A relatively narrow vertical zone (5–6 m thick) of NO3− containing groundwater was identified using multilevel sampling devices in a sand and gravel aquifer on Cape Cod, MA, USA. The aquifer has been chronically contaminated by surface disposal of treated sewage 0.3 km upgradient from the study area. The NO3− zone was anoxic and contained high concentrations of N2O (16.5 μM), suggesting that it was a zone of active denitrification. Denitrifying activity was confirmed with direct measurement using acetylene block incubations with aquifer core material; the peak rate was 2.4 nmol N reduced (g sed)−1 day−1. Concentrations of dissolved inorganic carbon and N2 were close to atmospheric equilibrium in uncontaminated groundwater, but were more than 2 times higher within the contaminant plume. Excess CO2 and N2 suggested in situ formation with a stoichiometry of C and N mineralized via denitrification of 0.8 (C/N). Denitrification within the aquifer resulted in an increase in the natural δ15N of NO3− (from +13.6 to +42.0%.) and the N2 produced, with an isotopic enrichment factor, ϵ, of −13.9%.. Vertical profiles of NH4+ and δ15N of NH4+ indicated that dissimilatory reduction of NO3− to NH4+ was also occurring but mass balance calculations indicated that denitrification was the predominant process. These results demonstrate that a combination approach using field mass balance, stable isotope analysis, and laboratory incubations yields useful insight as to the significance of denitrification in aquifer sediments and that closely spaced vertical sampling is necessary to adequately quantify the processes controlling C and N transport and transformation within these environments.
A primary source of dissolved inorganic carbon (DIC) in the Black Creek aquifer of South Carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter. Groundwater chemistry data indicate, however, that the available mass of inorganic electron acceptors (oxygen, Fe(III), and sulfate) and observed methane production is inadequate to account for observed CO2production. Although sulfate concentrations are low (approximately 0.05–0.10 mM) in aquifer water throughout the flow system, sulfate concentrations are greater in confining-bed pore water (0.4–20 mM). The distribution of culturable sulfate-reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate-reducing activity in sands than in clays. Calculations based on Fick's Law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of CO2 production (about 10−5mmoll−1 year−1), thus eliminating the apparent electron-acceptor deficit. Furthermore, concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction (2–6 nM), which provides independent evidence that sulfate reduction is the predominant terminal electron-accepting process in this system. The observed accumulation of pyrite- and calcite-cemented sandstones at sand-clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments.
The computer code MBSSAS uses two-parameter Margules-type excess-free-energy of mixing equations to calculate thermodynamic equilibrium, pure-phase saturation, and stoichiometric saturation states in binary solid-solution aqueous-solution (SSAS) systems. Lippmann phase diagrams, Roozeboom diagrams, and distribution-coefficient diagrams can be constructed from the output data files, and also can be displayed by MBSSAS (on IBM-PC compatible computers). MBSSAS also will calculate accessory information, such as the location of miscibility gaps, spinodal gaps, critical-mixing points, alyotropic extrema, Henry's law solid-phase activity coefficients, and limiting distribution coefficients. Alternatively, MBSSAS can use such information (instead of the Margules, Guggenheim, or Thompson and Waldbaum excess-free-energy parameters) to calculate the appropriate excess-free-energy of mixing equation for any given SSAS system.
Visible and near-infrared (VNIR; 0.4–2.4 μm) reflectance spectra were recorded for 35 saline minerals that represent the wide range of mineral and brine chemical compositions found in playa evaporite settings. The spectra show that many of the saline minerals exhibit diagnostic near-infrared absorption bands, chiefly attributable to vibrations of hydrogen-bonded structural water molecules. VNIR reflectance spectra can be used to detect minor hydrate phases present in mixtures dominated by anhydrous halite or thenardite, and therefore will be useful in combination with X ray diffraction data for characterizing natural saline mineral assemblages. In addition, VNIR reflectance spectra are sensitive to differences in sample hydration state and should facilitate in situ studies of minerals that occur as fragile, transitory dehydration products in natural salt crusts. The use of spectral reflectance measurements in playa studies should aid in mapping evaporite mineral distributions and may provide insight into the geochemical and hydrological controls on playa mineral and brine development.
","language":"English","publisher":"AGU Publications","doi":"10.1029/91JB01714","issn":"01480227","usgsCitation":"Crowley, J.K., 1991, Visible and near-infrared (0.4-2.5 μm) reflectance spectra of playa evaporite minerals: Journal of Geophysical Research, v. 96, no. B10, p. 16231-16240, https://doi.org/10.1029/91JB01714.","productDescription":"10 p.","startPage":"16231","endPage":"16240","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[],"links":[{"id":223373,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"96","issue":"B10","noUsgsAuthors":false,"publicationDate":"2012-09-20","publicationStatus":"PW","scienceBaseUri":"505bc289e4b08c986b32abd4","contributors":{"authors":[{"text":"Crowley, James K.","contributorId":10928,"corporation":false,"usgs":true,"family":"Crowley","given":"James","email":"","middleInitial":"K.","affiliations":[],"preferred":false,"id":373709,"contributorType":{"id":1,"text":"Authors"},"rank":1}]}} ,{"id":70016484,"text":"70016484 - 1991 - Pumping tests in non-uniform aquifers - The linear strip case","interactions":[],"lastModifiedDate":"2025-03-06T16:58:48.257499","indexId":"70016484","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2342,"text":"Journal of Hydrology","active":true,"publicationSubtype":{"id":10}},"title":"Pumping tests in non-uniform aquifers - The linear strip case","docAbstract":"Many pumping tests are performed in geologic settings that can be conceptualized as a linear infinite strip of one material embedded in a matrix of differing flow properties. A semi-analytical solution is presented to aid the analysis of drawdown data obtained from pumping tests performed in settings that can be represented by such a conceptual model. Integral transform techniques are employed to obtain a solution in transform space that can be numerically inverted to real space. Examination of the numerically transformed solution reveals several interesting features of flow in this configuration. If the transmissivity of the strip is much higher than that of the matrix, linear and bilinear flow are the primary flow regimes during a pumping test. If the contrast between matrix and strip properties is not as extreme, then radial flow should be the primary flow mechanism. Sensitivity analysis is employed to develop insight into the controls on drawdown in this conceptual model and to demonstrate the importance of temporal and spatial placement of observations. Changes in drawdown are sensitive to the transmissivity of the strip for a limited time duration. After that time, only the total drawdown remains a function of strip transmissivity. In the case of storativity, both the total drawdown and changes in drawdown are sensitive to the storativity of the strip for a time of quite limited duration. After that time, essentially no information can be gained about the storage properties of the strip from drawdown data. An example analysis is performed using data previously presented in the literature to demonstrate the viability of the semi-analytical solution and to illustrate a general procedure for analysis of drawdown data in complex geologic settings. This example reinforces the importance of observation well placement and the time of data collection in constraining parameter correlation, a major source of the uncertainty that arises in the parameter estimation procedure.
","language":"English","publisher":"Elsevier","doi":"10.1016/0022-1694(91)90132-2","issn":"00221694","usgsCitation":"Butler, J., and Liu, W., 1991, Pumping tests in non-uniform aquifers - The linear strip case: Journal of Hydrology, v. 128, no. 1-4, p. 69-99, https://doi.org/10.1016/0022-1694(91)90132-2.","productDescription":"31 p.","startPage":"69","endPage":"99","numberOfPages":"31","costCenters":[],"links":[{"id":223276,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"128","issue":"1-4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a9034e4b0c8380cd7fbcd","contributors":{"authors":[{"text":"Butler, J.J. Jr.","contributorId":12194,"corporation":false,"usgs":true,"family":"Butler","given":"J.J.","suffix":"Jr.","email":"","affiliations":[],"preferred":false,"id":373694,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Liu, W.Z.","contributorId":99301,"corporation":false,"usgs":true,"family":"Liu","given":"W.Z.","email":"","affiliations":[],"preferred":false,"id":373695,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016468,"text":"70016468 - 1991 - Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments: effect on sediment physical and chemical characteristics","interactions":[],"lastModifiedDate":"2024-03-28T00:14:53.430863","indexId":"70016468","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1924,"text":"Hydrological Processes","active":true,"publicationSubtype":{"id":10}},"title":"Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments: effect on sediment physical and chemical characteristics","docAbstract":"The use of a single-bowl continuous-flow centrifuge (CFC, Sharples-Pennwalt Model AS-12) for dewatering suspended sediment from large volumes of river water is evaluated. Sediment-recovery efficiency of 86-91 per cent is comparable to that of other types of CFC units. The recovery efficiency is limited by the particle-size distribution of the feed water and by the limiting particle diameter that is retained in the centrifuge bowl. The limiting particle diameter, using the parameters for this study (bowl radius = 10.5cm; bowl length = 71.1 cm; rotational velocity = 16000 r min−1; flow rate = 2 L min−1, and an assumed hydrated particle density = 1.7 gm cm−3), is 370 nm. There seems to be no particle-size fractionation within the centrifuge bowl—the median particle size was the same at the top as at the bottom. Particle electrophoretic mobility plays some role in fractionation of particles within the centrifuge. The mobility ranged from −1.19 to −2.01 × 10−8 m2 V−1 s−1, which is typical of clays coated with organic matter, the charge of which is partially neutralized by divalent cations and iron. Contamination by trace metals and organics is minimized by coating all surfaces that come in contact with the sample with either FEP or PFA Teflon and using a removable FEP Teflon liner in the centrifuge bowl. Because of the physical and chemical factors affecting particle fractionation within the centrifuge, care must be exercised in interpreting the environmental consequences of particles collected by continuous-flow centrifugation.
This study examines the relationship between the distribution of small earthquakes (ML≤4.3) and mechanisms of strain accumulation and relaxation in an area with long repeat times between large events, the Southern Great Basin Seismic Network (SGBSN) region. The Great Basin is a unique continental extensional province characterized by normal and strike-slip faulting, high heat flow, crust of thin to normal thickness, and high elevations. The SGBSN is operated to provide data to address suitability issues pertaining to Yucca Mountain, Nevada which is being evaluated as a potential site for a national mined geologic nuclear waste repository. Suitability issues include estimation of the probability of occurrence of future damaging earthquakes, the characterization of the mechanisms that drive hydrologic flow, and the identification of fractures (faults) that might act as flow conduits or barriers. This study attempts to explain the distribution of small earthquakes in terms of spatial variations in the shear strain field; where strain concentrates there should be a greater number of small earthquakes. Strain field models are constructed under the assumption that long term fault behavior perturbs an otherwise uniform strain field. These strain field models are then interpreted with regard to the regional tectonics and site suitability issues. Modeling results provide one possible explanation of why earthquake clusters cover regions much larger than the surface projections of any of mapped major faults; clusters in a wide band along and extending northeast of the northern half of the Furnace Creek fault may correspond to elevated shear strains along the fault and a broad cluster in the Pahranagat Shear Zone may be associated with shear strain arising from a distribution of smaller localized faults. The relatively large number of small earthquakes in the southern and eastern portions of the Nevada Test Site is consistent with the strain field models. A minimum in shear strain at Yucca Mountain is predicted by all models consistent with an almost total lack of earthquakes observed there. The region to the west of the Death Valley/Furnace Creek fault system, the portion of the study area with the most active deformation but few small earthquakes, is an area of low shear strain. A possible reason for this is that the fault configuration in the area is optimal for accommodating regional deformation via large earthquakes or creep. While there is also a relative lack of earthquakes at Yucca Mountain, this may be indicative of a lack of accumulating strain energy and thus, a lower potential for a large earthquake.
Manganese oxidation products were precipitated in an aerated open-aqueous system where a continuous influx of mixed Mn2+ and Cd2+ solution was supplied and pH was maintained with an automated pH-stat adding dilute NaOH. X-ray diffraction and electron diffraction identified the solids produced as mixtures of Cd2Mn34+O8, Mn2+2Mn4+3O8, MnO2 (ramsdellite), and CdCO3. Mean oxidation numbers of the total precipitated Mn as great as 3.6 were reached during titrations. During subsequent aging in solution, oxidation numbers between 3.8 and 3.9 were reached in some precipitates in less than 40 days. Conditional oxidation rate constants calculated from a crystal-growth equation applied to titration data showed the overall precipitation rate, without considering manganese oxidation state in the precipitate, was increased by a factor of ~4 to ~7 when the mole ratio (Cd/Mn + Cd) of cadmium in the feed solution was 0.40 compared with rate constants for hausmannite (Mn2+Mn23+O4 precipitation under similar conditions but without accessory metals. Kinetic experiments were made to test effects of various Cd/Mn + Cd mole ratios and rates of addition of the feed solution, different temperatures from 5.0 to 35°C, and pH from 8.0 to 9.0. Oxidation rates were slower when the Cd mole ratio was less than 0.40. The rate increased by a factor of ~10 when pH was raised one-half unit. The effect of temperature on the rate constants was also substantial, but the meaning of this is uncertain because the rate of formation of Mn4+ oxide in the absence of Cd or other accessory metals was too slow to be measurable in titration experiments.
The increased rate of Mn4+ oxide formation in the presence of Cd2+ can be ascribed to the formation of a labile adsorbed intermediate, CdMn2O4 Int, an analog of hausmannite, formed on precipitate surfaces at the beginning of the oxidation process. The increased lability of this structure, resulting from coordination-chemical behavior of Cd2+ during the titration, causes a rapid second-stage rearrangement and facilitates disproportionation of the Mn3+ ions. The Mn2+ ions thus released provide a positive feedback mechanism that couples the two steps of the conversion of Mn2+ to Mn4+ more closely than is possible when other metal ions besides manganese are not present. During aging of precipitates in contact with solutions, proportions of Cd2Mn3O8 and MnO2 increased at the expense of other precipitate components.
","language":"English","publisher":"Elsevier","doi":"10.1016/0016-7037(91)90364-B","issn":"00167037","usgsCitation":"Hem, J., and Lind, C.J., 1991, Coprecipitation mechanisms and products in manganese oxidation in the presence of cadmium: Geochimica et Cosmochimica Acta, v. 55, no. 9, p. 2435-2451, https://doi.org/10.1016/0016-7037(91)90364-B.","productDescription":"17 p.","startPage":"2435","endPage":"2451","numberOfPages":"17","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":223212,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"55","issue":"9","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"5059fc04e4b0c8380cd4e09f","contributors":{"authors":[{"text":"Hem, J.D.","contributorId":54576,"corporation":false,"usgs":true,"family":"Hem","given":"J.D.","affiliations":[],"preferred":false,"id":373423,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Lind, Carol J.","contributorId":36110,"corporation":false,"usgs":true,"family":"Lind","given":"Carol","email":"","middleInitial":"J.","affiliations":[],"preferred":false,"id":373422,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016362,"text":"70016362 - 1991 - Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 2. Modeling carbon sources, sinks, and δ13C evolution","interactions":[],"lastModifiedDate":"2015-05-29T11:14:11","indexId":"70016362","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2342,"text":"Journal of Hydrology","active":true,"publicationSubtype":{"id":10}},"title":"Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 2. Modeling carbon sources, sinks, and δ13C evolution","docAbstract":"Stable isotope data for dissolved inorganic carbon (DIC), carbonate shell material and cements, and microbial CO2 were combined with organic and inorganic chemical data from aquifer and confining-bed pore waters to construct geochemical reaction models along a flowpath in the Black Creek aquifer of South Carolina. Carbon-isotope fractionation between DIC and precipitating cements was treated as a Rayleigh distillation process. Organic matter oxidation was coupled to microbial fermentation and sulfate reduction. All reaction models reproduced the observed chemical and isotopic compositions of final waters. However, model 1, in which all sources of carbon and electron-acceptors were assumed to be internal to the aquifer, was invalidated owing to the large ratio of fermentation CO2 to respiration CO2 predicted by the model (5–49) compared with measured ratios (two or less). In model 2, this ratio was reduced by assuming that confining beds adjacent to the aquifer act as sources of dissolved organic carbon and sulfate. This assumption was based on measured high concentrations of dissolved organic acids and sulfate in confining-bed pore waters (60–100 μM and 100–380 μM, respectively) relative to aquifer pore waters (from less than 30 μM and 2–80 μM, respectively). Sodium was chosen as the companion ion to organic-acid and sulfate transport from confining beds because it is the predominant cation in confining-bed pore waters. As a result, excessive amounts of Na-for-Ca ion exchange and calcite precipitation (three to four times more cement than observed in the aquifer) were required by model 2 to achieve mass and isotope balance of final water. For this reason, model 2 was invalidated. Agreement between model-predicted and measured amounts of carbonate cement and ratios of fermentation CO2 to respiration CO2 were obtained in a reaction model that assumed confining beds act as sources of DIC, as well as organic acids and sulfate. This assumption was supported by measured high concentrations of DIC in confining beds (2.6–2.7 mM). Results from this study show that geochemical models of confined aquifer systems must incorporate the effects of adjacent confining beds to reproduce observed groundwater chemistry accurately.
","language":"English","publisher":"Elsevier","doi":"10.1016/0022-1694(91)90111-T","issn":"00221694","usgsCitation":"McMahon, P.B., and Chapelle, F.H., 1991, Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 2. Modeling carbon sources, sinks, and δ13C evolution: Journal of Hydrology, v. 127, no. 1-4, p. 109-135, https://doi.org/10.1016/0022-1694(91)90111-T.","productDescription":"27 p.","startPage":"109","endPage":"135","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[],"links":[{"id":223365,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"127","issue":"1-4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a16f2e4b0c8380cd55313","contributors":{"authors":[{"text":"McMahon, Peter B. 0000-0001-7452-2379 pmcmahon@usgs.gov","orcid":"https://orcid.org/0000-0001-7452-2379","contributorId":724,"corporation":false,"usgs":true,"family":"McMahon","given":"Peter","email":"pmcmahon@usgs.gov","middleInitial":"B.","affiliations":[{"id":191,"text":"Colorado Water Science Center","active":true,"usgs":true}],"preferred":true,"id":373274,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Chapelle, Francis H. chapelle@usgs.gov","contributorId":1350,"corporation":false,"usgs":true,"family":"Chapelle","given":"Francis","email":"chapelle@usgs.gov","middleInitial":"H.","affiliations":[{"id":13634,"text":"South Atlantic Water Science Center","active":true,"usgs":true},{"id":559,"text":"South Carolina Water Science Center","active":true,"usgs":true}],"preferred":true,"id":373275,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016343,"text":"70016343 - 1991 - The neutral oil in commercial linear alkylbenzenesulfonate and its effect on organic solute solubility in water","interactions":[],"lastModifiedDate":"2023-10-19T01:21:18.751516","indexId":"70016343","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1565,"text":"Environmental Science & Technology","onlineIssn":"1520-5851","printIssn":"0013-936X","active":true,"publicationSubtype":{"id":10}},"title":"The neutral oil in commercial linear alkylbenzenesulfonate and its effect on organic solute solubility in water","docAbstract":"No abstract available.
","language":"English","publisher":"American Chemical Society","doi":"10.1021/es00016a008","issn":"0013936X","usgsCitation":"Chiou, C.T., Kile, D.E., and Rutherford, D., 1991, The neutral oil in commercial linear alkylbenzenesulfonate and its effect on organic solute solubility in water: Environmental Science & Technology, v. 25, no. 4, p. 660-665, https://doi.org/10.1021/es00016a008.","productDescription":"6 p.","startPage":"660","endPage":"665","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":223107,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"25","issue":"4","noUsgsAuthors":false,"publicationDate":"2002-05-01","publicationStatus":"PW","scienceBaseUri":"505bae10e4b08c986b323ee7","contributors":{"authors":[{"text":"Chiou, C. T.","contributorId":97080,"corporation":false,"usgs":true,"family":"Chiou","given":"C.","email":"","middleInitial":"T.","affiliations":[],"preferred":false,"id":373231,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Kile, D. E.","contributorId":22758,"corporation":false,"usgs":true,"family":"Kile","given":"D.","email":"","middleInitial":"E.","affiliations":[],"preferred":false,"id":373230,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Rutherford, D.W.","contributorId":21244,"corporation":false,"usgs":true,"family":"Rutherford","given":"D.W.","email":"","affiliations":[],"preferred":false,"id":373229,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70016763,"text":"70016763 - 1991 - Solution of the one-dimensional consolidation theory equation with a pseudospectral method","interactions":[],"lastModifiedDate":"2016-05-25T16:06:40","indexId":"70016763","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":24,"text":"Conference Paper"},"publicationSubtype":{"id":19,"text":"Conference Paper"},"title":"Solution of the one-dimensional consolidation theory equation with a pseudospectral method","docAbstract":"The one-dimensional consolidation theory equation is solved for an aquifer system using a pseudospectral method. The spatial derivatives are computed using Fast Fourier Transforms and the time derivative is solved using a fourth-order Runge-Kutta scheme. The computer model calculates compaction based on the void ratio changes accumulated during the simulated periods of time. Compactions and expansions resulting from groundwater withdrawals and recharges are simulated for two observation wells in Santa Clara Valley and two in San Joaquin Valley, California. Field data previously published are used to obtain mean values for the soil grain density and the compression index and to generate depth-dependent profiles for hydraulic conductivity and initial void ratio. The water-level plots for the wells studied were digitized and used to obtain the time dependent profiles of effective stress.
","largerWorkTitle":"IAHS Publication (International Association of Hydrological Sciences)","conferenceTitle":"Proceedings of the 4th International Symposium on Land Subsidence","conferenceDate":"12 May 1991 through 17 May 1991","conferenceLocation":"Houston, TX, USA","language":"English","publisher":"Publ by Int Assoc of Hydrological Sciences","publisherLocation":"Wallingford, United Kingdom","issn":"0144-7815","isbn":"0947571922","usgsCitation":"Sepulveda, N., 1991, Solution of the one-dimensional consolidation theory equation with a pseudospectral method, in IAHS Publication (International Association of Hydrological Sciences), no. 200, Houston, TX, USA, 12 May 1991 through 17 May 1991, p. 555-564.","productDescription":"10 p.","startPage":"555","endPage":"564","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[{"id":156,"text":"Caribbean Water Science Center","active":true,"usgs":true}],"links":[{"id":224849,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"issue":"200","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505b925ae4b08c986b319e78","contributors":{"editors":[{"text":"Anon","contributorId":128316,"corporation":true,"usgs":false,"organization":"Anon","id":536350,"contributorType":{"id":2,"text":"Editors"},"rank":1}],"authors":[{"text":"Sepulveda, N.","contributorId":56805,"corporation":false,"usgs":true,"family":"Sepulveda","given":"N.","email":"","affiliations":[],"preferred":false,"id":374432,"contributorType":{"id":1,"text":"Authors"},"rank":1}]}} ,{"id":70016609,"text":"70016609 - 1991 - Use of electronic microprocessor-based instrumentation by the U.S. geological survey for hydrologic data collection","interactions":[],"lastModifiedDate":"2012-03-12T17:18:49","indexId":"70016609","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":24,"text":"Conference Paper"},"publicationSubtype":{"id":19,"text":"Conference Paper"},"title":"Use of electronic microprocessor-based instrumentation by the U.S. geological survey for hydrologic data collection","docAbstract":"The U.S. Geological Survey is acquiring a new generation of field computers and communications software to support hydrologic data-collection at field locations. The new computer hardware and software mark the beginning of the Survey's transition from the use of electromechanical devices and paper tapes to electronic microprocessor-based instrumentation. Software is being developed for these microprocessors to facilitate the collection, conversion, and entry of data into the Survey's National Water Information System. The new automated data-collection process features several microprocessor-controlled sensors connected to a serial digital multidrop line operated by an electronic data recorder. Data are acquired from the sensors in response to instructions programmed into the data recorder by the user through small portable lap-top or hand-held computers. The portable computers, called personal field computers, also are used to extract data from the electronic recorders for transport by courier to the office computers. The Survey's alternative to manual or courier retrieval is the use of microprocessor-based remote telemetry stations. Plans have been developed to enhance the Survey's use of the Geostationary Operational Environmental Satellite telemetry by replacing the present network of direct-readout ground stations with less expensive units. Plans also provide for computer software that will support other forms of telemetry such as telephone or land-based radio.","largerWorkTitle":"Proceedings - National Conference on Hydraulic Engineering","conferenceTitle":"Proceedings of the 1991 National Conference on Hydraulic Engineering","conferenceDate":"29 July 1991 through 2 August 1991","conferenceLocation":"Nashville, TN, USA","language":"English","publisher":"Publ by ASCE","publisherLocation":"New York, NY, United States","isbn":"0872628167","usgsCitation":"Shope, W.G., 1991, Use of electronic microprocessor-based instrumentation by the U.S. geological survey for hydrologic data collection, in Proceedings - National Conference on Hydraulic Engineering, Nashville, TN, USA, 29 July 1991 through 2 August 1991, p. 774-779.","startPage":"774","endPage":"779","numberOfPages":"6","costCenters":[],"links":[{"id":224838,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505bbef6e4b08c986b3298af","contributors":{"editors":[{"text":"Shane Richard M.","contributorId":128320,"corporation":true,"usgs":false,"organization":"Shane Richard M.","id":536335,"contributorType":{"id":2,"text":"Editors"},"rank":1}],"authors":[{"text":"Shope, William G. Jr.","contributorId":106649,"corporation":false,"usgs":true,"family":"Shope","given":"William","suffix":"Jr.","email":"","middleInitial":"G.","affiliations":[],"preferred":false,"id":374026,"contributorType":{"id":1,"text":"Authors"},"rank":1}]}} ,{"id":70185486,"text":"70185486 - 1991 - Fate of silicate minerals in a peat bog","interactions":[],"lastModifiedDate":"2022-12-22T15:49:43.43597","indexId":"70185486","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1796,"text":"Geology","active":true,"publicationSubtype":{"id":10}},"title":"Fate of silicate minerals in a peat bog","docAbstract":"An investigation of silicate weathering in a Minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic, organic-rich, neutral- pH environments. Vertical profiles of pH, dissolved silicon, and major cations were obtained at a raised bog and a spring fen and compared. Profiles of readily extractable silicon, diatom abundance, ash mineralogy, and silicate surface texture were determined from peat cores collected at each site.
In the bog, normally a recharge mound, dissolved silicon increases with depth as pH increases, exceeding the background silicon concentration by a factor of two. Silicate grain surfaces, including quartz, are chemically etched at this location, despite being in contact with pore water at neutral pH with dissolved silicon well above the equilibrium solubility of quartz. The increasing silica concentrations at circum-neutral pH are consistent with a system where silicate solubility is influenced by silica-organic-acid complexes. Silica-organic-acid complexes therefore may be the cause of the almost complete absence of diatoms in decomposed peat and contribute to the formation of silica-depleted underclays commonly found beneath coal.
","language":"English","publisher":"Geological Society of America","doi":"10.1130/0091-7613(1991)019<0328:FOSMIA>2.3.CO;2","usgsCitation":"Bennett, P.C., Siegel, D., Hillier, B.M., and Glaser, P.H., 1991, Fate of silicate minerals in a peat bog: Geology, v. 19, no. 4, p. 328-331, https://doi.org/10.1130/0091-7613(1991)019<0328:FOSMIA>2.3.CO;2.","productDescription":"4 p.","startPage":"328","endPage":"331","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":338079,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"Minnesota","otherGeospatial":"Lost River peatland","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"coordinates\": [\n [\n [\n -94.48107716216364,\n 48.20103577453631\n ],\n [\n -94.48107716216364,\n 48.1257567119583\n ],\n [\n -94.34359226272942,\n 48.1257567119583\n ],\n [\n -94.34359226272942,\n 48.20103577453631\n ],\n [\n -94.48107716216364,\n 48.20103577453631\n ]\n ]\n ],\n \"type\": \"Polygon\"\n }\n }\n ]\n}","volume":"19","issue":"4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"58d38d61e4b0236b68f98f88","contributors":{"authors":[{"text":"Bennett, Philip C.","contributorId":30567,"corporation":false,"usgs":true,"family":"Bennett","given":"Philip","email":"","middleInitial":"C.","affiliations":[],"preferred":false,"id":685706,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Siegel, Donald I.","contributorId":97499,"corporation":false,"usgs":true,"family":"Siegel","given":"Donald I.","affiliations":[],"preferred":false,"id":685707,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Hillier, Barbara M.","contributorId":19026,"corporation":false,"usgs":true,"family":"Hillier","given":"Barbara","email":"","middleInitial":"M.","affiliations":[],"preferred":false,"id":685708,"contributorType":{"id":1,"text":"Authors"},"rank":3},{"text":"Glaser, Paul H.","contributorId":178129,"corporation":false,"usgs":false,"family":"Glaser","given":"Paul","email":"","middleInitial":"H.","affiliations":[],"preferred":false,"id":685709,"contributorType":{"id":1,"text":"Authors"},"rank":4}]}} ,{"id":70179842,"text":"70179842 - 1991 - Response of Ned Wilson Lake watershed, Colorado, to changes in atmospheric deposition of sulfate","interactions":[],"lastModifiedDate":"2018-02-27T12:04:36","indexId":"70179842","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":3722,"text":"Water Resources Research","onlineIssn":"1944-7973","printIssn":"0043-1397","active":true,"publicationSubtype":{"id":10}},"title":"Response of Ned Wilson Lake watershed, Colorado, to changes in atmospheric deposition of sulfate","docAbstract":"The Ned Wilson Lake watershed responds directly and rapidly to changes in precipitation inputs of sulfate, which has important implications for effects of acid deposition on the aquatic system. Chemistry at three precipitation collection sites and three watershed sites (a pond, a lake, and a spring) has been monitored in and near the Flattops Wilderness Area in northwestern Colorado beginning in 1981–1983. Bulk snowpack concentration of sulfate in the watershed and volume-weighted annual mean concentration of sulfate in precipitation at two nearby sites generally decreased from 1981 to 1985, were small through 1987, and increased in 1988–1989. Changes in concentration of sulfate at the watershed sites are controlled by precipitation inputs. Responsiveness of the individual sites was dependent on their position along the hydrologic flow path. The fastest response was in the pond, which has a hydrologic residence time of less than 1 year; over 90% of the variance in concentration of sulfate in the pond was explained by changes in concentration in precipitation. The lake has a hydrologic residence time of 1 to 4 years; a regression model of the concentration of sulfate in the lake, as a function of the concentration in the lake during the previous year and the concentration in precipitation, explained 87% of the variance in concentration of sulfate in the lake. The hydrologic response time of the spring is unknown; it was not responsive to changes in concentration of sulfate in precipitation. The recent increase of sulfate concentration in precipitation and in the pond and lake is evidence for a rapid rather than a delayed response, which could not be determined when only a decreasing trend in sulfate concentration was reported in 1982–1987. Watersheds of this type are sensitive to acidification (acid-neutralizing capacity less than 60 μeq L−1), and these results indicate conservative behavior of sulfate. This is important in predicting effects of future changes in atmospheric deposition, which could potentially be caused by anthropogenic emissions or climatic change.
","language":"English","publisher":"American Geophysical Union","doi":"10.1029/91WR01189","usgsCitation":"Campbell, D.H., Turk, J.T., and Spahr, N.E., 1991, Response of Ned Wilson Lake watershed, Colorado, to changes in atmospheric deposition of sulfate: Water Resources Research, v. 27, no. 8, p. 2047-2060, https://doi.org/10.1029/91WR01189.","productDescription":"14 p.","startPage":"2047","endPage":"2060","costCenters":[{"id":191,"text":"Colorado Water Science Center","active":true,"usgs":true}],"links":[{"id":333405,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"Colorado","otherGeospatial":"Ned Wilson Lake watershed","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n -107.25,\n 39.91667\n ],\n [\n -107.5,\n 39.91667\n ],\n [\n -107.5,\n 40.01667\n ],\n [\n -107.25,\n 40.01667\n ],\n [\n -107.25,\n 39.91667\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"27","issue":"8","noUsgsAuthors":false,"publicationDate":"2008-01-08","publicationStatus":"PW","scienceBaseUri":"58808de2e4b01dfadfff15db","contributors":{"authors":[{"text":"Campbell, Donald H. dhcampbe@usgs.gov","contributorId":1670,"corporation":false,"usgs":true,"family":"Campbell","given":"Donald","email":"dhcampbe@usgs.gov","middleInitial":"H.","affiliations":[],"preferred":true,"id":658909,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Turk, John T.","contributorId":53363,"corporation":false,"usgs":true,"family":"Turk","given":"John","email":"","middleInitial":"T.","affiliations":[],"preferred":false,"id":658910,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Spahr, Norman E. nspahr@usgs.gov","contributorId":1977,"corporation":false,"usgs":true,"family":"Spahr","given":"Norman","email":"nspahr@usgs.gov","middleInitial":"E.","affiliations":[],"preferred":true,"id":658911,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70016287,"text":"70016287 - 1991 - New hydrologic instrumentation in the U.S. Geological Survey","interactions":[],"lastModifiedDate":"2012-03-12T17:18:41","indexId":"70016287","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":24,"text":"Conference Paper"},"publicationSubtype":{"id":19,"text":"Conference Paper"},"title":"New hydrologic instrumentation in the U.S. Geological Survey","docAbstract":"New water-level sensing and recording instrumentation is being used by the U.S. Geological Survey for monitoring water levels, stream velocities, and water-quality characteristics. Several of these instruments are briefly described. The Basic Data Recorder (BDR) is an electronic data logger, that interfaces to sensor systems through a serial-digital interface standard (SDI-12), which was proposed by the data-logger industry; the Incremental Shaft Encoder is an intelligent water-level sensor, which interfaces to the BDR through the SDI-12; the Pressure Sensor is an intelligent, nonsubmersible pressure sensor, which interfaces to the BDR through the SDI-12 and monitors water levels from 0 to 50 feet; the Ultrasonic Velocity Meter is an intelligent, water-velocity sensor, which interfaces to the BDR through the SDI-12 and measures the velocity across a stream up to 500 feet in width; the Collapsible Hand Sampler can be collapsed for insertion through holes in the ice and opened under the ice to collect a water sample; the Lighweight Ice Auger, weighing only 32 pounds, can auger 6- and 8-inch holes through approximately 3.5 feet of ice; and the Ice Chisel has a specially hardened steel blade and 6-foot long, hickory D-handle.","largerWorkTitle":"Cold Regions Engineering","conferenceTitle":"Sixth International Cold Regions Engineering Conference","conferenceDate":"26 February 1991 through 28 February 1991","conferenceLocation":"West Lebanon, NH, USA","language":"English","publisher":"Publ by ASCE","publisherLocation":"New York, NY, United States","isbn":"0872627985","usgsCitation":"Latkovich, V., and Shope, W., 1991, New hydrologic instrumentation in the U.S. Geological Survey, in Cold Regions Engineering, West Lebanon, NH, USA, 26 February 1991 through 28 February 1991, p. 739-747.","startPage":"739","endPage":"747","numberOfPages":"9","costCenters":[],"links":[{"id":222901,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a6592e4b0c8380cd72c22","contributors":{"editors":[{"text":"Sodhi Devinder S.","contributorId":128371,"corporation":true,"usgs":false,"organization":"Sodhi Devinder S.","id":536325,"contributorType":{"id":2,"text":"Editors"},"rank":1}],"authors":[{"text":"Latkovich, V.J.","contributorId":52576,"corporation":false,"usgs":true,"family":"Latkovich","given":"V.J.","email":"","affiliations":[],"preferred":false,"id":373084,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Shope, W.G.","contributorId":17272,"corporation":false,"usgs":true,"family":"Shope","given":"W.G.","email":"","affiliations":[],"preferred":false,"id":373083,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":1000607,"text":"1000607 - 1991 - Disturbance effects on aquatic vegetation in regulated and unregulated lakes in northern Minnesota","interactions":[],"lastModifiedDate":"2016-04-25T12:37:00","indexId":"1000607","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1167,"text":"Canadian Journal of Botany","active":true,"publicationSubtype":{"id":10}},"title":"Disturbance effects on aquatic vegetation in regulated and unregulated lakes in northern Minnesota","docAbstract":"The effects of water-level regulation on aquatic macrophyte communities were investigated by comparing two regulated lakes in northern Minnesota with a nearby unregulated lake (Lac La Croix). Natural annual fluctuations of about 1.8 m were replaced with fluctuations of 1.1 m and 2.7 m in the regulated lakes, and the timing of water-level changes was also altered. Quadrats were sampled along transects that followed depth contours representing different plant habitats in the unregulated lake. Ordinations showed that the macrophyte communities at all sampled depths of the regulated lakes differed from those in the unregulated lake. The unregulated lake supported structurally diverse plant communities at all depths. In the lake with reduced fluctuations, only four taxa were present along transects that were never dewatered; all were erect aquatics that extended through the entire water column. In the lake with increased fluctuations, rosette and mat-forming species dominated transects where drawdown occurred in early winter and disturbance resulted from ice formation in the sediments. The natural hydrologic regime at the unregulated lake resulted in intermediate disturbance and high diversity. There was either too little or too much disturbance from water-level fluctuations in the regulated lakes, both resulting in reduced structural diversity.
","language":"English","publisher":"NRC Research Press","doi":"10.1139/b91-198","usgsCitation":"Wilcox, D.A., and Meeker, J.E., 1991, Disturbance effects on aquatic vegetation in regulated and unregulated lakes in northern Minnesota: Canadian Journal of Botany, v. 69, no. 7, p. 1542-1551, https://doi.org/10.1139/b91-198.","productDescription":"10 p.","startPage":"1542","endPage":"1551","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[{"id":324,"text":"Great Lakes Science Center","active":true,"usgs":true}],"links":[{"id":479762,"rank":1,"type":{"id":41,"text":"Open Access External Repository Page"},"url":"http://hdl.handle.net/20.500.12648/2310","text":"External Repository"},{"id":133451,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"69","issue":"7","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"4f4e4a51e4b07f02db629a8e","contributors":{"authors":[{"text":"Wilcox, Douglas A.","contributorId":36880,"corporation":false,"usgs":true,"family":"Wilcox","given":"Douglas","email":"","middleInitial":"A.","affiliations":[],"preferred":false,"id":308899,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Meeker, James E.","contributorId":80228,"corporation":false,"usgs":true,"family":"Meeker","given":"James","email":"","middleInitial":"E.","affiliations":[],"preferred":false,"id":308900,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70015102,"text":"70015102 - 1991 - The Vigil Network: A means of observing landscape change in drainage basins","interactions":[],"lastModifiedDate":"2017-03-09T09:30:53","indexId":"70015102","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1927,"text":"Hydrological Sciences Journal","active":true,"publicationSubtype":{"id":10}},"title":"The Vigil Network: A means of observing landscape change in drainage basins","docAbstract":"Long-term monitoring of geomorphic, hydrological, and biological characteristics of landscapes provides an effective means of relating observed change to possible causes of the change. Identification of changes in basin characteristics, especially in arid areas where the response to altered climate or land use is generally rapid and readily apparent, might provide the initial direct indications that factors such as global warming and cultural impacts have affected the environment. The Vigil Network provides an opportunity for earth and life scientists to participate in a systematic monitoring effort to detect landscape changes over time, and to relate such changes to possible causes. The Vigil Network is an ever-increasing group of sites and basins used to monitor landscape features with as much as 50 years of documented geomorphic and related observations.
","language":"English","publisher":"Taylor & Francis","doi":"10.1080/02626669109492518","usgsCitation":"Osterkamp, W.R., Emmett, W.W., and Leopold, L.B., 1991, The Vigil Network: A means of observing landscape change in drainage basins: Hydrological Sciences Journal, v. 36, no. 4, p. 331-344, https://doi.org/10.1080/02626669109492518.","productDescription":"14 p.","startPage":"331","endPage":"344","costCenters":[],"links":[{"id":438943,"rank":1,"type":{"id":30,"text":"Data Release"},"url":"https://doi.org/10.5066/P9V0R02R","text":"USGS data release","linkHelpText":"The Vigil Network: long-term, broad spectrum data collected to observe landscape change in drainage basins"},{"id":223967,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"36","issue":"4","noUsgsAuthors":false,"publicationDate":"2009-12-29","publicationStatus":"PW","scienceBaseUri":"505ba977e4b08c986b3222a7","contributors":{"authors":[{"text":"Osterkamp, W. R.","contributorId":46044,"corporation":false,"usgs":true,"family":"Osterkamp","given":"W.","email":"","middleInitial":"R.","affiliations":[],"preferred":false,"id":370076,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Emmett, W. W.","contributorId":107695,"corporation":false,"usgs":true,"family":"Emmett","given":"W.","email":"","middleInitial":"W.","affiliations":[],"preferred":false,"id":370077,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Leopold, Luna Bergere","contributorId":93884,"corporation":false,"usgs":true,"family":"Leopold","given":"Luna","email":"","middleInitial":"Bergere","affiliations":[],"preferred":false,"id":370075,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70015033,"text":"70015033 - 1991 - Herbicides in surface waters of the midwestern United States: The effect of spring flush","interactions":[],"lastModifiedDate":"2019-03-28T07:18:50","indexId":"70015033","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1565,"text":"Environmental Science & Technology","onlineIssn":"1520-5851","printIssn":"0013-936X","active":true,"publicationSubtype":{"id":10}},"title":"Herbicides in surface waters of the midwestern United States: The effect of spring flush","docAbstract":"Approximately three-fourths of all preemergent herbicides used in the United States are applied to row crops over a 12-state area, called the \"corn belt\" (I). The application of these compounds may cause widespread degradation of water quality (2). Because herbicides are water soluble, there is the potential for leaching into groundwater and surface water (3, 4), as well as aerial transport and Occurrence in precipitation (5). Monitoring studies in the Midwest have shown widespread detection of herbicides in groundwater and in surface water (3,4); however, little is known about the regional impact of herbicide application (6). The objective of our research was to assess the mag. nitude and persistence of herbicide runoff in the spring flush at the regional scale.
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