Solid Organic Carbon Research Articles

Metal diagenesis in a shallow semi-enclosed marine system in the Aegean Sea, Greece

Trace metal and organic carbon distributions were examined in core sediments of Kalloni Bay during September 2000 in order to examine the diagenetic process and its impact on metal mobility. Solid sediment profiles show significant variations in Mn, Fe and Ni concentrations between sampling stations due to geological background variability and diagenetic processes in the sediment (for Mn). Solid phase organic carbon profiles reflect episodic input of organic matter from the land. The redox status of the sediments can be characterized from sub-oxic to anoxic, leading to dissolution of Mn oxides and enhancement of dissolved Mn at the surface sediment layers of the Bay. Dissolved Fe maximal concentrations were located at a sediment depth of few centimetres below the Mn maximum. Nickel distribution was mainly influenced by the geological background of a part of the Bay's watershed consisting of ultrabasic minerals. Partition coefficients between solid phase and porewater ( K ds) indicated the increase mobility of Mn (and to a lesser degree of Ni and Zn) in the upper sediment layers. Concentrations Factors indicated that metals (especially Mn and Zn) may flow from porewater to the overlying seawater because of concentration gradients.

Identification of a reactive degradation zone at a landfill leachate plume fringe using high resolution sampling and incubation techniques

Vertical small-scale variation in phenoxy acid herbicide degradation across a landfill leachate plume fringe was studied using laboratory degradation experiments. Sediment cores (subdivided into 5 cm segments) were collected in the aquifer and the sediment and porewater were used for microcosm experiments (50 experiments) and for determination of solid organic carbon, solid–water partitioning coefficients, specific phenoxy acid degraders and porewater chemistry. Results from a multi-level sampler installed next to the cores provided information on the plume position and oxygen concentration in the groundwater. Oxygen concentration was controlled individually in each microcosm to mimic the conditions at their corresponding depths. A highly increased degradation potential existed at the narrow plume fringe (37.7 to 38.6 masl), governed by the presence of phenoxy acids and oxygen. This resulted in the proliferation of a microbial population of specific phenoxy acid degraders, which further enhanced the degradation potential for phenoxy acids at the fringe. The results illustrate the importance of fringe degradation processes in contaminant plumes. Furthermore, they highlight the relevance of using high-resolution sampling techniques as well as controlled microcosm experiments in the assessment of the natural attenuation capacity of contaminant plumes in groundwater.

Evaluation By Respirometry of the Degradability of Retort Water using a Shale Ash and Overburden Packed Column

Oil shale processing produces an aqueous wastewater stream known as retort water. The fate of the organic content of retort water from the Stuart oil shale project (Gladstone, Queensland) is examined in a proposed packed bed treatment system consisting of a 1:1 mixture of residual shale from the retorting process and mining overburden. The retort water had a neutral pH and an average unfiltered TOC of 2,900 mg l−1. The inorganic composition of the retort water was dominated by NH4 +. Only 40% of the total organic carbon (TOC) in the retort water was identifiable, and this was dominated by carboxylic acids. In addition to monitoring influent and effluent TOC concentrations, CO2 evolution was monitored on line by continuous measurements of headspace concentrations and air flow rates. The column was run for 64 days before it blocked and was dismantled for analysis. Over 98% of the TOC was removed from the retort water. Respirometry measurements were confounded by CO2 production from inorganic sources. Based on predictions with the chemical equilibrium package PHREEQE, approximately 15% of the total CO2 production arose from the reaction of NH4 + with carbonates. The balance of the CO2 production accounted for at least 80% of the carbon removed from the retort water. Direct measurements of solid organic carbon showed that approximately 20% of the influent carbon was held-up in the top 20cm of the column. Less than 20% of this held-up carbon was present as either biomass or as adsorbed species. Therefore, the column was ultimately blocked by either extracellular polymeric substances or by a sludge that had precipitated out of the retort water.

A kinetic analysis of solid waste composting at optimal conditions

Six municipal solid waste (MSW) and yard waste components (food waste, mixed paper, yard waste, leaves, branches, grass clippings) were aerobically decomposed to measure the extent of decomposition under near optimal conditions. Decomposition was characterized by at least two principal stages, for most components, as was indicated by the carbon dioxide production rates. An aerobic biodegradation conceptual model is presented here based on the principle that solids hydrolysis is the rate-limiting step during solid waste composting. The mineralizable solid carbon of each solid waste component was assumed to comprise the readily, the moderately and the slowly (or refractory) hydrolysable carbons, each hydrolyzing at different rates to aqueous (water soluble) carbon. Aqueous carbon mineralizes to CO 2 at rapid rates that are not rate-limiting to the process. Solids hydrolysis rate constants were calculated after fitting the experimentally determined carbon dioxide production rate data to model results. Hydrolysis rates for the readily hydrolysable carbon in all components ranged from approximately 0.06 to 0.1 d −1; hydrolysis rates for the moderately hydrolysable carbon ranged from 0.005 to 0.06 d −1. Leaves, branches and grass clippings did not have a readily hydrolysable carbon fraction, whilst the leaves and branches had the largest slowly hydrolysable carbon fractions (70%, 82%, respectively, of the total solid organic carbon). Grass and yard waste did not contain slowly hydrolysable carbon fractions. Food waste had the largest readily hydrolysable carbon fraction and produced the highest amount of CO 2 among all substrates. Moderately hydrolysable solid carbon fractions ranged from 16% to 90% of the total solid organic carbon for all substrates used.

Biogeochemical processes at the fringe of a landfill leachate pollution plume: potential for dissolved organic carbon, Fe(II), Mn(II), NH 4, and CH 4 oxidation

Various redox reactions may occur at the fringe of a landfill leachate plume, involving oxidation of dissolved organic carbon (DOC), CH 4, Fe(II), Mn(II), and NH 4 from leachate and reduction of O 2, NO 3 and SO 4 from pristine groundwater. Knowledge on the relevance of these processes is essential for the simulation and evaluation of natural attenuation (NA) of pollution plumes. The occurrence of such biogeochemical processes was investigated at the top fringe of a landfill leachate plume (Banisveld, the Netherlands). Hydrochemical depth profiles of the top fringe were captured via installation of a series of multi-level samplers at 18, 39 and 58 m downstream from the landfill. Ten-centimeter vertical resolution was necessary to study NA within a fringe as thin as 0.5 m. Bromide appeared an equally well-conservative tracer as chloride to calculate dilution of landfill leachate, and its ratio to chloride was high compared to other possible sources of salt in groundwater. The plume fringe rose steadily from a depth of around 5 m towards the surface with a few meters in the period 1998–2003. The plume uplift may be caused by enhanced exfiltration to a brook downstream from the landfill, due to increased precipitation over this period and an artificial lowering of the water level of the brook. This rise invoked cation exchange including proton buffering, and triggered degassing of methane. The hydrochemical depth profile was simulated in a 1D vertical reactive transport model using PHREEQC-2. Optimization using the nonlinear optimization program PEST brought forward that solid organic carbon and not clay minerals controlled retardation of cations. Cation exchange resulted in spatial separation of Fe(II), Mn(II) and NH 4 fronts from the fringe, and thereby prevented possible oxidation of these secondary redox species. Degradation of DOC may happen in the fringe zone. Re-dissolution of methane escaped from the plume and subsequent oxidation is an explanation for absence of previously present nitrate and anaerobic conditions in pristine groundwater above the plume. Stable carbon isotope (δ 13C) values of methane confirm anaerobic methane oxidation immediately below the fringe zone, presumably coupled to reduction of sulfate, desorbed from iron oxide. Methane must be the principle reductant consuming soluble electron-acceptors in pristine groundwater, thereby limiting NA for other solutes including organic micro-pollutants at the fringe of this landfill leachate plume.

Changes in water extractable metals, pH and organic carbon concentrations at the soil-root interface of forested soils

Soluble metals are of nutritional and ecotoxicological interest as they are the most readily available form to the biota. Metal solubility in soils is mostly controlled by pH and the organic matter content. The rhizosphere is generally considered as an environment enriched in organic matter and often more acidic (depending on nutritional status of the plant) than the bulk soil. Yet, there is a lack of consensus on the distribution of metals at the soil-root interface. Consequently, the specific objectives of this paper are to compare the chemical properties and the water extractable metal concentrations of the rhizosphere and the bulk soil of forest soil (1) along a gradient in soil contamination and (2) under different tree species. Two study areas were used: (1) Rouyn-Noranda (Canada) where samples were collected along a gradient in metal contamination at a distance of 0.5, 2 and 8 km downwind from a copper smelter; (2) Saint-Hippolyte (Canada) where the effect of three tree species (Abies balsamea, Acer saccharum and Betula papyrifera) was studied. In the field, the rhizosphere was operationally defined as the soil adhering to the roots after agitation, soil falling from the roots and the rest of the soil composing the bulk soil. Once in laboratory, a second agitation was performed to separate the rhizosphere into an inner and an outer component. Water extractable metal concentrations (Al, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb and Zn) were quantified either with an ICP-AES or a GFAAS. Measurements of pH, electrical conductivity (EC), water-extractable organic carbon (WEOC) and solid phase organic carbon (SPOC) were performed. Results systematically indicate that EC, WEOC and SPOC follow the sequence inner rhizosphere > outer rhizosphere > bulk soil. The pH is always lower in the inner rhizosphere than in the bulk soil, while the outer rhizosphere frequently shows an inconstant behaviour. The results also show a clear gradient following inner rhizosphere > outer rhizosphere > bulk soil for water extractable Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb and Zn. Li, Co and Cr levels were below method detection limit in all cases. WEOC seems to be the main variable related to the water-extractable metals concentrations. The gradient in metal contamination at Rouyn-Noranda was not as expected in the water extracts with the site at 2 km frequently presenting higher metal concentrations than the sites at 0.5 and 8 km. Moreover, a tree species effect did not clearly immerge for any of the chemical properties studied. However, the water extractable Ca concentrations were higher in the soil under Acer saccharum. The effects of the metal gradient and of the tree species may be more pronounced if stronger extractants are used. The addition of an outer rhizosphere component is useful as its behaviour is not consistently intermediate between the inner rhizosphere and bulk soil.

EFFECTS OF HYDROLOGIC FLUCTUATIONS ON THE TRANSPORT OF FINE PARTICULATE ORGANIC MATTER IN THE NANAKITA RIVER

Field observations were conducted to investigate the transport process of fine particulate organic matter (FPOM) during a small flood in a lower reach of the Nanakita River. Sediment samples on riverbeds were collected at four stations before and after the flood. The flowing water was collected at three stations during the flood. The concentrations of suspended solid (SS) and particulate organic carbon (POC) were measured in both sediment and water samples. The total deposition and erosion rates of SS and POC were estimated from SS and POC in sediment samples. The time variation of the SS and POC concentrations, and the total transport rates were calculated from SS and POC concentrations in flowing water during the flood. The basic characteristics of the transport processes of SS and POC during a small flood in the Nanakita River were elucidated.

Paleoceanographic significance of sediment color on western North Atlantic drifts: I. Origin of color

Reflectance spectra collected during ODP Leg 172 were used in concert with solid phase iron chemistry, carbonate content, and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments. Factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color. On the western North Atlantic drifts, sediment color is the result of primary mineralogy as well as diagenetic changes. Sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and Fe 2+/Fe 3+ changes in clay minerals. Hematite, most likely derived from the Permo-Carboniferous red beds of the Canadian Maritimes, is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components. Various intensities for diagenesis result from changes in organic carbon content, sedimentation rates, and H 2S production via anaerobic methane oxidation. Iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and/or increased reactive iron flux in glacials.

A simple model for the distribution and fate of organic chemicals in a landfill: MOCLA.

A simple mathematical model (MOCLA: Model for Organic Chemicals in Landfills) is presented, describing the distribution of organic chemicals between leachate, gas and solid waste. The model also predicts the fate of the chemicals in terms of emissions with leachate and landfill gas and in terms of degradation and transformation in the landfill. Local equilibrium is assumed for the distribution of the chemicals in the landfill as expressed by Henry's Law for the leachate-gas interface, and by the linear partition coefficient based on the waste solid organic carbon content for the waste-leachate interface. Degradation of the chemicals is expressed as a first order reaction. Annual specific leachate and gas generation data in combination with data on landfill area and volume allow for prediction of main emission routes. Model simulations involving two landfill scenarios for a number of chemicals with different physico-chemical characteristics indicate that volatilisation is a likely route for some chemicals (e.g. vinyl chloride, and some of the freons), while other chemicals (e.g. phenol, lower chlorinated aliphatic compounds) more likely will appear as dissolved in the leachate. However, many chemicals will be strongly associated with the solid waste (e.g. dichlorobenzene, naphthalene, and higher Polycyclic Aromatic Hydrocarbons (PAHs), and the pool available will be able to supply the landfill gas and leachate with organic trace components for decades unless these are degraded in the landfill. The model suggests that, in addition to the physico-chemical characteristics of the organic chemical, the presence of free phases of organic chemicals and the degradability of the chemicals are the main factors controlling the fate and emissions of organic chemicals in the landfill environment.

Agricultural contaminants in Quaternary aquitards: A review of occurrence and fate in North America

The intensity of agriculture has increased significantly during the past 30 years, resulting in increased detection of agricultural contaminants (nutrients, pesticides, salts, trace elements, and pathogens) in groundwater. Till, glaciolacustrine, and loess deposits of Quaternary age compose the most common surficial deposits underlying agricultural areas in North America. Quaternary aquitards generally contain higher concentrations of solid organic carbon (SOC, as much as 1.4%), dissolved organic carbon (DOC, as much as 205 mg/L), and reduced sulfur (as much as 0.9%) than do aquifers. Their potential to sorb pesticides increases with the percent of older SOC, because diagenesis increases Koc. Denitrification consistently reduces nitrate to non-detectable levels in unweathered Quaternary aquitards. Organic carbon of Quaternary age is a more labile electron donor than carbon from shale clasts. Pyrite is a more labile electron donor than carbon in many instances. Unweathered Quaternary aquitards provide a high degree of protection for underlying aquifers, due to their large reserves of SOC and reduced sulfur for sorption and denitrification, combined with their typically low hydraulic conductivity. In contrast, agricultural contaminants are common in weathered Quaternary aquitards. Lower reserves of reduced sulfur and sorptive/labile organic carbon, and a higher bulk K due to fractures, limit their ability to attenuate nitrate and pesticides. Subsurface drainage, which is common in Quaternary aquitards because of high water tables, bypasses the attenuation capacity of Quaternary aquitards and facilitates the transport of agricultural contaminants to surface water.

Extrusion dynamics of mud volcanoes on the Mediterranean Ridge accretionary complex

Abstract Drilling of two submarine mud domes situated in the Olimpi field on the northern flank of the Mediterranean Ridge accretionary complex has documented episodic eruptive activity over the last 1 to >1.5 Ma. Mud extrusion is related to plate convergence between Africa and Eurasia, having caused backthrust faulting of accreted strata containing overpressured mud at depth. The domes mainly consist of mud breccia with up to 65% of polymictic clasts embedded in a clayey matrix. On the basis of modifications of Poiseuille’s and Stokes’ laws, mud extrusion rates were calculated for Milano and Napoli mud domes. Mud ascent velocities are estimated to be up to 60–300 km a −1 , and are comparable with those of silicate magmas. Using physical property, structural and flux data of the mud breccias, and compiled data from mud domes on land, the diameter of the feeder channel and the depth of origin for the overpressured muds could be reliably estimated for the first time. Feeder channels are likely to be only a few metres wide. Gas efflux estimates constrain a source depth to c. 1700 ± 50 m below sea floor in the Olimpi field, which is considerably shallower than estimations made from the thermal maturity of solid organic carbon in the mud breccias. The efflux data suggest that the overpressured muds were not mobilized at décollement depth, but at a shallower level within the accretionary prism. A comparison of mud ascent rates (as determined from Poiseuille flow) and the total volumes of mud extruded indicate that only a fraction of the time span constrained from biostratigraphic data ( c. 1 Ma) is needed to build up the Milano and Napoli mud domes. Durations of 12–58 ka of extrusive activity suggest mud volcanism here to have been a highly episodic phenomenon.

Diagenesis of carbon and nutrients and benthic exchange in sediments of the Northern Adriatic Sea

The characteristics of diagenesis and benthic biogeochemical cycling were studied at six stations in the Northern Adriatic during September, 1988. The objectives of this work were to quantify the mechanisms responsible for mass transport and to establish the stoichiometry of reactions involving carbon and nutrients. Stations were chosen to include sites near the Po delta that have rapid sediment accumulation, sites south of the Po delta that lie beneath its nutrient-rich plume but beyond the region of rapid accumulation, and one site further offshore in a zone with little or no modern sediment accumulation. Benthic flux measurements of oxygen, TCO , ammonia, alkalinity, phosphate, silicate and radon were made at five of the 2 study sites. Synthesis of this data shows that fluxes of oxygen and nutrients are similar at both high and low accumulation rate sites, but that the offshore site has fluxes that are at least two times smaller for all parameters except silica and radon. Cores were collected, and analyses of solid phases organic carbon, nitrogen, sulfur, total and organic phosphorus, and 210 . . Pb and pore waters alkalinity, pH, ammonia, silica, calcium, iron, and phosphate were carried out. Calculations indicated that pore waters were near equilibrium or slightly supersaturated with calcite, supersaturated with apatite, and undersaturated with vivianite. Pore water profiles of TCO and silica were used to calculate diffusive fluxes across the 2 sediment-water interface. Comparison of these calculated fluxes to in situ flux measurements indicated solute transport at the rapid accumulation sites is dominated by diffusive fluxes, while at the other sites about half is accomplished by irrigation; the contrast reflects the abundance of macrofauna. Rate constants for organic matter degradation were estimated and reflect the presence of fractions with mean lifetimes from a few months to several years. Diagenetic stoichiometry is dominated by degradation of organic carbon, which accounts for about 95% of the TCO flux. Ultimately, oxygen is the 2 principal terminal electron acceptor, although ferric iron, nitrate and sulfate must be important intermediates. Carbonate dissolution accounts for the remaining 5% of the TCO flux. The average CrN ratio of degrading organic material derived 2 from pore water profiles of TCO and ammonia is 5 2; this is 30-50% of the ratio measured in solid phases,

ADSORPTION OF FLUOMETURON AND NORFLURAZON: EFFECT OF TILLAGE AND DISSOLVED ORGANIC CARBON

Adsorption is an important process that influences the fate and behavior of herbicides in soil. The herbicide adsorption process is influenced by both the dissolved and the solid soil organic carbon (DOC and SOC) content of soil. Both properties are affected by tillage management and biosolid utilization. This study was undertaken to examine the influence of tillage practice and various DOC sources and concentrations on the adsorption and desorption of fluometuron (N, N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea) and norflurazon (4-chloro-5(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone) in the Lexington silt loam (fine-silty, mixed, thermic, Typic Paleudalf). Batch adsorption/desorption studies were performed in the presence and absence of DOC extracted from poultry litter, dairy manure, and no-till surface soil. Herbicide adsorption is influenced strongly by soil organic carbon (SOC) content, with all soils having a greater affinity for norflurazon, relative to fluometuron. Average Koc values of 100 and 500 were determined for fluometuron and norflurazon. The influence of DOC on herbicide adsorption was a function of DOC source and concentration. Poultry litter DOC, characterized as having greater hydrophobicity and high-molecular-mass organic compound content, and dairy manure DOC (containing both low- and high-molecular-mass organic compounds) reduced herbicide adsorption. No-till DOC (hydrophilic with low molecular mass organic compounds) did not influence herbicide adsorption. In general, herbicide desorption was completely reversible. However, the equilibration period required to achieve reversibility varied with herbicide type, adsorption condition (DOC vs. no DOC), and DOC source and concentration in the desorption system. The reduction in herbicide adsorption in the presence of DOC could be attributed to the formation of soluble herbicide-DOC complexes. Further, herbicide desorption from mineral surfaces (low SOC soil) was observed to be more kinetically restricted relative to desorption from SOC (high SOC soil).

Sewage Sludge Microwave Digestion Procedure Optimized by Temperature and Pressure Analysis

An investigation of the treating process within a closed vessel is reported. The decomposition behavior of a sample–acid mixture was studied by means of pressure (P)-versus-temperature (T) profiles. Adopting the slope variation of pressure as an indicator of the outcome of decomposition of the sample, the corresponding recorded temperature should be expected to be the specific temperature for rapid decomposition of a given organic matrix. Preliminary results obtained on acidified samples (concentrated nitric acid and sludge–HNO3mixture) exposed to 800 W of power showed that the pressure curve of the acidified sample coincides with that obtained for the pure reagent until the organic matrix begins to decompose. In fact, the pressure within the vessel containing the acidified sample is a combination of the partial pressure of HNO3and the pressures of the gaseous products arising during digestion. At temperatures greater than 160°C the nitric vapor pressure masks the additional pressure due to the reaction gases. Chemical analysis of digests from the four microwave programs considered provided interesting results for solid residue and total organic carbon in soluble and insoluble fractions.

Geology and sediment geochemistry of a landfill leachate contaminated aquifer (Grindsted, Denmark)

A landfill leachate affected aquifer was investigated with respect to the geology and sediment geochemistry (solid organic carbon, cation exchange capacity, oxidation capacity, reduced iron and sulfur species) involving 185 sediment samples taken along a 305-m-long and 10–12-m-deep transect downgradient from the landfill. The geology showed two distinct sand layers (upper Quaternary, Weichselian and a lower Tertiary, Miocene) sandwiching thin layers of silt/clay deposits, peat and brown coal. The organic carbon content (TOC) and the cation exchange capacity (CEC) of the sandy sediments were low (TOC, 100–300 μg C (g DW) −1 ; CEC, 0.1–0.5 meq per 100 g DW) and correlated fairly well with the geology. Processes in the contaminant plume caused depletion of oxidation capacity and precipitation of reduced iron and sulfur species. However, some of these parameters were also affected by the geology, e.g. the oxidation capacity (OXC) was significantly higher in the Quaternary layer (OXC, 14–35 μeq g DW −1) than in the Tertiary sand layer (OXC, <5 μeq g DW −1). The intermediate layers (silt/clay and brown coal) have significantly higher values of most of the parameters investigated. This work demonstrates the need for a small scale geological model and a detailed mapping of the geochemistry of the sediments in order to distinguish impacts caused by the contaminant plumes from natural variations in the aquifer geochemistry.

Assessing organic matter mineralization, degradability and mixing rate in an ocean margin sediment (Northeast Atlantic) by diagenetic modeling

We test whether organic matter degradability, mixing activity, and total sediment mineralization can be estimated by inversion of a coupled nonlinear numerical steady-state diagenetic model. We use a single data set comprising oxygen, nitrate, ammonium and organic carbon versus depth profiles from a slope station in the Goban Spur area (1034 m, Northeast Atlantic). Based on an extensive sensitivity analysis, it appears that (1) when using all data, the total mineralization rates can be determined with reasonable precision; bioturbation and degradability are less well constrained and (2) total mineralization rates can be determined based on nitrate and oxygen profiles only; estimates of organic matter mixing rates and degradability are refined when including the solid phase organic carbon profile. The bulk mixing rates obtained for organic carbon are one order of magnitude higher than mixing rates previously estimated from Pb-210 profiles, lending validity to the hypothesis that organic particles are mixed faster than inert particles. The degradability of the organic carbon prior to its incorporation in the sediment is in the order of 10-30 yr(-1), indicating that mineralization in this slope station of the Goban Spur area is fueled mainly by freshly deposited organic matter. [KEYWORDS: Benthic oxygen-demand; deep-sea sediments; marine-sediments; hemipelagic sediments; nutrient diagenesis; equatorial pacific; water interface; carbon; bioturbation; nitrogen]

Chemical and isotopic evidence of gas‐influenced flow at a transform plate boundary: Monterey Bay, California

Chemical and isotopic compositions of pore fluids document upward flow through communities of vesicomyid clams in Monterey Bay, California. Within the clam communities, the sulfate reduction zone is only 10 cm thick, and Ca and Mg concentrations decrease to values as low as 2.2 mM and 34.5 mM, respectively, at depths less than 30 cm below the sediment‐water interface. Less than 5 m outside the communities, the base of the sulfate reduction zone is deeper than the greatest penetration of the cores (∼30 cm), and Ca and Mg exhibit only minor changes from seawater values. The sediment exhibits no significant variation in grain size, mineralogy, organic carbon, nitrogen, or carbonate content throughout the region. The composition of pore fluid within clam communities results from upward flow of altered fluid rather than different diagenetic reactions within and outside the communities. Isotopically light dissolved inorganic carbon (DIC), with δ13C values ranging from −3.2 to −54.1‰, could reflect carbon sources from either oxidized thermogenic methane and/or a mixture of oxidized microbial methane and solid organic carbon. The C1/(C2+C3) ratios (ranging from 34 to 1142) and the hydrogen and carbon isotopic compositions of methane (δD values of −109 to −156‰; δ13C values of −30.6 to −86.6‰) suggest that methane is primarily microbial but that a minor component could be thermally generated. Any thermogenic methane would have migrated from great depths, possibly &gt;2 km. The presence of methane is likely to contribute to fluid flow by reducing the density of the fluids. Past fluid migration and venting are reflected by widespread carbonate mineralization at the sediment‐water interface. This mineralization and the geographic distribution and proportions of microbial and thermogenic methane suggest that vent sites migrate when permeability is reduced during carbonate cementation. These results demonstrate that along with convergent and divergent plate boundaries, transform plate boundaries are characterized by fluid flow and that the flow may be widespread, occurring at sites away from fault zones.

Determination of Nonvolatile Organic Carbon in Aquifer Solids After Carbonate Removal by Sulfurous Acid

AbstractThe precise determination of total organic carbon (TOC) in aquifer materials is important in the estimation of retardation coefficients for organic compound transport. Commonly used methods for TOC determination after carbonate removal by acidification include: weight loss on ignition of solids at 550° C, acid‐dichromate oxidation, and combustion at 800–950° C. Since carbonate carbon frequently is more abundant than organic carbon all TOC methods depend on efficient and complete carbonate removal prior to the TOC quantification step. A method for the determination of TOC in aquifer solids involving carbonate removal by 0.73 M sulfurous acid and subsequent combustion at 800° C was tested on solids from three aquifers and on mineral standards. The carbon quantification by combustion and infrared detection of CO2 was accurate at solid organic carbon contents between 30 and 10,000 μgC/g. The acid treatment added small amounts of carbon to the sample, and siderite removal was incomplete. For samples without siderite or dolomite, the accuracy of TOC determinations was enhanced by grinding the solids. Measurement of very low TOC contents (50–100 /μgC/g) requires supplementary testing of grinding and acid treatment effects.

Natural Protection of Spring and Well Drinking Water Against Surface Microbial Contamination. I. Hydrogeological Parameters

The fate and transport of microbes in groundwater are controlled by physicochemical characteristics of the microbe and of the groundwater/aquifer media. Key characteristics of the microbe include size, inactivation (die-off) rate, and surface electrostatic properties. Key properties of the groundwater/aquifer system include flow velocity, aquifer grain (or pore) size, porosity, solid organic carbon content, temperature, pH, and other chemical characteristics of water and mineral composition. Because of size and surface electrical properties, viruses are much more mobile in groundwater than Cryptosporidium and Giardia (which are about 100 times or more larger than viruses). The inactivation or die-off rate is usually the most important factor governing how far microbes can migrate in significant numbers in groundwater. Typical half-lives of microbes in groundwater range from a few hours to a few weeks. Examples of maximum reported migration distances of microbes in groundwater include: bacteria, 600 m in a sandy aquifer; viruses., 1000 to 1600 m in channeled limestones and 250 to 408 m in glacial silt-sand aquifers; Cryptosporidium and Giardia, no confirmed reports found of significant migration distances. Investigations by the EPA have indicated that distances of 210 to 325 m away from septic tanks are necessary to achieve with high confidence an 11 order of magnitude reduction in virus concentrations.

Organic inclusions in salt. Part I: Solid and liquid organic matter, carbon dioxide and nitrogen species in fluid inclusions from the Bresse basin (France)

Organic inclusions from the Etrez and Cormoz areas of the Paleogene Bresse salt basin (France) have been studied. Different organic fractions are trapped with brine solutions in fluid inclusions in halite. Isolated inclusions from both areas are brine-bearing, and organic matter is sometimes associated with daughter mineral phases (carbonate, sulfate, clay). Structured and unstructured solid organic matter is observed both in the Etrez area (central basin) and in the Cormoz area (Northern ridge), while liquid organic droplets are only observed in fluid inclusions from the Cormoz area. FTIR microspectroscopic measurements show a low aliphatic contribution, and the presence of aromatic and oxygen double bonds for the solid organic matter. Low to high aliphatic contents (C5 and C7+, deduced from CH 2 CH 3 ratio measurements), low to high CC and CO contributions, and the presence of characteristic CN functions of amino-acids are detected in liquid droplets by FTIR spectroscopy. Carbon dioxide, originating from the thermal degradation of solid organic matter, is generally detected. Organic two-phase inclusions (brine + liquid organic matter) in planes are located in clear halite crystals from the Cormoz area. High aliphatic contributions, and variable aromatic and oxygen contents are observed. Ammonium ions (NH 4 +) are detected in the brine solution, and no carbon dioxide contribution is recorded. Organic matter trapped in the halite of the Bresse basin is immature to early mature. In the deeper part of the basin (Etrez, 800–1000 m), the organic matter in the inclusions is slightly thermally degraded, with little or no generation of liquid organic compounds. This agrees with the data on organic matter previously published from this area. In the Northern ridge (Cormoz, 500–800 m), liquid heteroatomic compounds (C, H, O, N) were produced, migrated through the salt and were trapped without gas phases. This implies a slightly lower temperature in the deeper part (Etrez) of the Bresse basin. Differences in thermal gradients between the Northern ridge, and the deeper part of the Bresse basin, must be invoked to explain differences in organic matter maturation. The analysis of organic inclusions is a contribution to understanding the thermal and biochemical history of the Bresse basin by the in situ observation of organic evolution products which are preserved by entrapment in salt.