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At least 433 records · Page 24Linked to original sources
USGS2005

Sources of nitrate in snowmelt discharge: Evidence from water chemistry and stable isotopes of nitrate

To determine whether NO 3 − concentration pulses in surface water in early spring snowmelt discharge are due to atmospheric NO 3 − , we analyzed stream δ 15 N-NO 3 − and δ 18 O-NO 3 − values between February and June of 2001 and 2002 and compared them to those of throughfall, bulk precipitation, snow, and groundwater. Stream total Al, DOC and Si concentrations were used to indicate preferential water flow through the forest floor, mineral soil, and ground water. The study was conducted in a 135-ha subcatchment of the Arbutus Watershed in the Huntington Wildlife Forest in the Adirondack Region of New York State, U.S.A. Stream discharge in 2001 increased from 0.6 before to 32.4 mm day −1 during snowmelt, and element concentrations increased from 33 to 71 μmol L −1 for NO 3 − , 3 to 9 μmol L −1 for total Al, and 330 to 570 μmol L −1 for DOC. Discharge in 2002 was variable, with a maximum of 30 mm day −1 during snowmelt. The highest NO 3 − , Al, and DOC concentrations were 52, 10, and 630 μmol L −1 , respectively, and dissolved Si decreased from 148 μmol L −1 before to 96 μmol L −1 during snowmelt. Values of δ 15 N and δ 18 O of NO 3 − in stream water were similar in both years. Stream water, atmospherically-derived solutions, and groundwaters had overlapping δ 15 N-NO 3 − values. In stream and ground water, δ 18 O-NO 3 − values ranged from +5.9 to +12.9‰ and were significantly lower than the +58.3 to +78.7‰ values in atmospheric solutions. Values of δ 18 O-NO 3 − indicating nitrification, increase in Al and DOC, and decrease in dissolved Si concentrations indicating water flow through the soil suggested a dilution of groundwater NO 3 − by increasing contributions of forest floor and mineral soil NO 3 − during snowmelt.

Water, Air, & Soil Pollution↗
USGS2009

Changes in the chemistry of shallow groundwater related to the 2008 injection of CO2 at the ZERT field site, Bozeman, Montana

Approximately 300 kg/day of food-grade CO 2 was injected through a perforated pipe placed horizontally 2–2.3 m deep during July 9–August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO 2 . As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1–6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO 2 injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO 2 injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO 2 leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO 2 intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0–5.6), alkalinity (400–1,330 mg/l as HCO 3 ), and electrical conductance (600–1,800 μS/cm) following CO 2 injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90–240 mg/l), Mg (25–70 mg/l), Fe (5–1,200 ppb), and Mn (5–1,400 ppb) following CO 2 injection. These chemical changes could provide early detection of CO 2 leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO 2 injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 ± 2 mg/l, and the variations do not correlate with CO 2 injection. CO 2 injection, however, is responsible for detection of BTEX (e.g. benzene, 0–0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly below the maximum contaminant levels (MCLs). Sequential leaching of core samples is being carried out to investigate the source of metals and other solutes.

Montana↗
USGS1988

Chemistry, mineralogy and origin of the clay-hill nitrate deposits, Amargosa River valley, Death Valley region, California, U.S.A.

The clay-hill nitrate deposits of the Amargosa River valley, California, are caliche-type accumulations of water-soluble saline minerals in clay-rich soils on saline lake beds of Miocene, Pliocene(?) and Pleistocene age. The soils have a maximum thickness of ??? 50 cm, and commonly consist of three layers: (1) an upper 5-10 cm of saline-free soil; (2) an underlying 15-20 cm of rubbly saline soil; and (3) a hard nitrate-rich caliche, 10-20 cm thick, at the bottom of the soil profile. The saline constituents, which make up as much as 50% of the caliche, are chiefly Cl-, NO-3, SO2-4 and Na+. In addition are minor amounts of K+, Mg2+ and Ca2+, varying, though generally minor, amounts of B2O3 and CO2-3, and trace amounts of I (probably as IO-3), NO-2, CrO2-4 and Mo (probably as MoO2-4). The water-soluble saline materials have an I/Br ratio of ??? 1, which is much higher than nearly all other saline depostis. The principal saline minerals of the caliche are halite (NaCl), nitratite (NaNO3), darapskite (Na3(SO4)(NO3)??H2O), glauberite (Na2Ca(SO4)2), gypsum (CaSO4??2H2O) and anhydrite (CaSO4). Borax (Na2B4O5(OH)4??8H2O), tincalconite (Na2B4O5(OH)4??3H2O) and trona (Na3(CO3)(HCO3)??2H2O) are abundant locally. The clay-hill nitrate deposits are analogous to the well-known Chilean nitrate deposits, and probably are of similar origin. Whereas the Chilean deposits are in permeable soils of the nearly rainless Atacama Desert, the clay-hill deposits are in relatively impervious clay-rich soils that inhibited leaching by rain water. The annual rainfall in the Death Valley region of ??? 5 cm is sufficient to leach water-soluble minerals from the more permeable soils. The clay-hill deposits contain saline materials from the lake beds beneath the nitrate deposits are well as wind-transported materials from nearby clay-hill soils, playas and salt marshes. The nitrate is probably of organic origin, consisting of atmospheric nitrogen fixed as protein by photoautotrophic blue-green algae, which are thought to form crusts on soils at the sites of the deposits when moistened by rainfall. The protein is subsequently transformed to nitrate by autotophic bacteria. ?? 1988.

Chemical Geology↗
USGS1991

Subalkaline andesite from Valu Fa Ridge, a back-arc spreading center in southern Lau Basin: petrogenesis, comparative chemistry, and tectonic implications

Tholeiitic andesite was dredged from two sites on Valu Fa Ridge (VFR), a back-arc spreading center in Lau Basin. Valu Fa Ridge, at least 200 km long, is located 40-50 km west of the active Tofua Volcanic Arc (TVA) axis and lies about 150 km above the subducted oceanic plate. One or more magma chambers, traced discontinuously for about 100 km along the ridge axis, lie 3-4 km beneath the ridge. The mostly aphyric and glassy lavas had high volatile contents, as shown by the abundance and large sizes of vesicles. An extensive fractionation history is inferred from the high SiO2 contents and FeO* MgO ratios. Chemical data show that the VFR lavas have both volcanic arc and back-arc basin affinities. The volcanic arc characteristics are: (1) relatively high abundances of most alkali and alkaline earth elements; (2) low abundances of high field strength elements Nb and Ta; (3) high U/Th ratios; (4) similar radiogenic isotope ratios in VFR and TVA lavas, in particular the enrichment of 87Sr 86Sr relative to 206Pb 204Pb; (5) high 238U 230Th, 230Th 232Th, and 226Ra 230Th activity ratios; and (6) high ratios of Rb/Cs, Ba/Nb, and Ba/La. Other chemical characteristics suggest that the VFR lavas are related to MORB-type back-arc basin lavas. For example, VFR lavas have (1) lower 87Sr 86Sr ratios and higher 143Nd 144Nd ratios than most lavas from the TVA, except samples from Ata Island, and are similar to many Lau Basin lavas; (2) lower Sr/REE, Rb/Zr, and Ba/Zr ratios than in arc lavas; and (3) higher Ti, Fe, and V, and higher Ti/V ratios than arc lavas generally and TVA lavas specifically. Most characteristics of VFR lavas can be explained by mixing depleted mantle with either small amounts of sediment and fluids from the subducting slab and/or an older fragment of volcanic arc lithosphere. The eruption of subalkaline andesite with some arc affinities along a back-arc spreading ridge is not unique. Collision of the Louisville and Tonga ridges probably activated back-arc extension that ultimately led to the creation and growth of Valu Fa Ridge. Some ophiolitic fragments in circum-Pacific and circum-Tethyan allochthonous terranes, presently interpreted to have originated in volcanic arcs, may instead be fragments of lithosphere that formed during early stages of seafloor spreading in a back-arc basin. ?? 1991.

Chemical Geology↗
USGS1970

Some investigations of the deposition of travertine from Hot Springs-I. The isotopic chemistry of a travertine-depositing spring

The isotopic compositions of the travertine and of the hot spring solutions were studied at Main Springs and New Highland Terrace in the Mammoth Hot Springs area of Yellowstone Park. The springs issue at 74°C and a pH of 6.65 and the carbon isotopic composition of the travertine depositing at the orifice is +2%.δC 13 (PDB). As the water travels out from the orifice, it cools and loses CO 2 . The travertine depositing at lower temperature is enriched in C 13 , reaching values of +4.8%. and the solution has a pH of 8.2 at 27°C. The δC 13 of the carbon species in solution is about −2.3%. at 74° and about +4.3 at 27°C. Therefore, the difference in δC 13 between the solid and solution is approximately 4%. at 74° and decreases to zero at about 20°C. These differences are shown to be due to kinetic (non-equilibrium) factors. The δO 18 contents of the travertine and water show that in most samples the carbonate oxygen is in equilibrium with the water O 18 at the temperatures of deposition. This is especially true for travertine depositing slowly and at temperatures above about 50°C. Calculations based on pH and alkalinity titrations of the hot spring waters in situ show that at the spring orifice the water is very high in free CO 2 , which is quickly lost in transit. The springs are supersaturated with respect to both aragonite and calcite during most of their travel in the open air. The carbon isotopic composition of the travertine is similar to that in the marine carbonates that are adjacent to the springs and that are the probable source of the calcium carbonate. The travertine from inactive prehistoric springs near Mammoth has similar δC 13 and O 18 to that from the active springs. Soda Butte, an inactive center 25 miles east of Mammoth, contains heavier carbon and oxygen than the springs near Mammoth.

Geochimica et Cosmochimica Acta↗
USGS1989

Groundwater chemistry and water-rock interactions at Stripa

Groundwaters from near surface to a depth of 1232 m in the Stripa granite have been sampled and analyzed for major and trace constituents. The groundwater composition consists of two general types: a typical recharge water of Ca-HCO 3 type (<300 m depth) and a deeper Na-Ca-Cl type (>700 m depth) of high pH (8–10) that reaches a maximum of 1250 mg/L in total dissolved solids (TDS). Intermediate depths show mixtures of the two types that are highly fracture-dependent rather than depth-dependent. Any borehole can vary significantly and erratically in TDS for either a horizontal or vertical direction. The general transition from Ca-HCO 3 type to Na-Ca-Cl type correlates with the depth profile for hydraulic conductivity that drops from 10 −8 m/s to 10 −11 m/s or lower. Thermomechanical stress (from heater experiments) clearly shows an effect on the groundwater composition that could be caused by changing flow paths, leakage of fluid inclusions or both. Dissolution and precipitation of calcite, fluorite and barite, aluminosilicate hydrolysis, and addition of a saline source (possibly fluid inclusion leakage) play the major roles in defining the groundwater composition. The low permeability of the Stripa granite has produced a groundwater composition that appears intermediate between the dilute, shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth.

Geochimica et Cosmochimica Acta↗
USGS1989

Fluid inclusions in the Stripa granite and their possible influence on the groundwater chemistry

Fluid inclusions in quartz and calcite of the Proterozoic Stripa granite, central Sweden, demonstrate that the rock and its fracture fillings have a complex evolutionary history. The majority of inclusions indicate formation during a hydrothermal stage following emplacement of the Stripa pluton. Total salinities of quartz inclusions range from 0–18 eq.wt% NaCl for unfractured rock and from 0–10 eq.wt% for fractured rock. Vein calcites contain up to 25 eq.wt% NaCl but the inclusion size is larger and the population density is lower. Homogenization temperatures are 100–150°C for unfractured rock and 100–250° for fractured rock. Pressure corrections, assuming immediate post-emplacement conditions of 2 kbar, give temperatures about 160°C higher. Measurements of fluid-inclusion population-densities in quartz range from about 10 8 inclusions/cm 3 in grain quartz to 10 9 inclusions/cm 3 in vein quartz. Residual porosity from inclusion densities has been estimated to be at least 1% which is two orders of magnitude greater than the flow porosity. Breakage and leaching of fluid inclusions is proposed as an hypothesis for the origin of major solutes (Na-Ca-Cl) in the groundwater. Evidence for the hypothesis is based on (1) mass balance—only a small fraction of the inclusions need to leak to account for salt concentrations in the groundwater, (2) chemical signatures— Br Cl "> BrCl ratios of fluid inclusion leachates (0.0101) match those ratios for the deep groundwaters (0.0107), (3) leakage mechanisms—micro-stresses from isostatic rebound or mining activities acting on irregular-shaped inclusions could cause breakage and provide connection with the flow porosity, and (4) experimental studies—water forced through low permeability granites leach significant quantities of salt. This hypothesis is consistent with the available data although alternate hypotheses cannot be excluded.

Geochimica et Cosmochimica Acta↗
USGS1992

Interoceanic variation in the rare earth, major, and trace element depositional chemistry of chert: Perspectives gained from the DSDP and ODP record

Rare earth element (REE), major, and trace element abundances and relative fractionations in forty nodular cherts sampled by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) indicate that the REE composition of chert records the interplay between terrigenous sources and scavenging from the local seawater. Major and (non-REE) trace element ratios indicate that the aluminosilicate fraction within the chert is similar to NASC (North American Shale Composite), with average Pacific chert including ~7% NASC-like particles, Indian chert ~ 11% NASC, Atlantic chert ~ 17% NASC, and southern high latitude (SHL) chert 53% NASC. Using La as a proxy for ∑REE, approximations of La ex (the amount of La in excess of that supplied by the detrital aluminosilicate fraction) indicate that Pacific chert contains the greatest La ex (85% of La total ) and SHL chert the least (38% of La total ). As shown by interelement associations, this La ex is most likely an adsorbed component onto aluminosilicate and phosphatic phases. Accordingly, chert from the large Pacific Ocean, where deposition occurs relatively removed from significant terrigenous input, records a depositional REE signal dominated by adsorption of dissolved REEs from seawater. Pacific chert CeCe * ⪡ 1 and La n Yb n ~ 0.8-1, resulting from adsorption of local Ce-depleted seawater and preferential adsorption of LREEs from seawater (e.g., La n Yb n ~ 0.4), which increases the La n Yb n ratio recorded in chert. Chert from the Atlantic basin, a moderately sized ocean basin lined by passive margins and with more terrigenous input than the Pacific, records a mix of adsorptive and terrigenous REE signals, with moderately negative Ce anomalies and La n Yb n "> La n Yb n ratios intermediate to those of the Pacific and those of terrigenous input. Chert from the SHL region is dominated by the large terrigenous input on the Antarctic passive margin, with inherited Ce Ce * ~1 "> CeCe * ~1 and inherited La n Yb n "> La n Yb n values of ~1.2&#x2013;1.4. Ce Ce * "> ~1.2–1.4.CeCe * does not vary with age, either throughout the entire data base or within a particular basin. Overall, Ce Ce * "> CeCe * does not correlate with P 2 O 5 concentrations, even though phosphatic phases may be an important REE carrier. This and previous studies of the large-scale controlling parameters of sedimentary REEs across ocean basins collectively indicate that REE indices of depositional regime (e.g., Ce Ce * "> CeCe * , La n Yb n "> La n Yb n , La ex ) are reproducible in a variety of sediment and rock lithologies, ages, and ocean basins, and present a coherent tool for paleoceanographic and tectonic basin reconstructions.

Geochimica et Cosmochimica Acta↗
USGS1993

Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate

EXAFS spectra were collected on both the As and Fe K-edges from samples of two-line ferrihydrite with adsorbed (ADS) and coprecipitated (CPT) arsenate prepared over a range of conditions and arsenate surface coverages. Spectra also were collected for arsenate adsorbed on the surfaces of three FeOOH crystalline polymorphs, α (goethite), β (akaganeite), and γ (lepidocrocite), and as a free ion in aqueous: solution. Analyses of the As EXAFS show clear evidence for inner sphere bidentate (bridging) arsenate complexes on the ferrihydrite surface and on the surfaces of the crystalline FeOOH polymorphs. The bridging arsenate is attached to adjacent apices of edge-sharing Fe oxyhydroxyl octahedra. The arsenic-iron distance at the interface ( 3.28 &#xB1;0.01 A &#x30A; "> 3.28 ±0.01Å ) is close to that expected for this geometry on the FeOOH polymorph surfaces, but is slightly shorter on the ferrihydrite surfaces ( 3.25 &#xB1; 0.02 A &#x30A; "> 3.25 ± 0.02Å ). Mono-dentate arsenate linkages ( 3.60 &#xB1; 0.03 A &#x30A; "> 3.60 ± 0.03Å ) also occur on the ferrihydrite, but are not generally observed on the crystalline FeOOH polymorphs. The proportion of monodentate bonds appears largest for adsorption samples with the smallest As Fe "> AsFe molar ratio. In all cases the arsenate tetrahedral complex is relatively undistorted with As-O bonds of 1.66 &#xB1; 0.01 A &#x30A; "> 1.66 ± 0.01Å . Precipitation of arsenate or scorodite-like phases was not observed for any samples, all of which were prepared at a pH value of 8. The Fe EXAFS results confirm that the Fe-Fe correlations in the ferrihydrite are progressively disrupted in the CPT samples as the As Fe "> AsFe ratio is increased. Coherent crystallite size is probably no more than 10 Å in diameter and no Fe oxyhydroxyl octahedra corner-sharing linkages (as would be present in FeOOH polymorphs) are observed at the largest As Fe "> AsFe ratios. Comparison of the number and type of Fe-Fe neighbors with the topological constraints imposed by the arsenate saturation limit in the CPT samples (about 0.7 As Fe "> AsFe ) indicates ferrihydrite units consisting mainly of Fe oxyhydroxyl octahedra arranged in short dioctahedral chains with minimal interchain linking by octahedra corners. This is consistent with an enlarged surface area and a larger proportion of sites for bidentate arsenate bonding in CPT samples as compared to the ADS samples, which saturate with arsenate at lower As Fe "> AsFe ratios. The latter samples have larger crystallite sizes and a definite proportion of ferric octahedra sharing corners. The ratio of corner-sharing to edge-sharing Fe oxyhydroxyl octahedra in the ADS samples, and CPT samples with small As loadings, is very similar to what would be present in very small particles of goethite or akaganeite. The difference in the polymeric structure of ADS and CPT samples at higher As Fe "> AsFe ratios is due to strong arsenate bidentate adsorption that poisons the surface of particles of ferrihydrite precipitated in the presence of substantial arsenate, limiting their normal crystallization, and preventing further Fe-O-Fe polymerization. If the arsenate is applied after precipitation much less adsorption occurs since polymerization has already progressed. In both ADS and CPT samples, Fe-O-Fe polymerization increases with age, though at different rates for each type of sample.

Geochimica et Cosmochimica Acta↗
USGS1993

Surface chemistry of ferrihydrite: Part 2. Kinetics of arsenate adsorption and coprecipitation

The kinetics of As(V) adsorption by ferrihydrite was investigated in coprecipitation and postsynthesis adsorption experiments conducted in the pH range 7.5-9.0. In coprecipitation experiments, As(V) was present in solution during the hydrolysis and precipitation of iron. In adsorption experiments, a period of rapid (<5 min) As(V) uptake from solution was followed by continued uptake for at least eight days, as As(V) diffused to adsorption sites on ferrihydrite surfaces within aggregates of colloidal particles. The time dependence of As(V) adsorption is well described by a general model for diffusion into a sphere if a subset of surface sites located near the exterior of aggregates is assumed to attain adsorptive equilibrium rapidly. The kinetics of As(V) desorption after an increase in pH were also consistent with diffusion as a rate-limiting process. Aging of pure ferrihydrite prior to As(V) adsorption caused a decrease in adsorption sites on the precipitate owing to crystallite growth. In coprecipitation experiments, the initial As(V) uptake was significantly greater than in post-synthesis adsorption experiments, and the rate of uptake was not diffusion limited because As(V) was coordinated by surface sites before crystallite growth and coagulation processes could proceed. After the initial adsorption, As(V) was slowly released from coprecipitates for at least one month, as crystallite growth caused desorption of As(V). Adsorption densities as high as 0.7 mole As(V) per mole of Fe were measured in coprecipitates, in comparison to 0.25 mole As(V) per mole of Fe in post-synthesis adsorption experiments. Despite the high Concentration of As(V) in the precipitates, EXAFS spectroscopy (Waychunas et al., 1993) showed that neither ferric arsenate nor any other As-bearing surface precipitate or solid solution was formed. The high adsorption densities are possible because the ferrihydrite particles are extremely small, approaching the size of small dioctahedral chains at the highest As(V) adsorption density. The results suggest that the solid solution model proposed by Fox (1989, 1992) for control of arsenate and phosphate concentrations in natural waters may be invalid.

Geochimica et Cosmochimica Acta↗
USGS1994

Chemistry of manganese precipitation in Pinal Creek, Arizona, USA: A laboratory study

Groundwater underlying the valley of Pinal Creek downstream from Globe, Arizona, has been contaminated by low-pH metal-enriched wastewater from copper mining and ore processing at Miami, Arizona. At present, the acidity and most of the dissolved metal content, except for Mn, of the wastewater is removed by reactions with carbonate and other solids in the alluvial aquifer before the neutralized contaminated water enters the creek channel and becomes surface flow. Where flow in the creek is perennial, Mn-bearing precipitates are formed in the stream bed and in some places in the subsurface. As an aid to understanding the processes involved and explaining the mineralogy of the precipitates, closely controlled laboratory redox titration experiments were performed on samples of surface flow and groundwater taken near the head of perennial flow in the creek. The high content of dissolved Ca, Mg, Mn and COP 2 species in the neutralized contaminated groundwater caused precipitation of some of the Mn as kutnahorite, (Mn, Mg)Ca(CO 3 ) 2 , when the experimental system was held between pH 8.5 and 9.0 while CO 2 -free air was bubbled into the solution. Hausmannite and manganite also were precipitated, in somewhat lower amounts. When the concentrations of dissolved CO 2 species in the groundwater sample were decreased before the experiment was started, the Mn precipitated was predominantly in the oxides hausmannite and manganite. In some of the experimental titrations clinoenstatite, (MgSiO 3 ), was precipitated. After titrations were stopped the solutions and precipitates were allowed to stand, with limited access to the atmosphere, for several months. During this aging period the degree of oxidation of the precipitated Mn increased and in one precipitate from an experimental solution the Ca + Mn 4+ oxides todorokite and takanelite were identified. These oxides also have been identified in streambed precipitates. Some of these precipitates also gave X-ray diffraction reflections for kutnahorite. Thermodynamic feasibilities of eight potential chemical reactions forming solid phases of interest were evaluated by calculating their respective reaction affinities attained during titration and aging. The results are in general agreement with the indications for the presence of these species given by X-ray and electron diffraction. The presence of carbonates in precipitated encrustations formed from groundwater below the land surface and their occurrence in manganese oxide crusts that precipitate from the creek water, also are predicted by these results.

Geochimica et Cosmochimica Acta↗
USGS1996

Kinetic and mineralogic controls on the evolution of groundwater chemistry and 87Sr/86Sr in a sandy silicate aquifer, northern Wisconsin, USA

Substantial flowpath-related variability of 87Sr/86Sr is observed in groundwaters collected from the Trout Lake watershed of northern Wisconsin. In the extensive shallow aquifer composed of sandy glacial outwash, groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter-lake uplands. 87Sr/86Sr of groundwater derived mainly as seepage from a precipitation-dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase. In contrast, 87Sr/86Sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed, due to suppression of plagioclase dissolution together with preferential leaching of Sr from radiogenic phases such as K-feldspar and biotite. The results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic Sr, whereas stagnant waters obtain relatively radiogenic Sr. Nearly the entire range of strontium-isotope composition observed in groundwaters from the watershed was measured in the experimental product waters. The constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase, perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions. In contrast, episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution, perhaps due to accumulation of clay mineral nuclei on its reactive surfaces. Differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior. This study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths, and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations.

Geochimica et Cosmochimica Acta↗
USGS1993

Application of mixed-mode, solid-phase extraction in environmental and clinical chemistry. Combining hydrogen-bonding, cation-exchange and Van der Waals interactions

Silica- and styrene-divinylbenzene-based mixed-mode resins that contain C8, C18 and sulphonated cation-exchange groups were compared for their efficiency in isolation of neutral triazine compounds from water and of the basic drug, benzoylecgonine, from urine. The triazine compounds were isolated by a combination of Van der Waals and hydrogen-bonding interactions, and benzoylecgonine was isolated by Van der Waals interactions and cation exchange. All analytes were eluted with a polar organic solvent contaning 2% ammonium hydroxide. Larger recoveries (95%) were achieved on copolymerized mixed-mode resins where C18 and sulfonic acid are in closer proximity than on 'blended' mixed-mode resins (60-70% recovery).

Journal of Chromatography A↗
USGS1990

Topographic effects on flow path and surface water chemistry of the Llyn Brianne catchments in Wales

Topographic shape is a watershed attribute thought to influence the flow path followed by water as it traverses a catchment. Flow path, in turn, may affect the chemical composition of surface waters. Topography is quantified in the hydrological model TOPMODEL as the relative frequency distribution of the index ln(atanB), where a is the upslope area per unit contour that drains past a point and tanB is the local surface slope. Spatial distributions of ln(atanB) were calculated for eight catchments in Wales on a 25 m x 25 m grid. Among the catchments, mean observed stream H+ concentration during high flow periods was highly correlated with the mean of the ln(atanB) distribution. The steady-state gain of a transfer function (time series) model relating H+ to discharge was positively correlated with the mean of the ln(atanB) distribution. These results suggest that during high flow periods, both the average stream acidity and the magnitude of fluctuations in H+ are conditioned by the topographic shape of the catchment. By performing a sensitivity analysis on TOPMODEL, we also show that as the mean of the ln(atanB) distribution for a catchment increases, so does its theoretical likelihood to produce significant quantities of surface and near-surface runoff. Our observed results in the Llyn Brianne catchments are consistent with this theoretical expectation in that surface or near-surface runoff is often higher in acidity than are deeper sources of hillslope runoff.

Wales↗
USGS1987

The chemistry and mineralogy of haloed burrows in pelagic sediment at DOMES Site A: The equatorial North Pacific

The chemical and mineralogical composition of burrowed sediment, recovered in 66 box cores at latitude 9°25′N and longitude 151°15′W in the equatorial Pacific, demonstrates the important role of infauna in determining the geochemistry of pelagic sediment. Haloed burrows, approximately 3 cm across, were present in many of the cores. Within early Tertiary sediment that was covered by less than 5 cm of surface Quaternary sediment in several cores, the burrows in cross-section consist of three units: (1) a dark yellowish-brown central zone of Quaternary sediment surrounded, by (2) a pale yellowish-orange zone (the halo) of Tertiary sediment, which is surrounded by (3) a metal-oxide precipitate; the enclosing Tertiary sediment is dusky brown. Several elements — Mn, Ni, Cu, Co, Zn, Sb and Ce — have been leached from the light-colored halo, whereas Cr, Cs, Hf, Rb, Sc, Ta, Th, U, the rare earth elements exclusive of Ce, and the major oxides have not been leached. The metal-oxide zone, 1–5 mm thick, contains as much as 16% MnO 2 , as the mineral todorokite. The composition of the todorokite, exclusive of the admixed Tertiary sediment, resembles the composition of the metal deficit of the halo and also the composition of surface ferromanganese nodules that have been interpreted as having a predominantly diagenetic origin. Thus bioturbation contributes not only to the redistribution of metals within pelagic sediment, but also to the accretion of ferromanganese nodules on the sea floor.

Marine Geology↗
USGS1996

Chemistry and potential mutagenicity of humic substances in waters from different watersheds in Britain and Ireland

Humic substances are amorphous organic macromolecules responsible for the hue of natural waters. They are also known to be precursors of mutagens formed on chlorination prior to distribution of drinking water. In this study humic substances from the waters of primary streams, from major rivers, and from reservoirs were isolated and fractionated into humic acids (HA), fulvic acids (FA) and XAD-4 acids using columns of XAD-8 and of XAD-4 resins in tandem, and the fractions from the different sources were chlorinated and assayed for mutagenicity. CPMAS 13C NMR spectroscopy showed marked differences in compositions not only between HA, FA, and XAD-4 acids from the same water samples, but also between the same fractions from water samples from different watersheds. There were found to be strong similarities between the fractions from watersheds which had closely related soil types. Aromaticity was greatest in HAs, and lowest in XAD-4 acids, and carboxyl contents and aliphatic character were greatest in the XAD-4 acids. Carbon content decreased in the order HA > FA > XAD-4 acids, and amino acids and neutral sugars contents decreased in the order HA > XAD-4 > FA. Titration data complemented aspects of the NMR data, demonstrating that carboxyl content decreased in the order XAD-4 acids > FA > HA, and indicated that phenolic character was highest in HAs and lowest in the XAD-4 acids. All samples tested gave rise to bacterial mutagens on chlorination. Although the mutagenicities were of the same order of magnitude for the chlorinated humic samples from the different sources, the samples which showed the greatest number of revertant bacterial colonies were from the Thames and Trent, large rivers with humic materials from diverse environments, and relatively high in amino acid contents.

Water Research↗
USGS1989

The geology, botany and chemistry of selected peat-forming environments from temperate and tropical latitudes

Peat has been studied in several geologic settings: (1) glaciated terrain in cold temperate Maine and Minnesota, U.S.A.; (2) an island in the Atlantic Ocean off the coast of Maine, where sea level is rising; (3) the warm temperate U.S. Atlantic and Gulf Coastal Plains, where sea level has changed often; and (4) the tropical coast of Sarawak, Malaysia, and the tropical delta of the Batang Hari River, Sumatra, Indonesia. Most of these deposits are domed (ombrotrophic or partly ombrotrophic) bogs in which peat accumulation continued above the surface of the surrounding soil. However, the bogs of the U.S. Atlantic and Gulf Coastal Plains are comparatively not as domed, and many have almost level surfaces. In some bogs, aquatic or semi-aquatic plant materials accumulated, replaced water in the depressions, and formed a surface on which marsh or swamp vegetation could subsequently live, die, and accumulate. In others, the plant materials accumulated initially on level silt or sand surfaces supporting marshes or swamps. As the peat dome formed, plants growing on it changed from luxuriant ones near the base of the dome, where nutrients were brought into the bog by surface and ground water, to stunted ones at the top of the dome, where the raised bogs are fed by nutrient-poor precipitation. The physical and chemical changes that take place in the sequence of environments from the pond stage of deposit development, through the grassy marsh stage, through the forested swamp stage, and finally through the heath dome stage can be measured in terms of acidity and ash, volatile matter, carbon, hydrogen, nitrogen, sulfur and oxygen contents, as well as in the kind and distribution of trace elements. The organic and inorganic contents of the deposits relate to geomorphology, and geomorphology relates to their settings. As models of coal formation, some domed peat deposits may help in solving problems of distribution and character of ancient coal beds. But clearly not all peat deposits are precursors of coal. Most Holocene peat deposits are subject to destruction by erosion, fire and decomposition through microbial and chemical oxidation before burial. The best environments for coal precursors have biomass accumulation, a continuously rising water table within the mass, and minimum influx of clay and silt until preservation by burial. The most suitable settings for future economic coal deposits are domed bogs that accumulate thick, widespread peat having low ash and low sulfur contents. The ombrotrophic peat deposits of tropical Sarawak and Sumatra are thick and extensive, contain low-ash and low-sulfur peat, and have high heating values. They are considered to be the best tropical coal analogs because of their extent and chances of preservation; the base of the peat is below adjacent river levels, and chemical and structural conditions are favorable for accumulation.

International Journal of Coal Geology↗
USGS1989

Chemistry and origin of minor and trace elements in vitrinite concentrates from a rank series from the eastern United States, England, and Australia

A rank series consisting of twelve vitrinite concentrates and companion whole-coal samples from mined coal beds in the eastern United States, England, and Australia were analyzed for C, H, N, O, ash, and 47 trace and minor elements by standard elemental, instrumental neutron activation analysis (INAA), and direct-current-arc spectrographic (DCAS) techniques. The reflectance of vitrinite, atomic H:C and O:C, and ash-free carbon data were used to determine ranks that range from high-volatile C bituminous coal to meta-anthracite. A van Krevelen (atomic H:C vs. O:C) diagram of the vitrinite concentrates shows a smooth curve having its lowest point at H:C = 0.18 and O:C = 0.01. This improves the van Krevelen diagram by the addition of our vitrinite concentrate from meta-anthracite from the Narragansett basin of New England. Boron content (400–450 ppm) in two Illinois basin vitrinite concentrates was about an order of magnitude higher than B contents in other concentrates analyzed. We attribute this to marine origin or hydrothermal activity. The alkaline-earth elements Ca, Mg and Ba (DCAS) have higher concentrations in our vitrinite concentrates from bituminous coals of the Appalachian basin, than they do in vitrinite concentrates from the marine-roofed bituminous coals of the Illinois basin; therefore, a nonmarine origin for these alkaline-earth elements is postulated for the Appalachian basin coals. An ion-exchange mechanism due to high concentrations of these elements as ions in diagenetic water, but probably not recent ground water, may be responsible for the relatively high values of these elements in Appalachian concentrates. Higher concentrations of Ni and Cr in one of the English vitrinite concentrates and of Zr in the Australian concentrate probably indicate organic association and detrital influence, respectively.

International Journal of Coal Geology↗