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At least 1,639 records · Page 91Linked to original sources
USGS2012

Toxicity of elevated partial pressures of carbon dioxide to invasive New Zealand mudsnails

The authors tested the efficacy of elevated partial pressures of CO 2 to kill invasive New Zealand mudsnails. The New Zealand mudsnails were exposed to 100 kPa at three water temperatures, and the survival was modeled versus dose as cumulative °C-h. We estimated an LD50 of 59.4°C-h for adult and juvenile New Zealand mudsnails. The results suggest that CO 2 may be an effective and inexpensive lethal tool to treat substrates, tanks, or materials infested with New Zealand mudsnails.

Environmental Toxicology and Chemistry↗
USGS2017

Uranium-series dating of carbonate (tufa) deposits associated with quaternary fluctuations of Pyramid Lake, Nevada

Uranium-series dating of dense tufa deposited in a small cave, at former lake margins, and in large tufa mounds clarifies the timing of lake-level variation during the past 400,000 yr in the Pyramid Lake basin. A moderate-sized lake occasionally overflowed the Emerson Pass sill at elevation of ???1207 m between ca. 400,000 and 170,000 and from ca. 60,000 to 20,000 yr B.P., as shown by 230Th/234U ages of the cave samples, 230Th-excess ages of tubular tufas, and average isochron-plot ages of shoreline-deposited tufas. (By comparison, modern Pyramid Lake is ???50 m below this sill). There is a lack of tufa record during the intervening period from ca. 170,000 to 60,000 yr B.P. After ca. 20,000 yr, Pyramid Lake underwent abrupt changes in level and, based on previous 14C ages, reached its highest elevation (ca 1335 m) at ca. 14,000 yr B.P. The youngest uranium-series ages are comparable with previously reported 14C ages. ?? 1996 University of Washington.

Quaternary Research↗
USGS2005

Controlling for anthropogenically induced atmospheric variation in stable carbon isotope studies

Increased use of stable isotope analysis to examine food-web dynamics, migration, transfer of nutrients, and behavior will likely result in expansion of stable isotope studies investigating human-induced global changes. Recent elevation of atmospheric CO2 concentration, related primarily to fossil fuel combustion, has reduced atmospheric CO2 ??13C (13C/12C), and this change in isotopic baseline has, in turn, reduced plant and animal tissue ??13C of terrestrial and aquatic organisms. Such depletion in CO2 ??13C and its effects on tissue ??13C may introduce bias into ??13C investigations, and if this variation is not controlled, may confound interpretation of results obtained from tissue samples collected over a temporal span. To control for this source of variation, we used a high-precision record of atmospheric CO2 ??13C from ice cores and direct atmospheric measurements to model modern change in CO2 ??13C. From this model, we estimated a correction factor that controls for atmospheric change; this correction reduces bias associated with changes in atmospheric isotopic baseline and facilitates comparison of tissue ??13C collected over multiple years. To exemplify the importance of accounting for atmospheric CO2 ??13C depletion, we applied the correction to a dataset of collagen ??13C obtained from mountain lion (Puma concolor) bone samples collected in California between 1893 and 1995. Before correction, in three of four ecoregions collagen ??13C decreased significantly concurrent with depletion of atmospheric CO2 ??13C (n ??? 32, P ??? 0.01). Application of the correction to collagen ??13C data removed trends from regions demonstrating significant declines, and measurement error associated with the correction did not add substantial variation to adjusted estimates. Controlling for long-term atmospheric variation and correcting tissue samples for changes in isotopic baseline facilitate analysis of samples that span a large temporal range. ?? Springer-Verlag 2005.

Oecologia↗
USGS2019

Using carbon isotope ratios to verify predictions of a model simulating the interaction between coastal plant communities and their effect on ground water salinity

As sea level rises in low-lying coastal islands, salt-tolerant (halophytic) coastal vegetation communities may be able to migrate inland, replacing the freshwater vegetation that is unable to tolerate salt stress. The pace of such shifts may be accelerated by a self-reinforcing feedback between the halophytic vegetation and salinity, as well as by frequent and intensified salinity pulses associated with the increasing impact of storm surges as a consequence of sea-level rise. We used a modification of a previously published spatially explicit individual-based model that simulates impacts on upland freshwater hammock communities from sea-level rise and storm surge to predict the interaction between three coastal communities: mangroves, hammocks, and pinelands. The model simulation predicted two qualitative characteristics regarding the interaction between these three different coastal communities: (1) mangroves and hammock communities tend to have ground water with high salinities, while at the same time pineland ground water salinity is low, and (2) pineland located at lower elevation relative to adjacent hammock will be negatively influenced by higher ground water salinities in hammocks, as it flows toward the lower elevation pineland. We tested these predictions using foliar δ13C of Conocarpus erectus collected from Big Pine Key as a proxy for ground water salinity. Measurements of ground water salinity via this proxy confirmed the two predictions of the model. Our approach provides an approximation of the impacts of sea-level rise on terrestrial vegetation communities, including threatened pineland communities, and can be used as a tool for management decisions.

Ecosystems↗
USGS2012

Assessment of a ground water flow model of the Bangkok Basin, Thailand, using carbon-14-based ages and paleohydrology

A study was undertaken to understand the groundwater flow conditions in the Bangkok Basin, Thailand, by comparing 14 C-based and simulated groundwater ages. 14 C measurements were made on about 50 water samples taken from wells throughout the basin. Simulated ages were obtained using 1) backward-pathline tracking based on the well locations, and 2) results from a three-dimensional groundwater flow model. Comparisons of ages at these locations reveal a large difference between 14 C-based ages and ages predicted by the steady-state groundwater flow model. Mainly, 14 C and 13 C analyses indicate that groundwater in the Bangkok area is about 20,000 years old, whereas steady-state flow and transport simulations imply that groundwater in the Bangkok area is 50,000–100,000 years old. One potential reason for the discrepancy between simulated and 14 C-based ages is the assumption in the model of steady-state flow. Groundwater velocities were probably greater in the region before about 10,000 years ago, during the last glacial maximum, because of the lower position of sea level and the absence of the surficial Bangkok Clay. Paleoflow conditions were estimated and then incorporated into a second set of simulations. The new assumption was that current steady-state flow conditions existed for the last 8,000 years but were preceded by steady-state conditions representative of flow during the last glacial maximum. This “transient” paleohydrologic simulation yielded a mean simulated age that more closely agrees with the mean 14 C-based age, especially if the 14 C-based age corrected for diffusion into clay layers. Although the uncertainties in both the simulated and 14 C-based ages are nontrivial, the magnitude of the improved match in the mean age using a paleohydrologic simulation instead of a steady-state simulation suggests that flow conditions in the basin have changed significantly over the last 10,000–20,000 years. Given that the valid age range of 14 C-dating methods and the timing of the last glacial maximum are of similar magnitude, adjustments for paleohydrologic conditions may be required for many such studies.

Hydrogeology Journal↗
USGS2011

Effects of Bromus tectorum invasion on microbial carbon and nitrogen cycling in two adjacent undisturbed arid grassland communities

Soil nitrogen (N) is an important component in maintaining ecosystem stability, and the introduction of non-native plants can alter N cycling by changing litter quality and quantity, nutrient uptake patterns, and soil food webs. Our goal was to determine the effects of Bromus tectorum (C 3 ) invasion on soil microbial N cycling in adjacent non-invaded and invaded C 3 and C 4 native arid grasslands. We monitored resin-extractable N, plant and soil δ 13 C and δ 15 N, gross rates of inorganic N mineralization and consumption, and the quantity and isotopic composition of microbial phospholipid biomarkers. In invaded C 3 communities, labile soil organic N and gross and net rates of soil N transformations increased, indicating an increase in overall microbial N cycling. In invaded C 4 communities labile soil N stayed constant, but gross N flux rates increased. The δ 13 C of phospholipid biomarkers in invaded C 4 communities showed that some portion of the soil bacterial population preferentially decomposed invader C 3 -derived litter over that from the native C 4 species. Invasion in C 4 grasslands also significantly decreased the proportion of fungal to bacterial phospholipid biomarkers. Different processes are occurring in response to B. tectorum invasion in each of these two native grasslands that: 1) alter the size of soil N pools, and/or 2) the activity of the microbial community. Both processes provide mechanisms for altering long-term N dynamics in these ecosystems and highlight how multiple mechanisms can lead to similar effects on ecosystem function, which may be important for the construction of future biogeochemical process models.

Biogeochemistry↗
USGS2011

Carbon gas fluxes in re-established wetlands on organic soils differ relative to plant community and hydrology

We measured CO 2 and CH 4 fluxes for 6 years following permanent flooding of an agriculturally managed organic soil at two water depths (~25 and ~55 cm standing water) in the Sacramento–San Joaquin Delta, California, as part of research studying C dynamics in re-established wetlands. Flooding rapidly reduced gaseous C losses, and radiocarbon data showed that this, in part, was due to reduced oxidation of "old" C preserved in the organic soils. Both CO 2 and CH 4 emissions from the water surface increased during the first few growing seasons, concomitant with emergent marsh establishment, and thereafter appeared to stabilize according to plant communities. Areas of emergent marsh vegetation in the shallower wetland had greater net CO 2 influx (-485 mg Cm -1 h -1 ), and lower CH 4 emissions (11.5 mg Cm -2 h -1 ), than in the deeper wetland (-381 and 14.1 mg Cm -2 h -1 , respectively). Areas with submerged and floating vegetation in the deeper wetland had CH 4 emissions similar to emergent vegetation (11.9 and 12.6 mg Cm -2 h -1 , respectively), despite lower net CO 2 influx (-102 gC m -2 h -1 ). Measurements of plant moderated net CO 2 influx and CH 4 efflux indicated greatest potential reduction of greenhouse gases in the more shallowly flooded wetland.

California↗
USGS1992

Chemical fluxes and origin of a manganese carbonate-oxide-silicate deposit in bedded chert

Lens-like rhodochrosite-rich bodies within interbedded chert and shale are associated with basalt and/or graywacke in ophiolitic and orogenic zones. The Buckeye manganese mine in the Franciscan Complex of the California Coast Ranges is associated with metagraywacke. Despite blueschist-facies metamorphism, this deposit preserves the compositions and some textural features of its sedimentary protoliths. For this reason, it is a suitable deposit with which to compare more intensely altered deposits, or deposits originating in different paleoenvironments. Six Mn-rich and three Mn-poor minerals form monomineralic layers and mixtures: rhodochrosite, gageite, Mn-oxides (hausmannite, braunite), divalent Mn-silicates (caryopilite, taneyamalite), chlorite, quartz (metachert) and aegirine-augite. The Mn-rich protoliths have high Mn/Fe combined with relatively low concentrations of Ca, Al, Ti, Co, Ni, Cu, Th and REE. REE patterns of various protoliths are distinct. Rhodochrosite and gageite layers are depleted (seawater ?? 5 ?? 104) and flat, whereas patterns of metachert and the Mn-silicate-rich layers mimic the patterns of metashale and metagraywacke (seawater ?? 106). Hausmannite layers have flat patterns (seawater ?? 7 ?? 104) whereas braunite-rich layers are more enriched (seawater ?? 2 ?? 105) and show a distinct positive Ce anomaly. Factor analysis reveals components and fluxes attributed to sub-seafloor fluids (Ni, As, Zn, Sb, W, Mn), seawater (Mg, Au, V, Mo), detritus and veins (Ca, Ba, Sr). Silica is negatively correlated with the sub-seafloor factor. The observed variances indicate that water from the sediment column mixed with seawater, that deposition occurred near the sediment-seawater interface before mixtures of subsurface fluid and seawater homogenized, and that the system was not entirely closed during metamorphism. The variations in REE enrichment can be related to kinetics of deposition: rhodochrosite and gageite were precipitated most rapidly, and therefore were the protoliths that most effectively diluted the REE-rich background resulting from fine clastic material (derived from distal turbidites). The variation of the Ce anomaly and U/Th among diverse lithologies and the differences in Mn oxidation states are consistent with progressive dilution of reduced subsurface fluids with oxidized seawater. By this scheme, rhodochrosite, gageite and hausmannite were deposited from the most reduced fluids, braunite from intermediate mixtures, and Mn-silicates from the sub-seafloor fluids most diluted with fresh seawater. Comparison of the Buckeye with other lens-like and sheet-like deposits having high Mn/Fe and containing Mn3+ and/or Mn2+ suggests that each had three essential fluxes: a sub-seafloor source of Mn, a local source of very soluble silica and a source of relatively fresh, oxygenated water. Additional fluxes, such as clastics, appear to be more characteristic of the paleoenvironment than the three essential fluxes. ?? 1992.

Chemical Geology↗
USGS1981

The origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in Florida and Texas

The δ 34 S values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in Floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer. The dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer. In areas where the water is oldest, the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate ( Δ 34 S = 65 per mil) at the temperature (28°C) of the system. This approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria; this slow rate probably results from very low concentrations of organic matter in the aquifer. In the reducing part of the Edwards aquifer, Texas, there is a general down-gradient increase in both dissolved sulfide and sulfate concentrations, but neither the δ 34 S values of sulfide nor the sulfide-sulfate isotope fractionation correlates with the ground-water flow pattern. The dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of H 2 S gas from deeper oil field brines may be important in places. The sulfur isotope fractionation for sulfide-sulfate (about 38 per mil) is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present; contributions of isotopically heavy H 2 S from oil field brines are also possible.

Florida, Texas↗
USGS1990

Effect of faults on fluid flow and chloride contamination in a carbonate aquifer system

A unified, multidiscipline hypothesis is proposed to explain the anomalous pattern by which chloride has been found in water of the Upper Floridan aquifer in Brunswick, Glynn County, Georgia. Analyses of geophysical, hydraulic, water chemistry, and aquifer test data using the equivalent porous medium (EPM) approach are used to support the hypothesis and to improve further the understanding of the fracture-flow system in this area. Using the data presented herein we show that: (1) four major northeast-southwest trending faults, capable of affecting the flow system of the Upper Floridan aquifer, can be inferred from structural analysis of geophysical data and from regional fault patterns; (2) the proposed faults account for the anomalous northeastward elongation of the potentiometric surface of the Upper Floridan aquifer; (3) the faults breach the nearly impermeable units that confine the Upper Floridan aquifer from below, allowing substantial quantities of water to leak vertically upward; as a result, aquifer transmissivity need not be excessively large (as previously reported) to sustain the heavy, long-term pumpage at Brunswick without developing a steep cone of depression in the potentiometric surface; (4) increased fracturing at the intersection of the faults enhances the development of conduits that allow the upward migration of high-chloride water in response to pumping from the Upper Floridan aquifer; and (5) the anomalous movement of the chloride plume is almost entirely controlled by the faults.

Georgia↗
USGS1996

The stable oxygen and carbon isotopic record from a coral growing in Florida Bay: a 160 year record of climatic and anthropogenic influence

A 160 year record of skeletal δ 13 C and δ 18 O was examined in a specimen of the coral Solenastrea bournoni growing in Florida Bay. Variations in the δ 18 O of the skeleton can be correlated to changes in salinity while changes in the δ 13 C reflect cycling of organic material within the Bay. Based on the correlation between salinity and skeletal δ 18 O, we have concluded that there has been no long term increase in salinity in this area of Florida Bay over the past 160 years. Using salinity correlations between the various basins obtained from instrumental data, we have been able to extend our interpretations to other parts of Florida Bay reaching similar conclusions. In contrast to current ideas which have focused on changes in Florida Bay water quality over the past 20-yr history of the Bay as causative in its decline, we have determined that changes in water quality in this basin were already set in motion between 1905 and 1912 by the construction of the Florida East Coast Railway from Miami to Key West. The construction of the railway resulted in the restriction of the exchange of water between the Florida reef tract and the Gulf of Mexico causing Florida Bay to become more eutrophic. Evidence of this process is observed in the sudden shift to relatively lower δ 13 C values coincident with railway construction. Natural events also appear to have influenced the water in the Bay. Between 1912 and 1948 frequent hurricanes had the effect of increasing exchange of water between the Bay and reef tract and removing large quantities of organic rich sediments. However, since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions.

Florida↗
USGS1992

Ammonia fixation by humic substances: A nitrogen-15 and carbon-13 NMR study

The process of ammonia fixation has been studied in three well characterized and structurally diverse fulvic and humic acid samples. The Suwannee River fulvic acid, and the IHSS peat and leonardite humic acids, were reacted with 15N-labelled ammonium hydroxide, and analyzed by liquid phase 15N NMR spectrometry. Elemental analyses and liquid phase 13C NMR spectra also were recorded on the samples before and after reaction with ammonium hydroxide. The largest increase in percent nitrogen occurred with the Suwannee River fulvic acid, which had a nitrogen content of 0.88% before fixation and 3.17% after fixation. The 15N NMR spectra revealed that ammonia reacted similarly with all three samples, indicating that the functional groups which react with ammonia exist in structural configurations common to all three samples. The majority of nitrogcn incorporated into the samples appears to be in the form of indole and pyrrole nitrogen, followed by pyridine, pyrazine, amide and aminohydroquinone nitrogen. Chemical changes in the individual samples upon fixation could not be discerned from the 13C NMR spectra.

Science of Total Environment↗
USGS1991

Caution on the use of Viton® or FETFE® O-rings in carbon dioxide sample containers for δ 18 0 analysis

After 10 days, 3-&mu;mol CO 2 samples in containers having glass stopcocks with Viton &reg; or FETFE O-rings were enriched in 18 O by 1.5% as a result of absorption by the elastomer; this amount of enrichment is &sim;20 times greater than the precision of &delta; 18 O measurements of most laboratories. No change in 13 C content was observed. Increasing the sample size to 100 &mu;mol resulted in an 18 O enrichment of 0.2% and did not affect the 13 C content. Caution needs to be exercised in selecting sample containers for CO 2 isotope-ratio samples of < 200 &mu;mol. If stopcocks are used in construction of containers for such samples, the use of all-glass stopcocks with Apiezon N &reg; hydrocarbon-based grease will eliminate the fractionation of oxygen isotopes.

Chemical Geology: Isotope Geoscience Section↗
USGS1992

Geochemical effects of deep-well injection of the Paradox Valley brine into Paleozoic carbonate rocks, Colorado, U.S.A.

Brine seepage into the Dolores River from ground water in Paradox Valley, Colorado constitutes a major source of salt to the Colorado River. Plants are enderway to remove this source of salt by drawing down the Paradox Valley brine (PVB) and forcibly injecting it into a deep disposal well (4.8 km). Experiments were conducted to determine the effects of deep-well injection of PVB. The results show that PVB is near saturation with anhydrite at 25°C, and that heating results in anhydrite precipitation. The amount and the rate at which anhydrite forms is temperature, pressure, and substrate dependent. Paradox Valley brine heated in the presence of Precambrian rocks from the drill core produces the same amount of anhydrite as PVB heated alone, but at a greatly accelerated rate. A 30% dilution of PVB with Dolores River water completely eliminates anhydrite precipitation when the fluid is heated with the Precambrian rocks. Interaction of PVB and Leadville Limestone is characterized by dolomitization of calcite by brine Mg which releases Ca to solution. This added Ca reacts with SO 4 to form increased amounts of anhydrite. A 20% dilution of PVB by Dolores River water has no effect on dolomitization and reduces the amount of anhydrite only slightly. A 65% dilution of PVB by Dolores River water still does not prevent dolomitization but does suppress anhydrite formation. Computer modeling of PVB by programs utilizing the Pitzer ion-interaction parameters is in general agreement with the experimental results. Ion-activity products calculated by both SOLMINEQ and PHRQPITZ are close to equilibrium with both anhydrite and dolomite whenever these phases are present experimentally, although the calculations over-estimate by a factor of 2 the degree of saturation. Some discrepancies in the calculated results between the two programs are due largely to differences in mineral solubility data.

Colorado↗
USGS1993

Generation of aliphatic acid anions and carbon dioxide by hydrous pyrolysis of crude oils

Two crude oils with relatively high (0.60 wt%) and low (0.18 wt%) oxygen contents were heated in the presence of water in gold-plated reactors at 300??C for 2348 h. The high-oxygen oil was also heated at 200??C for 5711 h. The compositions of aqueous organic acid anions of the oils and of the headspace gases were monitored inn order to investigate the distribution of organic acids that can be generated from liquid petroleum. The oil with higher oxygen content generated about five times as much organic anions as the other oil. The dominant organic anions produced were acetate, propionate and butyrate. Small amounts of formate, succinate, methyl succinate and oxalate were also produced. The dominant oxygen-containing product was CO2, as has been observed in similar studies on the hydrous pyrolysis of kerogen. These results indicate that a significant portion (10-30%) of organic acid anions reported i be generated by thermal alteration of oils in reservoir rocks. The bulk of organic acid anions present in formation waters, however, is most likely generated by thermal alteration of kerogen in source rocks. Kerogen is more abundant than oil in sedimentary basins and the relative yields of organic acid anions reported from the hydrous pyrolysis of kerogen are much higher than the yields obtained for the two oils. ?? 1993.

Applied Geochemistry↗