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281.
Sulfur has played a central role in the acidification of many lakes in Scandinavia and other regions. As part of the research
into sulfur cycling, numerous studies have analyzed the sediment record in order to develop insights into past in-lake cycling
of sulfur, particularly in the context of reconstructing past deposition rates. Although many of these studies have shown
that it is not easy to interpret the sediment record in terms of past sulfur deposition rates, analyses of sulfur in sediment
still provide valuable information on the response of lakes to anthropogenic sulfur deposition. Here, we have analyzed sulfur
in top and bottom samples from short surface cores (25–35 cm, representing ≥250 years) as well as bulk cores from ∼110 lakes
located throughout Sweden, which were collected during 1986, as well as in more-detailed profiles from six lakes. The lakes
with the highest surface sediment concentrations (9–24 mg S g−1 dry mass) and the highest calculated inventories of ‘excess’ sulfur (20–180 g S m−2) are found in southern Sweden and around one industrial area along the northeastern coast where sulfur deposition rates and
lake-water concentrations have been highest. For many lakes in the central and northern inland region it is common that the
sediment cores exhibit either no enrichment or even a decline in sulfur concentrations in near-surface sediments, which we
suggest was the pre-pollution norm for lakes. Although interpreting sulfur sediment profiles is problematic for reconstructing
deposition, a more-comprehensive spatial sampling approach shows that there is a good geographic agreement between sulfur
deposition, lake-water chemistry and sediment sulfur accumulation. 相似文献
282.
Fausto Cupola Maria Giovanna Tanda Andrea Zanini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(1):169-182
Inverse methods can be used to recover the pollutant source location from concentration data. In this paper, the relative effectiveness of two proposed methods, simultaneous release function and source location identification (SRSI) and backward probability model based on adjoint state method (BPM-ASM) are evaluated using real data collected by using experimental equipment. The device is a sandbox that reproduces an unconfined aquifer in which all the variables are controlled. A numerical model was calibrated using experimental observations. The SRSI is a stochastic procedure which finds the source location and the release history by means of a Bayesian geostatistical approach (GA). The BPM-ASM provides the backward probability location of the pollutant detected at a monitoring point by means of a reverse transport simulation. The results show that both methods perform well. While the simultaneous release function and SRSI method requires a preliminary delineation of a probable source area and some weak hypotheses about the statistical structure of the unknown release function, the backward probability model requires some hypothesis about the contaminant release time. A case study was performed using two observation points only, and despite the scarcity of data, both methodologies were able to accurately reconstruct the true source location. The GA has the advantage to recover the release history function too, whilst the backward probability model works well with fewer data. If there are many observations, both methodologies may be computationally heavy. A transfer function approach has been adopted for the numerical definition of the sensitivity matrix in the SRSI method. The reliability of the experimental equipment was tested in previous laboratory works, conducted under several different conditions. 相似文献
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285.
Zolotarev Andrey A. Zhitova Elena S. Gabdrakhmanova Faina A. Krzhizhanovskaya Maria G. Zolotarev Anatoly A. Krivovichev Sergey V. 《Mineralogy and Petrology》2017,111(6):843-851
Mineralogy and Petrology - The crystal structure of batisite, Na2BaTi2 (Si4O12)O2, from the Inagli massif (Aldan, Yakutia, Russia) was refined to R 1 = 0.032 for 1449 unique... 相似文献
286.
Multidisciplinary inferences on a newly recognized active east‐dipping extensional system in Central Italy 下载免费PDF全文
Giusy Lavecchia Guido Maria Adinolfi Rita de Nardis Federica Ferrarini Daniele Cirillo Francesco Brozzetti Raffaella De Matteis Gaetano Festa Aldo Zollo 《地学学报》2017,29(1):77-89
We use a multidisciplinary approach to gather preliminary evidence for a Quaternary east‐dipping extensional detachment in Central Italy. This structure crops out in the Sabini‐Eastern Simbruini (SES) and would be hidden at mid‐crustal depths beneath the L'Aquila 2009 (Mw6.3) epicentral area. The SES geometry is reconstructed through geological mapping, structural analysis and seismic line interpretation. The geometry of the mid‐crustal segment, referred to as the Ocre Segment (OS), is interpreted through seismological analyses of the largest aftershock (Mw5.4) of the L'Aquila 2009 sequence. The kinematic compatibility between the SES and the OS under a common SW–NE tensional field is tested through stress inversion of both geological and seismological data. The reliability of OS activation is tested through slip tendency analysis. Like other Italian cases, the SES and the OS are preliminarily interpreted as expressions at different depths of the same unknown east‐dipping extensional detachment, characterized by a ramp–flat–ramp geometry. 相似文献
287.
Spatial distribution of physical and chemical variables and macroinvertebrate composition, structure and functional aspects were investigated in five microhabitats available (Ranunculus acquatilis+Ranunculus sardous, Spirogyra sp., Juncus effusus, and unvegetated littoral sediments and central sediments) in a temporary pond near Rome during spring 2004. The central sediments were found to differ greatly from the other substrates. They were characterized by higher nutrient contents (total P, total N), organic matter and organic C, and silt and clay in the sediments, and lower dissolved oxygen content and lower pH in the water. Species richness and densities of total macrofauna showed the lowest values in central sediments and the highest ones in submerged macrophytes (Ranunculus spp.) and emergent vegetation (Juncus effusus). Oligochaeta Tubificidae, some Nematoda (Dorylaimus spp.), and Chironomidae Tanypodinae (Procladius sp. and Psectrotanypus varius) and Chironominae (Chironomus plumosus group) characterized the central sediments, whereas Ephemeroptera and most of the Odonata and Coleoptera species were commonly found in submerged macrophyte beds. Some species of Coleoptera and Hemiptera (Hygrobia hermanni, Helochares lividus, Berosus signaticollis and Gerris maculatus) were mainly found in the algal substratum, and some Nematoda species (Tobrilus spp. and Aporcelaimellus obtusicaudatus), Oligochaeta Enchytraeidae, young larvae of Sympetrum and Diptera Ceratopogonidae in littoral sediments. Juncus effusus appeared to be mainly colonized by Chironomidae Orthocladiinae (Psectrocladius sordidellus group and Corynoneura scutellata) and Tanytarsini (Paratanytarsus sp.). Central sediments also favoured high abundances of collector-gatherers, burrowers and drought resistant forms with passive dispersal, whereas Ranunculus spp. hosted mainly scrapers, shredders, swimmers+divers and active dispersal forms without any resistant stages to desiccation. Juncus plants were mostly colonized by collector-filterers and by organisms capable of both active dispersal and surviving desiccation. Littoral sediments and algae showed similar functional organization and intermediate features between central sediments and submerged macrophyte beds. All these results demonstrate that microhabitat characteristics play a crucial role in selecting macroinvertebrate taxa according to their environmental requirement, feeding mechanism, movement and resistance to drought. Moreover, our study confirms the role of submerged and emergent vegetation in maintaining high biodiversity and suggests that all microhabitats should be considered to provide both an exhaustive collection of species for pond management and conservation and basic insights into the functioning of pond communities. 相似文献
288.
The impact of a single hydropeaking event was studied in the Alpine stream Noce Bianco. Four stations were selected, one upstream and three, respectively, at 0.25, 6, and 8 km downstream from a hydropower plant. We collected drifting invertebrates during a planned water release that increased the discharge 7-fold. At the onset of the hydropeaking wave the number of invertebrates lost from the riverbed per minute to the drift increased 9-fold at the first downstream station and the same effects propagated 8 km downstream. The drift was composed mainly of aquatic insect larvae (Chironomidae, Plecoptera, Ephemeroptera Baetidae, and Psychodidae, with Chironomidae as the most abundant taxon at all stations) and partly by larval and adult riparian insects, and by Oligochaeta, which were particularly abundant at the station 6 km downstream. We monitored drift for 30 min from the start of the water release: peaks in drifting invertebrates occurred within 5–10 min of the beginning of the hydropeaking wave, and most of the invertebrates were washed out within the first 15 min of the water release. The different timeframes were possibly due to habitat preferences (most of the taxa that increased in the drift at the arrival of the wave were associated with algae and organic debris, which were washed off quickly by the increase in discharge) and/or behavioral adaptations (other taxa initially resisted the shear stress and began to drift with a delay of 5–10 min). The temporal pattern and drift composition corresponded well with those reported in literature, and indicate that repeated high-flow events of similar magnitude cause considerable losses from benthic populations to drift. 相似文献
289.
Paola Tuccimei Michele Soligo Joaquin Ginés Angel Ginés Joan Fornós Jan Kramers Igor Maria Villa 《地球表面变化过程与地形》2010,35(7):782-790
Phreatic overgrowths on speleothems (POS) are carbonate formations deposited at the water table of caves in unique karstic coastal settings having morphologies that can be directly related to sea level at the time of formation. The U‐Th ages of calcite and aragonite overgrowths collected from the modern water table in coastal caves on Mallorca (Cova de Cala Varques A and Cova des Pas de Vallgornera) were determined using high‐precision MC‐ICPMS techniques. U‐Th ages indicate that phreatic carbonate deposition occurred between ca 2·8 and at least 0·6 ka BP and are in accord with an archeologically estimated age of 3·7–3·0 ka BP for a drowned prehistoric construction at a depth of 1 m below current sea level in a cave from the same area. Speleothem δ13C and δ18O and chemical composition of cave pools provide supportive evidence that POS reflect mixing between seawater and brackish water table. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
290.
Uncertainties in probability of occurrence of strong earthquakes for fault sources in the Central Apennines,Italy 总被引:1,自引:1,他引:0
Aybige Akinci David Perkins Anna Maria Lombardi Roberto Basili 《Journal of Seismology》2010,14(1):95-117
Using the characteristic earthquake model, we calculate the probability of occurrence of earthquakes M
w > 5.5 for individual fault sources in the Central Apennines for the 30-year period (2007–2037). We show the effect of time-dependent
and time-independent occurrence (Brownian passage time (BPT) and Poisson) models together with uncertain slip rates and uncertain
maximum magnitudes and, hence, uncertain recurrence times. In order to reduce the large prior geological slip rate uncertainty
distribution for most faults, we obtain a posterior slip rate uncertainty distribution using a likelihood function obtained
from regional historical seismicity. We assess the uncertainty of maximum magnitude by assuming that the uncertainty in fault
width and length are described by a normal distribution with standard deviation equal to ±20% of the mean values. We then
estimate the uncertainties of the 30-year probability of occurrence of a characteristic event using a Monte Carlo procedure.
Uncertainty on each parameter is represented by the 16th and the 84th percentiles of simulated values. These percentiles bound
the range that has a 68% probability of including the real value of the parameter. We do these both for the Poisson case and
for the BPT case by varying the aperiodicity parameter (α value) using the values 0.3, 0.5, and 0.7. The Bayesian posterior slip rate uncertainties typically differ by a factor of
about 2 from the 16th to the 84th percentile. Occurrence probabilities for the next 30 years at the 84th percentile typically
range from 1% to 2% for faults where the Poisson model dominates and from 2% to 21% where one of the BPT models dominates.
The uncertainty in occurrence probability under the time-dependent hypothesis is very large, when measured by the ratio of
the 84th to the 16th percentile, frequently being as much as two orders of magnitude. On the other hand, when measured by
standard deviation, these standard deviations range from 2% to 6% for those faults whose elapsed time since previous event
is large, but always 2% or less for faults with relatively recent previous occurrence, because the probability of occurrence
is always small. 相似文献