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81.
Alessandro Bosman Daniele Casalbore Claudia Romagnoli Francesco Latino Chiocci 《Bulletin of Volcanology》2014,76(7):1-12
Five consecutive multibeam bathymetries collected before, during, and after the 2007 Stromboli eruption, combined with visual inspections, allowed us to document the morphological evolution of an ‘a’ā lava-fed delta and to reconstruct the main processes acting during its submarine emplacement. The 2007 Stromboli delta extended down to 600-m water depth and covered an area of 420?×?103 m2, with a maximum thickness of 65 m and a total estimated volume of ≈7?×?106 m3, i.e., three times larger than its subaerial counterpart. The lava delta grew mainly through the emplacement of discrete lobes about 50–150 m in size. Lobes were fed from point sources along the paleoshoreline, and their subaqueous pathways seem to be mainly controlled by the submarine morphology, with flows mostly filling in depressions left by previous lobes. The main controlling factors on the lobe morphology and thickness are the effusion rates and the pre-eruption morphology, i.e., the geometry and gradients of the basal surface. Data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion, implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows. The present study is relevant for future monitoring and hazard assessment during the growth of active lava-fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland. 相似文献
82.
The dual-beam mini-DOAS technique—measurements of volcanic gas emission,plume height and plume speed with a single instrument 总被引:2,自引:0,他引:2
Mattias Johansson Bo Galle Yan Zhang Claudia Rivera Deliang Chen Klaus Wyser 《Bulletin of Volcanology》2009,71(7):747-751
The largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the
determination of the plume speed, and in the case of fixed scanning instruments also the plume height. We here present a newly
developed technique capable of measuring plume height, plume speed and gas flux using one single instrument by simultaneously
collecting scattered sunlight in two directions. The angle between the two measurement directions is fixed, removing the need
for time consuming in-field calibrations. The plume height and gas flux is measured by traversing the plume and the plume
speed is measured by performing a stationary measurement underneath the plume. The instrument was tested in a field campaign
in May 2005 at Mt. Etna, Italy, where the measured results are compared to wind fields derived from a meso-scale meteorological
model (MM5). The test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume
height. 相似文献
83.
This paper presents a method to reconstruct the gas distribution inside a vertical cross section of a gas plume by combining
data from two or more scanning DOAS instruments using a tomographic algorithm. The method can be applied to gas plumes from
any single, elevated point source, such as a volcano or industrial chimney. Such two-dimensional concentration distributions
may prove to be useful for example in plume chemistry, dispersion and environmental impact studies. Here we show the case
with one scanning DOAS instrument located on each side of the plume, which is the easiest and most economic setup as well
as the most useful in routine monitoring of e.g. volcanic gas emissions. The paper investigates the conditions under which
tomographic reconstructions can be performed and discusses limitations of this setup. The proposed method has been studied
theoretically by numerical simulations and has been experimentally tested during two field campaigns, with measurements of
SO2 emissions from a volcano and a power plant. The simulations show that, under good measurement conditions, the algorithm presented
performs well, which is further confirmed by the experimental results. 相似文献
84.
Phytoplankton composition and biomass, and microcystin content were determined on diverse dates between November 2001 and June 2006 in the final oxidation pond of the Nakuru town sewage treatment plant. The oxidation ponds as well as the rivulet that drains the same are important water sources for some wildlife in the park. The phytoplankton composition of the pond studied mostly comprised coccoid green alga species. However, occasionally cyanobacteria or euglenoids were dominant. Among the cyanobacteria, Microcystis sp. made periodic appearance in the phytoplankton, and was the dominant species on some occasions. Total phytoplankton biomass varied widely from 48 to 135 mg L−1 (wet weight) while cyanobacteria biomass ranged from undetectable levels to 130 mg L−1. Most phytoplankton biomass was due to one or a few species. Detectable cyanotoxin concentrations (sum of microcystins) of up to 551.08 μg mg−1 dry weight (DW) of cyanobacteria biomass or 0.28 μg mg−1 DW of total phytoplankton biomass were recorded in samples collected on different dates. Microcystin content did not appear to correspond to the biomass of cyanobacteria suggesting that toxin production is possibly triggered by environmental changes or changes in the proportion of toxic strains. An occasional presence of microcystins in the pond water suggests that the wildlife species, which regularly use the ponds as drinking water sources are potentially exposed to intoxication. A close monitoring of pond water phytoplankton composition is necessary to accurately quantify the potential impact of cyanotoxins on these wildlife species. 相似文献
85.
86.
The increased availability of global datasets and technologies such as global hydrologic models and the Gravity Recovery and Climate Experiment (GRACE) satellites have resulted in a growing number of global‐scale assessments of water availability using simple indices of water stress. Developed initially for surface water, such indices are increasingly used to evaluate global groundwater resources. We compare indices of groundwater development stress for three major agricultural areas of the United States to information available from regional water budgets developed from detailed groundwater modeling. These comparisons illustrate the potential value of regional‐scale analyses to supplement global hydrological models and GRACE analyses of groundwater depletion. Regional‐scale analyses allow assessments of water stress that better account for scale effects, the dynamics of groundwater flow systems, the complexities of irrigated agricultural systems, and the laws, regulations, engineering, and socioeconomic factors that govern groundwater use. Strategic use of regional‐scale models with global‐scale analyses would greatly enhance knowledge of the global groundwater depletion problem. 相似文献
87.
88.
The organic composition and organic‐inorganic interaction in paper mill sludge (PS) solvent extracts (hexane, ethyl acetate, acetone and ethanol) and humic fractions, humic acid (HA) and humin (HU) were studied by electron paramagnetic resonance spectroscopy (EPR), proton and carbon‐13 nuclear magnetic resonance spectroscopy (1H NMR; 13C NMR), Fourier‐transformed infrared spectroscopy (FTIR), and ultraviolet‐visible spectroscopy (UV‐vis). The strategy of fractionating the PS, sequentially, with organic solvents of increasing polarity is a reliable analytical procedure for humic substance sample separation because it results in more purified fractions. FTIR, 1H NMR and 13C NMR results showed that hexane extract consisted mainly of aliphatic hydrocarbon structures. Their contents in the extracts decreased as the polarity of the extracting solvent increased and the content of oxygen functional groups increased. Carboxylic and carboxylate functional groups were found in the acetone extract, and ester and ether functions were predominantly found in the ethanol extract. EPR spectra revealed some Fe3+ complexes with rhombic structure (g1 = 4.3; g2 = 9.0) in the humic fractions and in all solvent extracts, except hexane. Quasi‐octahedral Fe3+ complexes (g = 2.3; ΔHpp ≤ 400 G) were found in the HU fraction and in the acetone extract. The organic free radical content in the HA fraction was higher than the non‐fractionated PS sample and HU fraction. 相似文献
89.
90.
Claudia Hellmann Carola Winkelmann Susanne Worischka Jürgen Benndorf 《Limnologica》2011,41(3):256-265
Many predation experiments in streams are carried out in enclosures. Hence, the relevance of their results to predict population dynamics is often unclear due to the relatively small spatial and temporal scale of the experiments. To enhance the transferability of experimental results on the ecosystem scale the impact of fish predators on a prey population was observed in a reach scale approach over 2 years in a natural stream. A 400-m reach inhabited by the small benthivorous fishes gudgeon (Gobio gobio) and stone loach (Barbatula barbatula) was compared with a fishless reference reach.It was shown that fish predation may affect the population of the grazing mayfly Rhithrogena semicolorata on the ecosystem scale. Although the larvae grew slower in the fish reach than in the fishless reach, the adults reached the same size and fecundity because they emerged 2–3 weeks later. By this compensation, the prey species avoided a reduction of their individual fecundity. On the other hand, the extended exposure to the fish predators resulted in an enhanced mortality and a reduced density of adult mayflies. Thus, there was obviously a trade-off between maximising fecundity and minimising mortality from fish predation.The observed differences were almost certainly caused be fish predation and not by natural differences of the reaches. This was concluded from results gained after eliminating all benthivorous fish from the former fish reach.With the help of scenario analyses based on our empirical data and simple model assumptions we could demonstrate that compensating the potential loss in fecundity by extending development time led to higher average fitness of the prey population than emerging at an earlier fixed time to avoid additional predation losses. Therefore, we concluded that this strategy was adaptive in the presence of benthivorous fish. 相似文献