Absence of seasonal patterns in MBT-CBT indices in mid-latitude soils   总被引：1，自引：0，他引：1  

Johan W.H. Weijers  Beth Bernhardt  Francien Peterse  Josef P. Werne  Jennifer A.J. Dungait  Jaap S. Sinninghe Damsté 《Geochimica et cosmochimica acta》2011,75(11):3179-3190

The degree of methylation and cyclization of bacteria-derived branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in soils depends on temperature and soil pH. Expressed in the methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT), these relationships are used to reconstruct past annual mean air temperature (MAT) based on the distribution of branched GDGTs in ancient sediments; the MBT-CBT proxy. Although it was shown that the best correlation of this proxy is with annual MAT, it remains unknown whether a seasonal bias in temperature reconstructions could occur, such as towards a seasonal period of ‘optimal growth’ of the, as yet, unidentified soil bacteria which produce branched GDGTs. To investigate this possibility, soils were sampled from eight different plots in the USA (Minnesota and Ohio), The Netherlands (Texel) and the UK (Devon) in time series over 1 year and analyzed for their branched GDGT content. Further analyses of the branched GDGTs present as core lipids (CLs; the presumed fossil pool) and intact polar lipids (IPLs; the presumed extant pool) were undertaken for two of the investigated soil plots. The amount of IPL-derived branched GDGTs is low relative to the branched GDGT CLs, i.e. only 6-9% of the total branched GDGT pool. In all soils, no clear change was apparent in the distribution of branched GDGT lipids (either core or IPL-derived) with seasonal temperature change; the MBT-CBT temperature proxy gave similar temperature estimates year-round, which generally matched the mean annual soil temperature. In addition to a lack of coherent changes in relative distributions, concentrations of the branched GDGTs did not show clear changes over the seasons. For IPL-derived GDGTs these results suggest that their turnover time in soils is in the order of 1 year or more. Thus, our study does not provide evidence for seasonal effects on the distribution of branched GDGTs in soils, at least at mid-latitudes, and therefore, no direct evidence for a bias of MBT-CBT reconstructed temperatures towards a certain season of optimal growth of the source bacteria. If, however, there is a slight seasonal preference of branched GDGT production, which can easily be obscured by natural variability due to the heterogeneity of soils, then a seasonal bias may potentially still develop over time due to the long turnover time of branched GDGTs.  相似文献   

Differential kinetics and temperature dependence of abiotic and biotic processes controlling the environmental fate of TNT in simulated marine systems     

Chappell MA  Porter BE  Price CL  Pettway BA  George RD 《Marine pollution bulletin》2011,62(8):1736-1743

This work seeks to understand how the balance of abiotic and biotic kinetic processes in sediments control the residual concentration of TNT in marine systems after release from ocean-dumped source. Kinetics of TNT disappearance were followed using marine sediments at different temperatures and under both biotic and presumably abiotic conditions (through sodium azide addition). Sediments exhibiting the highest rate of TNT disappearance under biotic conditions also exhibited the highest sorption affinity for TNT under abiotic conditions. Significant temperature dependence in the abiotic processes was observed in the diffusion coefficient of TNT and not sediment sorption affinity. At higher temperature, kinetics of biotic processes outpaced abiotic processes, but at low temperature, kinetics of abiotic processes were much more significant. We concluded that the differential influence of temperature on the kinetics of abiotic and biotic processes could provide distinguishing predictions for the potential residual concentration of TNT contamination in marine-sediment systems.  相似文献   

Middle to late Holocene initiation of the annual flood pulse in Tonle Sap Lake,Cambodia     

Mary Beth Day  David A. Hodell  Mark Brenner  Jason H. Curtis  George D. Kamenov  Thomas P. Guilderson  Larry C. Peterson  William F. Kenney  Alan L. Kolata 《Journal of Paleolimnology》2011,45(1):85-99

Tonle Sap Lake, Cambodia, possesses one of the most productive inland fisheries in the world and is a vital natural resource for the country. The lake is connected to the Mekong River via the Tonle Sap River. Flow in the Tonle Sap River reverses seasonally, with water exiting the lake in the dry season and entering the lake during the summer monsoon. This flood pulse drives the lake’s biological productivity. We used Sr, Nd, and Pb isotopes and elemental concentrations in lake sediment cores to track changes in the provenance of deposits in Tonle Sap Lake. We sought to determine when the lake first began to receive water and sediment input via the Mekong River, which initiated flood pulse processes. The transition from a non-pulsing lake to the Mekong-connected system is marked by shifts to values of ⁸⁷Sr/⁸⁶Sr, ε_Nd, and ²⁰⁷Pb/²⁰⁴Pb that are characteristic of Mekong River sediments. In addition, magnetic susceptibility increased and sediment elemental composition changed. Elemental (P) measures point to enhanced phosphorus loading and C/N and isotope ratios of bulk organic matter indicate a shift to greater relative contribution of organic material from aquatic versus terrestrial environments, coinciding with the initiation of flood pulse processes. On the basis of radiocarbon dating in two cores, we estimate the initiation of the annual flood pulse occurred between ~4,450 and 3,910 cal year BP.  相似文献   

Effects of an Acute Hypoxic Event on Microplankton Community Structure in a Coastal Harbor of Southern California     

Beth A. Stauffer  Astrid Schnetzer  Alyssa G. Gellene  Carl Oberg  Gaurav S. Sukhatme  David A. Caron 《Estuaries and Coasts》2013,36(1):135-148

Fish mortality and hypoxic events occur in many coastal and inland systems and may result from natural or anthropogenically mediated processes. The effects of consequent changes in water biogeochemistry have been investigated for communities of benthic invertebrates and pelagic metazoans. The responses of micro-plankton assemblages, however, have remained largely unstudied. The northern basin of King Harbor, a small embayment within Santa Monica Bay, CA, USA, suffered a massive fish kill in March 2011 as a consequence of acute hypoxia. Dissolved oxygen concentrations < 0.1 ml?l^?1 were measured in the northern basin of the harbor for several days following the mortality event, and a strong spatial gradient of oxygen was observed from the northern basin to waters outside the harbor. The microplankton community within King Harbor differed significantly from a diatom-dominated community present in neighboring Santa Monica Bay. The latter region appeared unaffected by physicochemical changes, induced by the fish kill, that were observed within the harbor. A trophic shift was observed throughout King Harbor from a photoautotrophic-dominated assemblage to one of heterotrophic forms, with relative abundances of bacterivorous ciliates increasing by more than 80 % in the most impacted part of the harbor. Significant changes in community structure were observed together with dramatically reduced photosynthetic yield of the remaining phytoplankton, indicating severe physiological stress during the extreme hypoxia.  相似文献   

CAD-DRASTIC: chloride application density combined with DRASTIC for assessing groundwater vulnerability to road salt application     

Mansour Salek  Jana Levison  Beth Parker  Bahram Gharabaghi 《Hydrogeology Journal》2018,26(7):2379-2393

Road salt is pervasively used throughout Canada and in other cold regions during winter. For cities relying exclusively on groundwater, it is important to plan and minimize the application of salt accordingly to mitigate the adverse effects of high chloride concentrations in water supply aquifers. The use of geospatial data (road network, land use, Quaternary and bedrock geology, average annual recharge, water-table depth, soil distribution, topography) in the DRASTIC methodology provides an efficient way of distinguishing salt-vulnerable areas associated with groundwater supply wells, to aid in the implementation of appropriate management practices for road salt application in urban areas. This research presents a GIS-based methodology to accomplish a vulnerability analysis for 12 municipal water supply wells within the City of Guelph, Ontario, Canada. The chloride application density (CAD) value at each supply well is calculated and related to the measured groundwater chloride concentrations and further combined with soil media and aquifer vadose- and saturated-zone properties used in DRASTIC. This combined approach, CAD-DRASTIC, is more accurate than existing groundwater vulnerability mapping methods and can be used by municipalities and other water managers to further improve groundwater protection related to road salt application.  相似文献   

How the capacity of bedrock to collect dust and produce soil affects phosphorus bioavailability in the northern Appalachian Mountains of Pennsylvania     

Virginia Marcon  Beth Hoagland  Xin Gu  Wenjing Liu  Jason Kaye  Roman A. DiBiase  Susan L. Brantley 《地球表面变化过程与地形》2021,46(14):2807-2823

More above-ground biomass (kg m⁻²) grows in the northern Appalachian Mountains (USA) in forests on shale than on sandstone at all landscape positions other than ridgetops. This has been tentatively attributed to physical (rather than chemical) attributes of the substrates, such as elevation, particle size, and water capacity. However, shales have generally similar phosphorus (P) concentrations to sandstones and, in the Valley and Ridge province, they erode more quickly. This led us to hypothesize that faster replenishment of the lithogenic nutrient P in shale soils through erosion + soil production could instead control the differences in biomass. To test this, soils and foliage from 10 sites on shales and sandstones in the northern Appalachians from roughly the same elevation and aspect were analysed. We discovered that, when controlling for location, concentrations of bioavailable P in soils and P in foliage were higher and P resorbed from senescing red oak leaves was lower on slower-eroding sandstone than on faster-eroding shale. Lower resorption generally can be attributed to lower P limitation for trees. Further investigation of weathering and erosion on one of the sandstone–shale pairs within a larger, paired watershed study revealed that the differences in P concentrations in biomass and foliage between lithologies likely developed because sandstones act as ‘collectors’ that trap nutrients from residual and exogenous sources, while shales erode quickly and thus promote production of soil from bedrock that releases P to ecosystems. We concluded that the combined effects of differential rates of dust collection and erosion results in roughly equal biomass growing on sandstone and shale ridgetops. This work emphasizes the balance between a landscape's capacity to collect dust versus produce soil in controlling bioavailability of nutrients.  相似文献   

Asteroid (101955) 1999 RQ36: Spectroscopy from 0.4 to 2.4 μm and meteorite analogs     

Beth Ellen Clark  Richard P. Binzel  Ellen S. Howell  Edward A. Cloutis  Maureen Ockert-Bell  Phil Christensen  Maria Antonietta Barucci  Francesca DeMeo  Dante S. Lauretta  Harold Connolly Jr.  Alicia Soderberg  Carl Hergenrother  Lucy Lim  Josh Emery  Michael Mueller 《Icarus》2011,216(2):462-475

We present reflectance spectra from 0.4 to 2.4 μm of Asteroid (101955) 1999 RQ36, the target of the OSIRIS-REx spacecraft mission. The visible spectral data were obtained at the McDonald Observatory 2.1-m telescope with the ES2 spectrograph. The infrared spectral data were obtained at the NASA Infrared Telescope Facility using the SpeX instrument. The average visible spectrum is combined with the average near-infrared wavelength spectrum to form a composite spectrum. We use three methods to constrain the compositional information in the composite spectrum of Asteroid (101955) 1999 RQ36 (hereafter RQ36). First, we perform a least-squares search for meteorite spectral analogs using 15,000 spectra from the RELAB database. Three most likely meteorite analogs are proposed based on the least-squares search. Next, six spectral parameters are measured for RQ36 and their values are compared with the ranges in parameter values of the carbonaceous chondrite meteorite classes. A most likely meteorite analog group is proposed based on the depth of overlap in parameter values. The results of the least-squares search and the parametric comparisons point to CIs and/or CMs as the most likely meteorite analogs for RQ36, and COs and CHs as the least likely. RQ36 has a spectrally “blue” continuum slope that is also observed in carbonaceous chondrites containing magnetite. We speculate that RQ36 is composed of a “CM1”-like material. Finally, we compare RQ36 to other B-type asteroids measured by Clark et al. (Clark, B.E. et al. [2010]. J. Geophys. Res. 115, E06005). The results of this comparison are inconclusive. RQ36 is comparable to Themis spectral properties in terms of its albedo, visible spectrum, and near-infrared spectrum from 1.1 to 1.45 μm. However, RQ36 is more similar to Pallas in terms of its near-infrared spectrum from 1.6 to 2.3 μm. Thus it is possible that B-type asteroids form a spectral continuum and that RQ36 is a transitional object, spectrally intermediate between the two end-members. This is particularly interesting because Asteroid 24 Themis was recently discovered to have H₂O ice on the surface (Rivkin, A., Emery, J. [2010]. Nature 464, 1322–1323; Campins, H. et al. [2010a]. Nature 464, 1320–1321).  相似文献   

Radar observations of Asteroids 64 Angelina and 69 Hesperia     

Michael K. Shepard  Alan W. Harris  Beth Ellen Clark  Michael C. Nolan  Christopher Magri  Lance A.M. Benner 《Icarus》2011,215(2):547-551

We report new radar observations of E-class Asteroid 64 Angelina and M-class Asteroid 69 Hesperia obtained with the Arecibo Observatory S-band radar (2480 MHz, 12.6 cm). Our measurements of Angelina’s radar bandwidth are consistent with reported diameters and poles. We find Angelina’s circular polarization ratio to be 0.8 ± 0.1, tied with 434 Hungaria for the highest value observed for main-belt asteroids and consistent with the high values observed for all E-class asteroids (Benner, L.A.M., Ostro, S.J., Magri, C., Nolan, M.C., Howell, E.S., Giorgini, J.D., Jurgens, R.F., Margot, J.L., Taylor, P.A., Busch, M.W., Shepard, M.K. [2008]. Icarus 198, 294-304; Shepard, M.K., Kressler, K.M., Clark, B.E., Ockert-Bell, M.E., Nolan, M.C., Howell, E.S., Magri, C., Giorgini, J.D., Benner, L.A.M., Ostro, S.J. [2008b]. Icarus 195, 220-225). Our radar observations of 69 Hesperia, combined with lightcurve-based shape models, lead to a diameter estimate, D_eff = 110 ± 15 km, approximately 20% smaller than the reported IRAS value. We estimate Hesperia to have a radar albedo of , consistent with a high-metal content. We therefore add 69 Hesperia to the Mm-class (high metal M) (Shepard, M.K., Clark, B.E., Ockert-Bell, M., Nolan, M.C., Howell, E.S., Magri, C., Giorgini, J.D., Benner, L.A.M., Ostro, S.J., Harris, A.W., Warner, B.D., Stephens, R.D., Mueller, M. [2010]. Icarus 208, 221-237), bringing the total number of Mm-class objects to eight; this is 40% of all M-class asteroids observed by radar to date.  相似文献   

Book reviews     

H. -G. Kahle  M. Waldmeier 《Pure and Applied Geophysics》1976,114(5):877-878

  相似文献   

Bedload-to-suspended load ratio and rapid bedrock incision from Himalayan landslide-dam lake record   总被引：3，自引：0，他引：3  

Beth Pratt-Sitaula  Michelle Garde  Douglas W. Burbank  Arjun Heimsath 《Quaternary Research》2007,68(1):111-120

About 5400 cal yr BP, a large landslide formed a > 400-m-tall dam in the upper Marsyandi River, central Nepal. The resulting lacustrine and deltaic deposits stretched > 7 km upstream, reaching a thickness of 120 m. ¹⁴C dating of 7 wood fragments reveals that the aggradation and subsequent incision occurred remarkably quickly (∼ 500 yr). Reconstructed volumes of lacustrine (∼ 0.16 km³) and deltaic (∼ 0.09 km³) deposits indicate a bedload-to-suspended load ratio of 1:2, considerably higher than the ≤ 1:10 that is commonly assumed. At the downstream end of the landslide dam, the river incised a new channel through ≥ 70 m of Greater Himalayan gneiss, requiring a minimum bedrock incision rate of 13 mm/yr over last 5400 yr. The majority of incision presumably occurred over a fraction of this time, suggesting much higher rates. The high bedload ratio from such an energetic mountain river is a particularly significant addition to our knowledge of sediment flux in orogenic environments.  相似文献