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31.
Mixing experiments of seawater and the Hudson and Mississippi riverwaters with radiotracer spikes show that Co, Mn, Cs, Cd, Zn and Ba will be desorbed from river suspended particles, while significant fractions of “dissolved” Fe, Sn, Bi, Ce and Hg will be coagulated during estuarine mixing. 相似文献
32.
Calvin J. Heusser Linda E. Heusser Thomas V. Lowell Andrs Moreira M. Simn Moreira M. 《第四纪科学杂志》2000,15(2):101-114
The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 14C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 14C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 14C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 14C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 14C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 14C yr BP, invalidating earlier dates of between 15 800 and 16 590 14C yr BP. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
33.
Steven C. Schimmel James M. Patrick Linda F. Faas Jerry L. Oglesby Alfred J. Wilson 《Estuaries and Coasts》1979,2(1):9-15
Two long-term studies were conducted to determine toxicity, uptake and depuration of Kepone in blue crabs (Callinectes sapidus). In the first, Kepone was administered to crabs in seawater (0.03 or 0.3 μg Kepone/I) or food (eastern oyster,Crassostrea virginica, containing 0.25 μg/g Kepone). Uptake of Kepone in 28 days was primarily through the contaminated oysters. When these crabs were held in Kepone-free seawater and fed Kepone-free oysters for 28 days, no loss of the insecticide was evident. There were adverse effects on molting and survival in crabs fed oysters that contained 0.25 μg/g Kepone. A second study was conducted to determine: (1) the depuration of Kepone over a 90-day period in blue crabs fed oysters from the James River, Virginia (containing 0.15 μg/g Kepone); and (2) the effects of Kepone on molting and survival of blue crabs fed James River oysters or laboratory-contaminated oysters that contained 0.15 or 1.9 μg/g Kepone. Crabs fed Kepone-contaminated oysters followed by a diet of Kepone-free oysters for 90 days had detectable concentrations of the insecticide in tissues. Also, blue crabs that ate oysters containing Kepone in concentrations similar to those found in oysters from the James River, died or molted less frequently than crabs fed Kepone-free oysters meats. 相似文献
34.
Concentrations of Ca, Cd, Cu, Fe, and Pb and binding capacities for Cd, Cu, and Pb were determined for water samples collected
from 12 lakes in southwestern Maine using atomic absorption and ion-selective electrodes, respectively. Surface waters in
this area are soft and characterized by low pH. Some lakes were highly colored with refractory organics, whereas others had
very low organic carbon concentrations. Both Cu and Pb concentrations were positively correlated with organic carbon content.
Copper and Pb binding capacities were significantly correlated with organic carbon content, whereas Cd binding capacity was
positively correlated with pH, but not with organic carbon. Surface water binding capacity for Pb was greater than that for
Cu or Cd. More than 99% of the Ca from all waters studied was removed onto cationic exchange resins. Less than 1% of the total
Cu existed as cationic species in highly humic waters, whereas as much as 65% existed as cationic species in less huic waters.
Conversely, more than 99% of the Cd present in humic waters existed as cationic species, whereas as little as 50% existed
as cationic species in less humic, more alkaline waters. These correlative studies indicate that binding by organic carbon
is important for both Cu and Pb in this area and must be considered in models of trace metal speciation. However, Cd binding
in the same waters is not correlated with organic carbon, which does not need to be considered in speciation models for Cd. 相似文献
35.
Linda E. Bireley 《Estuaries and Coasts》1984,7(3):242-247
A nested design was used to analyze the variance of the proportions or percent species composition of shore-zone finfish assemblages in the vicinity of the Millstone Nuclear Power Station in eastern Long Island Sound. The relative importance of five selected shore-zone species was found to be significantly influenced by both station and season within a year. Also included in the nested ANOVA model were effects due to period of plant operation (no units operating, one unit operating and two units operating) and year within period. Neither of these two effects was found to influence the percent species composition. The results of this study suggest that a nested ANOVA of percent species composition can be useful for detecting changes in assemblages of finfish species over time and space. 相似文献
36.
Linda J. Anderson-Berry 《Natural Hazards》2003,30(2):209-232
This paper is a partial discussion of a four-year study that investigated the vulnerability of the people living in the Cairns region to the tropical cyclone hazard. The longitudinal case study, focussing on the Cairns Northern Beaches area, was unique in that it included a social and societal `pre-cyclone impact' evaluation of various resident communities within the region, and then two consecutive `post-cyclone impact' studies. The primary research method supported an inductive qualitative approach to the collection and analysis of survey data. Some quantitative methods were invoked to support qualitative research findings. Survey data was collected in five separate questionnaire-based social surveys that were administered between 1996 and 2000. During the study, residents experiencedthe direct impact of two land-falling tropical cyclones. In addition to this, targeted andfocussed tropical cyclone awareness education was made increasingly available withinthe community. The social and demographic attributes that influence the individual'sperception of risk and contribute to our understanding of community vulnerability were examined and evaluated. Changes in the residents' attitudes, cyclone preparednessbehaviours and willingness to respond to cyclone warnings were monitored and measured. Analysis of early survey data indicated that community residents generally had some knowledge of cyclones but a limited understanding of cyclone processes and very little direct personal experience of the cyclone hazard. Individually and collectively, residents frequently demonstrated a biased perception of the risks associated with cyclones. The resident community was shown to be fragmented, with limited support being available to individual households. Initially, residents were found to be poorly prepared for cyclones and unlikely to respond to warnings appropriately. It appeared that, in the event of a land-falling tropical cyclone impacting the area, the community was highly vulnerable to unnecessary loss of property, livelihood and – in extreme circumstances – life. By 2000, Cairns community residents were somewhat better informed about cyclones and certainly more experienced. This paper provides some insight into how cyclone experience and education may synergisticly have contributed to a change in risk perceptions and a reduction in the vulnerability of Cairns residents to the tropical cyclone and storm surge hazards. 相似文献
37.
38.
Ryan Mathur Wayne Powell Andrea Mason Linda Godfrey Junming Yao Mark E. Baker 《Geostandards and Geoanalytical Research》2017,41(4):701-707
Increased interest in the fractionation of Sn isotopes has led to the development of several techniques for preparing cassiterite (SnO2, the primary ore of Sn) for isotopic analysis. Two distinct methods have been applied in recent isotopic studies of cassiterite: (a) reduction to tin metal with potassium cyanide (KCN) at high temperature (800 °C), with subsequent dissolution in HCl, and (b) reduction to a Sn solution with hydriodic acid (HI) at low temperature (100 °C). This study compares the effectiveness and accuracy of these two methods and contributes additional methodological details. The KCN method consistently yielded more Sn (> 70% in comparison with < 5%), does not appear to fractionate Sn isotopes at high temperatures over a 2‐hour period and produced consistent Sn isotope values at flux mass ratios of ≥ 4:1 (flux to mineral) with a minimum reduction time of 40 min. By means of a distillation experiment, it was demonstrated that HI could volatilise Sn, explaining the consistently low yields by this method. Furthermore, the distillation generated Sn vapour, which is up to 0.38‰ per mass unit different from the starting material, the largest induced Sn fractionation reported to date. Accordingly, the HI method is not recommended for cassiterite preparation for Sn isotopic analysis. 相似文献
39.
Schinus terebinthifolius (Brazilian pepper), a native of South America, is currently naturalized in 20 countries worldwide and can alter native systems
by displacing flora and forming monotypic stands. The primary described mechanism of seed dispersal is through consumption
of fruits by birds and mammals. We evaluated an alternative dispersal method by evaluating the potential for S. terebinthifolius growing in freshwater and estuarine environments to disperse via water currents. Specifically, we: (1) determined the duration
fruits remained buoyant in three salinities, (2) estimated the viability of seeds after 7 days in water, (3) estimated the
dispersal rate of floating solitary fruits, and (4) examined the role of boat wakes in moving seeds above mean high water
at the shoreline. The length of time fruits floated in 0 ppt water (4.9 days) was significantly less than 15 ppt saltwater
(6.2 days), and 30 ppt saltwater (6.9 days). After 7 days, over 13% of seeds remained viable in 0 ppt, 15 ppt, and 30 ppt
water. By combining mean dispersal rates and the mean number of days fruits floated, we calculated individual fruits could
be transported 16.9 km in 0 ppt and over 22 km in 15 and 30 ppt water. To increase germination, seeds must be stranded above
the intertidal zone. Wind wakes alone never achieved this result; however, boat wakes plus wind wakes significantly increased
the movement of fruits above the intertidal region into drier soils. The use of both vertebrate dispersal vectors and water
dispersal may potentially increase the rate of invasion, establishment, and survival of S. terebinthifolius in freshwater and estuarine environments. 相似文献
40.
Three planktonic foraminiferal species Globigerina bulloides, Neogloboquadrina pachyderma (d), and Globorotalia inflata collected from core-tops spanning 35° to 65°N in the North Atlantic were used for U/Ca and Mg/Ca and foraminiferal shell weight analyses. Except for U/Ca in G. bulloides calcified under warm conditions (>∼13 °C), U/Ca ratios in all three studied species increase with decreasing latitude and show strong positive correlations with Mg/Ca ratios. A dissolution effect on planktonic U/Ca is suggested by decreased shell weight and U/Ca and Mg/Ca ratios for shells from very deep water depth (>4.4 km) along the latitudinal transect. G. bulloides from down core samples in the North Atlantic show low U/Ca ratios during the last glacial and high ratios during the Holocene, similar to the Mg/Ca evolution trend. In general, our data indicate that the U incorporation into planktonic foraminiferal carbonates is strongly influenced by calcification temperature, although U/Ca in G. bulloides may be affected by seawater carbonate ion concentration under warm conditions and/or other factors. 相似文献