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1.
Dr. Hans Rufli 《Aquatic Sciences - Research Across Boundaries》1978,40(1):7-31
During the past 25 years the effects of eutrophication in the oligo-to mesotrophic Lake Thun and the eutrophic Lake Biel have
changed the morphology and biology of theCoregonus spp., as well as the composition of the stock. Statistical procedures and immunodiffusion revealed the existence of threeCoregonus populations in
Lake Thun: 5% Kropfer, 28% ‘Albock’ and 67% Brienzlig (local names). Their gillrakers range between 20 and 32, 25 and 40,
and 29 and 46, respectively (mean: 22, 31, 40). In Lake Biel two populations were distinguished: 16% Palée and 84% Bondelle
with 22–35 and 30–40 gillrakers (mean: 30, 34). Changes of the spawning grounds and periods most probably have led to a bastardization
of two species (Schwebalbock and Bodenalbock) to the present ‘Albock’ in Lake Thun.
Overlapping values of all 20 morphological characters of the populations studies render the identification of forms difficult.
Only gillrakers and a few more characters show significant statistical differences between populations. The determination
ofCoregonus spp. of Lake Thun and Lake Biel thus often needs additional data on growth, feed, maturation, spawning ground and/or period.
相似文献
2.
3.
Food web manipulation without nutrient control: A useful strategy in lake restoration? 总被引:15,自引:0,他引:15
The results of long-term, full-scale experiments in biomanipulation (in the closer sense of top-down control of the food web)
in water bodies having extremely different phosphorus loads reveal that there is a close connection between the efficiency
of food web manipulation and the nutrient situation in the particular water body. Top-down control provides a high probability
of improving water quality with respect to Secchi depth and algal biomass only if it is connected with a decrease in the in-lake
phosphorus. If that decrease in phosphorus is not achieved for different reasons, the high probability of an efficient top-down
control is limited to zooplankton and to structural changes in the phytoplankton. A lake-specific ‘biomanipulation-efficiency
threshold’ of the phosphorus load should not be exceeded. The results show that integrated water quality control, i.e. a combination
of the strategy of load reduction with the strategy of ‘ectotechnology’, seems to be a very promising way.
Presented at the International Conference on Lake Restoration of Zürich, 3–4 November 1986 相似文献
4.
In the list of ’repeating pairs’ or ’doublets’ of earthquakes in China identified by Schaff and Richards using tele-seismic waveform cross-correlation, there were 23 repeating pairs located in Liaoning Province. In this study the waveforms of these events were cross-correlated using records from Liaoning Regional Seismograph Network (LRSN), and the ’repeating events’ in the sense of regional waveform cross-correlation were obtained. The result was compared with that of Schaff and Richards and was used for the assessment of the seismic phase picking and event location practice of LRSN. The result shows that ’repeating events’ in the sense of teleseismic waveform cross-correlation and those in the sense of regional waveform cross-correlation have significant difference, al-though with some overlap. However, the overall assessment of the location accuracy and the phase pick errors of LRSN by using these two sets of ’repeating events’, respectively, provides similar results, while ’repeating events’ in the sense of regional waveform cross-correlation seem to be better performing in such an assessment. With the assumption that the separation between the ’repeaters’ be less than 1 km, the uncertainty in routine earthquake location of LRSN is estimated to be below 5 km, with the average of 2 km. In the observational bulletins of LRSN the time error in phase picking is estimated to be within ±1s for 94% Pg readings and for 88% Sg readings. 相似文献
5.
Tephra dispersal and eruption dynamics of wet and dry phases of the 1875 eruption of Askja Volcano, Iceland 总被引:1,自引:1,他引:0
The 1875 rhyolitic eruption of Askja volcano in Iceland was a complex but well-documented silicic explosive eruption. Eyewitness
chronologies, coupled with examination of very proximal exposures and historical records of distal deposit thickness, provide
an unusual opportunity for study of Plinian and phreatoplinian eruption and plume dynamics. The ∼ 17 hour-long main eruption
was characterized by abrupt and reversible shifts in eruption style, e.g., from ‘wet’ to ‘dry’ eruption conditions, and transitions
from fall to flow activity. The main eruption began with a ‘dry’ subplinian phase (B), followed by a shift to a very powerful
phreatoplinian ‘wet’ eruptive phase (C1). A shift from sustained ‘wet’ activity to the formation of ‘wet’ pyroclastic density
currents followed with the C2 pyroclastic density currents, which became dryer with time. Severe ground shaking accompanied
a migration in vent position and the onset of the intense ‘dry’ Plinian phase (D). Each of the fall units can be modeled using
the segmented exponential thinning method (Bonadonna et al. 1998), and three to five segments have been recognized on a semilog plot of thickness vs. area1/2. The availability of very proximal and far-distal thickness data in addition to detailed observations taken during this eruption
has enabled calculations of eruption parameters such as volumes, intensities and eruption column heights. This comprehensive
dataset has been used here to assess the bias of volume calculations when proximal and distal data are missing, and to evaluate
power-law and segmented exponential thinning methods using limited datasets. 相似文献
6.
7.
A unified approach to environmental systems modeling 总被引:1,自引:0,他引:1
P. C. Young Marco Ratto 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(7):1037-1057
The paper considers the differences between hypothetico-deductive and inductive modeling: between modelers who put their primary
trust in their scientific intuition about the nature of an environmental model and tend to produce quite complex computer
simulation models; and those who prefer to rely on the analysis of observational data to identify the simplest form of model that can represent these data. The tension that sometimes arises because of the different philosophical outlooks
of these two modeling groups can be harmful because it tends to fractionate the effort that goes into the investigation of
important environmental problems, such as global warming. In an attempt to improve this situation, the paper will outline
a new Data-Based Mechanistic (DBM) approach to modeling that tries to meld together the best aspects of these two modeling philosophies in order to develop
a unified approach that combines the hypothetico-deductive virtues of good scientific intuition and simulation modeling with
the pragmatism of inductive data-based modeling, where more objective inference from data is the primary driving force. In
particular, it demonstrates the feasibility of a new method for complex simulation model emulation, in which the methodological
tools of DBM modeling are used to develop a reduced dynamic order model that represents the ‘dominant modes’ of the complex
simulation model. In this form, the ‘dynamic emulation’ model can be compared with the DBM model obtained directly from the
analysis of real data and any tensions between the two modeling approaches may be relaxed to produce models that suit multiple
modeling objectives. 相似文献
8.
The response of phytoplankton communities to changing lake environments 总被引:10,自引:0,他引:10
Colin S. Reynolds 《Aquatic Sciences - Research Across Boundaries》1987,49(2):220-236
In this paper, empirical relationships between the mean phytoplankton biomass and limiting nutrient availability and between
the underwater extinction of light and the biomass are used to define some of the physical aspects of lake environments subject
to cultural eutrophication or to corrective restoration measures. The distinctive floristic distributions of different algae
among such environments are shown to be closely related to general morphological and physiological properties of the algae
themselves and that species sharing similar size- and shape-adaptations also share similar ecological growth and survival
strategies. From these general predictions of the responses of phytoplankton to changing lake environments, it is deduced
that deep lakes are slower to respond than shallow ones but that the transition between nutrient-and light-limitation is relatively
abrupt: ‘resilience’ of the system to restoration measures may be an expression of their progress towards the transition.
Presented at the International Conference on Lake Restoration in Zürich, 3–4 November 1986 相似文献
9.
Long-lived basaltic eruptions often produce structurally complex, compound `a`ā flow fields. Here we reconstruct the development
of a compound flow field emplaced during the 2001 eruption of Mt. Etna (Italy). Following an initial phase of cooling-limited
advance, the reactivation of stationary flows by superposition of new units caused significant channel drainage. Later, blockages
in the channel and effusion rate variations resulted in breaching events that produced two new major flow branches. We also
examined small-scale, late-stage ‘squeeze-up’ extrusions that were widespread in the flow field. We classified these as ‘flows’,
‘tumuli’ or ‘spines’ on the basis of their morphology, which depended on the rheology, extrusion rate and cooling history
of the lava. Squeeze-up flows were produced when the lava was fluid enough to drain away from the source bocca, but fragmented
to produce blade-like features that differed markedly from `a`ā clinker. As activity waned, increased cooling and degassing
led to lava arriving at boccas with a higher yield strength. In many cases this was unable to flow after extrusion, and laterally
extensive, near-vertical sheets of lava developed. These are considered to be exogenous forms of tumuli. In the highest yield
strength cases, near-solid lava was extruded from the flow core as a result of ramping, forming spines. The morphology and
location of the squeeze-ups provides insight into the flow rheology at the time of their formation. Because they represent
the final stages of activity of the flow, they may also help to refine estimates of the most advanced rheological states in
which lava can be considered to flow. Our observations suggest that real-time monitoring of compound flow field evolution
may allow complex processes such as channel breaching and bocca formation to be forecast. In addition, documenting the occurrence
and morphology of squeeze-ups may allow us to determine whether there is any risk of a stalled flow front being reactivated.
This will therefore enhance our ability to track and assess hazard posed by lava flow emplacement. 相似文献
10.
Contains a synthesis of the principal manifestations of accelerated eutrophication of the waters of Lake Geneva, based on
a thorough study of the available publications and particularly on the reports of the ‘Commission internationale pour la protection
du Léman contre la pollution’ [12]. The analysis of the present biological (flora and fauna) and physicochemical characteristics
on the one hand, and the study of their evolution on the other, put the Lake of Geneva in the category of meso-eutrophic lakes.
相似文献
11.
12.
Statistical properties of reported earthquake precursors show apparent focal mechanism dependence. Intensity of anomaly is
described by the ‘anomaly ratio’ as defined by the number of stations/items reporting anomalies before the target earthquake
over the number of stations/items in operation around the target earthquake. Variation of the ‘anomaly ratio’ with the magnitude
of the target earthquake was studied for dip-slip earthquakes all over China, strike-slip earthquakes in eastern China, and
strike-slip earthquakes in western China, respectively. It is observed that for strike-slip earthquakes, the ‘anomaly ratio’
increases linearly with the magnitude of the target earthquake, while earthquakes in eastern China and western China have
different slopes. For dip-slip earthquakes, however, the ‘anomaly ratio’ has no statistically significant change with the
magnitude of the target earthquake. Limited data imply that the ‘anomaly ratio’ seems proportional to the apparent stress
of the target earthquake. The result might be heuristic for the analysis of candidate earthquake precursors.
Foundation item: National Natural Science Foundation of China (40274013) and MOST Project (2001BA601B02).
Contribution No.04FE1020, Institute of Geophysics, China Earthquake Administration. 相似文献
13.
Helen L. Moggridge Angela M. Gurnell 《Aquatic Sciences - Research Across Boundaries》2009,71(3):305-317
Salicaceae are key pioneer riparian tree species that have the ability to reproduce sexually and asexually. Recent research
has suggested that Salicaceae act as ‘ecosystem engineers’, modifying hydrological and geomorphological processes, resulting
in the stabilisation and growth of landforms. Understanding these interactions requires knowledge of the controls on Salicaceae
regeneration. This paper describes a study of Salicaceae establishment and growth along a reach of a highly dynamic, island-braided
river. The sexual and asexual regeneration of three species were investigated using experimental planting of cuttings and
observation of seedlings. Plots were located at a range of elevations, in different habitats associated with the established
riparian vegetation and in contrasting sediment types. Survival and growth were monitored over two growing seasons. Asexual
regeneration was more successful than sexual regeneration, with cuttings demonstrating faster growth rates and tolerance of
broader environmental conditions than seedlings. Cutting survival and growth was highest in sediments with a relatively high
organic content and in plots located between patchy Salicaceae stands or in the lee of islands. Seedling mortality was extremely
high due to fluvial disturbance, although seedlings in habitats that were protected from fluvial disturbance survived. Seedling
growth showed preferences for particular sedimentary conditions, which varied between species. The major control on regeneration
was the upstream presence of established Salicaceae, particularly on islands, which provided open sites that were protected
from fluvial disturbance and suitable for regeneration. Thus, asexual regeneration facilitated sexual regeneration by rapidly
colonising sites that provided habitats protected from fluvial disturbance for seedling establishment. This supports previous
work suggesting that Salicaceae can act as ‘ecosystem engineers’. 相似文献
14.
Hans van Haren 《Ocean Dynamics》2007,57(2):135-149
Relative ‘echo intensity’ data (dI) from a bottom-mounted four-beam 300 kHz acoustic Doppler current profiler (ADCP) are used to infer propagation of vigorous
processes above a continental slope. The 3- to 60-m horizontal beam spread and the 2-Hz sampling allow the distinction of
different arrival times t
i
, i = 1,..., 4, at different distances in the acoustic beams from sharp changes in dI-content associated with frontal non-linear and turbulent bores or ‘waves’. The changes in dI are partially due to variations in amounts of resuspended material carried by the near-bottom turbulence and partially due
to the fast variations in density stratification (‘stratified turbulence’), as inferred from 1-Hz sampled thermistor string
data above the ADCP. Such bores are observed to pass the mooring up to 80 m above the bottom, having typical propagation speeds
c = 0.15–0.5 m s−1, as determined from dI(t
i
). Particle speeds in the immediate environment of a bore amount to |u|env=c ± 0.05 m s−1, the equality being a necessary condition for kinematic instability, whilst the maximum particle speeds amount |u|max = 1.2–2c. The dI-determined directions of up-, down- and alongslope processes are all to within ±10° of the ADCP’s beam-spread averaged current
(particle velocity) data. 相似文献
15.
Davide D’Alimonte Dan Cornford 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):613-620
This paper, addresses the problem of novelty detection in the case that the observed data is a mixture of a known ‘background’ process contaminated with an unknown other process, which generates the outliers, or novel observations. The framework we
describe here is quite general, employing univariate classification with incomplete information, based on knowledge of the
distribution (the probability density function, pdf) of the data generated by the ‘background’ process. The relative proportion of this ‘background’ component (the prior ‘background’ probability), the pdf and the prior probabilities of all other components are all assumed unknown. The main contribution is a new classification scheme that
identifies the maximum proportion of observed data following the known ‘background’ distribution. The method exploits the Kolmogorov–Smirnov test to estimate the proportions, and afterwards data are Bayes
optimally separated. Results, demonstrated with synthetic data, show that this approach can produce more reliable results
than a standard novelty detection scheme. The classification algorithm is then applied to the problem of identifying outliers in the SIC2004 data set, in order
to detect the radioactive release simulated in the ‘joker’ data set. We propose this method as a reliable means of novelty
detection in the emergency situation which can also be used to identify outliers prior to the application of a more general
automatic mapping algorithm.
相似文献
Davide D’AlimonteEmail: |
Dan Cornford (Corresponding author)Email: |
16.
Retrospective forecasting test of a statistical physics model for earthquakes in Sichuan-Yunnan region 总被引:6,自引:0,他引:6
Pattern informatics (PI) model is one of the recently developed predictive models of earthquake phys- ics based on the statistical mechanics of complex systems. In this paper, retrospective forecast test of the PI model was conducted for the earthquakes in Sichuan-Yunnan region since 1988, exploring the possibility to apply this model to the estimation of time-dependent seismic hazard in continental China. Regional earthquake catalogue down to ML3.0 from 1970 to 2007 was used. The ‘target magnitude’ for the forecast test was MS5.5. Fifteen-year long ‘sliding time window’ was used in the PI calculation, with ‘anomaly training time window’ being 5 years and ‘forecast time window’ being 5 years, respectively. Receiver operating characteristic (ROC) test was conducted for the evaluation of the forecast result, showing that the PI forecast outperforms not only random guess but also the simple number counting approach based on the clustering hypothesis of earthquakes (the RI forecast). If the ‘forecast time window’ was shortened to 3 years and 1 year, respectively, the forecast capability of the PI model de- creased significantly, albeit outperformed random forecast. For the one year ‘forecast time window’, the PI result was almost comparable to the RI result, indicating that clustering properties play a more important role at this time scale. 相似文献
17.
2.5-D modeling and inversion techniques are much closer to reality than the simple and traditional 2-D seismic wave modeling
and inversion. The sensitivity kernels required in full waveform seismic tomographic inversion are the Fréchet derivatives
of the displacement vector with respect to the independent anisotropic model parameters of the subsurface. They give the sensitivity
of the seismograms to changes in the model parameters. This paper applies two methods, called ‘the perturbation method’ and
‘the matrix method’, to derive the sensitivity kernels for 2.5-D seismic waveform inversion. We show that the two methods
yield the same explicit expressions for the Fréchet derivatives using a constant-block model parameterization, and are available
for both the line-source (2-D) and the point-source (2.5-D) cases. The method involves two Green’s function vectors and their
gradients, as well as the derivatives of the elastic modulus tensor with respect to the independent model parameters. The
two Green’s function vectors are the responses of the displacement vector to the two directed unit vectors located at the
source and geophone positions, respectively; they can be generally obtained by numerical methods. The gradients of the Green’s
function vectors may be approximated in the same manner as the differential computations in the forward modeling. The derivatives
of the elastic modulus tensor with respect to the independent model parameters can be obtained analytically, dependent on
the class of medium anisotropy. Explicit expressions are given for two special cases—isotropic and tilted transversely isotropic
(TTI) media. Numerical examples are given for the latter case, which involves five independent elastic moduli (or Thomsen
parameters) plus one angle defining the symmetry axis. 相似文献
18.
Dr. Peter Baccini 《Aquatic Sciences - Research Across Boundaries》1976,38(2):121-158
In the mesotrophic Lake of Lucerne (Bay of Horw) and in the eutrophic Lake of Alpnach concentration and sedimentation of iron, copper, zinc, cadmium and lead were investigated as a function of time and depth, and compared with a series of physical and chemical parameters. A metal balance was made for the Lake of Alpnach. A model for the distribution of the metals between biomass, allochthonous material and dissolved phase was employed. Phenomenology and model lead to the following conclusions: the sedimentation of the metals is dominated by allochthonous particles, the biogenic particularization is partially reversed by lake internal decomposition processes and the trace metals reaching the sediment are partially redissolved. 相似文献
19.
千岛湖(新安江水库)是我国大水面生态渔业发展的典型湖库,其渔业主要以鲢、鳙等滤食性鱼类增殖为主,对鱼食性鱼类资源的研究和关注相对匮乏。而鱼食性鱼类是水生食物网的顶级捕食者,对维持水生态系统结构和功能具有重要作用。近年来,受过度捕捞、生境退化等影响,千岛湖鱼食性鱼类资源下降明显。鉴于此,2021年3月—2022年12月,逐月在千岛湖收集4种同域共存的鱼食性鱼类样品1032尾,包括翘嘴鲌(Culter alburnus)、蒙古鲌(Culter mongolicus)、大眼鳜(Siniperca knerii)和斑鳜(Siniperca scherzeri),系统研究并比较了4种鱼食性鱼类年龄、生长、繁殖等生活史策略的分化特征。结果表明,千岛湖4种鱼食性鱼类优势年龄组均未超过3龄,说明其种群呈现低龄化现象。生长式型上,翘嘴鲌和蒙古鲌属正异速生长,而大眼鳜和斑鳜属负异速生长,说明4种鱼食性鱼类具有不同的生长策略。条件系数(CF)的变化趋势与繁殖活动密切相关,其中大眼鳜的条件系数最高(1.92%±0.03%),其次为斑鳜(1.72%±0.02%)和蒙古鲌(1.14%±0.01%),翘嘴鲌的条件系... 相似文献
20.
Richard Eckersley 《Global Change & Human Health》2002,3(1):55-57
Bjorn Lomborg's critique of environmentalism has been praised by The Economist as ‘right’ on its main points and ‘just’ in
its criticism of much green activism, and damned by Scientific American as a ‘failure’ in its purpose of describing the state
of the world. Most of the debate has centred on Lomborg's treatment of environmental issues. But the book is about more than
the environment, and its flaws extend beyond his use and interpretation of the data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献