and width. In low-density reaches, streamwood pieces were associated with alluvium in the outer corridor and boulders in the baseflow channel and correlated moderately with bedrock in the channel and strongly with bedrock in the outer corridor, whereas streamwood area was associated with alluvium in the outer corridor and correlated moderately with bedrock in the channel and with sinuosity, and strongly with bedrock in the outer corridor. Results suggest that there may be important linkages between streamwood and riverine attributes that are not currently recognized due to the exclusion of smaller streamwood pieces such as those identified in this study. Heterogeneity of streamwood distribution patterns appears to be linked to distinct physical and biophysical controls in the river reaches where high- and low-densities of streamwood reside.

2012 Exit Seminars

Dylan Boyle (“The potential of groundwater recharge management to locally reverse non-point source groundwater contamination”)- Since the invention of the Haber–Bosch process, which transforms nitrogen gas (N2) to nitrate (NO3-), agriculture in California has experienced significant growth and intensification with the availability of this cheap synthetic fertilizer. Little regulation concerning its use has been implemented which has resulted in excessive application of nitrate (fertilizer) through time, impacting groundwater resources nationally and globally. A recent study investigating long term nitrate contamination in the Tulare Lake Basin and Salinas Valley showed that statistically significant increasing trends can be observed at the regional scale. A detailed flow and transport model indicate that nitrate contamination is expected to worsen in the future due to past activities. The long term trends of nitrate contamination will ultimately be influenced by the quality and quantity of water recharging groundwater aquifers. Large rivers exiting the Sierra Nevada mountains provide a source of groundwater recharge that is low in total dissolved solids (TDS) and nitrate. Groundwater near these sources of recharge is generally lower in nitrate and TDS. The city of Fresno has diverted surface water from the San Joaquin and Kings rivers to enhance surface water recharge since the 1970's. This has helped the city offset its groundwater pumping, and additionally has benefited local water quality by lowering TDS and nitrate concentrations.

Siqi Fan ("Walnut Pesticides in California: Use Patterns and Potential Impacts on Surface Water")- Walnuts are an important specialty crop in California. In 2010, they reached a statewide production of 503,000 tons which accounted for 99% of national production, and created profits over one billion dollars. The major basins for walnut cultivation in California are the Sacramento Basin, San Joaquin and Tulare Lake. To maximize crop production, a large amount of pesticides was applied to control pests: The amount of active ingredient (AI) used in pesticide products exceeded 1000 tons annually in 1995-2009, which posed potential pollution to surface water. This study looked into both pesticide use and its potential impact on surface water from 1995 to 2009 on California walnuts, focusing on the pesticide categories of fungicides, insecticides and herbicides. A pesticide risk evaluation model, Pesticide Use Risk Evaluation (PURE), was applied in this study to quantitatively analyze potential impact of pesticide use on surface water. Results showed that among the three main basins, the Sacramento Basin had the highest fungicide risk intensity on surface water (annual average value: 978.25 R/ha, 42% and 358% higher than San Joaquin and Tulare Lake), due to a heavy use of copper hydroxide and maneb. San Joaquin had the highest insecticide risk intensity (973.73 R/ha, 33% and 56% higher than the Sacramento Basin and Tulare Lake) resulting mainly from chlorpyrifos, azinphos-methyl, chloropicrin, and malathion use. Herbicide showed a consistent low risk intensity (<50 R/ha) in all basins. The Mann-Kendall test showed fungicide and insecticide risk intensity presented a consistently decreasing trend in all basins, while herbicide risk intensity presented an increasing trend in Tulare Lake. A finer spatial scale analysis was done at township level (6×6 mile2) to access the use and risk patterns in more details, the results of which are presented as GIS maps. Finally, a case study was carried out to examine the relationship between pyrethroid and miticide use on California walnuts and their potential impact on surface water. A developed model captured the relationship as the miticide use intensity is positively correlated with pyrethroid use intensity until it reaches a maximum value. Through a comprehensive pesticide use and risk analysis on California walnut, suggestions can be made to help local walnut growers make decisions on pesticide choices, and help regulators to make decisions and integrated pesticide management on critical regions. For example, pesticides such as copper hydroxide and chlorpyrifos have high toxicity in surface water. Our analysis indicates that if they were replaced by more environmentally benign pesticides--such as kaolin and petroleum oil--the overall risk scores and environmental impacts would decrease.

Yumiko Henneberry ("What the Floc?  Investigating the interaction of dissolved organic matter with metals in water and the subsequent effects on soil and water quality in a wetland environment")- The Sacramento San Joaquin Delta (Delta) in California is currently one of the largest production centers of agriculture in the State and also provides over 23 million residents with potable water. The conversion of this region, which was once a vast wetland, into a series of agricultural islands intertwined with levees has brought on various environmental issues including severe subsidence and water quality problems including high concentrations of dissolved organic matter (DOM) and mercury (Hg). Subsidence weakens the already fragile levee system, increasing flood risk, while high concentrations of dissolved organic carbon (DOC), largely originating from agricultural runoff and drainage water from the peat islands, react during the water purification process to form carcinogenic by-products. Hg is a neurotoxin that can bioaccumulate in the form of methylmercury (MeHg) to levels that adversely affect reproduction and behavior. The research presented attempts to assess the feasibility of applying metal based-coagulants to agricultural drainage water from the Delta and retaining the subsequent organo-metal complex (floc) in a wetland environment to reduce contaminant concentrations and reverse subsidence. We found that coagulation removes significant amounts of inorganic Hg (IHg) and MeHg as well as native and newly amended IHg. The Hg that was removed by coagulation was found to be associated with the larger molecular weight, aromatic fractions of DOC, the fraction forming disinfection by products.  Once formed, the floc can adsorb further IHg, withstand reductive crystallinity under abiotic reducing conditions, and retain the DOC incorporated within the floc structure. Results from this study offer new fundamental insights into the large scale removal of both DOC and IHg at environmentally relevant concentrations and also imply that using constructed wetlands to retain the floc is a viable method.

Danielle Moss (“Quantifying the Spatial and Temporal Impacts of Groundwater Pumping on Streams in the Sacramento Valley, California.”)- Water transfers during drought in California’s Sacramento Valley can lead to increased groundwater pumping, and as yet unknown effects on stream baseflow.  Two existing groundwater models of the greater Sacramento Valley together with localized, monitoring of groundwater level fluctuations adjacent to the Bear, Feather, and Yuba Rivers, indicate cause and effect relations between the pumping and streamflow. Using the Central Valley Hydrologic Model (CVHM) developed by the U.S. Geological Survey and C2VSIM developed by Department of Water Resources, which have similar complexity and data but differing approaches to the agricultural water boundary condition, illuminates both the water budget and its uncertainty.  Groundwater level measurements at nested, near-stream piezometers show seasonal variations in streamflow and groundwater levels as well as the timing and magnitude of recharge and pumping.  Results from the two models indicate significant differences between their local water levels compared to observed water levels as well as differences between the water budgets.  Within the study area, groundwater storage for the models changes from gains during wet and years to losses during dry and critically dry years.  Annual recharge and streamflow gains between the models differ by only 3% and 4% respectively.  However, pumping differs by as much as 30% of the relative water budget.  This leads to differing trends regarding pumping’s effects on stream baseflow.

Jenna Rodriguez ("Airborne-based evapotranspiration using MASTER imagery and the METRIC model: comparing annual water management in almond orchards")- California agriculture is an invaluable resource in the state's economy and global food exports. It is heavily dependent on proper irrigation water management. Competing water demands and changing climate trends exacerbate limited water resources, threatening agricultural productivity and food security at state and global levels.  One component of agricultural water management is to avoid over-watering,while applying a sufficient amount of water to avoid crop stress and minimize excess water loss.  This can be done utilizing remote sensing technologies to collect data quickly, remotely and over large areas.  This study explores applications of high spatial resolution imagery from MODIS/ASTER (MASTER) to estimate ET using the METRIC (Mapping ET at high Resolution using Internal Calibration) model.  ET estimates were produced for two different growing seasons (2010 and 2011) in eight different almond orchards managed by Paramount Farms in Kern County, California, USA.  Estimates of ET were compared against validation data measured from an in-field flux tower.  The almond industry is of special interest as the majority of almonds produced globally are from California, contributing to a $2 billion industry.  Advancement of crop water cost-effectiveness and resource conservation can be improved through better monitoring of irrigation management in such orchards.