Geology topics

Research about California

Source-linked reports with geographic coverage including California.

At least 883 records · Page 49Linked to original sources

USGS2021

Detection and measurement of land-surface deformation, Pajaro Valley, Santa Cruz and Monterey counties, California, 2015–18

Land-surface deformation (subsidence) caused by groundwater withdrawal is identified as an undesirable result in the Pajaro Valley Water Management Agency’s Basin Management Plan and California’s Sustainable Groundwater Management Act. In Pajaro Valley, groundwater provides nearly 90 percent of the total water supply. To aid the development of sustainable groundwater management criteria, the U.S. Geological Survey, in cooperation with the Pajaro Valley Water Management Agency, performed an analysis of land-surface deformation (subsidence and uplift) in Pajaro Valley for 2015–18, using Interferometric Synthetic Aperture Radar and continuous Global Positioning System methods. Land-surface deformation results were then compared with subsurface geology and groundwater altitudes to better understand the hydromechanical response of the coastal aquifer system. The results indicate the land surface is generally stable with only small magnitudes (less than 1 inch) of seasonal land-surface deformation (subsidence in the summer and uplift in the winter) during 2015–18. During this time, the largest magnitude of land-surface deformation was less than 2 inches of subsidence and was localized in one area just north of the city limits of Watsonville, California. Groundwater altitudes during 2015–18 demonstrated seasonal variability and annual to multi-annual increases after reaching historical lows by the mid-1990s. The small magnitudes of land-surface deformation coupled with groundwater-altitude increases in most areas indicate that the subsidence likely is largely elastic and recoverable. The Corralitos-Pajaro Valley groundwater basin contains fine-grained (clay) sediments that have the potential for permanent aquifer-system compaction and resultant land subsidence. However, groundwater altitudes throughout the Pajaro Valley have increased above historical lows, and observed increases in groundwater altitudes coincided with changes in groundwater management activities. Observed relations between groundwater management activities and groundwater altitudes indicate that management of groundwater supplies could minimize the potential for permanent land-surface deformation in Pajaro Valley.

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USGS2021

Protocol for route restoration in California’s desert renewable energy conservation plan area

In the deserts of the Southwestern United States, increased off-highway vehicle use can lead to widespread vehicular damage to desert ecosystems. As the popularity and intensity of vehicle use on public lands continues, the Bureau of Land Management (BLM) is challenged to manage the routes used by recreationists while minimizing activity beyond designated routes and mitigating environmental impacts. Ecosystem function and habitat quality can be degraded by vehicle activities, especially when the activities are occurring outside authorized routes or authorized open areas. Restoration mitigates damage to soils and vegetation; however, methods vary across the desert, results appear to be inconsistent, and standardized monitoring plans do not exist. The Desert Renewable Energy Conservation Plan Land Use Plan Amendment to the California Desert Conservation Area Land Use Plan identified the need for, and directed implementation of, standardized monitoring of restoration, which includes minimizing surface disturbance to agency prescribed levels in areas of critical environmental concern and on California Desert National Conservation Lands. To assist the BLM in implementing the Desert Renewable Energy Conservation Plan Land Use Plan Amendment, we define ecological restoration as the process of halting or minimizing future degradation while simultaneously assisting the recovery of ecosystem function and community composition in relation to intact reference sites. The monitoring strategies provided in this protocol are used to restore degraded ecosystems after use of non-routes has ceased (non-designated routes or vehicle-caused linear disturbances) by applying techniques to improve edaphic properties, hydrologic function, and biotic community composition. This protocol also provides criteria that can be used to distinguish the status of non-routes and land parcels as “restored” or “disturbed.” This protocol was developed by the U.S. Geological Survey, in collaboration with BLM restoration practitioners, to identify standard restoration methods and establish criteria to determine when restoration is achieved. This protocol also develops new methods to increase restoration rates and successes on public lands in the southern California deserts. BLM’s long-term implementation plan for the evaluation of road restoration described in this report is to transition toward managing the work, including developing the workforce and long-term storage and management of the data during the next several years. This report is intended to be regularly updated as the program develops.

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USGS2021

Incorporation of uncertainty to improve projections of tidal wetland elevation and carbon accumulation with sea-level rise

Understanding the rates and patterns of tidal wetland elevation changes relative to sea-level is essential for understanding the extent of potential wetland loss over the coming years. Using an enhanced and more flexible modeling framework of an ecosystem model (WARMER-2), we explored sea-level rise (SLR) impacts on wetland elevations and carbon sequestration rates through 2100 by considering plant community transitions, salinity effects on productivity, and changes in sediment availability. We incorporated local experimental results for plant productivity relative to inundation and salinity into a species transition model, as well as site-level estimates of organic matter decomposition. The revised modeling framework includes an improved calibration scheme that more accurately reconstructs soil profiles and incorporates parameter uncertainty through Monte Carlo simulations. Using WARMER-2, we evaluated elevation change in three tidal wetlands in the San Francisco Bay Estuary, CA, USA along an estuarine tidal and salinity gradient with varying scenarios of SLR, salinization, and changes in sediment availability. We also tested the sensitivity of marsh elevation and carbon accumulation rates to different plant productivity functions. Wetland elevation at all three sites was sensitive to changes in sediment availability, but sites with greater initial elevations or space for upland transgression persisted longer under higher SLR rates than sites at lower elevations. Using a multi-species wetland vegetation transition model for organic matter contribution to accretion, WARMER-2 projected increased elevations relative to sea levels (resilience) and higher rates of carbon accumulation when compared with projections assuming no future change in vegetation with SLR. A threshold analysis revealed that all three wetland sites were likely to eventually transition to an unvegetated state with SLR rates above 7 mm/yr. Our results show the utility in incorporating additional estuary-specific parameters to bolster confidence in model projections. The new WARMER-2 modeling framework is widely applicable to other tidal wetland ecosystems and can assist in teasing apart important drivers of wetland elevation change under SLR.

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USGS2021

Disentangling stationary and dynamic estuarine fish habitat to inform conservation: Species-specific responses to physical habitat and water quality in San Francisco Estuary

Estuaries represent critical aquatic habitat that connects surface water distributed between Earth’s landmasses and oceans. They are dynamic transitional ecosystems, which provide important habitat for fishes and other aquatic organisms. Effective conservation of species inhabiting estuaries requires knowledge of the habitat features that drive their abundance and distribution. We sought to elucidate how stationary (i.e., wetlands, shoals, and channels) and dynamic (i.e., salinity, temperature, turbidity, and chlorophyll concentration) habitat features interact to drive distributions of individual fish species. The Pacific coast of the conterminous United States has over 400 estuaries of various types. The largest (historical surface area) is San Francisco Estuary, California. We conducted extensive field observations of fishes in the central San Francisco Estuary among stationary habitat types (i.e., wetland, shoal, and channel) over a 19-month period encompassing substantial variability in dynamic water quality conditions. Most of the species observed, especially native species of special management interest, were associated with tidal wetland habitat. Few species exhibited associations with water quality conditions driven by seasonal (temperature) or a combination of broad- and fine-scale ecosystem processes (salinity and turbidity). Our study provides (1) an empirical demonstration of how researchers can deal with the complex and dynamic expressions of habitat in estuarine systems to address urgent natural resource problems and (2) a clear demonstration of the urgent need for habitat restoration and its likely outcome in systems such as San Francisco Estuary. Restoration of suitable tidal wetland habitat on the West Coast of the United States is likely to be an effective conservation tool to support estuarine fishes given that over 90% of historical tidal wetland habitat in San Francisco Estuary and 85% of vegetated wetland habitat along the Pacific coast of the United States has been lost due to human modification.

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USGS2021

Refinements to the Graves–Pitarka kinematic rupture generator, including a dynamically consistent slip‐rate function, applied to the 2019 Mw 7.1 Ridgecrest earthquake

The main objective of this study is to develop physics‐based constraints on the spatiotemporal variation of the slip‐rate function using a simplified dynamic rupture model. First, we performed dynamic rupture modeling of the 2019 M w 7.1 Ridgecrest, California, earthquake, to analyze the effects of depth‐dependent stress and material friction on slip rate. Then, we used our modeling results to guide refinements to the slip‐rate function that were implemented in the Graves–Pitarka kinematic rupture generation technique. The dynamic ruptures were computed on a surface‐rupturing, planar strike‐slip fault that includes a weak (negative to low‐stress‐drop) zone in the upper 4 km of the crust. Below the weak zone, we placed high‐stress‐drop patches designed to mirror the large‐slip areas seen in various rupture model inversions of the event. The locations of the high‐stress‐drop patches and the hypocenter were varied in multiple realizations to investigate how changing the dynamic conditions affected the resulting rupture kinematics, in particular, the slip rate. From these simulations, we observed a systematic change in the shape of the slip‐rate function from Kostrov type below the weak zone to a predominantly symmetric shape within the weak zone, along with a depth‐dependent reduction of peak slip rate. We generalized these shallow rupture features into a depth‐dependent parametric variation of the slip‐rate function and implemented it in the Graves–Pitarka kinematic rupture model generator. The performance of the updated kinematic approach was then verified in 0–4 Hz simulations of the M w 7.1 Ridgecrest earthquake, which showed that incorporating the depth‐dependent variation in the shape of the slip‐rate function improves the fit to the observed near‐fault ground motions in the 0.5–3 s period range.

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USGS2021

A new analysis of caldera unrest through the integration of geophysical data and FEM modeling: The Long Valley caldera case study

The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km 3 . We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa −1 (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa −1 . We obtained a density of 1856 ± 72 kg/m 3 . This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.

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USGS2021

Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2019

Trace-metal concentrations in sediment and in the clam Limecola petalum (formerly reported as Macoma balthica and M. petalum ), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, Calif. This report includes the data collected by the U.S. Geological Survey (USGS) for the period January 2019 to December 2019. These data append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2019 data within the context of the longer, multidecadal dataset. This dataset supports the City of Palo Alto’s Near-Field Receiving-Water Monitoring Program, initiated in 1994. Significant reductions in silver and copper contamination occurred at the site in the 1980s following the implementation by PARWQCP of advanced wastewater treatment and source control measures. Since the 1990s, concentrations of these elements in surface sediments have continued to decrease, although more slowly. Silver appears to have stabilized at concentrations about twice the regional background concentration. Presently, sediment copper concentrations appear to be near the regional background level. Over the same period (1994–2019), sedimentary iron and zinc also exhibited modest declines. Sedimentary aluminum, chromium, mercury, nickel, and selenium have not exhibited any trend. Since 1994, concentrations of silver and copper in L. petalum have varied seasonally, apparently in response to a combination of site-specific metal exposures and cyclic growth and reproduction, as reported previously. Seasonal patterns for other elements, including chromium, mercury, nickel, selenium, and zinc, were generally similar in timing and magnitude as those for silver and copper. The annual growth and reproductive cycle explained a small amount of the variance in annual silver and zinc tissue metal concentrations. However, interannual trends are not apparent for any element. Biological effects of elevated silver and copper contamination at the Palo Alto site have been interpreted from data collected during and after the recession of these contaminants. Concentrations of both elements in the soft tissues of L. petalum declined with sedimentary copper and silver. This pattern was associated with changes in the reproductive activity of L. petalum , as well as the structure of the benthic invertebrate community. Reproductive activity of L. petalum increased as metal concentrations in L. petalum declined and presently is stable with almost all animals initiating reproduction in the fall and spawning the following spring. Analyses of the benthic community structure indicate that the infaunal invertebrate community has shifted from one dominated by several opportunistic species when silver and copper exposures were highest to one in which the species abundance is more evenly distributed, a pattern that indicates a more stable community that is subjected to fewer stressors. Importantly, this long-term change is unrelated to other metals and other measured environmental factors, including salinity and sediment composition. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2019. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2019. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for deep-dwelling animals like L. petalum . However, within two months of this event, animals returned to the mudflat. The resilience of the community suggested that the disturbance was not caused by a persistent toxin or anoxia. The reproductive mode of most species that were present in 2019 was indicative of species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2019 benthic community data, which showed that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of species that consume the sediment, or filter feed, those that have pelagic larvae that must survive landing on the sediment, and those that brood their young. USGS scientists view the 2008 disturbance event as a response by the infaunal community to an episodic natural stressor (possibly sediment accretion or a pulse of freshwater), in contrast to the long-term recovery from metal contamination. We will compare this recovery to the long-term recovery observed after the 1970s when the decline in sediment pollutants was the dominating factor.

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USGS2021

A riverscape approach reveals downstream propagation of stream thermal responses to riparian thinning at multiple scales

Hydrological connectivity in river networks influences their response to environmental changes as local effects may extend downstream via flowing water. For example, localized changes in riparian forest conditions can affect stream temperatures, and these effects may propagate downstream. However, studies evaluating stream temperature responses to riparian forest management have not considered cumulative effects across entire watersheds. Improved understanding at these scales is needed because land managers are increasingly required to consider broad-scale consequences of their actions. To address this question, we deployed a high-density network of sensors across watersheds to examine stream temperature responses to experimental thinning of riparian forests. A riverscape approach that combined high-resolution data throughout the study watersheds made it possible to examine local and downstream patterns of stream temperature at multiple spatial and temporal scales. We found that local responses of temperature to thinning varied widely depending on the intensity of thinning treatments. Downstream propagation of local responses extended from 100 m to over 1000 m and depended on the magnitude of the local response. We characterized these responses as a series of waveforms. In the watersheds with more intensive thinning, thermal responses occurred most often as an extended pulse where downstream increases in temperature attenuated gradually at variable distances. Although we observed no evidence of cumulative effects associated with thinning at the downstream extent of stream networks, effects emerged where thinning treatments were closely spaced (<400 m apart) and local warming did not dissipate with downstream distance. In a watershed with less intensive thinning, there was either no response or a localized pulse with no downstream propagation. Collectively, these patterns suggest that riparian forest thinning influenced downstream thermal conditions to varying extents depending on the intensity, scale, and spatial proximity of treatments. We found that a multiscale riverscape approach and conceptual framework based on contrasting waveforms provided a foundation for understanding the cumulative watershed effects of riparian thinning. The approach developed here can be adapted more broadly when evaluating downstream propagation of local changes in river networks and has direct implications for guiding restoration in riparian ecosystems.

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USGS2021

The seismic hazard implications of declustering and poisson assumptions inferred from a fully time‐dependent model

We use the Third Uniform California Earthquake Rupture Forecast (UCERF3) epidemic‐type aftershock sequence (ETAS) model (UCERF3‐ETAS) to evaluate the effects of declustering and Poisson assumptions on seismic hazard estimates. Although declustering is necessary to infer the long‐term spatial distribution of earthquake rates, the question is whether it is also necessary to honor the Poisson assumption in classic probabilistic seismic hazard assessment. We use 500,000 yr, M ≥ 2.5 synthetic catalogs to address this question, for which UCERF3‐ETAS exhibits realistic spatiotemporal clustering effects (e.g., aftershocks). We find that Gardner and Knopoff (1974) declustering, used in the U.S. Geological Survey seismic hazard models, lowers 2% in 50 yr and risk‐targeted ground‐motion hazard metrics by about 4% on average (compared with the full time‐dependent [TD] model), with the reduction being 5% at 40% in 50 yr ground motions. Keeping all earthquakes and treating them as a Poisson process increases these same hazard metrics by about 3%–12%, on average, due to the removal of relatively quiet time periods in the full TD model. In the interest of model simplification, bias minimization, and consideration of the probabilities of multiple exceedances, we agree with others ( Marzocchi and Taroni, 2014 ) that we are better off keeping aftershocks and treating them as a Poisson process rather than removing them from hazard consideration via declustering. Honoring the true time dependence, however, will likely be important for other hazard and risk metrics, and this study further exemplifies how this can now be evaluated more extensively.

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USGS2021

Flooding duration and volume more important than peak discharge in explaining 18 years of gravel–cobble river change

Floods play a critical role in geomorphic change, but whether peak magnitude, duration, volume, or frequency determines the resulting magnitude of erosion and deposition is a question often proposed in geomorphic effectiveness studies. This study investigated that question using digital elevation model differencing to compare and contrast three hydrologically distinct epochs of topographic change spanning 18 years in the 37-km gravel–cobble lower Yuba River in northern California, USA. Scour and fill were analysed by volume at segment and geomorphic reach scales. Each epoch's hydrology was characterized using 15-min and daily averaged flow to obtain distinct peak and recurrence, duration, and volume metrics. Epochs 1 (1999–2008) and 3 (2014–2017) were wetter than average with large floods reaching 3206 and 2466 m 3 /s, respectively, though of different flood durations. Epoch 2 (2008–2014) was a drought period with only four brief moderate floods (peak of 1245 m 3 /s). Total volumetric changes showed that major geomorphic response occurred primarily during large flood events; however, total scour and net export of sediment varied greatly, with 20 times more export in epoch 3 compared to epoch 1. The key finding was that greater peak discharge was not correlated with greater net and total erosion; differences were better explained by duration and volume above floodway-filling stage. This finding highlights the importance of considering flood duration and volume, along with peak, to assess flood magnitude in the context of flood management, frequency analysis, and resulting geomorphic changes.

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USGS2021

Development of a groundwater-simulation model in the Los Angeles Coastal Plain, Los Angeles County, California

Executive Summary The Los Angeles Coastal Plain (LACP) covers about 580 square miles and is the largest coastal plain of semiarid southern California. The LACP is heavily developed with mostly residential, commercial, and industrial land uses that rely heavily on groundwater for water supply. In 2010, the LACP was home to about 14 percent of California’s population, or about 5.4 million residents. The LACP is also a major commercial and industrial hub with industries including manufacturing, aerospace, entertainment, and tourism. There has been a heavy reliance on groundwater from the LACP for many years. An average of 305,000 acre-feet per year (acre-ft/yr) of groundwater was used annually from the LACP from 1971 to 2015. The need to replenish the groundwater basins within the LACP was recognized as far back as the 1930s, when spreading grounds were first used to replenish groundwater basins and store water underground during times of water surplus to meet demands in times of shortage. Seawater intrusion resulting from freshwater pumping was first observed in the 1940s. As a result, injection of imported water through wells at what is now the West Coast Basin Barrier Project began on an experimental basis in 1951. Managed aquifer recharge from the spreading grounds and barrier wells is now a substantial component of the LACP’s groundwater supply. The average annual recharge from water spreading from 1971 to 2015 was about 120,000 acre-ft/yr, and the average annual injection into the barrier wells was about 33,000 acre-ft/yr. Other inflows include areal recharge, underflow from San Gabriel and San Fernando Valleys, and onshore flow from the ocean. The average annual recharge from these sources was 100,000 acre-feet (acre-ft) from 1971 to 2015. Additionally, cross-boundary flow from Orange County into the western Orange County subareas of the LACP was simulated as 48,000 acre-ft from 1971 to 2015. This study, conducted in cooperation with the Water Replenishment District of Southern California (WRD), involved an assessment of the historical and present status of groundwater resources in the LACP and the development of tools to better understand the groundwater system. These efforts were built upon results from previous studies and incorporate new information and developments in modeling capabilities to provide a more detailed analysis of the aquifer systems. This study includes a comprehensive compilation of geologic and hydrologic data (Chapter A), development of a chronostratigraphic model that provides a detailed description of the LACP aquifer systems (Chapter B), characterization of the groundwater hydrology of the LACP, including a down-hole analysis of grain size using lithologic and geophysical logs (Chapter C), and development and application of the Los Angeles Coastal Plain Groundwater-flow Model (LACPGM) to simulate past groundwater conditions, estimate groundwater-budget components and flow paths, and approximate future groundwater conditions under different scenarios (Chapter D).

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USGS2021

A simplified method for rapid estimation of emergency water supply needs after earthquakes

Researchers are investigating the problem of estimating households with potable water service outages soon after an earthquake. Most of these modeling approaches are computationally intensive, have large proprietary data collection requirements or lack precision, making them unfeasible for rapid assessment, prioritization, and allocation of emergency water resources in large, complex disasters. This study proposes a new simplified analytical method—performed without proprietary water pipeline data—to estimate water supply needs after earthquakes, and a case study of its application in the HayWired earthquake scenario. In the HayWired scenario—a moment magnitude (M w ) 7.0 Hayward Fault earthquake in the San Francisco Bay Area, California (USA)—an analysis of potable water supply in two water utility districts was performed using the University of Colorado Water Network (CUWNet) model. In the case study, application of the simplified method extends these estimates of household water service outage to the nine counties adjacent to the San Francisco Bay, aggregated by a ~250 m 2 (nine-arcsecond) grid. The study estimates about 1.38 million households (3.7 million residents) out of 7.6 million residents (2017, ambient, nighttime population) with potable water service outage soon after the earthquake—about an 8% increase from the HayWired scenario estimates.

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USGS2021

Breeding waterbird populations have declined in south San Francisco Bay: An assessment over two decades

In south San Francisco Bay, former salt ponds now managed as wildlife habitat support large populations of breeding waterbirds. In 2006, the South Bay Salt Pond Restoration Project began the process of converting 50% to 90% of these managed pond habitats into tidal marsh. We compared American Avocet ( Recurvirostra americana ) and Black-necked Stilt ( Himantopus mexicanus ) abundance in south San Francisco Bay before (2001) and after approximately 1,300 ha of managed ponds were breached to tidal action to begin tidal marsh restoration (2019). Over the 18-year period, American Avocet abundance declined 13.5% (2,765 in 2001 vs. 2,391 in 2019), and Black-necked Stilt abundance declined 30.0% (1,184 in 2001 vs. 828 in 2019). Forster’s Tern ( Sterna forsteri ) abundance was 2,675 birds in 2019. In 2019, managed ponds accounted for only 25.8% of suitable habitats, yet contained 53.9%, 38.6%, and 65.6% American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Conversely, tidal marsh and tidal mudflats accounted for 42.9% of suitable habitats, yet contained only 18.4%, 10.3%, and 19.8% of American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Using a separate nest-monitoring data set, we found that nest abundance in south San Francisco Bay declined for all three species from 2005–2019. Average annual nest abundance during 2017–2019 declined 53%, 71%, and 36%, for American Avocets, Back-necked Stilts, and Forster’s Terns, respectively, compared to 2005–2007. Loss of island nesting habitat as a result of tidal marsh conversion and an increasing population of predatory California Gulls ( Larus californicus ) are two potential causes of these declines. All three species established nesting colonies on newly constructed islands within remaining managed ponds; however, these new colonies did not make up for the steep declines observed at other historical nesting sites. For future wetland restoration, retaining more managed ponds that contain islands suitable for nesting may help to limit further declines in breeding waterbird populations.

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USGS2021

Wetland availability and salinity concentrations for breeding waterfowl in Suisun Marsh, California

Availability of wetlands with low salinities during the breeding season can influence waterfowl reproductive success and population recruitment. Salinities as low as 2 ppt (3.6 mScm–1) can impair duckling growth and influence behavior, with mortality occurring above 9 ppt (14.8 mScm–1). We used satellite imagery to quantify the amount of available water, and sampled surface water salinity at Grizzly Island, in the brackish Suisun Marsh, at three time-periods during waterfowl breeding (April, May, July) over 4 years (2016–2019). More water was available and salinity was lower during wetter years (2017, 2019) than during drier years (2016, 2018), and the amount of water in wetlands decreased 73%–86% from April to July. Across all time-periods and years, the majority (64%–100%) of wetland habitat area had salinities above what has been shown to negatively affect ducklings (> 2 ppt), and up to 42% of wetland area had salinities associated with duckling mortality (> 9 ppt). During peak duckling production in May, 81%–95% of available water had salinity above 2 ppt, and 5%–21% was above 9 ppt. In May of the driest year (2016), only 0.5 km2 of low-salinity water (< 2 ppt) was available to ducklings in the study area, compared to 2.6 km2 in May of the wettest year (2017). Private duck clubs own the majority of wetland habitat at Grizzly Island and consistently had a greater percentage of land flooded during summer than did publicly owned wetlands, but private wetlands generally had higher salinities than public wetlands, likely because they draw from higher-salinity water sources. By July, few wetlands remained flooded, and most had salinities high enough to impair duckling growth and survival. Local waterfowl populations would benefit from management practices that provide fresher water during peak duckling production in May and retain more water through July.

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USGS2021

Stratigraphic and structural controls on groundwater salinity variations in the Poso Creek Oil Field, Kern County, California, USA

Groundwater total dissolved solids (TDS) distribution was mapped with a three-dimensional (3D) model, and it was found that TDS variability is largely controlled by stratigraphy and geologic structure. General TDS patterns in the San Joaquin Valley of California (USA) are attributed to predominantly connate water composition and large-scale recharge from the adjacent Sierra Nevada. However, in smaller areas, stratigraphy and faulting play an important role in controlling TDS. Here, the relationship of stratigraphy and structure to TDS concentration was examined at Poso Creek Oil Field, Kern County, California. The TDS model was constructed using produced water TDS samples and borehole geophysics. The model was used to predict TDS concentration at discrete locations in 3D space and used a Gaussian process to interpolate TDS over a volume. In the overlying aquifer, TDS is typically <1,000 mg/L and increases with depth to ~1,200–3,500 mg/L in the hydrocarbon zone below the Macoma claystone—a regionally extensive, fine-grained unit—and reaches ~7,000 mg/L in isolated places. The Macoma claystone creates a vertical TDS gradient in the west where it is thickest, but control decreases to the east where it pinches out and allows freshwater recharge. Previously mapped normal faults were found to exhibit inconsistent control on TDS. In one case, high-density faulting appears to prevent recharge from flushing higher-TDS connate water. Elsewhere, the high-throw segments of a normal fault exhibit variable behavior, in places blocking lower-TDS recharge and in other cases allowing flushing. Importantly, faults apparently have differential control on oil and groundwater.

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USGS2021

Watershed sediment yield following the 2018 Carr Fire, Whiskeytown National Recreation Area, northern California

Wildfire risk has increased in recent decades over many regions, due to warming climate and other factors. Increased sediment export from recently burned landscapes can jeopardize downstream infrastructure and water resources, but physical landscape response to fire has not been quantified for some at-risk areas, including much of northern California, USA. We measured sediment yield from three watersheds (13–29 km 2 ) that drain to Whiskeytown Lake, California, within the area burned by the 2018 Carr Fire. Structure-from-Motion photogrammetry on aerial images combined with sonar bathymetric mapping of submerged areas indicated first-year post-fire sediment yields of 4,080 ± 598 t/km 2 (Brandy Creek), 2,700 ± 527 t/km 2 (Boulder Creek), and 305 ± 58.0 t/km 2 (Whiskey Creek)—some of the first post-fire yields measured in northern California and 64, 42, and 4.8 times greater than pre-fire yields, respectively. These were measured during a wet year and resulted largely from rilling erosion and fluvial sediment transport, without post-fire debris flows. Rilling preferentially developed in contact with dirt roads, aided by thin soils and exposed bedrock, and on slopes vegetated by chaparral pre-fire. The second post-fire year (a dry year) was characterized by fluvial reworking and delta progradation of the first-year deposits and relatively little new sediment export. First-year sedimentation of 111,000 m 3 represented minor loss of storage capacity in Whiskeytown Lake but would be detrimental to smaller reservoirs; in general, increased sediment yields from western US watersheds as fire and extreme rainfall increase will likely pose risks to water quality and storage.

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USGS2021

Kelp forest monitoring at Naval Base Ventura County, San Nicolas Island, California—Fall 2019, sixth annual repor

The U.S. Geological Survey conducts ecological monitoring of rocky subtidal communities at four permanent sites around San Nicolas Island. The sites—Nav Fac 100, West End, Dutch Harbor, and Daytona 100—were based on ones that had been monitored since 1980 by the U.S. Geological Survey and, in cooperation with the U.S. Navy, were combined or expanded in 2014 for better comparability with monitoring programs conducted at the other California Channel Islands. At the sites, we counted a suite of kelps and invertebrates on benthic band transects, measured bottom cover of algae and sessile invertebrate species in quadrats, and counted and sized fish on swimming transects. Holdfast diameter and number of stipes of giant kelp ( Macrocystis pyrifera ) were recorded on these transects and size data were collected for urchins, sea stars, and shelled mollusks. Bottom temperatures were recorded at hourly intervals by archival data loggers that were deployed at the sites. Typically, this monitoring work is conducted semi-annually, in fall and spring. Because the spring 2020 trip was cancelled due to the Coronavirus Disease 2019 pandemic, this report focuses primarily on data collected in fall 2019 and makes comparisons with data collected in previous years, beginning in fall 2014. The sites are distributed around the island and differ in their physical and ecological characteristics. Nav Fac 100, situated on the north side of San Nicolas Island, has a relatively low benthic profile. The invasive brown alga Sargassum horneri was first observed at this site in 2015. West End, to the southwest of the island, also lacks much bottom relief but has more crevice habitat associated with boulders. For almost three decades, West End has been a focal point for the small, but growing, population of southern sea otters ( Enhydra lutris nereis ) at the island. Dutch Harbor, on the south side, has many high relief rocky reefs and had the greatest fish and non-motile invertebrate densities. Daytona 100, on the southeast side, has moderate relief and has remained a patchwork of kelp and sea urchin dominated areas. There were no major changes at the sites since spring 2019, but some trends observed during the last few years continued whereas others changed. Red urchins continued a declining trend (observed during the last 4 years) at Daytona 100. The wavy turban snail ( Megastraea undosa ) began to increase rapidly at Nav Fav 100 in 2015 and has subsequently been increasing at the other sites as well, after more than a decade of very low numbers at all sites. Sea star wasting syndrome, which has devastated multiple species of sea stars along the Pacific coast of North America, affected most species at San Nicolas Island in the year prior to the fall 2014 sampling. Since then, there has been a reduction in the number of bat stars ( Patiria miniata ), and very few sea stars of other species have been observed. There has been a slight recovery of P. miniata since 2016 but little sign of change in other species. All the sites had a slight decline in the densities of purple urchins following an increase during the previous 2 years. Long-term data are presented to illustrate trends and changes during almost four decades of monitoring this dynamic system.

Naval Base Ventura County, San Nicolas Island↗

USGS2021

Effect of the emergency drought barrier on the distribution, biomass, and grazing rate of the bivalves Corbicula fluminea and Potamocorbula amurensis, False River, California

Executive Summary Benthic samples were collected from the Sacramento–San Joaquin Delta of northern California to examine the effect of the changing hydrologic flow on the bivalves Potamocorbula and Corbicula before, during, and after the False River Barrier (hereafter, barrier) was in operation (May–November 2015). Potamocorbula moved upstream in the Sacramento River as the salinity intruded. Given the lower electrical conductivity of the San Joaquin River, Potamocorbula did not move as far upriver as it did in the Sacramento River. Potamocorbula recruits settled in the Sacramento and False Rivers, whereas Corbicula recruits were mostly found in the San Joaquin River. When the grazing rates for the two bivalves were combined, new populations of Potamocorbula plus existing Corbicula likely reduced the net growth rate of the phytoplankton in and just upstream from the Sacramento and San Joaquin River confluence region when the barrier was in place. Prior to the barrier installation, a very dry period assumably aided the success of Potamocorbula in the confluence region; nonetheless, they also responded to the increasing salinity in the Sacramento River and their population spatially expanded. Potamocorbula’s upriver incursion was stopped owing to the return of freshwater flow due to the removal of the barrier, but the adults of the species were still present at the upstream end of Decker Island in January 2016. Corbicula adults did not seem to respond to the increased salinity caused by the barrier and maintained their biomass at all locations compared to what was recorded before the barrier.

California↗