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121.
122.
Factors affecting the transport and retention of Cd, Cr, Cu, Ni, Pb and Zn in acidic groundwaters as they pass through estuarine sediments were investigated using column experiments. Acidic groundwaters caused the rapid dissolution of iron sulfide (AVS) and other iron and manganese phases from sediments that are important for metal binding and buffering. Metal breakthrough to overlying water occurred in the order of Ni>Zn>Cd>Cu>Cr/Pb. Metal transport increased as the sediment permeability increased, reflecting the low resistance to flow caused by larger sand-sized particles and the decreased abundance of metal adsorption sites on these materials. Metal mobility increased as the groundwater pH decreased, as flow rate or metal concentrations increased, and as the exposure duration increased. Groundwater Cr and Pb were promptly attenuated by the sediments, the mobility of Cu was low and decreased rapidly as sediment pH increased above 4.5, while Cd, Ni and Zn were the most easily transported to the surface sediments and released to the overlying waters. For groundwaters of pH 3, metal migration velocities through sandy sediments were generally 0.5-2% (Cr, Pb), 1-6% (Cu) and 4-13% (Cd, Ni, Zn) of the total groundwater velocity (9-700 m/yr). The oxidative precipitation of Fe(II) and Mn(II) in the groundwaters did not affect metal mobility through the sediments. The results indicated that the efflux of acidic and metal-contaminated groundwater through estuarine sediments would affect organisms resident in sandy sediments more greatly than organisms resident in fine-grained, silty, sediments. 相似文献
123.
In the United States, it is necessary to analyze for toxaphene using approved, validated methods acceptable to the regulatory agencies. As a result of an interlaboratory study and technical exchanges among the US EPA Region IV (EPA), the State of Georgia Environmental Protection Division (EPD), and Hercules Incorporated, guidelines for the application of SW-846 Method 8080 were developed. Results of analyses for sludge, soil, and water samples agreed within a percent relative standard deviation (% RSD) range of 6.9-20%. Through continued technical interchanges, guidance for the application of SW-846 Method 8081 has been developed. The results of analyses of fourteen split samples of soil and sediment produced a percent relative standard deviation that ranged from 1.6% to 127%, with an average of 38%. When two unusually divergent results were removed from consideration, the average % RSD reduced to 26%. The results of analyses of split samples show agreement between the EPA laboratory and a Hercules contract laboratory. Therefore, the guidance has achieved its purpose of producing agreement among data from different laboratories so that data reviewers may have assurance that the analytical method has been applied correctly and consistently for the determination of toxaphene in environmental samples. 相似文献
124.
Changes in boreal climate of the magnitude projected for the 21st century have always caused vegetation changes large enough to be societally important. However, the rates and patterns of vegetation change are difficult to predict. We review evidence suggesting that these vegetation changes may be gradual at the northern forest limit or where seed dispersal limits species distribution. However, forest composition may be quite resilient to climate change in the central portions of a species range until some threshold is surpassed. At this point, changes can be rapid and unexpected, often causing a switch to very different ecosystem types. Many of these triggers for change are amenable to management, suggesting that our choice of policies in the coming decades will substantially influence the ecological and societal consequences of current climatic change. 相似文献
125.
126.
Conservation Biology and Carnivore Conservation in the Rocky Mountains 总被引:17,自引:0,他引:17
127.
128.
We review the fundamentals of a new numerical modeling technique called Renormalized Numerical Simulation (RNS). The goal
of RNS is to model the drag force produced by high Reynolds-number turbulent flow over objects that display scale-invariant
properties, objects such as tree-like fractals. The hallmark of RNS in this application is that the drag of the unresolved
tree branches is modeled using drag coefficients measured from the resolved branches and unresolved branches (as modeled in
previous iterations of the procedure). In the present paper, RNS is used to study the effects of branch orientation on the
drag force generated by highly idealized trees in which trunk and branches have square cross-section, and the branches all
lie in a plane perpendicular to the incoming flow. Then, the procedure is generalized to the more general case of non-planar
branch arrangements. Results illustrate that RNS may enable numerical modeling of environmental flow processes associated
with fractal geometries using affordable computational resolution. 相似文献
129.
Edward M. Sykes Tabitha M. Innocent Ido Pen David M. Shuker Stuart A. West 《Behavioral ecology and sociobiology》2007,61(11):1751-1758
Sex allocation theory offers excellent opportunities for testing how animals adjust their behaviour in response to environmental
conditions. A major focus has been on instances of local mate competition (LMC), where female-biased broods are produced to
maximise mating opportunities for sons. However, the predictions of LMC theory can be altered if there is both local competition
for resources during development and an asymmetry between the competitive abilities of the sexes, as has been seen in animals
ranging from wasps to birds. In this paper, we test the extent to which asymmetric larval competition alters the predictions
of LMC theory in the parasitoid wasp Nasonia vitripennis. We found that the body size of both sexes was negatively correlated with the number of offspring developing within the host.
Further, we found that when faced with high levels of competition, the body size of females, but not males, was influenced
by the sex ratio of the competing offspring; females were smaller when a higher proportion of the brood was female. This asymmetric
competition should favour less biased sex ratios than are predicted by standard LMC theory. We then develop a theoretical
model that can be parameterised with our data, allowing us to determine the quantitative consequences of the observed level
of asymmetric larval competition for sex allocation. We found that although asymmetric competition selects for less biased
sex ratios, this effect is negligible compared to LMC. Furthermore, a similar conclusion is reached when we re-analyse existing
data from another parasitoid species where asymmetric larval competition has been observed; Bracon hebetor. Consequently, we suspect that asymmetric larval competition will have its greatest influence on sex ratio evolution in species
that have smaller clutches and where local mate competition is not an issue, such as birds and mammals. 相似文献
130.
Peter Witzgall Jean-Pierre Chambon Marie Bengtsson C. Rikard Unelius Monica Appelgren Gyorgy Makranczy N. Muraleedharan Darwin W. Reed Klaus Hellrigl Hans-Ruedi Buser Eric Hallberg Gunnar Bergström Miklos Tóth Christer Löfstedt Jan Löfqvist 《Chemoecology》1996,7(1):13-23
Summary The geometric isomers (E,E)-, (E,Z)-, (Z,E)-, and (Z,Z)-8,10-dodecadien-1-yl acetate were identified as sex pheromone components or sex attractants in the tribes Eucosmini and Grapholitini of the tortricid subfamily Olethreutinae. Species belonging to the more ancestral Tortricinae were not attracted. Each one isomer was behaviourally active in males ofCydia andGrapholita (Grapholitini), either as main pheromone compound, attraction synergist or attraction inhibitor. Their reciprocal attractive/antagonistic activity in a number of species enables specific communication with these four compounds.Pammene, as well as otherGrapholita andCydia responded to the monoenic 8- or 10-dodecen-1-yl acetates. Of the tribes Olethreutini and Eucosmini,Hedya, Epiblema, Eucosma, andNotocelia trimaculana were also attracted to 8,10-dodecadien-1-yl acetates, but several otherNotocelia to 10,12-tetradecadien-1-yl acetates. The female sex pheromones ofC. fagiglandana, C. pyrivora, C. splendana, Epiblema foenella andNotocelia roborana were identified. (E,E)- and (E,Z)-8,10-dodecadien-1-yl acetate are producedvia a commonE9 desaturation pathway inC. splendana. CallingC. nigricana andC. fagiglandana females are attracted to wingfanning males. 相似文献