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241.
Laboratory experiments have shown that the juvenile migratory stage of banded kokopu (Galaxias fasciatus (Gray 1842)) is more sensitive to turbidity than other native fish species and avoids turbidity levels of >25 nephelometric turbidity units (NTU). Field trials using juvenile fish collected from the Tarawera River and Hays Stream, New Zealand, were used to test the results from these laboratory experiments by measuring the effects of turbidity on the migration direction and rate for banded kokopu in a natural stream setting. In the stream setting, neither the migration rate nor the migration direction were affected at turbidity <25 NTU. At higher turbidity levels, significantly fewer fish migrated up stream within a given time period. Because there was rarely any downstream movement, this suggests the fish either halted or slowed their upstream movement. A slower rate of migration could result in fewer juveniles reaching adult habitat, and would account for the reduced abundance of adult banded kokopu in rivers that are turbid during the migration season. Achieving turbidity levels of <25 NTU in rivers and streams during the migration season would therefore help maintain upstream migrations and populations of banded kokopu, and hence other native fish species. 相似文献
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Michael A. Mischna Mark Allen Mark I. Richardson Claire E. Newman Anthony D. Toigo 《Planetary and Space Science》2011,59(2-3):227-237
We utilize the MarsWRF general circulation model (GCM) to address the behavior of gas plumes in the Martian atmosphere, with the specific goal of characterizing the source of the recently identified methane detection in the Martian atmosphere. These observations have been interpreted as the release of methane from localized surface sources with spatial and temporal variabilities. Due to the limited temporal coverage of ground-based observations, we use a GCM to simulate the development of passive atmospheric plumes over relevant timescales. The observations can be reproduced best if the release occurred just before the time of observation—no more than 1–2 sols earlier—and if this release were nearly instantaneous rather than a slow, steady emission. Furthermore, it requires a source region spanning a broad latitudinal range rather than a point emission. While the accuracy of our conclusions about this specific methane release scenario is limited by the uncertainties inherent in GCM simulations of the Martian atmosphere, our findings regarding generalized plume behavior are robust, and illustrate the potential power of numerical modeling for constraining plume source conditions. 相似文献
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Green-lipped mussels (Perna viridis) were exposed to Aroclor 1254 (0.5, 5 and 50 microgl(-1)) and a mixture of benzo[a]pyrene (B[a]P) and Aroclor 1254 (0.3+0.5 and 3+5 microgl(-1)) for 12 days. On day 0, 1, 3, 6 and 12, the levels of DNA strand breaks in the mussel hepatopancreas were monitored using an alkaline unwinding assay. The results were compared to the findings of a previous study in which the levels of DNA strand breakage in the same species were measured following exposure to various concentrations of B[a]P (0.3, 3 and 30 microgl(-1)). The results indicated that Aroclor 1254 at a concentration =50 microgl(-1) did not cause any increase in DNA strand breaks while B[a]P at concentrations ranging from 0.3 to 3 microgl(-1) caused an increase in strand breaks after one day of exposure, followed by an apparent rapid recovery. In contrast, exposure to 30 microgl(-1) B[a]P caused no increase in DNA strand breaks over the exposure period. This was postulated to be due to an early elicitation of the DNA repair system by the relatively high exposure level of B[a]P. This hypothesis was tested in the present study, and the results suggest that exposure to the high B[a]P concentration might have elicited the defense mechanism within the mussels, resulting in no observed increase in DNA strand breaks. An increase in strand breaks was, however, evident when the mussels were exposed to lower B[a]P levels. The levels of DNA strand breaks were correlated with the body burden of B[a]P and Aroclor 1254 but no significant relationship was observed, possibly owing to the rapid metabolism of the toxicant and/or an effective DNA repair mechanism. As a result, DNA strand breakage in the hepatopancreas of green-lipped mussels may not be a suitable biomarker of exposure to the above toxicants in the marine environment. Our findings also suggest that it would be instructive to investigate (1) the role of DNA repair enzymes in the exposed mussels; and (2) the correlation between the activity of these enzymes and the body burden of specific toxicants. 相似文献
245.
D. L. Richardson 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):267-274
PARSEC is a PC-based, interactive algebraic manipulation package designed to manipulate series of the kind frequently found in Celestial Mechanics applications and perturbation procedures. The system is fundamentally an input/command interpreter which allows the user to enter algebraic expressions and procedures and to control the flow of series manipulations interactively. The system is designed to allow easy manipulations of polynomial-trigonometric series within the environment of an electronic scratchpad. 相似文献
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Richardson BJ Tse ES De Luca-Abbott SB Martin M Lam PK 《Marine pollution bulletin》2005,51(8-12):975-993
Semi-batch seawater experiments were conducted to follow the uptake and release of selected PAHs (anthracene, fluorathene, pyrene and B[a]P) and organochlorine pesticides (-HCH, aldrin, dieldrin, p,p′-DDT) in semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis). Mathematical models were applied to describe the uptake and elimination curves of the contaminants for SPMDs, and kinetic parameters, such as uptake rate constants, and equilibrium triolein/water partitioning coefficients were calculated. SPMD data showed a good fit to estimate rate constant and partition coefficient equations, but only those contaminants which partitioned mainly in the dissolved phase (-HCH and dieldrin) were well explained for mussels. Poor conformity of the other contaminants indicated mussels uptake by routes other than diffusion, such as ingestion of algae. An apparent equilibrium state was only noted for -HCH in mussels. Aldrin was not detected in mussels in the first few days of exposure, indicating potential metabolism of this compound. B[a]P was not detected in the triolein of SPMDs, which suggests that the membrane may act as a reservoir. Loss of spiked B[a]P from the triolein was evident in a depuration experiment, which may indicate transfer to the membrane. Rate constants for mussels were higher than those for SPMDs, but the reverse was true for partition coefficients. Overall, mussels and SPMDs had similar uptake rates for all compounds in this study, excluding p,p′-DDT and dieldrin. Contaminant elimination took place more rapidly in mussels, implying that SPMDs are better candidates for detecting episodic discharge of organic contaminants. 相似文献
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