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Research about San Joaquin Valley

Source-linked reports with geographic coverage including San Joaquin Valley.

At least 73 records · Page 4Linked to original sources
USGS1989

Relation of salinity and selenium in shallow groundwater to hydrologic and geochemical processes, Western San Joaquin Valley, California

Salinity and selenium concentrations in shallow groundwater of the western San Joaquin Valley, California, are related to the geomorphology and hydrology of the alluvial fans. The highest salinity and selenium concentrations in shallow groundwater occur in alluvium deposited by ephemeral streams and at the margins of the major alluvial fans, where there were naturally saline, fine-grained soils. Low-to-moderate salinity and selenium concentrations in shallow groundwater are associated with upper and middle areas of the major alluvial fans deposited by intermittent streams. Areas with the most naturally saline soils have been irrigated in the last 40 years. These are now the areas of highest salinity and selenium concentrations in the shallow groundwater. Present-day (1986) groundwater salinity is spatially correlated with natural soil salinity in these areas. Isotopic data indicate that the highest salinity and selenium concentrations in groundwater present at low altitudes resulted from evaporative concentration when the water table was shallow.

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USGS1989

Selenate reduction to elemental selenium by anaerobic bacteria in sediments and culture: Biogeochemical significance of a novel, sulfate-independent respiration

Interstitial water profiles of SeO 4 2− , SeO 3 2− , SO 4 2− , and Cl − in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO 4 2− occurred under anaerobic conditions, was more rapid with H 2 or acetate, and was inhibited by O 2 , NO 3 − , MnO 2 , or autoclaving but not by SO 4 2− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO 2 . A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters.

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USGS1989

Texture and depositional history of near-surface alluvial deposits in the central part of the western San Joaquin Valley, California

Saline conditions and associated high levels of selenium and other soluble trace elements in soil, shallow ground water, and agricultural drain water of the western San Joaquin Valley, California, have prompted a study of the texture of near-surface alluvial deposits in the central part of the western valley. Texture is characterized by the percentage of coarse-grained sediment present within a specified subsurface depth interval and is used as a basis for mapping the upper 50 feet of deposits. Resulting quantitative descriptions of the deposits are used to interpret the late Quaternary history of the area. Three hydrogeologic units--Coast Range alluvium, flood-basin deposits, and Sierran sand--can be recognized in the upper 50 feet of deposits in the central part of the western San Joaquin Valley. The upper 30 feet of Coast Range alluvium and the adjacent 5 to 35 feet of flood-basin deposits are predominantly fine grained. These fine-grained Coast Range deposits are underlain by coarse-grained channel deposits. The fine-grained flood basin deposits are underlain by coarse-grained Sierran sand. The extent and orientation of channel deposits below 20 feet in the Coast Range alluvium indicate that streams draining the Coast Range may have been tributary to the axial stream that deposited the Sierran sand and that streamflow may have been to the southeast. The fining-upward stratigraphic sequence in the upper 50 feet of deposits and the headward retreat of tributary stream channels from the valley trough with time support a recent hypothesis of climatic control of alluviation in the western San Joaquin Valley.

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USGS1988

Distribution of selenium in soils of agricultural fields, western San Joaquin Valley, California

Soils from three agricultural fields in the Panoche Creek alluvial fan area in the western San Joaquin Valley, California, were analyzed for soluble, adsorbed, and total concentrations of selenium (Se) to assess the distribution and forms of Se in relation to the leaching of Se from soils. This assessment is needed to evaluate the importance of soil Se in affecting ground water concentrations. Soil samples were collected from three fields with drainage systems of different ages (6, 15, 1.5 yr) and different Se concentrations in drain water (58, 430, 3700 µg L −1 , respectively). Concentrations of soluble Se and salinity were highest in soils from the field drained for 1.5 yr and lowest in the field drained for 6 yr. Of the total concentration of soil Se from all three fields, the proportion of adsorbed and soluble Se ranged from 1 to 11% and <1 to 63%, respectively. Most of the soluble Se was present as selenate and most of the adsorbed Se was found to be selenite. Consistent with a model of evaporative concentration of Se and salinity in soils and shallow ground water in this area, most of the variance in soluble Se is explained by salinity (r 2 > 0.68) in saturation extracts of soils sampled from below the water table. In contrast, most soluble salts and Se apparently have been leached from the unsaturated soils in the fields drained for 6 and 15 yr. For the leached soils, dissolution and precipitation of evaporite minerals containing Se may no longer control concentrations of soluble Se.

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USGS1988

Character and evolution of the ground-water flow system in the central part of the western San Joaquin Valley, California

The occurrence of selenium in agricultural drain water derived from the western San Joaquin Valley, California, has focused concern on the ground-water flow system of the western valley. In this investigation, previous work and recently collected texture and water-level data are used to evaluate the character and evolution of the regional ground-water flow system in the central part of the western valley, with particular emphasis on the deposits overlying the Corcoran Clay Member of the Tulare Formation. The Corcoran Clay Member, where present, divides the flow system into an upper semiconfined zone and a lower con-fined zone. Above the Corcoran, three hydrogeologic units can be recognized: Coast Range alluvium, Sierran sand, and flood-basin deposits. These units differ in texture, hydrologic properties, and oxidation state. The development of irrigated agriculture in the central part of the western valley has significantly altered the flow system. Percolation of irrigation water past crop roots has caused a rise in the altitude of the water table in midfan and distal-fan areas. Pumpage of ground water from wells has caused a lowering of the water table beneath parts of the fanheads and a lowering of the potentiometric surface of the confined zone over much of the western valley. The combination of percolation and pumpage has resulted in development of a large downward hydraulic head gradient in the semi-confined zone and has created a groundwater divide along the western margin of the valley. Surface-water deliveries from the California Aqueduct have allowed a decrease in pumpage and a consequent recovery in hydraulic head throughout the system.

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USGS1988

Relation of salinity and selenium in shallow ground water to hydrologic and geochemical processes, western San Joaquin Valley, California

Salinity and selenium concentrations in shallow ground water of the western San Joaquin Valley, California, are related to the geomorphology and hydrology of the alluvial fans. The highest salinity and selenium concentrations in shallow ground water occur in alluvium deposited by ephemeral streams and at the margins of the major alluvial fans, where there were naturally saline, fine-grained soils. Low-to-moderate salinity and selenium concentrations in shallow ground water are associated with upper and middle areas of the major alluvial fans deposited by intermittent streams. Areas with the most naturally saline soils have been irrigated in the last 40 years. These are now the areas of highest salinity and selenium concentrations in the shallow ground water. Present-day (1986) ground-water salinity is significantly correlated with natural soil salinity in these areas. Isotopic data indicate that the highest salinity and selenium concentrations in ground water present at low altitudes resulted from evaporative concentration when the water table was shallow.

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USGS1988

Comparison of methods to determine selenium species in saturation extracts of soils from the western San Joaquin Valley, California

Methods to determine soluble concentrations of selenite, selenate, and organic selenium were compared on saturation extracts of soil samples collected from three sites on the Panache Creek alluvial fan in the western San Joaquin Valley, California. The methods were used in combination with hydridegeneration atomic-absorption spectrometry for detection of selenium and included a selective chemical digestion method and three chromatography methods using XAD-8 resin, Sep-Pac C 18 cartridge, and a combination of XAD-8 resin and activated charcoal. Undigested organic matter in some of the extracts inhibited selenium detection when using the digestion and Sep-Pac C18 methods, but the interference was removed by using the XAD-8 method. Combining XAD-8 resin and activated charcoal was an unacceptable method, because the activated charcoal removed selenite and selenate. Ninety-eight percent of the selenium in the extracts was selenate and about 100 percent of the isolated organic selenium was associated with the humic acid fraction of dissolved-organic matter.

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USGS1987

Selenium in aquatic organisms from subsurface agricultural drainage water, San Joaquin Valley, California

Concentrations of total selenium were high in 1983 in water, sediment, organic detritus, aquatic plants and invertebrates, and mosquitofish ( Gambusia affinis ) from Kesterson Reservoir (San Joaquin Valley, California) and the San Luis Drain. Selenium concentrations in biota from the Reservoir and Drain (referred to here collectively as “Kesterson”) exceeded 300 (μg/g dry weight in some samples of algae, submerged rooted plants, chironomids, and mosquitofish, and were as high as 440 μg/g dry weight in decomposing detritus. Overall, selenium concentrations in samples from Kesterson averaged about 100-fold higher than those from the Volta Wildlife Area (here termed “Volta”), a nearby site that does not receive subsurface drainage water. Selenium concentrations generally increased from water to sediment to plants to animals. Spatial (geographic) patterns were observed for selenium concentrations in samples from Kesterson, but not in those from Volta. Higher concentrations were usually measured in samples from the San Luis Drain than from the evaporation ponds that comprise Kesterson Reservoir. At Kesterson, concentrations were usually higher in August than in May. The elevated levels of selenium measured in forage organisms from Kesterson are probably toxic to sensitive consumer animals, and may explain recent observations of dead and deformed embryos in eggs of aquatic birds that nest at the Reservoir. The effects of the selenium on fish living in subsurface agricultural drainage water are still poorly understood.

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USGS1987

Biogeochemical cycling of selenium in the San Joaquin Valley, California, USA

Subsurface agricultural drainage waters from western San Joaquin Valley, California, were found to contain elevated concentrations of the element selenium in the form of selenate. In 1978, these drainage waters began to replace previous input to Kesterson Reservoir, a pond system within Kesterson National Wildlife Refuge; this substitution was completed by 1982. In the 1983 nesting season, unusual rates of deformity and death in embryos and hatchlings of wild aquatic birds (up to 64% of eared grebe and American coot nests) occurred at the refuge and were attributed to selenium toxicosis. Features necessary for contamination to have taken place included geologic setting, climate, soil type, availability of imported irrigation water, type of irrigation, and the unique chemical properties of selenium. The mechanisms of biogeochemical cycling raise questions about other ecosystems and human exposure.

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USGS1987

Processes affecting the distribution of selenium in shallow ground water of agricultural areas, western San Joaquin Valley, California

A study was undertaken to evaluate the processes affecting the chemistry of shallow ground water associated with agricultural drainage systems in the western San Joaquin Valley, California. The study was prompted by a need for an understanding of selenium mobility in areas having high selenium concentrations in shallow ground water. Groundwater samples were collected along transects in three artificially drained fields where the age of the drainage system varied (15, 6, and 1.5 years). Selenium concentrations in the drainage water also varied (0F30, 58, and 3700 micrograms per liter, respectively). Isotopic enrichment and chemical composition of the ground-water samples indicate that saline- and selenium-enriched water has evolved as a result of evaporation of ground water. This evaporated, isotopically enriched water is being displaced by more recent, less saline irrigation water percolating through the root zone. This displace-ment seems to be a process whereby sodium chloride and sodium sulfate water is being replaced by more dilute calcium sulfate and calcium bicarbonate water.

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USGS1986

Distribution and mobility of selenium and other trace elements in shallow ground water of the western San Joaquin Valley, California

Samples of shallow ground water that underlies much of the irrigated area in the western San Joaquin Valley of California were analyzed for various major ions and trace elements, including selenium. Concentrations of the major ions generally were similar for ground water collected in the two primary geologic zones--the alluvial fan and basin trough. Soils in the alluvial-fan zone are derived from Coast Range rocks, and soils in the basin-trough zone are from a mixture of Sierra Nevada and Coast Range sources. Most of the variance in concentrations of major ions, as determined by principal components analysis, was associated with ground-water salinity and the dominant ions--magnesium, sodium, sulfate, and chloride. Most of the variance in trace elements was associated with concentrations of boron, molybdenum, selenium, and vanadium, which are present as mobile oxyanions. The concentrations of oxyanions trace elements were significantly correlated (a=0.05) with groundwater salinity, but the correlations between selenium and salinity and molybdenum and salinity were significantly different (a=0.05) in the alluvial-fan geologic zone compared with the basin-trough geologic zone. In addition, selenium concentrations are significantly (a=0.05) higher in the ground water of the alluvial-fan zone than in the basin-trough zone. The evidence suggests that the main factors influencing selenium concentrations in the shallow ground water are the degree of ground-water salinity and the geologic source of the alluvial soil material.

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USGS1984

Ground-water-quality monitoring network design for the San Joaquin Valley ground-water basin, California

Ideal and actual ground-water-quality monitoring networks are proposed for the San Joaquin Valley basin in California. The ideal network, which comprises several subnetworks, provides direction in the development of an actual network of wells currently monitored by known operating agencies. The ideal network can serve as a basis for the future expansion of the actual network as more wells are included in the inventory of active monitoring networks. The management objectives of these networks are to develop a general baseline of ground-water quality, to identify temporal and spatial trends in ground-water quality, and to identify large-scale sources of contamination of ground water. The networks are based on an information structure that includes land use, surface and subsurface geology, ground-water levels, surface- and ground-water quality, possible sources of contamination, and active ground-water-quality monitoring networks. Development of the categories and subcategories of network objectives, which are needed to describe the quality of the ground water in the basin, makes clear the inadequacy of the currently operated networks. The expansion of ground-water-quality monitoring in the San Joaquin Valley, therefore, would be necessary to approximate adequately the ideal network.

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USGS1977

Late Cenozoic stratigraphic units, northeastern San Joaquin Valley, California

Recent mapping of late Tertiary and Quaternary deposits in the northeastern San Joaquin Valley has shown the need for clarification, revision, and subdivision of some of the previously mapped stratigraphic units. We propose a uniform nomenclature for deposits younger than the Mehrten Formation in this region. The Laguna Formation (late Pliocene) is now recognized as far south as the Merced area, where it is overlain by the North Merced Gravel (Pliocene or Pleistocene). The China Hat pediment of Hudson (1960, p. 1552) is interpreted as the uppermost gravel member of the Laguna Formation and is believed to represent an old fan deposit rather than a pediment. The Laguna, Turlock Lake, Riverbank, and Modesto Formations are lithologically similar but may be distinguished and subdivided on the basis of soil profile development, topographic position and expression, local lithologic differences, unconformities, and associated buried soils. The Turlock Lake Formation is subdivided into two units (lower, upper) and the Riverbank Formation into three units (lower, middle, upper), separated by unconformities and well-developed buried soils. The Modesto Formation is subdivided into two informally designated members, separated by a minor unconformity and weakly developed buried soil. The lower (oldest) member of the Modesto is in places associated with two geomorphic surfaces, and as many as four terraces showing slightly different soil development are associated with deposits of the upper (youngest) member. Post-Modesto deposits are informally subdivided into four stratigraphic units, designated Post-Modesto I, II, III, and IV. Most of the stratigraphic units discussed are believed to represent separate alluvial episodes, recorded by fill terraces opening westward onto alluvial fans. Substantial time intervals between periods of aggradation are represented by buried paleosols. Some of the properties of relict and buried paleosols are summarized and their relations to the proposed stratigraphic units are described.

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USGS1973

Geologic factors affecting compaction of deposits in a land-subsidence area

In the west-central San Joaquin Valley, California, pumping of ground water has changed water levels, thereby increasing the stresses that tend to compact alluvium by as much as 50 percent and creating a large area of intense land subsidence. The estimated 1943–1960 specific unit compaction (compaction during a time period, per unit thickness, per unit applied-stress increase) of the deposits in a northern subarea is four times that of a southern subarea, which suggests marked differences in the compressibility of the deposits. A third of the compressibility difference is real and is due to less prior total applied stress in the northern than in the southern subarea. The other two-thirds of the compressibility difference is only apparent and is attributed to different water-expulsion rates in the clayey beds of different depositional environments. In the northern subarea, the deposits are mainly flood-plain sediments that contain extensive sand beds and thin clayey beds that are dewatered relatively quickly under increasing effective stress. In the southern subarea, the sediments are mainly alluvial-fan deposits that contain thick clayey sequences adjacent to lensing sandy beds. These deposits are de-watered more slowly than those in the northern subarea. Variations of mean lithology in the chief compacting zone could not be correlated with variations in the specific unit compaction of the deposits.

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