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1.
Secondary mineralization pathways induced by dissimilatory iron reduction of ferrihydrite under advective flow 总被引：6，自引：0，他引：6
Colleen M Hansel Shawn G Benner Jim Neiss Ravi K Kukkadapu 《Geochimica et cosmochimica acta》2003,67(16):2977-2992
Iron (hydr)oxides not only serve as potent sorbents and repositories for nutrients and contaminants but also provide a terminal electron acceptor for microbial respiration. The microbial reduction of Fe (hydr)oxides and the subsequent secondary solid-phase transformations will, therefore, have a profound influence on the biogeochemical cycling of Fe as well as associated metals. Here we elucidate the pathways and mechanisms of secondary mineralization during dissimilatory iron reduction by a common iron-reducing bacterium, Shewanella putrefaciens (strain CN32), of 2-line ferrihydrite under advective flow conditions. Secondary mineralization of ferrihydrite occurs via a coupled, biotic-abiotic pathway primarily resulting in the production of magnetite and goethite with minor amounts of green rust. Operating mineralization pathways are driven by competing abiotic reactions of bacterially generated ferrous iron with the ferrihydrite surface. Subsequent to the initial sorption of ferrous iron on ferrihydrite, goethite (via dissolution/reprecipitation) and/or magnetite (via solid-state conversion) precipitation ensues resulting in the spatial coupling of both goethite and magnetite with the ferrihydrite surface. The distribution of goethite and magnetite within the column is dictated, in large part, by flow-induced ferrous Fe profiles. While goethite precipitation occurs over a large Fe(II) concentration range, magnetite accumulation is only observed at concentrations exceeding 0.3 mmol/L (equivalent to 0.5 mmol Fe[II]/g ferrihydrite) following 16 d of reaction. Consequently, transport-regulated ferrous Fe profiles result in a progression of magnetite levels downgradient within the column. Declining microbial reduction over time results in lower Fe(II) concentrations and a subsequent shift in magnetite precipitation mechanisms from nucleation to crystal growth. While the initial precipitation rate of goethite exceeds that of magnetite, continued growth is inhibited by magnetite formation, potentially a result of lower Fe(III) activity. Conversely, the presence of lower initial Fe(II) concentrations followed by higher concentrations promotes goethite accumulation and inhibits magnetite precipitation even when Fe(II) concentrations later increase, thus revealing the importance of both the rate of Fe(II) generation and flow-induced Fe(II) profiles. As such, the operating secondary mineralization pathways following reductive dissolution of ferrihydrite at a given pH are governed principally by flow-regulated Fe(II) concentration, which drives mineral precipitation kinetics and selection of competing mineral pathways. 相似文献
2.
Ernest S. GLADNEY Colleen E. BURNS Iwan Roelandts 《Geostandards and Geoanalytical Research》1985,9(1):35-68
Concentration data for as many as 72 constituents in the four Canadian Certified Reference Materials Project (CCRMP) soil samples have been collected from journal articles and technical reports published since these soil standards were issued in 1978. These data are summarized into mean +/- one standard deviation values and compared with available certification data from CCRMP. All literature data located or calculated are presented in the appendices. 相似文献
3.
Ernest S. GLADNEY Colleen E. BURNS Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1983,7(1):3-6
Elemental composition data on eight older (AGV-1, BCR-1, DTS-1, G-1, G-2, GSP-1, PCC-1 and W-1) and three newer (BIR-1, DNC-1 and W-2) USGS rock standards have been collected from institutional reports and journal articles from 1972–1981. This collection was combined with data from previous compilations and "consensus values" for up to 79 elements determined by comparing overall means, medians, and individual means based on analytical techniques. 相似文献
4.
David T. Long Matthew J. Parsons Catherine H. Yansa Sharon S. Yohn Colleen E. McLean Ryan G. Vannier 《Applied Geochemistry》2010
Geochemical profiles of sediment cores from two oligotrophic lakes (Elk and Mullett) in northern Lower Michigan were studied to examine the response and recovery of watersheds to large-scale logging that occurred between 1850 and 1920. Specific questions addressed were: can the impact of extensive clear-cutting of forests be recognized in the sediment-chemical chronologies, can states of system stability be identified prior to the logging, and are there indications that the systems are recovering and possibly returning to a stable state? To answer these questions, elements were put into four groups as proxies for watershed runoff or export (e.g., Al, Mg), pollution (e.g., Pb, Cu), redox (e.g., Fe, As), and productivity (e.g., Ca, P). It was observed that vertical patterns of all proxies were influenced by logging and the early increases in concentration of pollution proxies were due to increased watershed export, not pollution. System stability might be recognized by relatively symmetrical vertical patterns among all of the proxies or secular changes of slowly increasing or decreasing vertical concentration trajectories. Some pre-logging trajectories were punctuated by episodes of slightly elevated concentrations that appear to be related to comparatively warmer periods during the Little Ice Age. Iron and Mn enrichments caused by increased watershed runoff might be misinterpreted as paleo-redox horizons. Results are interpreted to indicate that (1) reference conditions may be better defined as the temporal trends among proxy groups and not individual concentrations, (2) simply assuming pre-1800 conditions as a reference may not be appropriate, (3) inter-proxy group comparisons are needed to help for interpretations of intra-proxy group patterns, (4) the possible regime shift identified here might be expected for other ecosystems because of the intensity of human disturbances and secular changes, and (5) without consideration of a possible regime shift, recovery from logging is estimated to be on the order of 75–130 a, but shorter if regime shifts are considered. 相似文献
5.
Alexandre Forest Jean-Éric Tremblay Yves Gratton Johannie Martin Jonathan Gagnon Gérald Darnis Makoto Sampei Louis Fortier Mathieu Ardyna Michel Gosselin Hiroshi Hattori Dan Nguyen Roxane Maranger Dolors Vaqué Cèlia Marrasé Carlos Pedrós-Alió Amélie Sallon Christine Michel Colleen Kellogg Jody Deming Elizabeth Shadwick Helmuth Thomas Heike Link Philippe Archambault Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436
Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m−2 calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m−2, which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m−2, a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m−2), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m−2). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain. 相似文献
6.
John M. Kennish Colleen Montoya Jane Whitsett John S. French 《Marine environmental research》1985,17(2-4)
Hydrocarbons are being introduced into the marine environment from a variety of sources including combustion processes, crude oil spills, fuel oil spills, and controlled disposal such as processed ballast water. Even in the relatively clean waters of Alaska hydrocarbons are being released at an alarming rate. The purpose of this study was to determine the optimum conditions for the metabolism of a representative hydrocarbon by Coho Salmon Oncorhynchus kisutch liver microsomes. The product of cyclohexane metabolism in the salmon microsomal system was identified by gas chromatography-mass spectrometry as cyclohexanol. Conditions of the microsome incubation were varied systematically to determine the optimum temperature, pH, and ionic strength for cyclohexanol production. Cyclohexanol was quantified by capillary column gas chromatography. Maximum cyclohexanol formation was achieved at 20°C, a pH of 8·0–8·5 and an ionic strength of 0·026. A linear rate of cyclohexanol formation is seen from 0–60 min of incubation and there is an apparent decrease in the rate from 60–90 min. Poor stability of the microsomal preparation from the species studied was also identified and several stability studies have been undertaken using cyclohexane metabolism as a monitor. 相似文献
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8.
Rebecca Grey-Ross Colleen T. Downs Kevin Kirkman 《Applied geography (Sevenoaks, England)》2009,29(3):371-376
Increasing transformation and fragmentation of rural landscapes for economic reasons is causing concern to conservationists worldwide. With this trend likely to continue, perhaps conservation agencies and development corporations need to co-operate and plan housing developments that are environmentally and ecologically sustainable and can serve as refuges for endangered species. In KwaZulu-Natal, South Africa, grasslands are particularly threatened by land transformation for housing developments. A case study is presented of a housing development, Wedgewood Estate in KwaZulu-Natal that has been developed and managed for conserving grassland habitat and associated species, particularly the endangered oribi (Ourebia ourebi). Feedback from the Estate's managers about the development and ecological impact were obtained. Wedgewood is an example of the viability of housing estates as refuges for endangered species and shows that the density and placement of housing and management of the natural habitat are important. It emphasizes the need for reviewing the types and amount of housing development, management of natural habitat, and the rules and regulations they put in place to assure the integrity of the conservancy is preserved. This case study also shows the potential of such ecologically sensitive housing developments as sources of surplus game for translocation, especially in the case of endangered species such as oribi. 相似文献
9.
Ranger Ilona M. Heaman Larry M. Pearson D. Graham Muntener Colleen Zhuk Volodymyr 《Mineralogy and Petrology》2018,112(2):639-651
Kimberlites are rare volatile-rich ultramafic magmas thought to erupt in short periods of time (<1 Myr) but there is a growing body of evidence that the emplacement history of a kimberlite can be significantly more protracted. In this study we report a detailed geochronology investigation of a single kimberlite pipe from the Renard cluster in north-central Québec. Ten new high precision ID-TIMS (isotope dilution – thermal ionization mass spectrometry) U-Pb groundmass perovskite dates from the main pipe-infilling kimberlites and several small hypabyssal kimberlites from the Renard 2 pipe indicate kimberlite magmatism lasted at least ~20 Myr. Two samples of the main pipe-infilling kimberlites yield identical weighted mean 206Pb/238U perovskite dates with a composite date of 643.8 ± 1.0 Myr, interpreted to be the best estimate for main pipe emplacement. In contrast, six hypabyssal kimberlite samples yielded a range of weighted mean 206Pb/238U perovskite dates between ~652-632 Myr. Multiple dates determined from these early-, syn- and late-stage small hypabyssal kimberlites in the Renard 2 pipe demonstrate this rock type (commonly used to date kimberlites) help to constrain the duration of kimberlite intrusion history within a pipe but do not necessarily reliably record the emplacement age of the main diatreme in the Renard cluster. Our results provide the first robust geochronological data on a single kimberlite that confirms the field relationships initially observed by Wagner (1914) and Clement (1982); the presence of antecedent (diatreme precursor) intrusions, contemporaneous (syn-diatreme) intrusions, and consequent (post-diatreme) cross-cutting intrusions. The results of this detailed U-Pb geochronology study indicate a single kimberlite pipe can record millions of years of magmatism, much longer than previously thought from the classical viewpoint of a rapid and short-duration emplacement history.
相似文献10.
Christopher K. Uejio Megan Christenson Colleen Moran Mark Gorelick 《Hydrogeology Journal》2017,25(4):969-979
This study examined the relative importance of climate change and drinking-water treatment for gastrointestinal illness incidence in children (age <5 years) from period 2046–2065 compared to 1991–2010. The northern Wisconsin (USA) study focused on municipalities distributing untreated groundwater. A time-series analysis first quantified the observed (1991–2010) precipitation and gastrointestinal illness associations after controlling for seasonality and temporal trends. Precipitation likely transported pathogens into drinking-water sources or into leaking water-distribution networks. Building on observed relationships, the second analysis projected how climate change and drinking-water treatment installation may alter gastrointestinal illness incidence. Future precipitation values were modeled by 13 global climate models and three greenhouse-gas emissions levels. The second analysis was rerun using three pathways: (1) only climate change, (2) climate change and the same slow pace of treatment installation observed over 1991–2010, and (3) climate change and the rapid rate of installation observed over 2011–2016. The results illustrate the risks that climate change presents to small rural groundwater municipalities without drinking water treatment. Climate-change-related seasonal precipitation changes will marginally increase the gastrointestinal illness incidence rate (mean: ～1.5%, range: ?3.6–4.3%). A slow pace of treatment installation somewhat decreased precipitation-associated gastrointestinal illness incidence (mean: ～3.0%, range: 0.2–7.8%) in spite of climate change. The rapid treatment installation rate largely decreases the gastrointestinal illness incidence (mean: ～82.0%, range: 82.0–83.0%). 相似文献