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Long-term impacts of increased metal loading (Hg, Cu, Cd, Zn and Pb) on phytoplankton communities of large limno-corrals (diameter
12 m, depth 10 m) were studied. Increased metal concentrations initially lowered phytoplankton biomass, as well as species
number and photosynthetic activity of phytoplankton. They caused changes in metal speciation and shifts in phytoplankton community
structure, favoring less susceptible species. Although adaptation was not sufficient to completely prevent the metal-induced
depression of photosynthesis, due to depressed zooplankton grazing, at the end of the experiment even higher phytoplankton
densities were observed in the metal-loaded corrals than in the control. 相似文献
3.
S. N. Grover 《Pure and Applied Geophysics》1976,114(4):509-520
Summary Numerical calculations were carried out to determine the effect of a vertical electric field on the efficiency with which electrically charged or uncharged cloud drops and small raindrops of diameters ranging from 84 m to 1.248 mm collide with electrically charged or uncharged particles of density 2 gm/cm3 and diameters between 1 and 20 m. For this purpose, numerical flow fields about spheres of Reynolds numbers ranging from 1 to 400 were used to integrate the trajectory of the particle relative to the drop, and the force between two conducting spheres was used to represent the electrostatic force on the particle. The effect of thunderstorm strength electric charges and field on the collision efficiency was found to be highly significant for the smaller collector drops, and declined to insignificance for the largest collector drop. 相似文献
4.
In two limno-corrals loaded with heavy metals the density of tubificid worms and chironomid larvae was higher than in the
control. The better oxygen conditions observed in the heavy metal loaded corrals might explain this discrepancy. The higher
oxygen concentration at the sediment-water interface was due to lower organic sedimentation, consequence of the primary production
reduced by heavy metals. In all limno-corrals, the tubificid populations consisted ofTubifex tubifex. The size structure of tubificid populations in the heavy metal loaded corrals indicated a delayed reproduction compared
to the control. 相似文献
5.
Lesley A. Warren Ann P. Zimmermann 《Aquatic Sciences - Research Across Boundaries》1994,56(4):348-362
We examined particle size distributions of suspended particulate matter (SPM); physical and environmental influences on the observed distributions; and relationships between particle size and geochemical partitioning of metals, over the fall and winter period in a small urban river (Don River, Toronto, Ontario, Canada). For this dataset, the majority of particles (80%) in suspension were less than 10 µm in size. In addition, while total SPM concentrations showed a positive trend with increasing discharge (Q); the proportions of particles found within given size classes were independent of both SPM concentration and Q. Temperature was the only measured environmental variable related to the particle concentrations within size classes. As water temperature increased, the concentration of particles in the smallest size class (1–4 µm) decreased, while the concentration of silt and/or algae sized particles (10–50 µm) increased. Increasing water temperatures may promote bacterial attachment to particles and their subsequent flocculation into larger sized particles. Decreasing concentrations of leachable (most labile) Cd, Zn and Mn were associated with increasing concentrations of the largest particles (70–150 µm) in suspension. In contrast, higher reducible (oxides) associated concentrations of Cd, Zn and Mn occurred with increasing concentrations of smaller particles (1–10 µm) in suspension. Both of these trends are speculated to reflect the importance of particle surface area for metal sorption reactions. 相似文献
6.
Radio-frequency identification (RFID) transponders are now widely used to track sediment in a variety of environments. A recent innovation placed the transponder inside of a rotating inner mechanism that is designed to minimize missed detections due to burial and shielding or ‘signal collision’ effects between tracers, while also allowing a rapid measurement of the burial depth of the particle. Here we test a developed protocol for burial depth measurement and deploy the ‘Wobblestone’ tracers in the field for the first time. Results show that new tracers can be reliably positioned in the horizontal plane (median error ± 0.03 m) and that the burial depth can be accurately measured (~0.02 m maximum error). The field study was characterized by high mobility and travel lengths, and ~20% of the tracers were buried at depths up to 0.15 m. A comparison of exponential distributions for travel length of surface deposited and buried tracers indicate that the buried tracers on average traveled farther and earlier in the flood event. Tracers that did not move were also buried at one site as a result of sediment transport from upstream. Overall the technique has great potential for characterizing vertical mixing and understanding this rarely considered control on sediment transport. © 2020 John Wiley & Sons, Ltd. 相似文献
7.
Significant natural attenuation may occur on the passage of groundwater plumes through streambed sediments because of the transition from anaerobic to aerobic conditions and an increased microbial activity. Varying directions and magnitudes of water flow in the streambed may enhance or inhibit the supply of oxygen to the streambed and thus influence the redox zoning. In a field study at a small stream in the industrial area of Bitterfeld‐Wolfen, we observed the variability of hydraulic gradients, streambed temperatures, redox conditions and monochlorobenzene (MCB) concentrations in the streambed over the course of 5 months. During the observation period, the hydrologic conditions changed from losing to gaining. Accordingly, the temperature‐derived water fluxes changed from recharge to discharge. Redox conditions were highly variable between ? 170 and 368 mV in the shallow streambed at a depth of 0·1 m below the streambed surface. Deeper in the streambed, at depths of 0·3 m and 0·5 m, the redox conditions were more stable between ? 198 and ? 81 mV and comparable to those typically found in the aquifer. MCB concentrations in the streambed at 0·3 and 0·5 m depth increased with increasing upward water flux. The MCB concentrations in the shallow streambed at 0·1 m depth appeared to be independent of the hydrologic conditions suggesting that degradation of MCB may have occured. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
《Earth and Planetary Science Letters》2003,205(3-4):155-172
Vertical profiles of dissolved rare earth elements (REEs) were obtained in the Bay of Bengal and the Andaman Sea. The REE concentrations at various depths in the Bay of Bengal are the highest in the Indian Ocean. This is attributable ultimately to the large outflow of the Ganges–Brahmaputra and Irrawaddy rivers, but the dissolved REE flux to surface waters alone cannot explain the large and near-constant REE enrichment throughout the entire water column. The underlying fan sediments serve as not a source but a sink for dissolved REE(III)s. Absence of excess 228Ra in the deep waters suggests that lateral input of dissolved REEs from slope sediments is also small in these regions. Partial (<0.3%) dissolution of detrital particles, which are carried by the rivers and lateral surface currents and subsequently settle through the water column, appears to be a predominant source for the dissolved REEs. Vertical profiles showing an almost linear increase with depth are common features for the light and middle REEs everywhere, but their concentration levels are variable from basin to basin and from element to element. This suggests that their oceanic distributions respond quickly to the variation of particle flux and its REE composition through reversible exchange equilibrium with suspended and sinking particles much like the case for Th. The relative importance of the vertical geochemical processes of reversible scavenging over the horizontal basin-scale ocean circulation with passive regeneration like nutrients decreases systematically from the light to the heavy REEs. Using a model, the mean oceanic residence times of REEs in the Bay of Bengal are estimated to range from 37 years for Ce to 140–1510 years for the strictly trivalent REEs. In the deep water of the Andaman Sea, isolated from the Bay of Bengal by the Andaman–Nicobar Ridge (maximum sill depth of ∼1800 m), the REE concentrations are almost uniform presumably due to rapid vertical mixing. The REE(III) concentrations are similar to that of ∼1250 m depth water in the Bay of Bengal, consistent with other oceanographic properties. However, the REE composition of the deep water appears to be altered slightly by preferential scavenging of the light REE(III) at the bottom boundary of the basin. 相似文献
9.
Glucose uptake in lake water samples has been determined with short-time14C-experiments at different additions of the single heavy metals Cu++, Zn++, Cd++, Pb++, Hg++ and at different additions of a combination of all metals. The degree of a metal induced inhibition of glucose uptake varied from lake to lake and from season to season, whereby the addition of legally tolerated concentrations of 10 μg Cu/l and 200 μg Zn/l inhibited glucose uptake in most samples significantly, as well as the simultaneous addition of all metals. The legally tolerated limit of 1 μg Hg/l inhibited glucose uptake in Lake Lucerne samples almost completely, showed however no effect in samples of Lake Baldegg. The equimolar toxicity sequence of heavy metals for heterotrophic microorganisms has been determined as: Hg>Cu>Cd>(Zn. Pb). Glucose uptake of plankton sampled from metal polluted limno-corrals was less inhibited than that of the control plankton, when heavy metals were added to the samples singly or in combination. It is assumed that this effect is due to the natural selection of more resistant plankton species. 相似文献
10.
Jacques Urech 《Aquatic Sciences - Research Across Boundaries》1979,41(2):247-260
The crustacea plankton of three artificial model lakes in Lake Baldegg was observed during 15 months. Two were loaded continuously
with low concentrations of five heavy metals (Hg, Cu, Cd, Zn, Pb).
It was attempted to explain the significant lower abundances of the loaded limno-corrals. The results suggest that the decrease
was not, or only partially, caused by the lower food supply in the loaded limnocorrals, but directly by the heavy metals.
Accompaning laboratory tests show significantly increased egg-development-times for two species of those animals from the
loaded limno-corrals. Two other species show a decrease of the egg production/♀. It cannot be determined if increased mortality
of particular animal stages was caused by heavy metals.
Résumé On a observé pendant 15 mois les crustacés planctoniques des trois modèles de lac installés dans le lac de Baldegg. Dans deux de ceux-ci, une charge constante de cinq métaux lourds (Hg, Cu, Cd, Zn, Pb) de faible concentration a été maintenue. On a essayé d'expliquer la faible concentration significative de plancton dans les bassins limnologiques chargés. Les résultats montrent que la diminution n'était que partiellement ou pas du tout causée par le faible approvisionnement en nourriture dans les bassins chargés, mais directement par les métaux lourds. Les tests de laboratoire montrent significativement l'augmentation du temps de développement des œufs pour deux espèces animales des bassins chargés. Deux autres espèces montrent une diminution de la production d'œufs/♀. On ne peut pas déterminer l'augmentation de la mortalité des animaux causée par les métaux lourds à des stades particuliers de développement.相似文献
11.
Time–space fractional governing equations of one‐dimensional unsteady open channel flow process: Numerical solution and exploration 
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下载免费PDF全文 Although fractional integration and differentiation have found many applications in various fields of science, such as physics, finance, bioengineering, continuum mechanics, and hydrology, their engineering applications, especially in the field of fluid flow processes, are rather limited. In this study, a finite difference numerical approach is proposed to solve the time–space fractional governing equations of 1‐dimensional unsteady/non‐uniform open channel flow process. By numerical simulations, results of the proposed fractional governing equations of the open channel flow process were compared with those of the standard Saint‐Venant equations. Numerical simulations showed that flow discharge and water depth can exhibit heavier tails in downstream locations as space and time fractional derivative powers decrease from 1. The fractional governing equations under consideration are generalizations of the well‐known Saint‐Venant equations, which are written in the integer differentiation framework. The new governing equations in the fractional‐order differentiation framework have the capability of modelling nonlocal flow processes both in time and in space by taking the global correlations into consideration. Furthermore, the generalized flow process may possibly shed light on understanding the theory of the anomalous transport processes and observed heavy‐tailed distributions of particle displacements in transport processes. 相似文献
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13.
N. Emir 《洁净——土壤、空气、水》1994,22(6):280-288
This research has been undertaken to determine the zooplanktonic fauna (Rotatoria, Crustacea) and their seasonal distribution in two lakes with different characters. Çavu?cu lake has a surface area of 1000 ha with a maximum depth of 4 m and is classified as an oligo-mesotrophic lake. Eber lake has a surface area of 5200…17000 ha with a maximum depth of 2.5 m and is classified as an eutrophic lake. Zooplankton samples have been collected seasonally between the period of 1990 to 1993 from three stations with a zooplankton net of 44 μm mesh size. From Çavu?cu lake totally 50 Rotifera, 2 Copepoda, and 7 Cladocera species; 49 phytoplankton genera and 5 macrophytes have been identified while, 37 Rotifera, 3 Copepoda, 5 Cladocera; 45 phytoplankton genera and 6 macrophytes have been identified from Eber lake. 13 new rotifer records for the Turkey were found, which were Brachionus diversicornis, Macrochaetus collinsi, Lecane stichaeta, Cephalodella sterea, Cephalodella auriculata, Trichocerca iernis, Encentrum saundersiae. Pompholyx complanata, Floscularia ringens, Conochilus natans, Filinia pejleri, Rotaria rotatoria, and Philodina megalotrocha. 相似文献
14.
Dr. René Gächter Dr. Wolfgang Geiger 《Aquatic Sciences - Research Across Boundaries》1979,41(2):277-290
Phytoplankton, periphyton and zooplankton samples, chironomid andSialis sp. larvae, and fry of trout and bream collected from unpolluted and artificially metal-polluted limno-corrals were analyzed
for mercury, copper, cadmium, zinc and lead. The results indicate that these metals are not accumulated through the food chain
and suggest that increased metal concentrations in the environment favor the growth of phytoplankton organisms with a low
metal sorption capacity. 相似文献
15.
J.N. Goswami D. Lal M.N. Rao T.R. Venkatesan 《Earth and Planetary Science Letters》1979,44(2):325-334
Six soil samples from various depths of the Luna 24 drill core column have been analysed for their particle track records and light noble gas compositions. The observed particle track records indicate higher degree of maturity for the upper zone (～1 m) of this regolith column as compared to the soils in the lower zone (～0.4 m). The cosmogenic21Ne concentrations decrease rapidly with depth to 1 m, after which the concentrations level off or increase slightly. These data suggest a multi-stage depositional history for this drill core soil column consisting of: (1) rapid deposition of regolith material, (2) a cratering event about 400 m.y. B.P., leading to excavation to a depth of ～1 m from the present regolith surface, (3) a relatively rapid fill up of the crater with near-surface irradiated material, and (4) in-situ irradiation during the last about 250–300 m.y. Such a depositional sequence can also explain the observed lack of correlation between different surface exposure-correlated maturity indices in these drill core soil samples. 相似文献
16.
Dr. P. Baccini Dr. J. Ruchti Dr. O. Wanner E. Grieder 《Aquatic Sciences - Research Across Boundaries》1979,41(2):202-227
In three limno-corrals of the MELIMEX project the transport paths of the trace metals Cu, Zn, Cd, Hg and Pb and the reaction
of the systems on increased metal loads were investigated. The metal balances lead to the conclusion that the biomass is the
main factor responsible for the regulation of trace metal concentration. The observed sequence of relative residence times
of the trace metals can be described with a steady-state model. Additional metal load decreases the ability of the limnic
system to lower the metal concentration. The production of phytoplankton and its assimilation capacity for metals are reduced
leading to relatively higher metal concentrations in the lake. 相似文献
17.
Sediment resuspension under action of wind in Taihu Lake,China 总被引：2，自引：0，他引：2
A field study was undertaken to investigate the changes of the current speed, wave parameters and sediment resuspension under different wind speeds in the Taihu Lake. The Acoustic Doppler Current Profi... 相似文献
18.
M. Eneva J.L. Stevens B.D. Khristoforov J. Murphy V.V. Adushkin 《Pure and Applied Geophysics》2001,158(3):605-626
—?As part of a collaborative research program for the purpose of monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT), we are in the process of examining and analyzing hydroacoustic data from underwater explosions conducted in the former Soviet Union. We are using these data as constraints on modeling the hydroacoustic source as a function of depth below the water surface. This is of interest to the CTBT because although even small explosions at depth generate signals easily observable at large distances, the hydroacoustic source amplitude decreases as the source approaches the surface. Consequently, explosions in the ocean will be more difficult to identify if they are on or near the ocean surface. We are particularly interested in records featuring various combinations of depths of explosion, and distances and depths of recording.¶Unique historical Russian data sets have now become available from test explosions of 100-kg TNT cast spherical charges in a shallow reservoir (87?m length, 25?m to 55?m width, and 3?m depth) with a low-velocity air-saturated layer of sand on the bottom. A number of tests were conducted with varying water level and charge depths. Pressure measurements were taken at varying depths and horizontal distances in the water. The available data include measurements of peak pressures from all explosions and digitized pressure-time histories from some of them. A reduction of peak pressure by about 60–70% is observed in these measurements for half-immersed charges as compared with deeper explosions. In addition, several peak-pressure measurements are also available from a 1957 underwater nuclear explosion (yield <10?kt and depth 30?m) in the Bay of Chernaya (Novaya Zemlya).¶The 100-kg TNT data were compared with model predictions. Shockwave modeling is based on spherical wave propagation and finite element calculations, constrained by empirical data from US underwater chemical and nuclear tests. Modeling was performed for digitized pressure-time histories from two fully-immersed explosions and one explosion of a half-immersed charge, as well as for the peak-pressure measurements from all explosions carried out in the reservoir with water level at its maximum (3?m). We found that the model predictions match the Russian data well.¶Peak-pressure measurements and pressure-time histories were simulated at 10?km distance from hypothetical 1-kt and 10-kt nuclear explosions conducted at various depths in the ocean. The ocean water was characterized by a realistic sound velocity profile featuring a velocity minimum at 700?m depth. Simulated measurements at that same depth predict at least a tenfold increase in peak pressures from explosions in the SOFAR channel as compared with very shallow explosions (e.g., ～3?m depth).¶ The observations and the modeling results were also compared with predictions calculated at the Lawrence Livermore National Laboratory using a different modeling approach. All results suggest that although the coupling is reduced for very shallow explosions, a shallow 1-kt explosion should be detectable by the IMS hydroacoustic network. 相似文献
19.
Regional groundwater flow systems often contain both strong sinks and weak sinks. A strong sink extracts water from the entire aquifer depth, while a weak sink lets some water pass underneath or over the actual sink. The numerical groundwater flow model MODFLOW may allow a sink cell to act as a strong or weak sink, hence extracting all water that enters the cell or allowing some of that water to pass. A physical strong sink can be modeled by either a strong sink cell or a weak sink cell, with the latter generally occurring in low‐resolution models. Likewise, a physical weak sink may also be represented by either type of sink cell. The representation of weak sinks in the particle tracing code MODPATH is more equivocal than in MODFLOW. With the appropriate parameterization of MODPATH, particle traces and their associated travel times to weak sink streams can be modeled with adequate accuracy, even in single layer models. Weak sink well cells, on the other hand, require special measures as proposed in the literature to generate correct particle traces and individual travel times and hence capture zones. We found that the transit time distributions for well water generally do not require special measures provided aquifer properties are locally homogeneous and the well draws water from the entire aquifer depth, an important observation for determining the response of a well to non‐point contaminant inputs. 相似文献
20.
地球内部的热事件与地壳上地幔结构的相关研究 总被引：1，自引：0，他引：1
本文计算并讨论了当地球内部有热脉动事件发生时非稳态的热作用模型及其对地热场和大地热流的影响。理论计算和实际资料表明,构造活动区和稳定地区应有不同的热作用过程,在构造活动区地壳内的低速,低阻层和上地幔的低速,低阻层的埋藏深度之差与该地的热活动史有一定的对应关系。如华北平原地区,观测的二层深度差为40—60公里,推测热脉动持续时间为40百万年,活动史为50—70百万年:而银川盆地二层间隔为36—40公里,活动史为30—40百万年 相似文献