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At least 163 records · Page 9Linked to original sources
USGS2013

DOM composition in an agricultural watershed: assessing patterns and variability in the context of spatial scales

Willow Slough, a seasonally irrigated agricultural watershed in the Sacramento River valley, California, was sampled synoptically in order to investigate the extent to which dissolved organic carbon (DOC) concentrations and compositions from throughout the catchment are represented at the mouth. DOC concentrations ranged from 1.8 to 13.9 mg L −1 , with the lowest values in headwater 1st and 2nd order streams, and the highest values associated with flood irrigation. Carbon-normalized vanillyl phenols varied from 0.05 to 0.67 mg 100 mg OC −1 (0.37 mean), indicative of considerable contributions from vascular plants. DOC concentrations and compositions at the mouth appear to be primarily influenced by land use (agriculture) in the lower reaches, and therefore very little of the headwater chemistry (1st and 2nd order streams) can be discerned from the chemistry at or near the mouth (3rd and 4th order streams), indicating the need for synoptic sampling to capture the breadth of organic carbon cycling within a catchment. Field sampling during irrigation showed the large impact that flood irrigation can have on DOC concentrations and compositions, likely a primary cause of significantly elevated Willow Slough DOC concentrations during the summer irrigation season. Optical proxies exhibited varying degrees of correlation with chemical measurements, with strongest relationships to DOC and dissolved lignin ( r 2 = 0.95 and 0.73, respectively) and weaker relationships to carbon-normalized lignin yields and C:V ( r 2 from 0.31 to 0.42). Demonstrating the importance of matching scale to processes, we found no relationship between dissolved lignin concentrations and total suspended sediments (TSS) across all sites, in contrast to the strong relationship observed in weekly samples at the mouth. As DOC concentrations and compositions at the mouth of Willow Slough are closely tied to anthropogenic activities within the catchment, future changes in land-use driven by climate change, water availability, and economic pressures on crop types will also bring about changes in the overall biogeochemistry.

California↗
USGS2018

Increasing soil organic carbon to mitigate greenhouse gases and increase climate resiliency for California

Rising air temperatures are projected to continue to drive up urban, agricultural, and rangeland water use, straining both surface and groundwater resources. Scientific studies have shown that managing farms, ranches, and public lands to increase soil carbon can increase soil waterholding capacity and increase hydrologic benefits such as increased baseflows and aquifer recharge, reduced flooding and erosion, and reduced climate-related water deficits. Coincident improvements in forage and crop yields are also indicated, while simultaneously sequestering carbon, reducing atmospheric greenhouse gases and mitigating climate change. This study was developed to consider the multiple benefits of increasing the organic matter content of soils across California’s working lands. Study results indicate that a one-time ¼” application of compost to rangelands can lead to carbon sequestration rates in soils that are maximized after approximately 15 years, and more than offset greenhouse gas emissions stimulated by the compost addition for at least five decades longer. Modeled increases in total soil organic matter of 3% enhanced hydrologic benefits across 97% of working lands, and reduced climate change impacts. Economic valuation indicated all benefits increasing over time, demonstrating a large potential for the California carbon market to support incentives in regionalizing the impacts in the coming decades. Socioeconomic and related land use pressures pose barriers to implementing management practices to increase soil organic matter by driving conversion of rangeland to urban or to more greenhouse-gas emission intensive agriculture. Results can be effectively used with land use change scenarios to identify where on California’s working lands hydrologic benefits of soil organic matter enhancement coincide with development risk, highlighting counties in California in which there may be resilience to climate change when strategic soil management and land conservation are combined.

California↗
USGS2006

Geology, ground-water hydrology, geochemistry, and ground-water simulation of the Beaumont and Banning Storage Units, San Gorgonio Pass area, Riverside County, California

Ground water has been the only source of potable water supply for residential, industrial, and agricultural users in the Beaumont and Banning storage units of the San Gorgonio Pass area, Riverside County, California. Ground-water levels in the Beaumont area have declined as much as 100 feet between the early 1920s and early 2000s, and numerous natural springs have stopped flowing. In 1961, the San Gorgonio Pass Water Agency (SGPWA) entered into a contract with the California State Department of Water Resources to receive 17,300 acre-feet per year of water to be delivered by the California State Water Project (SWP) to supplement natural recharge. Currently (2005), a pipeline is delivering SWP water into the area, and the SGPWA is artificially recharging the ground-water system using recharge ponds located along Little San Gorgonio Creek in Cherry Valley with the SWP water. In addition to artificial recharge, SGPWA is considering the direct delivery of SWP water for the irrigation of local golf courses and for agricultural supply in lieu of ground-water pumpage. To better understand the potential hydrologic effects of different water-management alternatives on ground-water levels and movement in the Beaumont and Banning storage units, existing geohydrologic and geochemical data were compiled, new data from a basin-wide ground-water level and water-quality monitoring network were collected, monitoring wells were installed near the Little San Gorgonio Creek recharge ponds, geohydrologic and geochemical analyses were completed, and a ground-water flow simulation model was developed. The San Gorgonio Pass area was divided into several storage units on the basis of mapped or inferred faults. This study addresses primarily the Beaumont and Banning storage units. The geologic units in the study area were generalized into crystalline basement rocks and sedimentary deposits. The younger sedimentary deposits and the surficial deposits are the main water-bearing deposits in the San Gorgonio Pass area. The water-bearing deposits were divided into three aquifers: (1) the perched aquifer, (2) the upper aquifer, and (3) the lower aquifer based on lithologic and downhole geophysical logs. Natural recharge in the San Gorgonio Pass area was estimated using INFILv3, a deterministic distributed- parameter precipitation-runoff model. The INFILv3 model simulated that the potential recharge of precipitation and runoff in the Beaumont and Banning storage units was about 3,710 acre-feet per year and that the potential recharge in 28 sub-drainage basins upstream of the storage units was about 6,180 acre-feet per year. The water supply for the Beaumont and Banning storage units is supplied by pumping ground water from wells in the Canyon (Edgar and Banning Canyons), Banning Bench, Beaumont, and Banning storage units. Total annual pumpage from the Beaumont and Banning storage units ranged from about 1,630 acre-feet in 1936 to about 20,000 acre-feet in 2003. Ground-water levels declined by as much as 100 feet in the Beaumont storage unit from 1926-2003 in response to ground-water pumping of about 450,160 acre-feet during this period. Since ground-water development began in the San Gorgonio Pass area, there have been several sources of artificial recharge to the basin including return flow from applied water on crops, golf courses, and landscape; septic-tank seepage; and infiltration of storm runoff diversions and imported water into recharge ponds. Return flow from applied water and septic-tank seepage was estimated to reach a maximum of about 8,100 acre-feet per year in 2003. Owing to the great depth of water in much of study area (in excess of 150 feet), the return flow and septic-tank seepage takes years to decades to reach the water table. Stable-isotope data indicate that the source of ground-water recharge was precipitation from storms passing through the San Gorgonio Pass as opposed to runoff from the higher altitudes of the San Bernar

Scientific Investigations Report↗
USGS1994

Subsidence and carbon fluxes in the Sacramento/San Joaquin Delta, California

The Sacramento/San Joaquin Delta was once tidal marshland and was formed by the confluence of the Sacramento and the San Joaquin Rivers. The delta covers more than 1,000 square miles and is bordered by the major population centers of the San Francisco Bay area, Sacramento, and Stockton (fig. 1). The delta took its current form by the 1930's when drainage of 100 islands and tracts and construction of 2,250 miles of levees were completed. The land surface on the delta islands has progressively subsided below sea level since the early 20th century. The integrity of the levee network is threatened because subsidence increases the differences in water levels maintained by the levees, which can cause levee failure and consequent flooding of the delta islands. Levee failure affects the quality and beneficial use of water in the delta, which is the major source of California's water supply to millions of residents and acres of agricultural land. This Fact Sheet briefly summarizes the research done by the U.S. Geological Survey, in cooperation with the California Department of Water Resources to assess the causes of subsidence, processes that affect subsidence, and carbon fluxes in the delta.

California↗
USGS2011

Seasonal variation in nutritional characteristics of the diet of greater white-fronted geese

We studied diet and habitat use of greater white-fronted geese ( Anser albifrons ) from autumn through spring on their primary staging and wintering areas in the Pacific Flyway, 1979–1982. There have been few previous studies of resource use and forage quality of wintering greater white-fronted geese in North America, and as a consequence there has been little empirical support for management practices pertaining to habitat conservation of this broadly distributed species. Observations of >2,500 flocks of geese and collections of foraging birds revealed seasonal and geographic variation in resource use reflective of changes in habitat availability, selection, and fluctuating physiological demands. Autumn migrants from Alaska arrived first in the Klamath Basin of California and southern Oregon, where they fed on barley, oats, wheat, and potatoes. Geese migrated from the Klamath Basin into the Central Valley of California in late autumn where they exploited agricultural crops rich in soluble carbohydrates, with geese in the Sacramento Valley feeding almost exclusively on rice and birds on the Sacramento–San Joaquin Delta primarily utilizing corn. White-fronted geese began their northward migration in late winter, and by early spring most had returned to the Klamath Basin where 37% of flocks were found in fields of new growth cultivated and wild grasses. Cereal grains and potatoes ingested by geese were low in protein (7–14%) and high in soluble nutrients (17–47% neutral detergent fiber [NDF]), whereas grasses were low in available energy (47–49% NDF) but high in protein (26–42%). Greater white-fronted geese are generalist herbivores and can exploit a variety of carbohydrate-rich cultivated crops, likely making these geese less susceptible to winter food shortages than prior to the agriculturalization of the North American landscape. However, agricultural landscapes can be extremely dynamic and may be less predictable in the long-term than the historic environments to which geese are adapted. Thus far greater white-fronted geese have proved resilient to changes in land cover in the Pacific Flyway and by altering their migration regime have even been able to adapt to changes in the availability of suitable forage crops.

Pacific Flyway↗
USGS2026

Quantifying post-fire live tree presence and spatial variation using Sentinel-2 time series

Accurate mapping of post-fire surviving trees is important for tracking forest recovery and prioritizing land management decisions. Satellite-based remote sensing is an effective method to assess post-fire forest conditions. Traditionally, differenced satellite-derived burn severity indices are computed by differencing one year pre- and post-fire spectral reflectance values. Differenced burn severity indices are useful for quantifying and mapping the magnitude of ecological change, but their application to detecting and mapping post-fire live trees may not be as appropriate, particularly for delayed tree mortality. Delayed tree mortality (“delayed mortality”) is a phenomenon where trees that initially survive fire then die over an extended period (between one and five years), and it can be challenging to measure and predict. In this study, we demonstrate the potential of mapping delayed mortality using readily available remotely sensed imagery alone. We used random forest models to detect post-fire live trees using 10-m resolution Sentinel-2 data at one-, three-, and five-years post-fire for four fires in the southern Sierra Nevada, California, USA. Using imagery from the National Agriculture Imagery Program (NAIP; 60-cm resolution), we manually classified live tree presence in 6000 Sentinel-2 pixels (500 pixels for each fire-year combination) to calibrate and validate models. Sentinel-2 based model accuracies ranged from 65 % to 86 % with F-scores ranging from 0.52 to 0.86, and their predictions of live pixel area were on average 44 % lower than inferred from more traditional indices such as relative differenced normalized burn ratio (RdNBR). This work represents a promising first step in using freely available post-fire spectral reflectance imagery to detect live trees over an extended period to support post-fire management.

California↗
USGS2021

Groundwater residence time estimates obscured by anthropogenic carbonate

Groundwater is an important source of drinking and irrigation water. Dating groundwater informs its vulnerability to contamination and aids in calibrating flow models. Here, we report measurements of multiple age tracers ( 14 C, 3 H, 39 Ar, and 85 Kr) and parameters relevant to dissolved inorganic carbon (DIC) from 17 wells in California’s San Joaquin Valley (SJV), an agricultural region that is heavily reliant on groundwater. We find evidence for a major mid-20th century shift in groundwater DIC input from mostly closed- to mostly open-system carbonate dissolution, which we suggest is driven by input of anthropogenic carbonate soil amendments. Crucially, enhanced open-system dissolution, in which DIC equilibrates with soil CO 2 , fundamentally affects the initial 14 C activity of recently recharged groundwater. Conventional 14 C dating of deeper SJV groundwater, assuming an open system, substantially overestimates residence time and thereby underestimates susceptibility to modern contamination. Because carbonate soil amendments are ubiquitous, other groundwater-reliant agricultural regions may be similarly affected.

California↗
USGS2022

Groundwater quality of the Lucerne Valley groundwater basin, California

Anthropogenic activities, including groundwater withdrawals, return flow from irrigated agriculture, and treated wastewater-effluent disposal have the potential to affect groundwater quality in the Lucerne Valley groundwater basin, located in the southwest Mojave Desert. Questions regarding the current state and potential future of groundwater quality in this basin were addressed by (1) considering groundwater data from and findings of historical water-quality studies, (2) evaluating recent (1990–2021) U.S. Geological Survey water-quality and geochemical-tracer data, and (3) assessing groundwater-quality results from samples collected in 2021 to better understand the transport of applied treated wastewater effluent in the subsurface and associated effects of this practice on water quality. As observed by previous studies, differences in groundwater quality existed among the upper, middle, and lower aquifers of the Lucerne Valley groundwater basin, with the lower aquifer characterized by high dissolved-solid content relative to the middle and upper aquifers. Stable and radioisotope tracers indicate that most of the groundwater sampled in the basin was recharged during cooler, wetter climate conditions than those of the present day (2022). Analyses of the 2021 samples collected to examine the subsurface transport of applied treated wastewater effluent were not conclusive but indicate that water from applied treated wastewater effluent is currently (2022) limited to the upper aquifer and likely to remain so given the extensive confining unit below the upper aquifer.

California↗
USGS2026

Assessing natural recharge in Indian Wells Valley, California: A Basin Characterization Model case study

The communities in Indian Wells Valley (IWV), in the northern Mojave Desert in California, rely on groundwater for domestic and agricultural use. Mountain front recharge from the surrounding Sierra Nevada is the main source of natural recharge to the valley. Increased urbanization, agricultural development, and groundwater pumping during recent decades put IWV in a state of critical overdraft. The U.S. Geological Survey Basin Characterization Model, version 8 (BCMv8) was used to evaluate historical and future climate and hydrologic conditions in IWV. The BCMv8 estimated natural recharge in IWV at 10.7 million cubic meters (Mm 3 ) per year for the period from 1981 to 2010. Future patterns of water balance variables using three future climate scenarios, hot-wet, hot-dry, and warm-moderately wet, were calculated for mid-century (2040–69) and end-of-century (2070–99) periods. Results for both wet models projected an increase in recharge in both periods, whereas the hot-dry model projected a decrease in recharge in both periods. All models reported a large increase in seasonal variability in recharge, indicating more future availability and frequent occurrences of drought years. All climate scenarios projected an increase in climatic water deficit in both periods. These increases in irrigation demand and variability of water supply highlight the importance of strategic management planning for the sustainability of water resources in IWV.

California↗
USGS2024

Groundwater sustainability and land subsidence in California’s Central Valley

The Central Valley of California is one of the most prolific agricultural regions in the world. Agriculture is reliant on the conjunctive use of surface-water and groundwater. The lack of available surface-water and land-use changes have led to pumping-induced groundwater-level and storage declines, land subsidence, changes to streamflow and the environment, and the degradation of water quality. As a result, in part, the Sustainable Groundwater Management Act (SGMA) was developed. An examination of the components of SGMA and contextualizing regional model applications within the SGMA framework was undertaken to better understand and quantify many of the components of SGMA. Specifically, the U.S. Geological Survey (USGS) updated the Central Valley Hydrologic Model (CVHM) to assess hydrologic system responses to climatic variation, surface-water availability, land-use changes, and groundwater pumping. MODFLOW-OWHM has been enhanced to simulate the timing of land subsidence and attribute its inelastic and elastic portions. In addition to extending CVHM through 2019, the new version, CVHM2, includes several enhancements as follows: managed aquifer recharge (MAR), pumping with multi-aquifer wells, inflows from ungauged watersheds, and more detailed water-balance subregions, streamflow network, diversions, tile drains, land use, aquifer properties, and groundwater level and land subsidence observations. Combined with historical approximations, CVHM2 estimates approximately 158 km 3 of storage loss in the Central Valley from pre-development to 2019. About 15% of the total storage loss is permanent loss of storage from subsidence that has caused damage to infrastructure. Climate extremes will likely complicate the efforts of water managers to store more water in the ground. CVHM2 can provide data in the form of aggregated input datasets, simulate climatic variations and changes, land-use changes or water management scenarios, and resulting changes in groundwater levels, storage, and land subsidence to assist decision-makers in the conjunctive management of water supplies.

California↗
USGS2008

Pesticides in rain in four agricultural watersheds in the United States

Rainfall samples were collected during the 2003 and 2004 growing seasons at four agricultural locales across the USA in Maryland, Indiana, Nebraska, and California. The samples were analyzed for 21 insecticides, 18 herbicides, three fungicides, and 40 pesticide degradates. Data from all sites combined show that 7 of the 10 most frequently detected pesticides were herbicides, with atrazine (70%) and metolachlor (83%) detected at every site. Dacthal, acetochlor, simazine, alachlor, and pendimethalin were detected in more than 50% of the samples. Chlorpyrifos, carbaryl, and diazinon were the only insecticides among the 10 most frequently detected compounds. Of the remaining pesticide parent compounds, 18 were detected in fewer than 30% of the samples, and 13 were not detected. The most frequently detected degradates were deethylatrazine; the oxygen analogs (OAs) of the organophosphorus insecticides chlorpyrifos, diazinon, and malathion; and 1-napthol (degradate of carbaryl). Deethylatrazine was detected in nearly 70% of the samples collected in Maryland, Indiana, and Nebraska but was detected only once in California. The OAs of chlorpyrifos and diazinon were detected primarily in California. Degradates of the acetanilide herbicides were rarely detected in rain, indicating that they are not formed in the atmosphere or readily volatilized from soils. Herbicides accounted for 91 to 98% of the total pesticide mass deposited by rain except in California, where insecticides accounted for 61% in 2004. The mass of pesticides deposited by rainfall was estimated to be less than 2% of the total applied in these agricultural areas.

Journal of Environmental Quality↗
USGS2022

Characterization of subsurface conditions and recharge at the irrigated four-plex baseball field, Fort Irwin National Training Center, California, 2018–20

The U.S. Geological Survey performed subsurface and geophysical site characterization of the irrigated four-plex baseball field in the Langford Valley–Irwin Groundwater Subbasin, as part of a research study in cooperation with the U.S. Environmental Protection Agency, the Agricultural Research Service, and the Fort Irwin National Training Center, California. To help meet future demands, the Fort Irwin National Training Center is evaluating the efficacy of gravity-fed drywells to enhance storm-water recharge into the Langford Valley–Irwin Groundwater Subbasin by bypassing fine-grained, less permeable deposits between land surface and the water table. The amount, rate, and location of recharge beneath an irrigated baseball field in the groundwater basin at the Fort Irwin National Training Center is not well understood, so data were collected using physical and geophysical techniques to characterize subsurface materials, geologic controls, and the vertical movement of water through the unsaturated zone to the water table near the drywell at the Fort Irwin National Training Center. Based on the data collected and interpreted from these techniques, several fine-grained deposits were identified. Although these deposits appear to impede the downward movement of water through the unsaturated zone locally, they are not laterally continuous, and water appears to continue to move downward when it reaches the edges of the deposits. These data will help managers evaluate recharge at the site and determine if the use of gravity-fed drywells enhances recharge from surface runoff.

California↗
USGS1988

Selenium teratogenesis in natural populations of aquatic birds in central California

The frequency and types of malformations are described that were encountered during the spring of 1983 in a natural population of aquatic birds exposed to agricultural drainwater ponds and food items containing high concentrations of selenium in central California. A total of 347 nests of aquatic birds containing 1,681 eggs was selected for study at Kesterson Reservoir located in the Kesterson National Wildlife Refuge (NWR), Merced County, California. Embryos collected during incubation or from eggs that failed to hatch were examined to determine the age at death and presence of malformations. Embryonic death was generally high; approximately 17–60% of the nests of different species contained at least one dead embryo. The incidence of malformed embryos was also high; approximately 22–65% of the nests where at least two embryos were examined contained abnormal embryos. American coots ( Fulica americana ) and black-necked stilts ( Himantopus mexicanus ) experienced the highest incidence of malformed embryos. For all species, the average percentage of eggs containing dead or live abnormal embryos was 16.1 whereas the average percentage containing live abnormal embryos was 10.7. Multiple gross malformations of the eyes, brain, and feet were often present. Brain defects included hydrocephaly and exencephaly. Eye defects included both unilateral and bilateral anophthalmia and microphthalmia. Eye and foot defects with ectrodactyly and swollen joints were the most common in coots. Beak defects also occurred frequently and most often included incomplete development of the lower beak of ducks ( Anas spp.) and stilts. Wing and leg defects were most prevalent in stilts and ducks, with ectromelia and amelia most prevalent in stilts. Other malformations occurring at lower frequencies included enlarged hearts with thin ventricular walls, liver hypopiasia, and gastroschisis. Based upon simultaneous examination of a control population of aquatic birds of the same species and published studies, the incidences of embryonic mortality and deformities were 9–30 times greater than expected. The role of the form of selenium responsible for teratogenesis in laboratory studies is discussed.

California↗
USGS2012

Pyrethroid insecticides in bed sediments from urban and agricultural streams across the United States

Pyrethroid insecticides are hydrophobic compounds that partition to streambed sediments and have been shown to cause toxicity to non-target organisms; their occurrence is well documented in parts of California, but there have been limited studies in other urban and agricultural areas across the United States. To broaden geographic understanding of pyrethroid distributions, bed sediment samples were collected and analyzed from 36 streams in 25 states, with about 2/3 of the sites in urban areas and 1/3 in agricultural areas. At least one pyrethroid (of the 14 included in the analysis) was detected in 78% of samples. Seven pyrethroids were detected in one or more samples. Bifenthrin was the most frequently detected (58% of samples), followed by permethrin (31%), resmethrin (17%), and cyfluthrin (14%). The other three detected pyrethroids (cyhalothrin, cypermethrin and delta/tralomethrin) were found in two or fewer of the samples. Concentrations ranged from 0.3 to 180 ng g -1 dry weight. The number of pyrethroids detected were higher in the urban samples than in the agricultural samples, but the highest concentrations of individual pyrethroids were split between urban and agricultural sites. The pyrethroids detected in the agricultural areas generally followed use patterns. Predicted toxicity was greater for urban areas and attributed to bifenthrin, cyfluthrin and cypermethrin, while in agricultural areas the toxicity was mainly attributed to bifenthrin.

Journal of Environmental Monitoring↗
USGS2025

Central Valley Hydrologic Model version 2 (CVHM2): Decision support tool for groundwater and land subsidence management

The San Joaquin Valley (SJV) of California is one of the world’s most productive agricultural regions. Reliance on groundwater has led to some of the greatest rates of human-induced land subsidence in the world in the 20th century, as well as more recently. The United States Geological Survey (USGS) has recently developed an integrated surface–subsurface hydrologic model, the Central Valley Hydrologic Model 2 (CVHM2), that represents the major components of the hydrologic system of California’s Central Valley. In this study, CVHM2 was applied as a decision support tool while simulating various management strategies to mitigate the land subsidence caused by the extraction of groundwater. CVHM2 was extended through to 2073 and applied to simulate management scenarios in terms of three primary drivers and their impact on subsidence along the Delta–Mendota Canal (DMC), a critical piece of infrastructure in the western SJV. The drivers considered were agricultural water demands, managed aquifer recharge (MAR), and changes in future climate. The results show that future subsidence is most sensitive to water demands, second most sensitive to future changes in climate, and relatively insensitive to MAR when it is applied as a surface application in the western SJV. However, we demonstrate via proof-of-concept scenarios that the MAR is capable of arresting subsidence when implemented via injection below the Corcoran Clay Member of the Tulare Formation instead of as a surface application. We also examine the uncertainty that is the result of climate variability and how to use the tool to identify the most appropriate strategies to constrain future subsidence to acceptable levels.

California↗
USGS2013

Carnivore use of avocado orchards across an agricultural-wildland gradient

Wide-ranging species cannot persist in reserves alone. Consequently, there is growing interest in the conservation value of agricultural lands that separate or buffer natural areas. The value of agricultural lands for wildlife habitat and connectivity varies as a function of the crop type and landscape context, and quantifying these differences will improve our ability to manage these lands more effectively for animals. In southern California, many species are present in avocado orchards, including mammalian carnivores. We examined occupancy of avocado orchards by mammalian carnivores across agricultural-wildland gradients in southern California with motion-activated cameras. More carnivore species were detected with cameras in orchards than in wildland sites, and for bobcats and gray foxes, orchards were associated with higher occupancy rates. Our results demonstrate that agricultural lands have potential to contribute to conservation by providing habitat or facilitating landscape connectivity.

California↗
USGS2017

Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape

Most extant giant gartersnake ( Thamnophis gigas ) populations persist in an agro-ecosystem dominated by rice, which serves as a surrogate to the expansive marshes lost to flood control projects and development of the Great Central Valley of California. Knowledge of how giant gartersnakes use the rice agricultural landscape, including how they respond to fallowing, idling, or crop rotations, would greatly benefit conservation of giant gartersnakes by informing more snake-friendly land and water management practices. We studied adult giant gartersnakes at 11 sites in the rice-growing regions of the Sacramento Valley during an extended drought in California to evaluate their response to differences in water availability at the site and individual levels. Although our study indicated that giant gartersnakes make little use of rice fields themselves, and avoid cultivated rice relative to its availability on the landscape, rice is a crucial component of the modern landscape for giant gartersnakes. Giant gartersnakes are strongly associated with the canals that supply water to and drain water from rice fields; these canals provide much more stable habitat than rice fields because they maintain water longer and support marsh-like conditions for most of the giant gartersnake active season. Nonetheless, our results suggest that maintaining canals without neighboring rice fields would be detrimental to giant gartersnake populations, with decreases in giant gartersnake survival rates associated with less rice production in the surrounding landscape. Increased productivity of prey populations, dispersion of potential predators across a larger landscape, and a more secure water supply are just some of the mechanisms by which rice fields might benefit giant gartersnakes in adjacent canals. Results indicate that identifying how rice benefits giant gartersnakes in canals and the extent to which the rice agro-ecosystem could provide these benefits when rice is fallowed would inform the use of water for other purposes without harm to giant gartersnakes. Our study also suggests that without such understanding, maintaining rice and associated canals in the Sacramento Valley is critical for the sustainability of giant gartersnake populations.

California↗
USGS2010

Analysis of current-use pesticides in aquatic and terrestrial organisms collected throughout California, USA

A wide variety of pesticides are applied concurrently in agricultural and urban areas and transported off site dissolved in water and bound to sediments. But the exposure of aquatic and terrestrial organisms to current-use pesticides and the resulting effects are not well understood. One approach is to directly analyze tissue concentrations of contaminants. The overall objective of this study was to develop a sensitive method to analyze current-use pesticides with a wide range of Kow's in tissue to better understand the accumulation of these contaminants in different aquatic and terrestrial organisms. This method was then used to analyze current-use pesticides in tissues from a variety of organisms from sites with different land-use practices.

California↗