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151.
152.
This study was undertaken to determine if dissolution of 226Radium from pipe-scale deposits contributes to enhanced waterborne 226Radium concentrations at the point of use. Water samples were collected from residential water customers of a small rural Iowa town. Sites were evenly divided between new and old water main connections. Daily samples were collected from the point-of-entry water. Point-of-use 226Radium concentrations ranged from 0.4 to 12.9 pCi L-1 (0.01 to 0.5 Bq L-1). The mean 226 Radium concentration for homes connected to old water mains was significantly higher than the mean 226Radium concentration of homes connected to new water mains, mean(standard deviation) equal 8.3(1.1) and 5.3(0.8) pCi L-1 [0.3(1.1) and 0.2(0.8) Bq L-1], respectively. 226Radium concentrations of the point-of-entry water ranged from 5.0 pCi L-1 to 10.3 pCi L-1 (0.2 Bq L-1 to 0.4 Bq L-1). This study indicates considerable variability of 226Radium exposure from drinking water among residents of the same water supply and has implications for regulatory compliance and exposure assessment in epidemiologic studies. 相似文献
153.
Heavy metals and marine diatoms: Influence of dissolved organic compounds on toxicity and selection for metal tolerance among four species 总被引:2,自引:0,他引:2
Experiments were conducted to determine whether diatom clones isolated from waters (Corio Bay or Hobson's Bay, Australia) chronically contaminated with heavy metals were more metal-resistant than clones of the same species isolated from cleaner waters (Bass Strait). Four species (2 clones per species) and 3 metals (Cu, Zn, Cd) were examined. The growth response of each clone to metal additions was assessed in both Corio Bay water and Bass Strait water. Generally, Cu was readily chelated and the most toxic metal and Cd the least chelated and least toxic. Toxicity of Cu to growth was found to be directly related to cellular Cu levels, which in turn were mediated by dissolved organic compounds in seawater. Corio Bay water had a greater metal-complexing capacity than Bass Strait water, and metal additions generally proved more toxic to each clone when in Bass Strait water. Ultraviolet irradiation eliminated differences between the water types. Relative to Bass Strait clones, no trend of enhanced metal tolerance was noted among the Corio Bay and Hobson's Bay clones; on the contrary the Corio Bay and Hobson's Bay cells were generally less to lerant of metals than were their Bass Strait counterparts, being particularly affected when in Bass Strait water. The results suggest that metal additions to waters rich in dissolved organic compounds would likely have less effect (in terms of direct toxicity and as a selective agent for metal tolerance) on resident phytoplankters than similar additions to waters low in organics.Publication No. 274 in the Ministry for Conservation, Environmental Studies Series 相似文献
154.
T. R. Fisher 《Marine Biology》1977,41(4):361-369
The bioenergetic basis of the biannual reproductive cycle of the solitary tunicate Styela plicata was investigated in order to evaluate hypotheses concerning the lack of larval settlement in summer. The rate of ingestion and absorption efficiency were measured in order to provide an estimate of the rate at which material was made available for maintenance, growth, and reproduction. At a given temperature the rate of ingestion was proportional to the 0.7 power of wet mass. the ingestion rate increased rapidly with increasing temperature between 12° and 18°C (Q103), but was independent of temperature between 18° and 28°C. Absorption efficiency was independent of temperature and body size and averaged approximately one-third for both carbon and nitrogen. Metabolic maintenance costs were estimated from measurements of oxygen consumption and excretion of ammonia and urea reported for s. plicata. These require only 18±11% of the carbon and 37±22% of the nitrogen absorbed from the gut of S. plicata over the temperature range 12° to 28°C. Metabolic maintenance makes no excessive demands on the material absorbed in the gut at a particular time of year, and a surplus of carbon and nitrogen substrate is available throughout the year for growth and reproduction. Predation on larvae and young adults may be responsible for the low rate of settlement observed in summer months. 相似文献
155.
Determination of self-accelerating decomposition temperatures using the Accelerating Rate Calorimeter 总被引:5,自引:0,他引:5
Harold G. Fisher David D. Goetz 《Journal of Loss Prevention in the Process Industries》1991,4(5):305-316
A self-accelerating decomposition temperature (TSADT is the minimum ambient air temperature at which a reactive material of specified stability decomposes in a specified commercial package in a period of 7 days or less. Values for TSADT are determined to decide whether a substance should be subject to temperature control during transport. Values of TSADT calculated using the Accelerating Rate Calorimeter (ARC) and techniques suggested by Wilberforce and the authors are compared to those measured by oven stability testing. The methodology and the advantages of using the ARC to obtain TSADT values are discussed. 相似文献
156.
Stuart G. Fisher 《Environmental management》1990,14(5):725-736
The concept of succession has a distinguished history in general ecology and has been applied to stream ecosystems with some
success. Succession in streams is largely secondary, follows initial floristics models, and occurs through a variety of mechanisms.
The process is moderately predictable but is highly influenced by “climatic” factors, particularly nutrient chemistry. In
desert streams, succession does not result in a climax state. While evidence is slim, succession may not be a significant
process in streams of certain types or in certain regions.
Successional theory is difficult to apply in spatially heterogeneous, hierarchically organized ecosystems. It also suffers
in being only one component of a better integrated concept, that of ecosystem stability, which deals more directly with disturbance
and ecosystem resistance in addition to resilience (which encompasses succession). Succession has so suffered from a half
century of confusion that a strong case can be made for abandoning the term, at least as it applies in streams, in favor of
the broader view provided by stability theory. 相似文献
157.
Patterns of phytoplankton carbon (C) metabolism were examined in å combined laboratory and field study to assess the influence of light conditions on 14C assimilation into photosynthetic end-products. Laboratory studies with three species representing distinct size classes and taxonomic groups tested the influence of low light on patterns of C flow. Prorocentrum mariae-lebouriae (dinoflagellate) and Ditylum brightwellii (diatom) showed decreased movement of photoassimilated 14C into protein following a shift to low light 14C assimilation into lipids and photosynthetic pigments increased in low light and was paralleled by increased chl a per cell. The proportion of 14C fixed into protein returned to the pre-shift level upon return to initial light conditions. Monochrysis lutheri (chrysophyte) did not show this pattern of reduced % 14C protein. Incubations of 12 and 24 h demonstrated significant rearrangements in labeling patterns at night, wherein 14C flow into protein in darkness was favored. % 14C protein at night was lower for M. lutheri than for the other species, suggesting some interspecific differences in the low light response. Measurements of 14C assimilation in phytoplankton assemblages from Chesapeake Bay demonstrated movement of a higher proportion of photo-assimilated C into protein in samples collected in the surface mixed layer than in those below the pycnocline. In comparison, phytoplankton collected below the pycnocline fixed a higher proportion of 14C into lipids, photosynthetic pigments, and low molecular weight metabolites, as was observed in low light laboratory cultures. A comparison of 12- and 24-h incubations for measuring patterns of C flow into photosynthetic end-products confirmed the inadequacy of short-term measurements, as significant changes in 14C allocation occurred in the dark phase of the photocycle. Together, these results suggest that 14C assimilation into photosynthetic end-products can be a useful measure of adaptive state in changing light conditions, but point out some difficulties in applying this approach in situ. 相似文献
158.
Assimilation efficiencies and turnover rates of trace elements in marine bivalves: a comparison of oysters, clams and mussels 总被引:2,自引:0,他引:2
Assimilation efficiencies (AEs) and physiological turnover-rate constants (k) of six trace elements (Ag, Am, Cd, Co, Se, Zn) in four marine bivalves (Crassostrea virginica Gmelin, Macoma balthica Linnaeus, Mercenaria mercenaria Linnaeus, and Mytilus edulis Linnaeus) were measured in radiotracer-depuration experiments. Egestion rates of unassimilated elements were highest during
the first 24 h of depuration and declined thereafter. Significant egestion of unassimilated Co, however, continued for up
to 5 d in Macoma balthica, Mercenaria mercenaria and Mytilus edulis. With the exception of the extremely low values for 110 mAg, 109Cd, and 65Zn in C. virginica, physiological turnover-rate constants (k) showed no general pattern of variation among elements, bivalve species or food types, and were relatively invariant. Values
from ≤0.001 to 0.1 d−1 were observed, but excluding those for Co, most values were ≤0.04 d−1. In all four species, the AEs of Ag, Am, and Co were generally lower than those of Cd, Se, and Zn. The AEs of Ag, Cd, Se,
and Zn in these bivalves are directly related to the proportion of each element in the cytoplasmic fraction of ingested phytoplankton,
indicating that >80% of elements in a prey alga's cytoplasm was assimilated. C. virginica, Macoma balthica, and Mercenaria mercenaria assimilated ∼36% of the Ag and Cd associated with the non-cytoplasmic (membrane/organelle) fraction of ingested cells in
addition to the cytoplasmic fraction. The ratio of AE:k, which is proportional to the consumer–prey trace-element bioaccumulation factor (concentration in consumer:concentration
in prey) was generally greater for Cd, Se, and Zn than for Ag, Am, and Co. This ratio was lowest in Mytilus edulis, suggesting that this bivalve, the most widely employed organism in global biomonitoring, is relatively inefficient at accumulating
important elements such as Ag, Cd, and Zn from ingested phytoplankton.
Received: 7 February 1997 / Accepted: 24 February 1997 相似文献
159.
160.
Past and Present Status of Central Valley Chinook Salmon 总被引:1,自引:0,他引:1
Frank W. Fisher 《Conservation biology》1994,8(3):870-873