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1.
Microbial mineralization and assimilation of black carbon: Dependency on degree of thermal alteration 总被引:4,自引:0,他引:4
Black carbon is degraded slowly in the environment and its formation can therefore be an effective sink for atmospheric CO2. This study examined whether charcoal is assimilated by microorganisms or not and estimated the rate of mineralization depending on the degree of thermal alteration of the black carbon. Charcoals were produced at three different temperatures from homogeneously 14C labelled plant material and incubated in soil, and 14C in the evolved CO2 and the microbial biomass was measured. Unlike parallel plant samples, CO2 evolution from the charcoals showed no lag phase, but a period of faster CO2 evolution for the first 5–8 days followed by a period of slow evolution. The mineralization of charcoal appeared to decrease with increasing temperature at which it was produced. This was also the case after the initial period of fast CO2 evolution. With the techniques used, it was not possible to observe any microbial assimilation of charcoal, either because it did not occur, or because the methods used were not sufficiently sensitive. However, the lack of a lag phase in the CO2 evolution from the charcoals is in line with earlier evidence that charcoal is initially oxidized at the surfaces by abiotic processes. 相似文献
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Hydrodynamics coefficients for vertical circular cylinders at finite water depth are obtained and presented for different depth to radius and draft to radius ratios. A summary of equations for computer application is presented. Limiting values for heave added mass for zero frequency are discussed. A matching technique is used to satisfy the continuity of pressure and normal velocities. 相似文献
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The saltmarsh sharp-tailed sparrow (Ammodramus caudacutus) and the morphologically similar seaside sparrow (Ammodramus maritimus) occur together in Atlantic coast salt marshes. Over 2 yr we examined food exploitation patterns to gain an understanding
of how these species coexist and to characterize the trophic conditions that allow the maintenance of different mating systems
within the same habitat. In the promiscuous saltmarsh sharp-tailed sparrow, only females feed the young, while the young of
the socially monogramous seaside sparrow are fed by both parents. To determine dietary patterns, we used a nonlethal method
(throat constriction) to obtain food samples from nestlings. Resource states were determined by sweep-netting the vegetation
and by taking cores from the marsh surface. Based on volume, the same 4 prey groups (flies, amphipods, grasshoppers, moths)
composed > 80% of each species diet. The main food of both sparrows was adult and juvenile (larval and pupal) soldier flies
(Stratiomyidae:Odontomyia microstomata). Measures of dietary overlap, based on resource states, indicated that nestling diets did not differ between species on
a seasonal basis or over 2-wk intervals. As the season progressed, each species tracked in parallel changes in resource abundance.
Diets did not diverge from what was expected if food was exploited randomly; diets frequently overlapped significantly more
than expected. Interspecific resource-use patterns were congruent over 2 yr. Based on the results of this study, and on an
evaluation of hypotheses based on life history information from previously published work, we conclude that food usually is
not limiting for these sparrows and that resource abundance has fostered behavioral and dietary opportunism. 相似文献
4.
A record of accelerated erosion in the recent sediments of Blelham Tarn in the English Lake district 总被引:1,自引:0,他引:1
K. D. van der Post F. Oldfield E. Y. Haworth P. R. J. Crooks P. G. Appleby 《Journal of Paleolimnology》1997,18(2):103-120
Two frozen cores from Blelham Tarn were subsampled and measured using mineral magnetic, loss-on-ignition (LOI), radiometric, granulometric and diatom analyses. A detailed chronology was established using varves, radioisotopes and diatoms. This has enabled an accurately dated reconstruction of sedimentation over the past forty years. Despite a large increase in lake productivity, evidence suggests that the observed exponential increase in sedimentation rates can be attributed to erosion within the catchment. The predominant sediment source has been identified as surface soil. A comparison between the trend of accelerated sedimentation and the record of increased sheep stocking density for the area within which the most of the catchment lies, as well as observations of contemporary surface processes within the catchment, both suggest that much of the recent erosion is a direct response to increased pressure from sheep grazing. 相似文献
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Coastal lagoons and beach ridges as complementary sedimentary archives for the reconstruction of Holocene relative sea‐level changes 下载免费PDF全文
Lasse Sander Mikkel U. Hede Mikkel Fruergaard Lars Nielsen Lars B. Clemmensen Aart Kroon Peter N. Johannessen Lars H. Nielsen Morten Pejrup 《地学学报》2016,28(1):43-49
Coastal lagoons and beach ridges are genetically independent, though non‐continuous, sedimentary archives. We here combine the results from two recently published studies in order to produce an 8000‐year‐long record of Holocene relative sea‐level changes on the island of Samsø, southern Kattegat, Denmark. The reconstruction of the initial mid‐Holocene sea‐level rise is based on the sedimentary infill from topography‐confined coastal lagoons (Sander et al., Boreas, 2015b). Sea‐level index points over the mid‐ to late Holocene period of sea‐level stability and fall are retrieved from the internal structures of a wide beach‐ridge system (Hede et al., The Holocene, 2015). Data from sediment coring, georadar and absolute dating are thus combined in an inter‐disciplinary approach that is highly reproducible in micro‐tidal environments characterised by high sediment supply. We show here that the commonly proximate occurrence of coastal lagoons and beach ridges allows us to produce seamless time series of relative sea‐level changes from field sites in SW Scandinavia and in similar coastal environments. 相似文献
8.
The customary representation of climate using sample moments is generally biased due to the noticeably nonstationary behaviour of many climate series. In this study, we introduce a moment-free climate representation based on a statistical model fitted to a long-term daily air temperature anomaly series. This model allows us to separate the climate and weather scale variability in the series. As a result, the climate scale can be characterized using the mean annual cycle of series and local air temperature tolerance, where the latter is computed using the fitted model. The representation of weather scale variability is specified using the frequency and the range of outliers based on the tolerance. The scheme is illustrated using five long-term air temperature records observed by different European meteorological stations. 相似文献
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Latest thinking on the Malpasset accident 总被引:2,自引:0,他引:2