Recent Events:

Congratulations to undergraduate Jeff Salacup!

Jeff has been selected for a 2006 Summer Student Fellowship at the DFG Research Center Ocean Margins, Bremen, Germany. Jeff worked with Prof. Kai-Uwe Hinrichs on biomarker signatures of ecosystem stress across the K-T boundary, and has returned to us in to begin M.S. thesis research in the Biogeochemistry Lab.

You can view a .ppt file summarizing Jeff's activities from this summer here

Below is Jeff's abstract from the recent Five-Colleges Undergraduate Geosciences Research Symposium:

Anaerobic Biodegradation of Organic Matter In the Devonian Antrim shale

Abstract. The Antrim Shale, one of the largest unconventional natural gas reserves in North America, is a finely laminated, pyritic, organic-matter rich, thermally immature Devonian black shale located in the Michigan Basin. Previous studies have demonstrated an anaerobic microbial origin for this gas by measuring δ¹³C fractionation between produced methane and DIC, as well as ∆D fractionation between co-produced methane and water. This geologic setting may resemble documented syntrophic communities in which high molecular weight organic molecules are biodegraded into acetate, CO₂ and H₂ with subsequent and rapid product removal by acetoclastic methanogenesis and CO 2 reduction with H 2. Unknown, however, are which suite of organic materials within the shale is most readily degraded by these communities, and how they provide the necessary substrates to support methanogenesis.

Investigations on anaerobic biodegradation of organic matter have focused on migrated petroleum, petroleum-contaminated aquifers, or deep marine sediments, and have established a quasi-stepwise elimination of increasingly complex and refractory classes of molecules. In this study, we investigate the geochemical imprint left by in-situ anaerobic decomposition of organic matter on a pair of archived Antrim Shale cores. Four samples were obtained: two from methane-producing and two from non-producing sections of the Michigan Basin. Variability in bulk geochemical parameters is greater within each core than between cores, suggesting that OM biodegradation and methanogenesis have not substantially impacted rock TOC content or kerogen elemental composition. However, analysis of n-alkanes and isoprenoids isolated from the cores reveals substantial degradation of saturated straight-chain and branched hydrocarbons within the methane-producing core. This is the first documented occurrence of in-situ anaerobic hydrocarbon degradation in an organic matter-rich sedimentary rock. These results suggest that these two classes of molecules may be especially available and susceptible to degradation by the microbial communities within the producing core. The anaerobic degradation of organic matter in sedimentary rocks holds implications for the viability of associated metabolic pathways in the absence of electron acceptors (O₂, SO₄^-2, or NO₃^-), as well as the subsequent distortion or removal of biomarker signatures important in petroleum exploration.

Congratulations to Microbiology Graduate Student Patricia Waldron!

Patricia has successfully completed her M.S. in the Biogeochemistry Lab working on salinity gradients as controls on Archaea community structure in the methane-generating zone of the Antrim Shale, and will enter the Ph.D. program at the University of Oklahoma in Fall 2006. Below is the abstract of Patricia's presentation the American Society for Microbiology meeting in May 2006.

Salinity of pore water affects microbial growth and diversity in subsurface shale

The Antrim Shale of the Michigan Basin (Michigan, USA) is a ~360 million year old sedimentary rock currently under intense development for natural gas production. Geochemical and stable isotope ratio analyses of harvested gas indicate that methane produced from the Antrim is mainly the product of subsurface microbial methanogenesis. Molecular (16S and mcrA) community analysis of waters from Antrim natural gas wells shows a diversity of methanogenic, acetogenic and fermentative organisms. Methane generation varies in mode and intensity across the study area coincident with a steep salinity gradient in shale porewaters. Measured Antrim porewater increases from <10 mM Cl- to >4 M Cl- over a lateral distance of 40 kilometers. This study examines if pore water salinity is a key factor influencing the types of microorganisms and thus the rates and mechanisms of methane generation in the shale. A suite of growth media was established that mimics the pore water chemistry of the shale, ranging from 20 – 4000 mM Cl-. This suite was inoculated with water from productive methane wells sampled along a north-south transect of the study area. Incubations from the majority of wells exhibited growth within six months at salinities between 20 – 1000 mM Cl-. No growth was observed in incubations from the most saline sampled well (3490 mM Cl-), but the second most saline well (2268 mM Cl-) showed growth between up to 1500 mM Cl-; this well exhibits growth at higher salinity than other wells, indicating that a community is present in this well that is distinct from other wells. Maximum methane generation occurs at different salinities for each well, correlating to individual porewater salinities. RFLP analysis of Archaeal 16S rNA genes amplified from well waters indicates that similar RFLP patterns correlate with similar well geochemistries, indicating a suite of methane-generating microbial communities in this environment, each adapted to particular environment characteristics within this sedimentary basin. This research shows that pore water salinity is an important factor controlling methanogenic diversity in susburface shale in the Antrim Shale.

Look for our presentations from the following recent meetings:

(2006) ASLO/AGU Ocean Sciences Meeting, Honolulu, HI. Feb. 19-24, 2006

OFFSHORE MOBILIZATION AND MICROBIAL UPTAKE OF AGED FLOODPLAIN ORGANIC MATTER IN RESPONSE TO HURRICANE KATRINA
Gordon, E S, Allison, M A, Petsch, S T

Coastal erosion associated with Katrina, a Category 4 hurricane that made landfall in coastal Louisiana on August 29, 2005, likely resulted in significant mobilization and offshore delivery of aged, terrigenous organic matter (OM) from floodplain-delta deposits. The primary objectives of this study are to examine the microbial uptake of this aged, floodplain OM in near- and offshore sediment communities and to determine OM sources, age, and lability along a portion of the Louisiana shelf adjacent to the most severe storm surge and coastal erosion associated with the hurricane. Five weeks following the passage of Katrina, sediment cores were collected from 18 inner- and mid- shelf locations, on the east and west sides of the Mississippi birdsfoot delta. Additional cores were collected in shallow bays on the east side of the delta. Isotopic and biomarker analyses are underway to determine the content and composition of OM in nearshore and offshore sediments deposited before and after passage of Katrina. Microbial communities in Katrina-associated sediments will be determined by phospholipid profiles and DNA-based community assays. The uptake of remobilized, aged OM will be evaluated by the distribution and isotopic composition (¹³C, ¹⁴C) of phospholipids isolated from pre- and post-Katrina sediments. Combined, these data will yield important information about the impact of storm events on the incorporation of OM isotopic characteristics into active microbial communities, the stochastic nature of aged OM delivery to marine sediments, and the lability of reworked floodplain OM once remobilized and deposited offshore.

BLACK SHALES: A SOURCE OF DISSOLVED, BIODEGRADABLE, AND ASSIMILABLE ORGANIC MATTER TO NATURAL WATERS
Schillawski, S. and Petsch, S.T.

Black shales are fine-grained laminated sedimentary rocks rich in organic matter (OM). Exposure of shales to earth surface environments results in oxidative weathering of the shale. Prior studies have demonstrated a loss of organic carbon during weathering of shales, while other efforts have shown that rivers draining watersheds underlain by black shales transport significantly aged (¹⁴C-depleted) dissolved and particulate OM when compared to rivers draining other lithologies. Consequently, it is uncertain if complete oxidation of ancient sedimentary OM occurs within an outcrop during weathering, or whether black shales can be a source to rivers of OM that is distinct in composition and isotopic character from other pools such as soils, decaying vegetation, and autochthonous production. To address this, column experiments were initiated in which sterile, air-saturated water was passed through glass flow-thru cells containing shale substrates. A Late Devonian black shale containing Type II kerogen (representative of compositions found in many marine sedimentary rocks) from the Appalachian Basin, USA, (7.60% TOC) was used. Three parallel column experiments [crushed shale, solvent-extracted crushed shale, and a baked-sand blank] were monitored for several months. Effluent from the columns was routinely collected and analyzed for dissolved organic carbon concentrations (DOC); shale-derived DOC stabilized at approx. 0.5mg L^-1 at a flow rate of 40mL hr^-1. DOC in the effluent was evaluated for biodegradable organic carbon (BDOC) or assimilable organic carbon (AOC) contents following established protocols. The BDOC and AOC assays clearly demonstrated that this pool of shale-derived DOC is biologically available. ¹H NMR spectra of effluent were obtained from DOC concentrated by solid-phase-extraction. No significant differences were noted in DOC, BDOC and AOC assays and ¹H NMR spectra between either shale substrates. Compared to riverine and marine DOM, the column effluent lacked carbohydrate and amino acid groups. These results show that OM-rich sedimentary rocks provide a source of bioavailable dissolved organic matter to natural waters. Although weathering removes less than 100% of shale OM at the outcrop, kerogen dissolution along both active and passive margins may deliver biologically available DOM to downstream reservoirs. Furthermore, this pool of rock-derived OM will be rapidly incorporated into river and coastal ocean ecosystems, delivering a distinct flux of DOC to the modern carbon cycle, estimated here to possibly be as much as 0.2 Pg yr^-1.

SOURCES, AGE AND COMPOSITION OF DISSOLVED AND PARTICULATE ORGANIC MATTER DELIVERED TO PASSIVE-MARGIN RIVER SYSTEMS
Petsch, S.T., Gordon, E.S., Longworth, B., Schillawski, S., and Raymond, P.A.

Rivers play an important role in the modern and long-term carbon cycles, serving as the primary link between terrestrial carbon sources and remineralization and burial in the ocean. Weathering and erosion of ancient, OM-bearing sedimentary rocks may deliver a significant pool of aged, refractory organic matter to downstream river environments and the coastal ocean. If significant, this flux of aged, relict OM could have significant impacts on river and coastal ecosystem carbon and nutrient dynamics, oxygen utilization, estimates of carbon remineralization rates, marine DOM turnover, and the stable and radiocarbon isotope systems in the ocean. A suite of fourteen small headwater watersheds of the Hudson-Mohawk River system (New York, USA) were investigated to examine the relative importance of land use type and underlying lithology as controlling factors on POM composition and isotopic characteristics. Mixing models suggest that weathering of ancient sedimentary rocks may contribute approximately 5-10% of total stream POM load; land use practices associated with agriculture are also significant factors in delivery of aged soil OM fractions to downstream reservoirs. A suite of water samples collected upstream of the mouths of major NE USA rivers was examined to evaluate the composition and isotopic characteristics of DOM and POM. DOM was concentrated using solid phase extraction and examined using ¹H NMR spectroscopy. POM and DOM concentrations do not co-vary with dominant watershed lithology or land use type, but variations in DOM composition do indicate a contribution of more carbohydrate- and amino-poor material in watersheds containing significant amounts of ancient, OM-rich sedimentary rocks. These results demonstrate that OM derived from weathering of ancient sedimentary rocks contributes a distinct and detectable signature to downstream OM pools and to river and coastal ocean ecosystems along passive continental margins where modest erosion rates and long transit times provide for extensive transformation, assimilation and biodegradation of riverine OM.