| 1. |
- Routh, Joyanto, 1968-, et al.
(author)
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Sedimentary organic matter sources and depositional environment in the Yegua formation (Brazos County, Texas)
- 1999
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In: Organic Geochemistry. - : Elsevier. - 0146-6380 .- 1873-5290. ; 30:11, s. 1437-1453
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Journal article (peer-reviewed)abstract
- The complex depositional environment of the Eocene Yegua formation (Brazos County, Texas) can be better understood by integrating organic matter (OM) geochemistry with stratigraphy. Yegua sediments represent parasequences separated by exposure surfaces. Organic petrography and geochemistry (biomarkers, C/N ratios, and carbon isotopes) indicate the presence of both terrestrial and marine OM in transgressive sediments. In contrast, regressive sediments contain only terrestrial OM. These differences relate to contrasting OM sources and depositional styles on the shelf. OM in the sediments is immature and the potential for generating hydrocarbons is poor. The study suggests that organic geochemical data can help in distinguishing transgressive and regressive environments in sedimentary formations.
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| 2. |
- Berglund, B. E., et al.
(author)
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Holocene forest dynamics and climate changes in the Abisko area, northern Sweden : the Sonesson model of vegetation history reconsidered and confirmed
- 1996
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In: Ecological Bulletins. - 0346-6868. ; 1996:1, s. 15-30
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Journal article (peer-reviewed)abstract
- A new palaeoecological and palaeoclimatic project in the subalpine Abisko area, N Scandes, founded upon the pollen zone system defined by Sonesson is described. This model of vegetation history has been confirmed, although the chronology is partly revised. Sonesson's pollen diagrams are combined with new results from a lake sediment sequence at the tree-limit, which include sedimentologic, mineral magnetic, oxygen isotope and plant macrofossil studies. Since the deglaciation at c9000-8500 14C yr BP the vegetation of the Abisko area has generally been dominated by a subalpine birch Betula woodland tundra. The cliamte has generally been subarctic-oceanic since the deglaciation except for the period c.5500-3500 BP when temperate-continental conditions prevailed. This climatic development differs from the situation in the central Scandes.
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| 3. |
- Routh, Joyanto, 1968-, et al.
(author)
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Trace-element geochemistry of Onion Creek near Van Stone lead-zinc mine (Washington, USA) — Chemical analysis and geochemical modeling
- 1996
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In: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 133:1, s. 211-224
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Journal article (peer-reviewed)abstract
- Van Stone lead-zinc mine in Washington is a possible contamination source of Columbia River water. Breaching of an old tailings pond, seepage of contaminated water, and surficial transport of mine tailings have increased trace-element (TE) concentrations in the Onion Creek water and sediments. Chemical analyses of water and sediment samples indicate high TE levels near the breached tailings pond. TE contamination indices for sediments indicate high values of Pb, Zn, and other TE’s which decrease downstream. High Kd values (> 104) for several TE’s (e.g., Al, Cd, Fe, Mn, Pb, V, and Zn) suggest their enrichment in the solid phase. TE concentrations in Onion Creek water and sediment sharply attenuate downstream due to: (1) enhanced carbonate dissolution, thereby increasing pH and immobilizing TE’s; (2) sorption to oxides; and (3) change in lithology from carbonate to granite. Speciation model MINTEQA2 was used to study the effect on TE dispersion due to dissolution-precipitation reactions and adsorption to ferrihydrite. In addition to the field and chemical data, the model also supports the hypothesis that Onion Creek sediments are the major sink for TE’s at VSM. Model runs indicate precipitation of Al, Ba, Ca, Fe, Mg, and Mn minerals from oversaturation, whereas TE’s with low concentrations (Cr, Cu, Ni, Se) or geochemically more mobile (As, Mo, Sb) remain dissolved in water. Near the tailings ponds, high pH and abundance of sorption sites in sediments contribute to the complete adsorption of Pb and Zn species. Because ambient conditions result in the sorption of most Pb and Zn ions, Onion Creek water quality meets EPA regulatory standards. These species will persist in Onion Creek sediments as sorbed or insoluble complexes, and without drastic pH changes (< 4.0) they will remain immobilized. However, continued TE enrichment in sediments will prove hazardous to filter feeding and aquatic organisms.
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| 4. |
- Lundin, Lars-Christer, et al.
(author)
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Continuous long-term measurements of soil-plant-atmosphere variables at a forest site
- 1999
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In: Agricultural and Forest Meteorology. - 0168-1923 .- 1873-2240. ; 98-99, s. 53-73
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Journal article (peer-reviewed)abstract
- It is a major challenge in modem science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetation-atmosphere-transfer (SVAT) system. Continuous, long-term data are needed in order to correctly quantify balances of water, energy and CO2 in this system and to correctly model it. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from a forested site under almost all environmental conditions. The Central Tower Site (CTS) system was set up in 1993-1994 in a 25 m high boreal forest growing on a highly heterogeneous till soil with a high content of stones and blocks. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of temperature, water vapour, CO2, short-and long-wave radiation, heat storage in soil and trees, sap-dow and a variety of ecophysiological properties, soil-water contents and tensions, and groundwater levels, rainfall and throughfall. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation include e.g., budgets for energy, water and CO2, information on important but rarely occurring events such as evaporation from snow-covered canopies, and reactions of the forest to extreme drought. The carbon budget shows that the forest may be a sink of carbon although it is still growing. The completeness of the data has made it possible to test the internal consistency of SVAT models. The pioneering set-up at the CTS has been adopted by a large number of SVAT-monitoring sites around the world. Questions concerning tower maintenance, long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual research-funding agencies. The full value of data generated by the CTS system can best be appreciated after a decade or more of continuous operation. Main uses of the data would be to evaluate how SVAT models handle the natural variability of climate conditions, quantification of water. carbon and energy budgets during various weather conditions, rind development of new parameterisation schemes in global and regional climate models.
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| 5. |
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| 6. |
- Strandh, Heléne, 1968-
(author)
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Mineral dissolution from molecular to field scale
- 1999
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Doctoral thesis (other academic/artistic)abstract
- Mineral reactivity contributes to the global biogeochemical cycling of elements. CO2is consumed during the chemical weathering of many silicates and during formation of carbonates in the oceans. The balance of nutrients in soils and waters is coupled to the release of elements during weathering and the retention of elements during mineral precipitation. Dissolution of many minerals involves acid neutralization and the rate of most mineral reactions is dependent on the pH of the solution. The acid input to the atmosphere has increased drastically during the last century affecting our environment severely, with problems such as deterioration of the bronze-age rock carvings in the world heritage area Tanum, SW Sweden.This thesis compiles studies of quantum chemical calculations of the siloxane bond strength, laboratory dissolution experiments of quartz and brucite as well as field studies of the water chemistry of a rock surface in Tanum, SW Sweden.Quartz consists of only SiO2and provides the possibility to investigate specifically the siloxane bond, which is present in most silicates. Quartz dissolution is performed using plug-flow reactors during long-term experiments. This produced among the slowest rates reported in the literature, which suggests that long runtime is needed to approach natural dissolution rates. A rate minimum was obtained at pH 3-4, which was observed also after a short reaction time. Alkali metal cations increased the rate at pH>3, and KCl decreased the rate at pH<3, similar to results obtained for feldspar dissolution. The alkali metal effects and the pH dependence of the quartz dissolution emphasize the importance of surface species for the dissolution kinetics of silicate minerals, which may indicate the rate determining mechanisms in natural weathering environments.Quantum chemical methods are used to investigate the effects of different surface species on the siloxane bond strength. Direct adsorption of alkali metal cations reduces the bond strength for alkaline surface models and increases the bond strength for acid surface models, indicating that the surface species contribute to the rate of the quartz dissolution. Interaction with water molecules proved to be very important for the ion specific effects. For effects from protonation and deprotonation of the quartz surface, the hydration was essential. Further quantum chemical calculations showed that the pH dependence of the dissolution rate at high surface charge coverage could be due to acid-base repulsion within the surface layer.Brucite is a fast dissolving mineral that gives the possibility to investigate the rate dependence on the transport of ions. Rotating disc experiments are used to separate between surface reaction controls and molecular diffusion controls. Numerical modeling of the fluid equations is used to model a reaction zone near the brucite surface. The experiments and the model revealed that the solution pH determines the reaction mechanism in terms of surface reaction or diffusion reaction control. This is important information for the conclusion of the rate controlling mechanism of fast dissolving minerals on a rock surface.The water chemistry on the rock surface in Tanum gives information of rate controlling factors that can be used to reduce the chemical weathering rate. Extensive sampling of deposition, influenced by sea salt and acid rain, and runoff is performed on a rock surface in Tanum, SW Sweden. Two rock surfaces are investigated and compared; a roof protected, washed surface and a reference surface. The chemical weathering rate calculated as anorthite dissolution was 10 times slower than in literature data, due to a difference between the specific surface area and the reactive surface area in field. The chemical weathering rate of both surfaces was correlated with temperature and large differences in dissolution rate between the two ponds are due to differences in temperature and pH. Control of these parameters should give a surface that is preserved longer than an unprotected rock surface.
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| 7. |
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| 8. |
- Ulrich, G. A., et al.
(author)
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Sulfur Cycling in the Terrestrial Subsurface : Commensal Interactions, Spatial Scales, and Microbial Heterogeneity
- 1998
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In: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 36:2, s. 141-151
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Journal article (peer-reviewed)abstract
- Microbiological, geochemical, and isotopic analyses of sediment and water samples from the unconsolidated Yegua formation in east-central Texas were used to assess microbial processes in the terrestrial subsurface. Previous geochemical studies suggested that sulfide oxidation at shallow depths may provide sulfate for sulfate-reducing bacteria (SRB) in deeper aquifer formations. The present study further examines this possibility, and provides a more detailed evaluation of the relationship between microbial activity, lithology, and the geochemical environment on meter-to-millimeter scales. Sediment of varied lithology (sands, silts, clays, lignite) was collected from two boreholes, to depths of 30 m. Our findings suggest that pyrite oxidation strongly influences the geochemical environment in shallow sediments ( 5 m), and produces acidic waters (pH 3.8) that are rich in sulfate (28 mM) and ferrous iron (0.3 mM). Sulfur and iron-oxidizing bacteria are readily detected in shallow sediments; they likely play an indirect role in pyrite oxidation. In consistent fashion, there is a relative paucity of pyrite in shallow sediments and a low 34S/32S-sulfate ratio (0.2ￜ) (reflecting contributions from 34S-depleted sulfides) in shallow regions. Pyrite oxidation likely provides a sulfate source for both oxic and anoxic aquifers in the region. A variety of assays and direct-imaging techniques of 35S-sulfide production in sediment cores indicates that sulfate reduction occurs in both the oxidizing and reducing portions of the sediment profile, with a high degree of spatial variability. Narrow zones of activity were detected in sands that were juxtaposed to clay or lignite-rich sediments. The fermentation of organic matter in the lignite-rich laminae provides small molecular weight organic acids to support sulfate reduction in neighboring sands. Consequently, sulfur cycling in shallow sediments, and sulfate transport represent important mechanisms for commensal interaction among subsurface microorganisms by providing electron donors for chemoautotrophic bacteria and electron acceptors for SRB. The activity of SRB is linked to the availability of suitable electron donors from spatially distinct zones.
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| 9. |
- Andersson, Annika
(author)
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Frazil ice at water intakes
- 1997
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Doctoral thesis (other academic/artistic)abstract
- To provide a better understanding of how frazil ice deposits on trash racks at water intakes, the phenomenon was video recorded at two hydropower plants and in a refrigerated laboratory flume. Initial accretion of frazil ice around a single bar and the motion of particles in the vicinity of an obstacle was simulated through numerical modelling and studied using plastic particles in a laboratory flume. Ice initially accumulates on the upstream face of the bars, and it progresses then to the upstream sides of the bars. Tha frazil ice layer grows in all directions, and it finally bridges over the spaces between bars. The ice blockage starts at the upper part of the rack and progresses downward. The head losses across each intake, which are observed continuously at the plants, illustrate the degree and importance of ice growth. Observations from laboratory experiments with a single bar in a flume, showed that frazil ice particles deposited on all bar surfaces. Separate flume tests were run with plastic particles simulating ice particles. The frequency of collision of these particles with the front face of a rectangular bar varied with the particle density and the fluid velocity. In a test with particles of various sizes, the smaller particles were more likely to enter the side wake than larger ones. A mathematical model can be used to predict patterns of ice deposition that correspond to the observed results. Such a model must include a hydrodynamic part for viscous flows and a particle trajectory model. Some models neglect the term for force due to pressure gradient in their calculations of a particle trajectory because the particles had larger density than the surrounding fluid. Ice particles have almost the same density as the water and simulated results showed that this term, caused by the pressure gradient, is the dominant force that counter the momentum of the particles when they move in the region close to the obstacle. The simulated results were affected by the particle size distribution, therefore the size distribution of frazil ice particles in a river is a factor in further studies. In tests in which no particles were allowed to deposit on the front part of the bar, in a simulation of a heated bar, lesser amounts deposited on the other parts of the bar. Knowledge of the way frazil ice accumulates on water intakes and the initial ice accretion on individual trash racks should be valuable in future work for finding methods to reduce the ice blockage and in the verification of more detailed model studies.
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| 10. |
- Andersson, Eva, 1967-
(author)
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Hydrothermal alteration of organic matter at spreading centers
- 1998
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Doctoral thesis (other academic/artistic)abstract
- Alteration of organic matter, mainly amino acids, at sub-seafloor hydrothermal conditions has been investigated by performing laboratory experiments and by studying deep-sea sediments from hydrothermally active areas on the northern Juan de Fuca Ridge, northeast Pacific Ocean.Quaternary sediments from Middle Valley and the eastern flank of the Juan de Fuca Ridge recovered during the Ocean Drilling Program Legs 139 and 168 have been analyzed for total hydrolyzable amino acid concentrations, individual amino acid abundances and stereochemistry in order to evaluate the effects of hydrothermal stress on the decomposition of sedimentary amino acids. In near surface sediments, amino acids account for up to 3.3% of the total organic carbon content and up to 12% of the total nitrogen content. The non-protein amino acid b-alanine and g-aminobutyric acid become increasingly abundant with depth in low temperature holes (Leg 168) as a result of enzymatic decarboxylation of aspartic acid and glutamic acid, respectively. The decomposition of amino acid in high temperature holes (Leg 139) is enhanced with depth and the amino acid patterns indicates that most amino acids are incorporated into geopolymers and that condensation results in increased stability of some amino acids.The effects of low temperature hydrothermal activity on microbially mediated organic matter diagenesis were studied by comparing depth concentration profiles of interstitial sulfate and methane of Holes 1023A, 1024B, 1025B and 1028A, ODP Leg 168. Diffusional exchange between sulfate-rich basement fluids and pore-waters increases the interstitial sulfate concentrations with depth below local sulfate minima caused by bacterial sulfate reduction. The effects of diffusional processes on pore-water chemistry in the sediment column is reflected by the inhibition of methane production and is largely dependent on sediment thickness.The decomposition of alanine, leucine, aspartic acid and serine in aqueous solutions was studied at 200oC and 50 bar with the purpose of evaluating the effect dissolved oxygen on decomposition rates. The redox buffering mineral assemblage pyrite-pyrrhotite-magnetite was used to constrain the oxygen fugacity to geologically realistic values. Comparisons between results obtained from buffered and nonbuffered runs show that the decomposition is faster for most amino acids but serine in nonbuffered experiments.
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