Geologyhttp://hdl.handle.net/10211.3/56672024-03-28T15:23:00Z2024-03-28T15:23:00ZIdentification of the Source of H2s and Characterization of Vertical Groundwater-Chemistry Trends in the San Joaquin Valley’s Unconfined AquiferGooding, Benjaminhttp://hdl.handle.net/10211.3/2111782020-04-20T23:09:22Z2019-08-01T00:00:00ZIdentification of the Source of H2s and Characterization of Vertical Groundwater-Chemistry Trends in the San Joaquin Valley’s Unconfined Aquifer
Gooding, Benjamin
The San Joaquin Valley’s (Valley) unconfined aquifer (Aquifer) is saturated with
hydrogen sulfide (H2S) contaminated groundwater that has no verified source. H2S in the
Aquifer was initially observed by Mendenhall et al. in 1916, but no thorough investigations
into the source of H2S have been conducted. As a result, the surficial and vertical extent of
H2S has not been estimated. To estimate surficial extent this study compiled H2S data from
the water-quality databases of the National Water Quality Monitoring Council and the
California State Water Resources Control Board. Based on the estimated H2S extent and
the Aquifer’s hydrogeologic characteristics this study hypothesized that H2S was generated
as a byproduct of microbial mediated sulfate-reduction. Bacterial sulfate-reduction (BSR)
is associated with the ecological succession of the terminal electron accepting processes
(TEAP). This study classified the predominant TEAP in groundwater by measuring the
concentration of redox related constituents and comparing results to the known evolution of
microbial reduction. Results demonstrated the progressive depletion of dissolved oxygen,
manganese, and iron from 50 to 200-feet (ft) below ground surface (bgs). From 200 to 240
ft bgs, these constituents, plus sulfate, were abruptly removed from the groundwater system
due to the onset of BSR resulting in the initial detection of aqueous H2S. At 240-ft bgs, the
depletion of sulfate, production of H2S, detection of sulfate-reducing bacteria (SRB), and
the assigned sulfate-reducing TEAP were sufficient evidence to unambiguously conclude
that the Aquifer’s source of H2S is H2S generated as a byproduct of BSR mediated by SRB.
In the future, the defined vertical groundwater-chemistry trends of redox related
constituents can predict whether H2S is actively being produced within a portion of the
Aquifer.
2019-08-01T00:00:00ZQuantifying Fluvial Erosional Response to Volcanic Deposition in the Southern CascadesSpencer, Seanhttp://hdl.handle.net/10211.3/2111742020-04-20T23:09:22Z2019-08-01T00:00:00ZQuantifying Fluvial Erosional Response to Volcanic Deposition in the Southern Cascades
Spencer, Sean
Prior research on stream incision has focused on tectonic and climatic forcing
factors, whereas ultra-fast aggradation of volcanic material has received far less attention.
Over a ca. 3 Ma span on the western flank of the southernmost Cascade arc of western
North America, several pulses of volcanic material with varying composition and volume
inundated stream channels causing the gradient to increase and reset incision. Incision
rates associated with volcanic deposition were estimated using stratigraphic and
geomorphic relationships.
Stream incision rates were high over timescales associated with multiple inset
subunits from the Maidu and Lassen Volcanic Centers. Measuring stream interaction
with these repeated flows show stream incision rates ranging from 48.286 mm/yr
averaged over ~7 ka to 0.299 mm/yr averaged over ~400 ka. Incision rates show an
asymptotic decrease with elapsed time after volcanic deposition. In much of the region,
the lack of detailed volcanic stratigraphy required estimation of stream incision rates
using the age of a volcanic center and the time elapsed since the eruptive episode,
yielding relatively lower incision rates ranging from 0.2491 to 0.0315 mm/yr over
relatively longer time intervals ranging from ~1080 to ~3400 ka.
Stream profile analysis in the southernmost Cascades shows multiple knickpoints
in the various streams, whereas streams in the northern Sierra Nevada, a region with well
documented tectonic uplift, typically have one major knickpoint. The multiple
knickpoints along southernmost Cascade streams are associated with drainages that lack
hanging tributaries, in contrast to the northern Sierra streams where hanging tributaries
are typical. These differences suggest knickpoints in the southernmost Cascades formed
in response to volcanic aggradation instead of tectonic uplift, consistent with the lack of
incision into basement beneath the volcanics. This contrasts the northern Sierra streams
that have significant (up to 1.2 km) incision into basement beneath the base of volcanic
deposits, as well as hanging tributaries.
2019-08-01T00:00:00ZAssessing the Environmental Impacts of a Beach Nourishment Operation, Morro Bay, CaAlfving, Cameron Jameshttp://hdl.handle.net/10211.3/2111722020-04-20T23:09:22Z2019-08-01T00:00:00ZAssessing the Environmental Impacts of a Beach Nourishment Operation, Morro Bay, Ca
Alfving, Cameron James
Dredging is carried out worldwide to maintain navigable water channels and to
source sediments for beach nourishment operations. As sea level continues to rise throughout the 21st century, dredging for beach nourishment is poised to become
increasingly prevalent, and increasingly important in California, where as much as 86%
of the coast is erosional. In repurposing dredge to nourish beaches, the impact of placing
dredge material at a dumpsite (e.g., a beach or nearshore zone) is not well understood, as
most studies on the impact of dredging focus only on the dredge pit from which material
is excavated. To help understand impacts of using dredge material to nourish beaches, we
use the recent 2016-2017 dredging operation in Morro Bay, CA, which placed between 3.9 x 105 to 7.6 x 105 cubic meters of sediment onto the nearby beaches. During the
operation, the dredged sediments appeared to be significantly darker than the in-situ
beach sand, leaving questions about ecosystem and sediment impacts to the original
beaches. Spatial-temporal analyses of grainsize, mineralogy, biota, and stratigraphy were
used to assess the impacts of the dredging event to the dumpsite and surrounding area.
Grainsize results indicated that the dredge material was a unique facies with a median
grainsize smaller than anything else observed in the study area. Mineralogy results
supported the grainsize results in showing that the dredge material was a unique facies
with a different percent abundance of quartz, intermediates, and lithics to the in-situ
beach sand. Biology results suggested a correlation between finer sediments and
increased biodiversity and organic matter. Stratigraphy results indicated that the dredge
material remained buried at the dumpsite as a distinct facies for approximately one year
before becoming visually undetectable. Applying the principle of the Littoral Cutoff
Diameter (LCD), we posit that approximately one third of the dredge material was
naturally deposited offshore while the remaining either remained at the dumpsite or was
dispersed throughout the study area. Despite the initial sediment incompatibility
introduced by the dredging, these findings lead to the conclusion that the dredge event
had no discernible negative long-term impacts on the study area.
2019-08-01T00:00:00ZGeophysical Investigation of the Royal Arches Meadow Rock Avalanche in Yosemite Valley – CAPacheco, Marcus Vinicius Azevedo de Oliveirahttp://hdl.handle.net/10211.3/2110422020-04-20T23:09:22Z2019-05-01T00:00:00ZGeophysical Investigation of the Royal Arches Meadow Rock Avalanche in Yosemite Valley – CA
Pacheco, Marcus Vinicius Azevedo de Oliveira
Since the retreat of the Last Glacial Maximum (~15,000 years ago), rockfalls have
been the major force shaping Yosemite Valley, California. Rock avalanches are an
especially large rockfall/rock slide that extends far beyond the cliff where they originate.
These events are infrequent, but can reach hundreds of meters into the valley, and deposit
an extremely large volume of debris when compared with regular rockfall events.
Yosemite Valley is home of at least ten rock avalanche deposits, with the Royal Arches
Meadow rock avalanche (RAMRA), situated in eastern Yosemite Valley, being the oldest
event (~14,000 yr BP). Because this event occurred shortly after the Last Glacial
Maximum (LGM), mapping the interface between this rock avalanche and the underlying
valley sediments can give us insights about the valley elevation and overall geomorphic
state of Yosemite Valley shortly after the LGM. Holocene aggradation covers parts of
the deposit, reducing its surface expression. This represents a challenge for estimating the
dimensions of the deposit. To overcome this obstacle, we used a combination of
geophysical methods (Electrical Resistivity Tomography (ERT) and Ground Penetrating
Radar (GPR)) to image the interface between the RAMRA and underlying valley
sediments. The strong dielectric permittivity and electrical resistivity contrast between
the rock avalanche and the underlying sediments make both electrical resistivity
tomography and ground penetrating radar ideal methods for our purpose. This then
allowed us to infer that the surface of the valley underneath the Royal Arches Meadow
Rock Avalanche is in average 1209m with a variation of +/- 3.2m.
2019-05-01T00:00:00Z