D. Dale Werkema

The Microbial Community Structure in Petroleum-Contaminated Sediments Corresponds to Geophysical Signatures

ABSTRACT The interdependence between geoelectrical signatures at underground petroleum plumes and the structures of subsurface microbial communities was investigated. For sediments contaminated with light non-aqueous-phase liquids, anomalous high conductivity values have been observed. Vertical changes in the geoelectrical properties of the sediments were concomitant with significant changes in the microbial community structures as determined by the construction and evaluation of 16S rRNA gene libraries. DNA sequencing of clones from four 16S rRNA gene libraries from different depths of a contaminated field site and two libraries from an uncontaminated background site revealed spatial heterogeneity in the microbial community structures. Correspondence analysis showed that the presence of distinct microbial populations, including the various hydrocarbon-degrading, syntrophic, sulfate-reducing, and dissimilatory-iron-reducing populations, was a contributing factor to the elevated geoelectrical measurements. Thus, through their growth and metabolic activities, microbial populations that have adapted to the use of petroleum as a carbon source can strongly influence their geophysical surroundings. Since changes in the geophysical properties of contaminated sediments parallel changes in the microbial community compositions, it is suggested that geoelectrical measurements can be a cost-efficient tool to guide microbiological sampling for microbial ecology studies during the monitoring of natural or engineered bioremediation processes.

The Effects of LNAPL Biodegradation Products on Electrical Conductivity Measurements

Field geophysical studies have identified anomalously high conductivities in and below the free product zone at many sites with aged contamination by light, non-aqueous phase liquids (LNAPL). Laboratory experiments were conducted to test the hypothesis that these anomalously high conductivities can result from products of LNAPL biodegradation. Soil from a hydrocarbon-impacted site with anomalously high conductivities was washed repeatedly to remove soluble constituents, recontaminated with diesel fuel (DF), and the pores filled with water to simulate a saturated smear zone. Nutrients were provided at levels observed at the site, which resulted in anaerobic conditions due to DF biodegradation. Within 120days, the increase in specific conductivity from microbial activity was 2,100μS∕cm, caused by an increase in total dissolved solids (DS) of over 1,700mg∕L. The increase in DS was due to mineral (mostly carbonate) dissolution and to the production of organic acids and biosurfactants. Under aerobic conditions...

Geophysical Investigation of Vadose Zone Conductivity Anomalies at a Hydrocarbon Contaminated Site: Implications for the Assessment of Intrinsic Bioremediation

Electromagnetic (EM-31), dc resistivity, and ground penetrating radar (GPR) methods were used to investigate part of a former refinery site in Kalamazoo, Michigan, USA. The study area is underlain by about 9–12m of heterogeneous glacial drift deposits overlying a sandy outwash unit. Three large above ground storage tanks (ASTs) formerly occupied the study area and were removed by the U.S. Environmental Protection Agency (USEPA) in 1997. EM-31 surveys revealed eight remnants of buried pipe ranging from 20m to more than 100m in length. Emanating from some of these abandoned pipe segments are extensive near surface conductivity anomalies, with values ranging from 16mS∕m to greater than 100mS∕m vs. background values of less than 15mS∕m. GPR and dipole-dipole resistivity surveys performed along selected profiles with anomalous conductive zones revealed a channel form within the shallow subsurface. Shallow hand augured soil borings into these conductive zones encountered hydrocarbons perched on thin clay lenses...

1DTempPro: Analyzing Temperature Profiles for Groundwater/Surface‐water Exchange

A new computer program, 1DTempPro, is presented for the analysis of vertical one-dimensional (1D) temperature profiles under saturated flow conditions. 1DTempPro is a graphical user interface to the U.S. Geological Survey code Variably Saturated 2-Dimensional Heat Transport (VS2DH), which numerically solves the flow and heat-transport equations. Pre- and postprocessor features allow the user to calibrate VS2DH models to estimate vertical groundwater/surface-water exchange and also hydraulic conductivity for cases where hydraulic head is known.

Biogeophysics: The Effects of Microbial Processes on Geophysical Properties of the Shallow Subsurface

ThegeologicrecordsuggeststhepresenceofmicrobesonEarthasearlyasthePrecambrian(Hall-Stoodleyetal.,2004).Microbesareinvolvedinpracticallyevery aspect of earth evolution. The term microbe is a general descriptor fortiny organisms that individually are too small to be seen with the unaided eye.Microbes may include bacteria, archaea, fungi, and protists. Viruses are alsoincluded as a major type of microbe, although there is some debate whetherviruses can be classified as living organisms. The role microbes play in al-tering environmental systems is well documented in many biogeochemicalstudies. Notable is the role of microbes in water-rock interactions (Chapelleand Bradley, 1997). Field observations and laboratory experiments suggestthat bacteria can accelerate silicate weathering either by direct contact withminerals or by producing organic and inorganic acids that enhance the dis-solution of silicates (Heibert and Bennett, 1992). Thus, microbes are able todirectly alter mineral surface chemistry and pore water chemistry over shortto geologic time scales. Microbial induced changes in water-rock-regolith en-vironments over variable time scales cause changes in the physical propertiesof these environments that may be detected and measured using geophysicalmethodologies.The reader should take note that we have used the term regolith insteadof sediment or soil to distinguish between these terms. As determined froma classical geologic definition we use regolith to describe fragmental andunconsolidated rock derived material, whether residual or transported, andoverlies bedrock. This definition includes rock debris of all origins such asvolcanic ash, glacial drift, alluvium, loess, vegetal accumulations and soil. Inthe text, the use of sediment or sediments will refer to the more general termrepresenting solid fragmental material transported and deposited by wind,water or ice, chemically precipitated from solution or secreted by organisms,and forms in layers in loose unconsolidated form. We use the definition ofsoil as the natural medium for the growth of land plants.

High-resolution magnetic susceptibility measurements for investigating magnetic mineral formation during microbial mediated iron reduction

Disimilatory iron-reducing bacteria play an important role in the reduction of Fe(hydr)oxides and the production of secondary solid-iron mineral phases that can have magnetic properties. Magnetic susceptibility can therefore play an important role in identifying zones where microbial-mediated iron reduction is occurring. We investigated the magnetic susceptibility variations in a hydrocarbon-contaminated aquifer where methanogenesis and iron reduction are the main biogeochemical processes. Our objectives are to (1) determine the variability of magnetic susceptibility, (2) determine the hydrobiogeochemical controls on the magnetic susceptibility variability, and (3) evaluate the use of magnetic susceptibility as a viable technique for identifying zones where the coupling of iron and organic carbon cycling is occurring. Magnetic susceptibility data were acquired down 11 boreholes within contaminated and uncontaminated locations. We show that magnetic susceptibility values for boreholes within the free phase plume are higher than values for boreholes within the dissolved phase plume and background. Magnetic susceptibility values are highest within the zone of water table fluctuation with peaks predominantly occurring at the highest water table marks and are also coincident with high concentrations of dissolved Fe(II) and organic carbon content, suggesting that the zone of water table fluctuation is most biologically active. High magnetic susceptibility values within the vadose zone above the free phase plume are coincident with a zone of methane depletion suggesting aerobic or anaerobic oxidation of methane coupled to iron reduction. Our results suggest that magnetic susceptibility can be used as a viable tool in iron and carbon cycling studies.

Temporal geophysical signatures from contaminant-mass remediation

We have previously documented changes in bulk electrical conductivity, self-potential (SP), and ground-penetrating-radar (GPR) reflections in a field setting caused by biogeochemical transformations of hydrocarbon-contaminated media. These transformations are associated with hydrocarbon biodegradation. The results of surface geophysical surveys acquired in 1996, 2003, and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone. Initial investigations in 1996 showed that relative to background, the contaminated area was characterized by higher bulk electrical conductivity, positive SP anomaly, and attenuated GPR reflections. Repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007, the bulk electrical conductivityhad reverted to near-background conditions, the positive SP anomaly became more negative, and the zone of attenuated GPR reflections showed increased signal strength. Removal of hydrocarbon mass in the vadose zone o...

In situ rhamnolipid production at an abandoned petroleum refinery

A simple screening method was developed to detect in situ biosurfactant production by exploiting the relationship between surface tension (ST) and surfactant concentration. Filtered groundwater from contaminated wells with ST values of 60 to 70 dynes/cm decreased to 29 dynes/cm after being concentrated 10 to 15 times in a rotary evaporator, indicating that biosurfactants in the sample reached the critical micelle concentration (CMC). Samples from uncon-taminated groundwater concentrated 25 times showed no decrease in ST below 72 dynes/cm, suggesting that biosurfactants were not present. Microorganisms from soil cores were cultured on diesel fuel and identified using fatty acid methyl ester (FAME) analysis. Pseudomonas aeruginosa was found at very low numbers in uncontami-nated soil but was the dominant species in contaminated soil, indicating that hydrocarbon release impacted microbial diversity significantly. High-performance liquid chromatography (HPLC) was used to quantify rhamnolipids, biosurfactants produced by P. aeruginosa, in concentrated ground-water samples. Rhamnolipid concentrations in samples from contaminated soil were observed equal to their CMC (50 mg/L), but were not detected in samples from un-contaminated wells. We conclude that biosurfactant production may be an indicator of intrinsic bioremediation.

Microbial-Induced Heterogeneity in the Acoustic Properties of Porous Media

Received 10 June 2009; revised 25 August 2009; accepted 13 October 2009; published 13 November 2009. [1] It is not known how biofilms affect seismic wave propagation in porous media. Such knowledge is critical for assessing the utility of seismic techniques for imaging biofilm development and their effects in field settings. Acoustic wave data were acquired over a two-dimensional region of a microbial-stimulated sand column and an unstimulated sand column. The acoustic signals from the unstimulated column were relatively uniform over the 2D scan region. The data from the microbial-stimulated column exhibited a high degree of spatial heterogeneity in the acoustic wave amplitude, with some regions exhibiting significant increases in attenuation while others exhibited decreases. Environmental scanning electron microscopy showed differences in the structure of the biofilm between regions of increased and decreased acoustic wave amplitude. We conclude from these observations that variations in microbial growth and biofilm structure cause heterogeneity in the elastic properties of porous media with implications for the validation of bioclogging models. Citation: Davis, C. A., L. J. Pyrak-Nolte, E. A. Atekwana, D. D. Werkema Jr., and M. E. Haugen (2009), Microbial-induced heterogeneity in the acoustic properties of porous media, Geophys. Res. Lett., 36, L21405, doi:10.1029/2009GL039569.

Actively heated high‐resolution fiber‐optic‐distributed temperature sensing to quantify streambed flow dynamics in zones of strong groundwater upwelling

Zones of strong groundwater upwelling to streams enhance thermal stability and moderate thermal extremes, which is particularly important to aquatic ecosystems in a warming climate. Passive thermal tracer methods used to quantify vertical upwelling rates rely on downward conduction of surface temperature signals. However, moderate to high groundwater flux rates (>−1.5 m d−1) restrict downward propagation of diurnal temperature signals, and therefore the applicability of several passive thermal methods. Active streambed heating from within high-resolution fiber-optic temperature sensors (A-HRTS) has the potential to define multidimensional fluid-flux patterns below the extinction depth of surface thermal signals, allowing better quantification and separation of local and regional groundwater discharge. To demonstrate this concept, nine A-HRTS were emplaced vertically into the streambed in a grid with ∼0.40 m lateral spacing at a stream with strong upward vertical flux in Mashpee, Massachusetts, USA. Long-term (8–9 h) heating events were performed to confirm the dominance of vertical flow to the 0.6 m depth, well below the extinction of ambient diurnal signals. To quantify vertical flux, short-term heating events (28 min) were performed at each A-HRTS, and heat-pulse decay over vertical profiles was numerically modeled in radial two dimension (2-D) using SUTRA. Modeled flux values are similar to those obtained with seepage meters, Darcy methods, and analytical modeling of shallow diurnal signals. We also observed repeatable differential heating patterns along the length of vertically oriented sensors that may indicate sediment layering and hyporheic exchange superimposed on regional groundwater discharge.