Atmospheric methyl tert‐butyl ether (MTBE) concentrations in southern New Jersey generally exceeded concentrations in samples taken from the unsaturated zone. A simple unsaturated zone transport model indicates that MTBE degradation can explain the attenuation with half‐lives from a few months to a couple of years. Tert‐butyl alcohol (TBA), a possible degradation product of MTBE, was detected in unsaturated‐zone samples at concentrations exceeding atmospheric levels at some sites, suggesting the possible conversion of MTBE to TBA. At sites where MTBE was detected in shallow groundwater, the concentration was typically higher than the overlying unsaturated‐zone concentration. This observation is consistent with outgassing from the aquifer and combined with the unsaturated‐zone attenuation suggests some of the MTBE detections in shallow groundwater are nonatmospheric in origin, coming from leaking tanks, road runoff, or other sources. The identification of sources of MTBE in groundwater and attenuation mechanisms through the hydrologic cycle is critical in developing an understanding of the long‐term effect of MTBE releases.
","language":"English","publisher":"American Geophysical Union","doi":"10.1029/2000WR900292","usgsCitation":"Baehr, A.L., Charles, E., and Baker, R.J., 2001, Methyl tert‐butyl ether degradation in the unsaturated zone and the relation between MTBE in the atmosphere and shallow groundwater: Water Resources Research, v. 37, no. 2, p. 223-233, https://doi.org/10.1029/2000WR900292.","productDescription":"11 p.","startPage":"223","endPage":"233","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":488090,"rank":1,"type":{"id":40,"text":"Open Access Publisher Index Page"},"url":"https://doi.org/10.1029/2000wr900292","text":"Publisher Index Page"},{"id":232333,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"37","issue":"2","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a5616e4b0c8380cd6d348","contributors":{"authors":[{"text":"Baehr, Arthur L.","contributorId":104523,"corporation":false,"usgs":true,"family":"Baehr","given":"Arthur","email":"","middleInitial":"L.","affiliations":[],"preferred":false,"id":398078,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Charles, Emmanuel G. 0000-0002-3338-4958","orcid":"https://orcid.org/0000-0002-3338-4958","contributorId":3637,"corporation":false,"usgs":false,"family":"Charles","given":"Emmanuel G.","affiliations":[],"preferred":false,"id":398077,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Baker, Ronald J. rbaker@usgs.gov","contributorId":1436,"corporation":false,"usgs":true,"family":"Baker","given":"Ronald","email":"rbaker@usgs.gov","middleInitial":"J.","affiliations":[{"id":470,"text":"New Jersey Water Science Center","active":true,"usgs":true}],"preferred":true,"id":398079,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70023560,"text":"70023560 - 2001 - User interface for ground-water modeling: Arcview extension","interactions":[],"lastModifiedDate":"2012-03-12T17:20:01","indexId":"70023560","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2341,"text":"Journal of Hydrologic Engineering","active":true,"publicationSubtype":{"id":10}},"title":"User interface for ground-water modeling: Arcview extension","docAbstract":"Numerical simulation for ground-water modeling often involves handling large input and output data sets. A geographic information system (GIS) provides an integrated platform to manage, analyze, and display disparate data and can greatly facilitate modeling efforts in data compilation, model calibration, and display of model parameters and results. Furthermore, GIS can be used to generate information for decision making through spatial overlay and processing of model results. Arc View is the most widely used Windows-based GIS software that provides a robust user-friendly interface to facilitate data handling and display. An extension is an add-on program to Arc View that provides additional specialized functions. An Arc View interface for the ground-water flow and transport models MODFLOW and MT3D was built as an extension for facilitating modeling. The extension includes preprocessing of spatially distributed (point, line, and polygon) data for model input and postprocessing of model output. An object database is used for linking user dialogs and model input files. The Arc View interface utilizes the capabilities of the 3D Analyst extension. Models can be automatically calibrated through the Arc View interface by external linking to such programs as PEST. The efficient pre- and postprocessing capabilities and calibration link were demonstrated for ground-water modeling in southwest Kansas.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Journal of Hydrologic Engineering","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1061/(ASCE)1084-0699(2001)6:3(251)","issn":"10840699","usgsCitation":"Tsou, M., and Whittemore, D.O., 2001, User interface for ground-water modeling: Arcview extension: Journal of Hydrologic Engineering, v. 6, no. 3, p. 251-257, https://doi.org/10.1061/(ASCE)1084-0699(2001)6:3(251).","startPage":"251","endPage":"257","numberOfPages":"7","costCenters":[],"links":[{"id":232176,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":207323,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1061/(ASCE)1084-0699(2001)6:3(251)"}],"volume":"6","issue":"3","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505bbfc5e4b08c986b329d68","contributors":{"authors":[{"text":"Tsou, Ming-shu","contributorId":20507,"corporation":false,"usgs":false,"family":"Tsou","given":"Ming-shu","email":"","affiliations":[],"preferred":false,"id":398039,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Whittemore, Donald O.","contributorId":28748,"corporation":false,"usgs":false,"family":"Whittemore","given":"Donald","email":"","middleInitial":"O.","affiliations":[],"preferred":false,"id":398040,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023559,"text":"70023559 - 2001 - Evaluation of mixed-population flood-frequency analysis","interactions":[],"lastModifiedDate":"2012-03-12T17:20:02","indexId":"70023559","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2341,"text":"Journal of Hydrologic Engineering","active":true,"publicationSubtype":{"id":10}},"title":"Evaluation of mixed-population flood-frequency analysis","docAbstract":"A mixed population of flood flows was shown to cause quality-of-fit problems if a single-population flood-frequency distribution was used to describe the flood data. The three populations in this mix were \"ordinary,\" tropical cyclone, and ice-jam-release floods. Parametric descriptions of the single and separated flood populations were evaluated using probability-plot correlation-coefficient tests. These tests quantified how well the flood-probability distributions agreed with plotting-position descriptions of the data and quantified the differences due to the mixed-population analysis. High outliers caused the high skewness found in the single- population analyses. The tropical cyclone component was underestimated by single-population analyses at gauging stations in Massachusetts that had little data.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Journal of Hydrologic Engineering","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1061/(ASCE)1084-0699(2001)6:1(62)","issn":"10840699","usgsCitation":"Murphy, P., 2001, Evaluation of mixed-population flood-frequency analysis: Journal of Hydrologic Engineering, v. 6, no. 1, p. 62-70, https://doi.org/10.1061/(ASCE)1084-0699(2001)6:1(62).","startPage":"62","endPage":"70","numberOfPages":"9","costCenters":[],"links":[{"id":207302,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1061/(ASCE)1084-0699(2001)6:1(62)"},{"id":232138,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"6","issue":"1","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a0c9be4b0c8380cd52c06","contributors":{"authors":[{"text":"Murphy, P.J.","contributorId":91903,"corporation":false,"usgs":true,"family":"Murphy","given":"P.J.","email":"","affiliations":[],"preferred":false,"id":398038,"contributorType":{"id":1,"text":"Authors"},"rank":1}]}} ,{"id":70023557,"text":"70023557 - 2001 - Urbanization effects on the hydrology of the Atlanta, Georgia (USA)","interactions":[],"lastModifiedDate":"2012-03-12T17:20:10","indexId":"70023557","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1934,"text":"IAHS-AISH Publication","active":true,"publicationSubtype":{"id":10}},"title":"Urbanization effects on the hydrology of the Atlanta, Georgia (USA)","docAbstract":"For the period from 1958 to 1996, streamflow and rainfall characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds in the vicinity of Atlanta, Georgia (USA). Water levels in several wells completed in surficial and crystalline-rock aquifers also were evaluated. Annual runoff coefficients (runoff as a fractional percentage of precipitation) ranged from 0.31 to 0.34 and were not significantly different for the urban stream (Peachtree Creek). Peak flows for the largest 25 stormflows at Peachtree Creek were 30% to 80% greater than peak flows for the other streams. A 2-day storm recession constant for Peachtree Creek was much larger, that is streamflow decreased more rapidly than for the other streams. Average low flow of Peachtree Creek was 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of storm water and the paving of groundwater recharge areas. The timing of groundwater level variations was similar annually in each well, reflecting the seasonal recharge. Although water level monitoring only began during the late 1970s and early 1980s for the two urban wells, water levels in these wells have been declining compared to non-urban wells since then. The water level decline is attributed to decreased groundwater recharge in the urban watersheds due to increased imperviousness and related rapid storm runoff. Likewise, the increased urbanization from the 1960s to the 1990s of the Peachtree Creek watershed produced more runoff than urbanization in the less urbanized Big Creek and Sweetwater Creek watersheds.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"IAHS-AISH Publication","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","issn":"01447815","usgsCitation":"Peters, N., and Rose, S., 2001, Urbanization effects on the hydrology of the Atlanta, Georgia (USA): IAHS-AISH Publication, no. 269, p. 109-116.","startPage":"109","endPage":"116","numberOfPages":"8","costCenters":[],"links":[{"id":232739,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"issue":"269","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505bbe45e4b08c986b3294c6","contributors":{"authors":[{"text":"Peters, N.E.","contributorId":33332,"corporation":false,"usgs":true,"family":"Peters","given":"N.E.","email":"","affiliations":[],"preferred":false,"id":398035,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Rose, S.","contributorId":56002,"corporation":false,"usgs":true,"family":"Rose","given":"S.","email":"","affiliations":[],"preferred":false,"id":398036,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023555,"text":"70023555 - 2001 - Effect of the 1997-1998 ENSO-related drought on hydrology and salinity in a Micronesian wetland complex","interactions":[],"lastModifiedDate":"2022-10-13T16:10:50.202353","indexId":"70023555","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1583,"text":"Estuaries","active":true,"publicationSubtype":{"id":10}},"title":"Effect of the 1997-1998 ENSO-related drought on hydrology and salinity in a Micronesian wetland complex","docAbstract":"The potential effects of global climate change on coastal ecosystems have attracted considerable attention, but the impacts of shorter-term climate perturbations such as ENSO (El Niño-Southern Oscillation) are lesser known. In this study, we determined the effects of the 1997–1998 ENSO-related drought on the hydrology and salinity of a Micronesian mangrove ecosystem and an adjacent freshwater swamp. A network of 9 piezometer clusters installed at the study site served as sampling points for continuous and manual measurements of salinity and water level. During the drought period from January through April 1998, mean water table levels in the mangroves and freshwater swamp were approximately 12 and 54 cm lower, respectively, than during May through December when precipitation returned to near normal levels. At the peak of the drought (February 1998), the most dramatic result was a reversal in groundwater flow that sent groundwater from the mangroves upstream toward the freshwater swamp. Flow nets constructed for this period and immediately after illustrate the strong hydrological linkage between the two systems. This linkage was also illustrated by measurements of groundwater salinity in the piezometer network. Ninety-six percent of the salinity measurements taken in the mangroves during the study were at least 10‰ less than the salinity of sea water, indicating that the mangroves were consistently receiving freshwater flows. An analysis of variance of groundwater salinity measurements during and after the drought showed that salinity levels in the 0.5 and 1.0 m depth piezometers were greater during than after the drought. In a comparison of salinity values in 0.5-m wells during low tide, mean salinity was approximately twice as high during the drought than after (14.7‰ versus 6.2‰, respectively). This study demonstrates that short-term climate perturbations such as ENSO can disrupt important coastal processes. Over repeated drought cycles, such perturbations have the potential to affect the structure and function of mangrove forests and upstream ecosystems.
Microbial communities indigenous to a shallow groundwater system near Beaufort, SC, degraded milligram per liter concentrations of methyl tert-butyl ether (MTBE) under natural and artificial oxic conditions. Significant MTBE biodegradation was observed where anoxic, MTBE-contaminated groundwater discharged to a concrete-lined ditch. In the anoxic groundwater adjacent to the ditch, concentrations of MTBE were >1 mg/L. Where groundwater discharge occurs, dissolved oxygen (DO) concentrations beneath the ditch exceeded 1.0 mg/L to a depth of 1.5 m, and MTBE concentrations decreased to <1 μg/L prior to discharge. MTBE mass flux calculations indicate that 96% of MTBE mass loss occurs in the relatively small oxic zone prior to discharge. Samples of a natural microbial biofilm present in the oxic zone beneath the ditch completely degraded [U-14C]MTBE to [14C]CO2 in laboratory liquid culture studies, with no accumulation of intermediate compounds. Upgradient of the ditch in the anoxic, MTBE- and BTEX-contaminated aquifer, addition of a soluble oxygen release compound resulted in oxic conditions and rapid MTBE biodegradation by indigenous microorganisms. In an observation well located closest to the oxygen addition area, DO concentrations increased from 0.4 to 12 mg/L in <60 days and MTBE concentrations decreased from 20 to 3 mg/L. In the same time period at a downgradient observation well, DO increased from <0.2 to 2 mg/L and MTBE concentrations decreased from 30 to <5 mg/L. These results indicate that microorganisms indigenous to the groundwater system at this site can degrade milligram per liter concentrations of MTBE under natural and artificial oxic conditions.
Using extended X-ray absorption fine structure (EXAFS) and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) measurements, we examined the sorption of Pb(II) to hematite in the presence of malonic acid. Pb LIII-edge EXAFS measurements performed in the presence of malonate indicate the presence of both Fe and C neighbors, suggesting that a major fraction of surface-bound malonate is bonded to adsorbed Pb(II). In the absence of Pb(II), ATR-FTIR measurements of sorbed malonate suggest the formation of more than one malonate surface complex. The dissimilarity of the IR spectrum of malonate sorbed on hematite to those for aqueous malonate suggest at least one of the sorbed malonate species is directly coordinated to surface Fe atoms in an inner-sphere mode. In the presence of Pb, little change is seen in the IR spectrum for sorbed malonate, indicating that geometry of malonate as it coordinates to sorbed Pb(II) adions is similar to the geometry of malonate as it coordinates to Fe in the hematite surface. Fits of the raw EXAFS spectra collected from pH 4 to pH 8 result in average Pb–C distances of 2.98 to 3.14 Å, suggesting the presence of both four- and six-membered Pb–malonate rings. The IR results are consistent with this interpretation. Thus, our results suggest that malonate binds to sorbed Pb(II) adions, forming ternary metal-bridging surface complexes.
In dealing with the passive transport of organic contaminants from soils to plants (including crops), a partition-limited model is proposed in which (i) the maximum (equilibrium) concentration of a contaminant in any location in the plant is determined by partition equilibrium with its concentration in the soil interstitial water, which in turn is determined essentially by the concentration in the soil organic matter (SOM) and (ii) the extent of approach to partition equilibrium, as measured by the ratio of the contaminant concentrations in plant water and soil interstitial water, αpt (≤ 1), depends on the transport rate of the contaminant in soil water into the plant and the volume of soil water solution that is required for the plant contaminant level to reach equilibrium with the external soil-water phase. Through reasonable estimates of plant organic-water compositions and of contaminant partition coefficients with various plant components, the model accounts for calculated values of αpt in several published crop-contamination studies, including near-equilibrium values (i.e., αpt ≅ 1) for relatively water-soluble contaminants and lower values for much less soluble contaminants; the differences are attributed to the much higher partition coefficients of the less soluble compounds between plant lipids and plant water, which necessitates much larger volumes of the plant water transport for achieving the equilibrium capacities. The model analysis indicates that for plants with high water contents the plant-water phase acts as the major reservoir for highly water-soluble contaminants. By contrast, the lipid in a plant, even at small amounts, is usually the major reservoir for highly water-insoluble contaminants.
The concentration and distribution of inorganic Hg was measured using cold-vapor atomic fluorescence spectrometry in samples collected at selected sites on the Sacramento River from below Shasta Dam to Freeport, CA, at six separate times between 1996 and 1997. Dissolved (ultrafiltered, 0.005 μm equivalent pore size) Hg concentrations remained relatively constant throughout the system, ranging from the detection limit (< 0.4 ng/L) to 2.4 ng/L. Total Hg (dissolved plus colloidal suspended sediment) concentrations ranged from the detection limit at the site below Shasta Dam in September 1996 to 81 ng/L at the Colusa site in January 1997, demonstrating that colloidal sediment plays an important role in the downriver Hg transport. Sequential extractions of colloid concentrates indicate that the greatest amount of Hg associated with sediment was found in the “residual” (mineral) phase with a significant quantity also occurring in the “oxidizable” phase. Only a minor amount of Hg was observed in the “reducible” phase. Dissolved Hg loads remained constant or increased slightly in the downstream direction through the study area, whereas the total inorganic Hg load increased significantly downstream especially in the reach of the river between Bend Bridge and Colusa. Analysis of temporal variations showed that Hg loading was positively correlated to discharge.
","language":"English","publisher":"Springer","doi":"10.1007/s002440010159","issn":"00904341","usgsCitation":"Roth, D., Taylor, H.E., Domagalski, J.L., Dileanis, P.D., Peart, D., Antweiler, R.C., and Alpers, C.N., 2001, Distribution of inorganic mercury in Sacramento River water and suspended colloidal sediment material: Archives of Environmental Contamination and Toxicology, v. 40, no. 2, p. 161-172, https://doi.org/10.1007/s002440010159.","productDescription":"12 p.","startPage":"161","endPage":"172","costCenters":[{"id":154,"text":"California Water Science Center","active":true,"usgs":true},{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":232737,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":207627,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1007/s002440010159"}],"volume":"40","issue":"2","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a02dbe4b0c8380cd5021e","contributors":{"authors":[{"text":"Roth, D.A.","contributorId":100864,"corporation":false,"usgs":true,"family":"Roth","given":"D.A.","email":"","affiliations":[],"preferred":false,"id":397892,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Taylor, Howard E. hetaylor@usgs.gov","contributorId":1551,"corporation":false,"usgs":true,"family":"Taylor","given":"Howard","email":"hetaylor@usgs.gov","middleInitial":"E.","affiliations":[{"id":5044,"text":"National Research Program - Central Branch","active":true,"usgs":true}],"preferred":true,"id":397887,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Domagalski, Joseph L. 0000-0002-6032-757X joed@usgs.gov","orcid":"https://orcid.org/0000-0002-6032-757X","contributorId":1330,"corporation":false,"usgs":true,"family":"Domagalski","given":"Joseph","email":"joed@usgs.gov","middleInitial":"L.","affiliations":[{"id":154,"text":"California Water Science Center","active":true,"usgs":true}],"preferred":true,"id":397890,"contributorType":{"id":1,"text":"Authors"},"rank":3},{"text":"Dileanis, Peter D. dileanis@usgs.gov","contributorId":71541,"corporation":false,"usgs":true,"family":"Dileanis","given":"Peter","email":"dileanis@usgs.gov","middleInitial":"D.","affiliations":[{"id":154,"text":"California Water Science Center","active":true,"usgs":true}],"preferred":false,"id":397891,"contributorType":{"id":1,"text":"Authors"},"rank":4},{"text":"Peart, D.B.","contributorId":45304,"corporation":false,"usgs":true,"family":"Peart","given":"D.B.","email":"","affiliations":[],"preferred":false,"id":397888,"contributorType":{"id":1,"text":"Authors"},"rank":5},{"text":"Antweiler, Ronald C. 0000-0001-5652-6034 antweil@usgs.gov","orcid":"https://orcid.org/0000-0001-5652-6034","contributorId":1481,"corporation":false,"usgs":true,"family":"Antweiler","given":"Ronald","email":"antweil@usgs.gov","middleInitial":"C.","affiliations":[{"id":5044,"text":"National Research Program - Central Branch","active":true,"usgs":true}],"preferred":true,"id":397889,"contributorType":{"id":1,"text":"Authors"},"rank":6},{"text":"Alpers, Charles N. 0000-0001-6945-7365 cnalpers@usgs.gov","orcid":"https://orcid.org/0000-0001-6945-7365","contributorId":411,"corporation":false,"usgs":true,"family":"Alpers","given":"Charles","email":"cnalpers@usgs.gov","middleInitial":"N.","affiliations":[{"id":154,"text":"California Water Science Center","active":true,"usgs":true}],"preferred":true,"id":397893,"contributorType":{"id":1,"text":"Authors"},"rank":7}]}} ,{"id":70023512,"text":"70023512 - 2001 - Online bibliographic sources in hydrology","interactions":[],"lastModifiedDate":"2016-08-25T12:24:42","indexId":"70023512","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":3345,"text":"Science and Technology Libraries","active":true,"publicationSubtype":{"id":10}},"title":"Online bibliographic sources in hydrology","docAbstract":"Traditional commercial bibliographic databases and indexes provide some access to hydrology materials produced by the government; however, these sources do not provide comprehensive coverage of relevant hydrologic publications. This paper discusses bibliographic information available from the federal government and state geological surveys, water resources agencies, and depositories. In addition to information in these databases, the paper describes the scope, styles of citing, subject terminology, and the ways these information sources are currently being searched, formally and informally, by hydrologists. Information available from the federal and state agencies and from the state depositories might be missed by limiting searches to commercially distributed databases.
","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Science and Technology Libraries","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1300/J122v21n03_05","issn":"0194262X","usgsCitation":"Wild, E.C., and Havener, W.M., 2001, Online bibliographic sources in hydrology: Science and Technology Libraries, v. 21, no. 3-4, p. 63-86, https://doi.org/10.1300/J122v21n03_05.","startPage":"63","endPage":"86","numberOfPages":"24","costCenters":[],"links":[{"id":232695,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"21","issue":"3-4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a6e40e4b0c8380cd75564","contributors":{"authors":[{"text":"Wild, Emily C. 0000-0001-6157-7629 ecwild@usgs.gov","orcid":"https://orcid.org/0000-0001-6157-7629","contributorId":1810,"corporation":false,"usgs":true,"family":"Wild","given":"Emily","email":"ecwild@usgs.gov","middleInitial":"C.","affiliations":[{"id":5081,"text":"Libraries","active":false,"usgs":true}],"preferred":false,"id":397883,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Havener, W. Michael","contributorId":29996,"corporation":false,"usgs":true,"family":"Havener","given":"W.","email":"","middleInitial":"Michael","affiliations":[],"preferred":false,"id":397882,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023494,"text":"70023494 - 2001 - Identification of alkyl dimethylbenzylammonium surfactants in water samples by solid-phase extraction followed by ion trap LC/MS and LC/MS/MS","interactions":[],"lastModifiedDate":"2021-05-27T18:49:24.646915","indexId":"70023494","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","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":"Identification of alkyl dimethylbenzylammonium surfactants in water samples by solid-phase extraction followed by ion trap LC/MS and LC/MS/MS","docAbstract":"A novel methodology was developed for the determination of alkyl (C12, C14, and C16) dimethylbenzylammonium chloride (benzalkonium chloride or BAC, Chemical Abstract Service number: 8001-54-5) in water samples. This method is based on solid-phase extraction (SPE) using polymeric cartridges, followed by high-performance liquid chromatography/ion trap mass spectrometry (LC/MS) and tandem mass spectrometry(MS/MS) detection, equipped with an electrospray interface in positive ion mode. Chromatographic separation was achieved for three BAC homologues by using a C18 column and a gradient of acetonitrile/10 millimolar aqueous ammonium formate. Total method recoveries were higher than 71% in different water matrices. The main ions observed by LC/MS were at mass-to-charge ratios (m/z) of 304, 332, and 360, which correspond to the molecular ions of the C12, C14, and C16 alkyl BAC, respectively. The unequivocal structural identification of these compounds in water samples was performed by LC/MS/MS after isolation and subsequent fragmentation of each molecular ion. The main fragmentation observed for the three different homologues corresponded to the loss of the toluyl group in the chemical structure, which leads to the fragment ions at m/z 212, 240, and 268 and a tropylium ion, characteristic of all homologues, at m/z 91. Detection limits for the methodology developed in this work were in the low nanogram-per-liter range. Concentration levels of BAC - ranging from 1.2 to 36.6 micrograms per liter - were found in surface-water samples collected downstream from different wastewater-treatment discharges, thus indicating its input and persistence through the wastewater-treatment process.","language":"English","publisher":"ACS","doi":"10.1021/es001742v","issn":"0013936X","usgsCitation":"Ferrer, I., and Furlong, E., 2001, Identification of alkyl dimethylbenzylammonium surfactants in water samples by solid-phase extraction followed by ion trap LC/MS and LC/MS/MS: Environmental Science & Technology, v. 35, no. 12, p. 2583-2588, https://doi.org/10.1021/es001742v.","productDescription":"6 p.","startPage":"2583","endPage":"2588","costCenters":[{"id":452,"text":"National Water Quality Laboratory","active":true,"usgs":true},{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":232447,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":207468,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1021/es001742v"}],"volume":"35","issue":"12","noUsgsAuthors":false,"publicationDate":"2001-05-19","publicationStatus":"PW","scienceBaseUri":"505a3820e4b0c8380cd61454","contributors":{"authors":[{"text":"Ferrer, I.","contributorId":97260,"corporation":false,"usgs":true,"family":"Ferrer","given":"I.","email":"","affiliations":[],"preferred":false,"id":397828,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Furlong, E. T. 0000-0002-7305-4603","orcid":"https://orcid.org/0000-0002-7305-4603","contributorId":98346,"corporation":false,"usgs":true,"family":"Furlong","given":"E. T.","affiliations":[],"preferred":false,"id":397829,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023483,"text":"70023483 - 2001 - Effects of urbanization on streamflow in the Atlanta area (Georgia, USA): A comparative hydrological approach","interactions":[],"lastModifiedDate":"2012-03-12T17:20:00","indexId":"70023483","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","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":"Effects of urbanization on streamflow in the Atlanta area (Georgia, USA): A comparative hydrological approach","docAbstract":"For the period from 1958 to 1996, streamflow characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds within a 20 000 km2 region in the vicinity of Atlanta, Georgia: In the Piedmont and Blue Ridge physiographic provinces of the southeastern USA. Water levels in several wells completed in surficial and crystalline-rock aquifers were also evaluated. Data were analysed for seven US Geological Survey (USGS) stream gauges, 17 National Weather Service rain gauges, and five USGS monitoring wells. Annual runoff coefficients (RCs; runoff as a fractional percentage of precipitation) for the urban stream (Peachtree Creek) were not significantly greater than for the less-urbanized watersheds. The RCs for some streams were similar to others and the similar streams were grouped according to location. The RCs decreased from the higher elevation and higher relief watersheds to the lower elevation and lower relief watersheds: Values were 0.54 for the two Blue Ridge streams. 0.37 for the four middle Piedmont streams (near Atlanta), and 0.28 for a southern Piedmont stream. For the 25 largest stormflows, the peak flows for Peachtree Creek were 30% to 100% greater then peak flows for the other stream. The storm recession period for the urban stream was 1-2 days less than that for the other streams and the recession was characterized by a 2-day storm recession constant that was, on average, 40 to 100% greater, i.e. streamflow decreased more rapidly than for the other streams. Baseflow recession constants ranged from 35 to 40% lower for Peachtree Creek than for the other streams; this is attributed to lower evapotranspiration losses, which result in a smaller change in groundwater storage than in the less-urbanized watersheds. Low flow of Peachtree Creek ranged from 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of stormwater and the paving of groundwater rechange areas. The timing of daily or monthly groundwater-level fluctuations was similar annually in each well, reflecting the seasonal recharge. Although water-level monitoring only began in the 1980s for the two urban wells, water levels displayed a notable decline compared with non-urban wells since then; this is attributed to decreased groundwater rechange in the urban watersheds due to increased imperviousness and related rapid storm runoff. Copyright ?? 2001 John Wiley & Sons, Ltd.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Hydrological Processes","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1002/hyp.218","issn":"08856087","usgsCitation":"Rose, S., and Peters, N., 2001, Effects of urbanization on streamflow in the Atlanta area (Georgia, USA): A comparative hydrological approach: Hydrological Processes, v. 15, no. 8, p. 1441-1457, https://doi.org/10.1002/hyp.218.","startPage":"1441","endPage":"1457","numberOfPages":"17","costCenters":[],"links":[{"id":207359,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1002/hyp.218"},{"id":232252,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"15","issue":"8","noUsgsAuthors":false,"publicationDate":"2001-05-25","publicationStatus":"PW","scienceBaseUri":"505a0829e4b0c8380cd519da","contributors":{"authors":[{"text":"Rose, S.","contributorId":56002,"corporation":false,"usgs":true,"family":"Rose","given":"S.","email":"","affiliations":[],"preferred":false,"id":397794,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Peters, N.E.","contributorId":33332,"corporation":false,"usgs":true,"family":"Peters","given":"N.E.","email":"","affiliations":[],"preferred":false,"id":397793,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023476,"text":"70023476 - 2001 - Factors controlling the configuration of the fresh-saline water interface in the Dead Sea coastal aquifers: Synthesis of TDEM surveys and numerical groundwater modeling","interactions":[],"lastModifiedDate":"2012-03-12T17:20:01","indexId":"70023476","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1923,"text":"Hydrogeology Journal","active":true,"publicationSubtype":{"id":10}},"title":"Factors controlling the configuration of the fresh-saline water interface in the Dead Sea coastal aquifers: Synthesis of TDEM surveys and numerical groundwater modeling","docAbstract":"TDEM (time domain electromagnetic) traverses in the Dead Sea (DS) coastal aquifer help to delineate the configuration of the interrelated fresh-water and brine bodies and the interface in between. A good linear correlation exists between the logarithm of TDEM resistivity and the chloride concentration of groundwater, mostly in the higher salinity range, close to that of the DS brine. In this range, salinity is the most important factor controlling resistivity. The configuration of the fresh-saline water interface is dictated by the hydraulic gradient, which is controlled by a number of hydrological factors. Three types of irregularities in the configuration of fresh-water and saline-water bodies were observed in the study area: 1. Fresh-water aquifers underlying more saline ones (\"Reversal\") in a multi-aquifer system. 2. \"Reversal\" and irregular residual saline-water bodies related to historical, frequently fluctuating DS base level and respective interfaces, which have not undergone complete flushing. A rough estimate of flushing rates may be obtained based on knowledge of the above fluctuations. The occurrence of salt beds is also a factor affecting the interface configuration. 3. The interface steepens towards and adjacent to the DS Rift fault zone. Simulation analysis with a numerical, variable-density flow model, using the US Geological Survey's SUTRA code, indicates that interface steep- ening may result from a steep water-level gradient across the zone, possibly due to a low hydraulic conductivity in the immediate vicinity of the fault.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Hydrogeology Journal","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1007/s100400100146","issn":"14312174","usgsCitation":"Yechieli, Y., Kafri, U., Goldman, M., and Voss, C., 2001, Factors controlling the configuration of the fresh-saline water interface in the Dead Sea coastal aquifers: Synthesis of TDEM surveys and numerical groundwater modeling: Hydrogeology Journal, v. 9, no. 4, p. 367-377, https://doi.org/10.1007/s100400100146.","startPage":"367","endPage":"377","numberOfPages":"11","costCenters":[],"links":[{"id":232172,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":207321,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1007/s100400100146"}],"volume":"9","issue":"4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a0ebce4b0c8380cd535d1","contributors":{"authors":[{"text":"Yechieli, Y.","contributorId":23308,"corporation":false,"usgs":true,"family":"Yechieli","given":"Y.","email":"","affiliations":[],"preferred":false,"id":397779,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Kafri, U.","contributorId":22942,"corporation":false,"usgs":true,"family":"Kafri","given":"U.","email":"","affiliations":[],"preferred":false,"id":397778,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Goldman, M.","contributorId":84540,"corporation":false,"usgs":true,"family":"Goldman","given":"M.","affiliations":[],"preferred":false,"id":397781,"contributorType":{"id":1,"text":"Authors"},"rank":3},{"text":"Voss, C.I.","contributorId":79515,"corporation":false,"usgs":true,"family":"Voss","given":"C.I.","email":"","affiliations":[],"preferred":false,"id":397780,"contributorType":{"id":1,"text":"Authors"},"rank":4}]}} ,{"id":70023474,"text":"70023474 - 2001 - Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA","interactions":[],"lastModifiedDate":"2018-12-03T09:09:06","indexId":"70023474","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1923,"text":"Hydrogeology Journal","active":true,"publicationSubtype":{"id":10}},"title":"Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA","docAbstract":"Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions affecting the 14C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and (4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting, at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted 14C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during the last glacial period. All of the paleowaters are enriched in 18O and 2H relative to modern infiltration, with maximum enrichment in δ18O of approximately 2.0‰.
","language":"English","publisher":"Springer","doi":"10.1007/s100400000121","issn":"14312174","usgsCitation":"Plummer, N., and Sprinkle, C., 2001, Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA: Hydrogeology Journal, v. 9, no. 2, p. 127-150, https://doi.org/10.1007/s100400000121.","productDescription":"24 p.","startPage":"127","endPage":"150","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":232133,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":207299,"rank":9999,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1007/s100400000121"}],"volume":"9","issue":"2","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a93dfe4b0c8380cd81098","contributors":{"authors":[{"text":"Plummer, Niel 0000-0002-4020-1013 nplummer@usgs.gov","orcid":"https://orcid.org/0000-0002-4020-1013","contributorId":190100,"corporation":false,"usgs":true,"family":"Plummer","given":"Niel","email":"nplummer@usgs.gov","affiliations":[{"id":436,"text":"National Research Program - Eastern Branch","active":true,"usgs":true}],"preferred":true,"id":397772,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Sprinkle, C.L.","contributorId":10811,"corporation":false,"usgs":true,"family":"Sprinkle","given":"C.L.","email":"","affiliations":[],"preferred":false,"id":397771,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023461,"text":"70023461 - 2001 - Formation and transport of the sulfonic acid metabolites of alachlor and metolachlor in soil","interactions":[],"lastModifiedDate":"2018-11-30T06:32:50","indexId":"70023461","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","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":"Formation and transport of the sulfonic acid metabolites of alachlor and metolachlor in soil","docAbstract":"Alachlor and metolachlor are dechlorinated and transformed into their corresponding ethane sulfonic acid (ESA) metabolites in soil. In a field-disappearance study, it was shown that alachlor ESA was formed at a faster rate and at concentrations 2−4 times higher than metolachlor ESA, conforming with the observed longer disappearance half-life of metolachlor (15.5 d) in the field as compared to alachlor (8 d). Runoff data also showed higher concentrations of alachlor ESA as compared to metolachlor ESA, even though they were applied at the same levels. Data from soil cores showed transport of the ESA compounds in soil to as far down as 75−90 cm below the surface, at concentrations ranging from less than 0.5 μg/L to about 50 μg/L. In contrast, no parent herbicide was detected at these depths. This observation correlates with the higher log Koc values for alachlor (3.33) and metolachlor (3.01) relative to their corresponding ESA metabolites, alachlor ESA (2.26), and metolachlor ESA (2.29).
Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table. Estimates within a rectilinear volume of sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m3/year of water enters and exits by lateral groundwater flow; 40–50 m3/year enters by upward leakage; and 640 m3/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the sabkha, 7–8 pore volumes of brine have entered the sabkha from below since the time the sabkha became saturated (7,000 years ago) as a result of the last global sea-level rise.
","language":"English","publisher":"Springer","publisherLocation":"Berlin, Germany","doi":"10.1007/s100400100137","issn":"14312174","usgsCitation":"Sanford, W.E., and Wood, W., 2001, Hydrology of the coastal sabkhas of Abu Dhabi, United Arab Emirates: Hydrogeology Journal, v. 9, no. 4, p. 358-366, https://doi.org/10.1007/s100400100137.","productDescription":"9 p.","startPage":"358","endPage":"366","numberOfPages":"9","onlineOnly":"N","additionalOnlineFiles":"N","costCenters":[],"links":[{"id":232285,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United Arab Emirates","city":"Abu Dhabi","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [\n [\n [\n 53.7506103515625,\n 24.046463999666567\n ],\n [\n 53.7506103515625,\n 25.055745117015316\n ],\n [\n 55.21728515625,\n 25.055745117015316\n ],\n [\n 55.21728515625,\n 24.046463999666567\n ],\n [\n 53.7506103515625,\n 24.046463999666567\n ]\n ]\n ]\n }\n }\n ]\n}","volume":"9","issue":"4","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a3765e4b0c8380cd60e52","contributors":{"authors":[{"text":"Sanford, Ward E. 0000-0002-6624-0280 wsanford@usgs.gov","orcid":"https://orcid.org/0000-0002-6624-0280","contributorId":2268,"corporation":false,"usgs":true,"family":"Sanford","given":"Ward","email":"wsanford@usgs.gov","middleInitial":"E.","affiliations":[{"id":37778,"text":"WMA - Integrated Modeling and Prediction Division","active":true,"usgs":true},{"id":436,"text":"National Research Program - Eastern Branch","active":true,"usgs":true}],"preferred":true,"id":397539,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Wood, Warren W.","contributorId":47770,"corporation":false,"usgs":false,"family":"Wood","given":"Warren W.","affiliations":[{"id":6601,"text":"Michigan State University","active":true,"usgs":false}],"preferred":false,"id":397538,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70023380,"text":"70023380 - 2001 - Major herbicides in ground water: Results from the National Water-Quality Assessment","interactions":[],"lastModifiedDate":"2022-10-26T17:19:13.783285","indexId":"70023380","displayToPublicDate":"2001-01-01T00:00:00","publicationYear":"2001","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2262,"text":"Journal of Environmental Quality","active":true,"publicationSubtype":{"id":10}},"title":"Major herbicides in ground water: Results from the National Water-Quality Assessment","docAbstract":"To improve understanding of the factors affecting pesticide occurrence in ground water, patterns of detection were examined for selected herbicides, based primarily on results from the National Water-Quality Assessment (NAWQA) program. The NAWQA data were derived from 2227 sites (wells and springs) sampled in 20 major hydrologic basins across the USA from 1993 to 1995. Results are presented for six high-use herbicides—atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), cyanazine (2-[4-chloro-6-ethylamino-1,3,5-triazin-2-yl]amino]-2-methylpropionitrile), simazine (2-chloro-4,6-bis[ethylamino]-s-triazine), alachlor (2-chloro-N-[2,6-diethylphenyl]-N-[methoxymethyl]acetamide), acetochlor (2-chloro-N-[ethoxymethyl]- N-[2-ethyl-6-methylphenyl]acetamide), and metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxy-1-methylethyl]acetamide)— as well as for prometon (2,4-bis[isopropylamino]-6-methoxy-s-triazine), a nonagricultural herbicide detected frequently during the study. Concentrations were <1 μg L−1 at 98% of the sites with detections, but exceeded drinking-water criteria (for atrazine) at two sites. In urban areas, frequencies of detection (at or above 0.01 μg L−1) of atrazine, cyanazine, simazine, alachlor, and metolachlor in shallow ground water were positively correlated with their nonagricultural use nationwide (P < 0.05). Among different agricultural areas, frequencies of detection were positively correlated with nearby agricultural use for atrazine, cyanazine, alachlor, and metolachlor, but not simazine. Multivariate analysis demonstrated that for these five herbicides, frequencies of detection beneath agricultural areas were positively correlated with their agricultural use and persistence in aerobic soil. Acetochlor, an agricultural herbicide first registered in 1994 for use in the USA, was detected in shallow ground water by 1995, consistent with previous field-scale studies indicating that some pesticides may be detected in ground water within 1 yr following application. The NAWQA results agreed closely with those from other multistate studies with similar designs.
Advances in technology have resulted in a new instrument that is designed for in-situ determination of particle size spectra. Such an instrument that can measure undisturbed particle size distributions is much needed for sediment transport studies. The LISST-100 (Laser In-Situ Scattering and Transmissometry) uses the principle of laser diffraction to obtain the size distribution and volume concentration of suspended material in 32 size classes logarithmically spaced between 1.25 and 250 μm. This paper describes a laboratory evaluation of the ability of LISST-100 to determine particle sizes using suspensions of single size, artificial particles. Findings show the instrument is able to determine particle size to within about 10% with increasing error as particle size increases. The instrument determines volume (or mass) concentration using a volume conversion factor Cv. This volume conversion factor is theoretically a constant. In the laboratory evaluation Cv is found to vary by a factor of about three over the particle size range between 5 and 200 μm. Results from field studies in South San Francisco Bay show that values of mass concentration of suspended marine sediments estimated by LISST-100 agree favorably with estimates from optical backscatterance sensors if an appropriate value of Cv, according to mean size, is used and the assumed average particle (aggregate) density is carefully chosen. Analyses of size distribution of suspended materials in South San Francisco Bay over multiple tide cycles suggest the likelihood of different sources of sediment because of different size characteristics during flood and ebb cycles.