Archaeol as a methanogen biomarker in ombrotrophic bogs     

Richard D. Pancost  Erin L. McClymont  Elizabeth M. BinghamZoë Roberts  Dan J. CharmanEdward R.C. Hornibrook  Anthony BlundellFrank M. Chambers  Katie L.H. LimRichard P. Evershed 《Organic Geochemistry》2011,42(10):1279-1287

In order to develop new tools in the reconstruction of microbiological processes in ancient continental settings, we determined the concentration of archaeol and sn-2-hydroxyarchaeol in four Holocene ombrotrophic peatlands, spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal water table, archaeol and sn-2-hydroxyarchaeol concentration markedly increased at all four sites, again consistent with an anaerobic source, but differed strongly among sites. The differences apparently reflect a combination of vegetation - ericaceous and graminoid plants as opposed to Sphagnum spp. and other mosses lacking root systems - and temperature influence on methanogenesis. In particular, low ether lipid concentrations in Finland probably reflect the lack of vascular vegetation possessing well-developed root systems, together with low mean annual temperature. Similarly low concentrations of archaeol and sn-2-hydroxyarchaeol in a German bog likely result from winter temperatures below 0 °C and a relatively shorter growing season. The occurrence of sn-2-hydroxyarchaeol is limited to a narrow and shallow depth range, indicating that it is poorly preserved, but archaeol persists throughout the cores. Decoupling the concentration of archaeol and the more labile sn-2-hydroxyarchaeol below ca. 50 cm suggests that the former records fossil biomass rather than living biomass. If so, then downcore variation in archaeol concentration likely reflects past changes in methane cycling, and archaeol, pending further developmental research, could serve as a new tool for reconstruction of past peatland biogeochemistry.  相似文献   

Pyrolysis GC-MS as a rapid screening tool for determination of peat-forming plant composition in cores from ombrotrophic peat     

Erin L. McClymont  Elizabeth M. BinghamChris J. Nott  Frank M. ChambersRichard D. Pancost  Richard P. Evershed 《Organic Geochemistry》2011,42(11):1420-1435

Peat cores provide decadal to centennial records of climatic and environmental change, including evidence for human/environment interaction. Existing palaeoenvironmental proxies (macrofossils, pollen, humification, testate amoebae, lipid composition) require multiple laboratory preparation steps and may be subject to differential preservation that can limit production of a continuous time series. The potential for pyrolysis gas-chromatography-mass-spectrometry (Py-GC-MS) to be applied to bulk peat samples is investigated here. The only preparatory step required was freeze drying. Analysis of a range of important peat-forming plants demonstrates that Sphagnum moss species are unique in containing the pyrolysis product of sphagnum acid, 4-isopropenylphenol. In contrast, non-Sphagnum species are rich in lignin pyrolysis products, which are absent from Sphagnum. The presence of these pyrolysis markers is reflected in bulk peat composition and tested here using archives from Bolton Fell Moss and Butterburn Flow (UK), Kontolanrahka (Finland) and Bissendorfer Moor (Germany). A ratio between 4-isopropenylphenol and two lignin pyrolysis products is proposed as a proxy for total Sphagnum input to peat archives and shows potential for use as a rapid screening tool for characterising bulk peat composition before more intensive analysis.  相似文献   

On Convective Style and Vigor in Sheet-like Magma Chambers   总被引：2，自引：4，他引：2  

MARSH  BRUCE D. 《Journal of Petrology》1989,30(3):479-530

The well known absence of magrnatic superheat is held here tobe a direct reflection of the ease and efficiency of large Rayleighnumber (Ra) convection in evacuating all convectable heat fromthe magma. Magmatic temperature is thus continually bufferedat or below the convective liquidus where the temperature differencedriving convection is vanishingly small and the governing Rais also always small regardless of body size. It is furtherheld here that for bodies where side wall cooling is of lesserimportance, the more common perception of magma chambers isof cooling from above and below where both the initial, isothermal(i.e. isodensity), and final (solid) states are dynamicallystable and that convection is necessarily a transient processconnecting these states. Extensive theoretical and experimentalstudies of cooling from above show that regardless of boundaryconditions transient, small Ra convection is independent oflayer thickness. Instead, convection is driven by formationof a thin, cool, and dense sublayer along the top boundary,and the characteristic length scale of the governing Rayleighnumber, which is time-dependent, is the sublayer thickness (d<<L).All dynamic features of the flow, including heat transfer relyon this length scale and not body thickness; virtually any sheet-likemagmatic body appears infinitely thick to such convection. BecauseRa is small, this transient stage persists for most, if notall, of the period of solidification to mush, whence the bodyis dynamically dead. Under conditions of strongly variable viscosity, only the leadingpart of d (i.e. d'), forward of a critical rheological front,is unstable. Convection itself is restricted to a region whereviscosity changes by no more than a factor of about 3 to 10.Most of the cool, dense sublayer is rigid, immobile crust, unableto participate in convection and cool the body. Rapid advanceof this crust due to cooling inhibits convection by consuminginstabilities before maturation to finite amplitude. Inclusionof solidification in the stability analysis changes the lengthscale in the governing Rayleigh number (Ra_v) to K/V (thermaldiffusivity/advance velocity). Ra is subcritical for large V₀(early times) and only with time becomes supcrcritical. Thisis in striking contrast to the usual Ra_L, which is initiallythe largest it will ever be. Because of continual collapse ofthe unstable sublayer, convection may remain near the criticalRa_v. Convection is thus initially weak and, because the heatflux from the system monotonically decreases with time due tothe thickening conductive crust and cooling, it is preventedfrom becoming indefinitely strong and instead slowly diminisheswith time. Conduction through the advancing crust is balanced by latentheat of crystallization at the crystallization front and convectionoccurs in response to this cooling. Because convection is confinedto the nearly isoviscous, nonsuperheated magma, crust growthis unaffected by convection, even when it is artificially forcedat unnatural rates. The crusts of Hawaiian lava lakes reflectthis in growing at the same rate regardless of lake thicknessand, in numerical convective modeling, imposed Rayleigh number.Overall cooling is well approximated by that of a stagnant,purely conducting layer whose central temperature is constantuntil arrival of the slowly moving cooling front In fact, therate of change of a body's central temperature is a direct measureof the total rate of heat transfer (i.e. Nusselt number, Nu)from that region. This is shown to be very nearly zero for Hawaiianlava lakes, precluding all but the weakest of convective heattransfer within the magma itself. The maximum heat transfer in terms of Nusselt number of anyunheated body within a conductive medium and always kept perfectlywell mixed thermally, relative to the same stagnant body, isshown to be Nu=2 regardless of shape and size. This thermalevolution is closely followed by previous calculations thatassume a large Rayleigh number based on layer thickness. Thermal convection in unheated, sheetlike magma chambers isa transient, sluggish process governed by solidification andsmall scale, small Rayleigh number instabilities; thermallydriven convective turbulence, in the usual sense, is out ofthe question.  相似文献   

Assimilation of Crustal Material by Basaltic Magma: Strontium Isotopic and Trace Element Data from the Edgecumbe Volcanic Field, SE Alaska     

MYERS  JAMES D.; SINHA  A. KRISHNA; MARSH  BRUCE D. 《Journal of Petrology》1984,25(1):1-26

The Edgecumbe volcanics, which range from basalt through rhyodacite,have Sr contents between 125 and 370 p.p.m., Rb contents of1 to 70 p.p.m., Ba ranging from 50–550 p.p.m. and initial⁸⁷Sr/⁸⁶Sr ratios between 0.70291 and 0.70404. No simple correlationexists between these components and silica. The highest ⁸⁷Sr/⁸⁶Srvalues occur in a group of intermediate lavas (55–60 wt.per cent SiO₂) while the rhyodacites have initial ratios between0.7035 and 0.7038. With increasing silica, Sr increases to amaximum in the andesites and then steadily decreases; Ba andRb increase over the same compositional range. The highest ⁸⁷Sr/⁸⁶Srlavas have major and trace element concentrations which departfrom trends defined by most of the lavas. The variation in strontiumisotopic compositions suggests interaction between parentalbasaltic magma and crustal material. Attempts to model the assimilationprocess using fixed end-member assimilation and assimilation-fractionalcrystallization models have failed to produce the observed chemicaltrends. Because the parental basaltic liquid underwent littlefractionation, the variability in hybrid lavas is attributedto variation in contaminant composition. Initial melts werelow in CaO, A1₂O₃, MgO and Sr and enriched in SiO₂. K₂O, Na₂O,Rb and Ba. As melting progressed, melts became enriched in themore refractory components. Because hybrid strontium isotopiccomposition is a function of Sr concentration as well as isotopiccompositions, the Sr content of the assimilant strongly influencesresultant isotopic systematics. The development of the assimilantssuggests plagioclase was a residual phase during early melting.This model of crustal assimilation represents one end-memberin the spectrum of processes responsible for the generationof continental volcanic suites.  相似文献   

Comparative phylogeography and population genetic structure of three widespread mollusc species in the Mediterranean and near Atlantic          下载免费PDF全文

Rosa Fernández  Sarah Lemer  Erin McIntyre  Gonzalo Giribet 《Marine Ecology》2015,36(3):701-715

Although several studies have evaluated the genetic structure and phylogeographic patterns in many species of marine invertebrates, a general model that applies to all of them remains elusive. For example, some species present an admixture of populations with high gene flow, whereas others exhibit more complex patterns characterized by small‐scale unstructured genetic heterogeneity, even at a local scale. These differences are thought to be due to clear biological aspects such as direct versus indirect development, or the presence of lecithotrophic versus planktotrophic larvae, but few studies compare animals with similar distributions and life modes. Here, we explore the phylogeographic and genetic structure patterns in two chiton (Chiton olivaceus and Lepidopleurus cajetanus) and one abalone (Haliotis tuberculata) species co‐occurring in the same habitat. Samples were obtained from shallow rocky bottoms along the Iberian Peninsula (Atlantic and Mediterranean coasts), Italy, Croatia and Greece, and the mitochondrial markers COI and 16S rRNA gene were sequenced. Our data show evidence of admixture and population expansion in C. olivaceus and H. tuberculata, whereas L. cajetanus exhibited a ‘chaotic patchiness’ pattern defined by a high genetic variability with locality‐exclusive haplotypes, high genetic divergence, and a lack of geographic structure. Shared haplotypes were sampled in both coasts of Iberia (for H. tuberculata) and in the Western and Eastern Mediterranean (for C. olivaceus), potentially indicating high dispersal ability and a recent expansion. The processes underlying the fine‐scale structuring in L. cajetanus remain a mystery. These results are especially interesting because the reproductive mode of the two chitons is similar but differs from that of the abalone, with a veliger larva, while instead the genetic structure of C. olivaceus and H. tuberculata are similar, thus contrasting with predictions based on the life history of the three molluscs and showing that the genetic patterns of marine species may be shaped by many factors, including historical ones.  相似文献   

Fishing‐induced evolution of growth: concepts,mechanisms and the empirical evidence     

Katja Enberg  Christian Jørgensen  Erin S. Dunlop  Øystein Varpe  David S. Boukal  Loïc Baulier  Sigrunn Eliassen  Mikko Heino 《Marine Ecology》2012,33(1):1-25

The interest in fishing‐induced life‐history evolution has been growing in the last decade, in part because of the increasing number of studies suggesting evolutionary changes in life‐history traits, and the potential ecological and economic consequences these changes may have. Among the traits that could evolve in response to fishing, growth has lately received attention. However, critical reading of the literature on growth evolution in fish reveals conceptual confusion about the nature of ‘growth’ itself as an evolving trait, and about the different ways fishing can affect growth and size‐at‐age of fish, both on ecological and on evolutionary time‐scales. It is important to separate the advantages of being big and the costs of growing to a large size, particularly when studying life‐history evolution. In this review, we explore the selection pressures on growth and the resultant evolution of growth from a mechanistic viewpoint. We define important concepts and outline the processes that must be accounted for before observed phenotypic changes can be ascribed to growth evolution. When listing traits that could be traded‐off with growth rate, we group the mechanisms into those affecting resource acquisition and those governing resource allocation. We summarize potential effects of fishing on traits related to growth and discuss methods for detecting evolution of growth. We also challenge the prevailing expectation that fishing‐induced evolution should always lead to slower growth.  相似文献   

Development and testing of a physically based,three-dimensional model of surface and subsurface hydrology   总被引：2，自引：0，他引：2  

Marco Bittelli  Fausto Tomei  Alberto Pistocchi  Markus Flury  Jan Boll  Erin S. Brooks  Gabriele Antolini 《Advances in water resources》2010

We present a numerical, catchment-scale model that solves flow equations of surface and subsurface flow in a three-dimensional domain. Surface flow is described by the two-dimensional parabolic approximation of the St. Venant equation, using Manning’s equation of motion; subsurface flow is described by the three-dimensional Richards’ equation for the unsaturated zone and by three-dimensional Darcy’s law for the saturated zone, using an integrated finite difference formulation. The hydrological component is a dynamic link library implemented within a comprehensive model which simulates surface energy, radiation budget, snow melt, potential evapotranspiration, plant development and plant water uptake. We tested the model by comparing distributed and integrated three-dimensional simulated and observed perched water depth (PWD), stream flow data, and soil water contents for a small catchment. Additional tests were performed for the snow melting algorithm as well as the different hydrological processes involved. The model successfully described the water balance and its components as evidenced by good agreement between measured and modelled data.  相似文献   

Interaction of wind and cold-season hydrologic processes on erosion from complex topography following wildfire in sagebrush steppe     

Samantha P. Vega  C. Jason Williams  Erin S. Brooks  Frederick B. Pierson  Eva K. Strand  Peter R. Robichaud  Robert E. Brown  Mark S. Seyfried  Kathleen A. Lohse  Kayla Glossner  Jennifer L. Pierce  Clay Roehner 《地球表面变化过程与地形》2020,45(4):841-861

Wildfire is a natural component of sagebrush (Artemisia spp.) steppe rangelands that induces temporal shifts in plant community physiognomy, ground surface conditions, and erosion rates. Fire alteration of the vegetation structure and ground cover in these ecosystems commonly amplifies soil losses by wind- and water-driven erosion. Much of the fire-related erosion research for sagebrush steppe has focused on either erosion by wind over gentle terrain or water-driven erosion under high-intensity rainfall on complex topography. However, many sagebrush rangelands are geographically positioned in snow-dominated uplands with complex terrain in which runoff and sediment delivery occur primarily in winter months associated with cold-season hydrology. Current understanding is limited regarding fire effects on the interaction of wind- and cold-season hydrologic-driven erosion processes for these ecosystems. In this study, we evaluated fire impacts on vegetation, ground cover, soils, and erosion across spatial scales at a snow-dominated mountainous sagebrush site over a 2-year period post-fire. Vegetation, ground cover, and soil conditions were assessed at various plot scales (8 m² to 3.42 ha) through standard field measures. Erosion was quantified through a network of silt fences (n = 24) spanning hillslope and side channel or swale areas, ranging from 0.003 to 3.42 ha in size. Sediment delivery at the watershed scale (129 ha) was assessed by suspended sediment samples of streamflow through a drop-box v-notch weir. Wildfire consumed nearly all above-ground live vegetation at the site and resulted in more than 60% bare ground (bare soil, ash, and rock) in the immediate post-fire period. Widespread wind-driven sediment loading of swales was observed over the first month post-fire and extensive snow drifts were formed in these swales each winter season during the study. In the first year, sediment yields from north- and south-facing aspects averaged 0.99–8.62 t ha⁻¹ at the short-hillslope scale (~0.004 ha), 0.02–1.65 t ha⁻¹ at the long-hillslope scale (0.02–0.46 ha), and 0.24–0.71 t ha⁻¹ at the swale scale (0.65–3.42 ha), and watershed scale sediment yield was 2.47 t ha⁻¹. By the second year post fire, foliar cover exceeded 120% across the site, but bare ground remained more than 60%. Sediment yield in the second year was greatly reduced across short- to long-hillslope scales (0.02–0.04 t ha⁻¹), but was similar to first-year measures for swale plots (0.24–0.61 t ha⁻¹) and at the watershed scale (3.05 t ha⁻¹). Nearly all the sediment collected across all spatial scales was delivered during runoff events associated with cold-season hydrologic processes, including rain-on-snow, rain-on-frozen soils, and snowmelt runoff. Approximately 85–99% of annual sediment collected across all silt fence plots each year was from swales. The high levels of sediment delivered across hillslope to watershed scales in this study are attributed to observed preferential loading of fine sediments into swale channels by aeolian processes in the immediate post-fire period and subsequent flushing of these sediments by runoff from cold-season hydrologic processes. Our results suggest that the interaction of aeolian and cold-season hydrologic-driven erosion processes is an important component for consideration in post-fire erosion assessment and prediction and can have profound implications for soil loss from these ecosystems. © 2019 John Wiley & Sons, Ltd.  相似文献   

Observations of bedload transport in a gravel bed river during high flow using fiber‐optic DTS methods          下载免费PDF全文

Erin N. Bray  Thomas Dunne 《地球表面变化过程与地形》2017,42(13):2184-2198

The question: ‘how does a streambed change over a minor flood?’ does not have a clear answer due to lack of measurement methods during high flows. We investigate bedload transport and disentrainment during a 1.5‐year flood by linking field measurements using fiber optic distributed temperature sensing (DTS) cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near‐bed pore‐water temperature. The method facilitates the study of gravel transport by using near‐bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation. The observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low Shields Number for the median particle size, and were re‐deposited on the lee side of the bar at rates that varied over time during a constant flow. Approximately 1–6% of the bed was predicted to be mobile during the 1.5‐year flood, indicating that large inactive regions of the bed, particularly between riffles, persist between years despite field observations of narrow zones of local transport and bar growth on the order ~3–5 times the median particle size. In contrast, during a seven‐year flood approximately 8–55% of the bed was predicted to become mobile, indicating that the continuous along‐stream mobility required to mobilize coarse gravel through long pools and downstream to the next riffle is infrequent. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Thermal Imagery of Groundwater Seeps: Possibilities and Limitations          下载免费PDF全文

Erin Mundy  Tom Gleeson  Mark Roberts  Michel Baraer  Jeffrey M. McKenzie 《Ground water》2017,55(2):160-170

Quantifying groundwater flow at seepage faces is crucial because seepage faces influence the hydroecology and water budgets of watersheds, lakes, rivers and oceans, and because measuring groundwater fluxes directly in aquifers is extremely difficult. Seepage faces provide a direct and measurable groundwater flux but there is no existing method to quantitatively image groundwater processes at this boundary. Our objective is to determine the possibilities and limitations of thermal imagery in quantifying groundwater discharge from discrete seeps. We developed a conceptual model of temperature below discrete seeps, observed 20 seeps spectacularly exposed in three dimensions at an unused limestone quarry and conducted field experiments to examine the role of diurnal changes and rock face heterogeneity on thermal imagery. The conceptual model suggests that convective air‐water heat exchange driven by temperature differences is the dominant heat transfer mechanism. Thermal imagery is effective at locating and characterizing the flux of groundwater seeps. Areas of active groundwater flow and ice growth can be identified from thermal images in the winter, and seepage rates can be differentiated in the summer. However, the application of thermal imagery is limited by diverse factors including technical issues of image acquisition, diurnal changes in radiation and temperature, and rock face heterogeneity. Groundwater discharge rates could not be directly quantified from thermal imagery using our observations but our conceptual model and experiments suggest that thermal imagery could quantify groundwater discharge when there are large temperature differences, simple cliff faces, non‐freezing conditions, and no solar radiation.  相似文献