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排序方式: 共有254条查询结果,搜索用时 15 毫秒
101.
Kit Yu Karen Chan Daniel Grünbaum Maj Arnberg Michael Thorndyke Sam T. Dupont 《Marine Biology》2013,160(8):2129-2135
Ocean acidification (OA), the reduction of ocean pH due to hydration of atmospheric CO2, is known to affect growth and survival of marine invertebrate larvae. Survival and transport of vulnerable planktonic larval stages play important roles in determining population dynamics and community structures in coastal ecosystems. Here, we show that larvae of the purple urchin, Strongylocentrotus purpuratus, underwent high-frequency budding (release of blastula-like particles) when exposed to elevated pCO2 level (>700 μatm). Budding was observed in >50 % of the population and was synchronized over short periods of time (~24 h), suggesting this phenomenon may be previously overlooked. Although budding can be a mechanism through which larval echinoids asexually reproduce, here, the released buds did not develop into viable clones. OA-induced budding and the associated reduction in larval size suggest new hypotheses regarding physiological and ecological tradeoffs between short-term benefits (e.g. metabolic savings and predation escape) and long-term costs (e.g. tissue loss and delayed development) in the face of climate change. 相似文献
102.
103.
Environmental Geochemistry and Health - A bioelectrochemical sensor (BES) was constructed for toxicity assessment of copper in contaminated domestic sewage. Electrochemically active bacteria (EAB),... 相似文献
104.
105.
There are two predominant views of organizational commitment: instrumental and affective. The purpose of the paper is to explore the extent to which an adapted version of Etzioni's macro organizational model of involvement may serve as a single model of both affective and instrumental perspectives of organizational commitment. Moral commitment and alienative commitment are treated as affective forms of organizational attachment, and calculative commitment is treated as an instrumental form of organizational attachment. The paper employs five samples for the investigation. It develops scales for measuring each of the three dimensions of commitment. The paper concludes that organizational commitment is multidimensional. It also concludes that employees report a mixture of commitment types. Evidence is offered in support of the affective character of moral and alienative commitment. Although the evidence is equivocal, there is support for the independence of the two dimensions of affective commitment: moral and alienative. Evidence is also offered for the differential association of the three dimensions of organizational commitment with related aspects of organizational behavior. The paper extends our understanding of organizational commitment by providing a place for both instrumental and affective forms of psychological attachment to organizations. It offers scales which may be used for future research, and it suggests research which may extend the adapted model in this paper as well as provide direction for practising managers. 相似文献
106.
Sam Cudjoe Ofori 《The Environmentalist》1991,11(1):45-54
Summary Environmental Impact Assessment (EIA) now enjoys at least statutory status in a number of Third World Countries (TWCs), including Ghana. Indeed, it is now considered an important tool of policy and control, both at the central government and local/district government levels. One of the difficulties, however, in implementing EIA has been the design of an appropriate methodology, in view of the fact that most, if not all the existing methodologies are more suitable to developed countries than developing ones.It is argued that in the absence of very sound indigenous methods and approaches, some of the existing inappropriate methodologies could be adapted or domesticated in a developing country like Ghana. The current administration and survey procedure used by the Ghana EIA Authority is examined and among other recommendations, an adapted form of the matrice approach is suggested.Mr Sam C. Ofori is a Lecturer in the Department of Geography at the University of Cape Coast, Ghana. He is currently a PhD research worker at the Centre for Planning, University of Strathclyde. A recent paper by Mr Ofori (then Cudjoe) appeared inThe Environmentalist,10(2), 115–126. 相似文献
107.
Kumar T Stanley VA Lal AA Balasubramanian M Pillai KS 《Journal of environmental biology / Academy of Environmental Biology, India》2002,23(4):407-410
Alloxan-induced diabetic rats were treated with multiple herbal preparation besides a control group receiving distilled water. The levels of glucose and alkaline phosphatase (ALP) increased abnormally in the alloxan treated group and the same were normalized upon treatment with the herbal preparation. The levels of blood urea nitrogen (BUN), alanine aminotransferase (ALT), protein and albumin in all groups remained unaltered. However, weekly body weight gain which got significantly altered in the alloxan-treated group was normalized by treatment with the herbal preparation. On the whole, a profound hypoglycemic effect was observed by the multiple herbal treatment in the diabetic rats. 相似文献
108.
Activity concentration levels and ratios of (226)Ra, (210)Pb and (210)Po are presented in multicellular marine algae, molluscs, coral as well as in surface marine sediments collected from the shallower waters of the fringing reefs area extending towards north and south (Flamingo bay) of PortSudan harbour, Sudan. The analyses were performed adopting alpha-spectrometry, liquid scintillation and Cerenkov counting techniques. Surface sediments from this coastal region are poor in their radioactivity content in contrast to similar data reported from different coastal areas around the globe. There is surface enrichment of (210)Pb and (210)Po with respect to their progenitor (226)Ra as it is evident from the activity ratios of (210)Pb/(226)Ra (3.03+/-1.79) and (210)Po/(226)Ra (2.23+/-1.56). Among marine plants and animals investigated, the green algae species, Halimeda, and coral species, Favites, show substantial concentration of radium at 8.2Bq/kg and 21.9Bq/kg dry weight, respectively. Similarly, the highest concentration of (210)Po was met in Favites at 38.7Bq/kg followed by brown algae, Cystoseria sp., at 32.6Bq/kg. There is no variation seen among algal species for (210)Pb uptake, however, converse to radium and polonium, Favites (coral) was found to contain the minimum concentration of lead (3.88Bq/kg). In most species there is preferential accumulation of polonium over its parent radium as indicated by (210)Po:(226)Ra activity ratio with Cystoseria (brown algae) showing the highest value at 8.81. On the other hand, (210)Po:(210)Pb activity concentration ratio revealed that coral species Favites (9.97) and the brown algae Sargassum (1.85) have a greater tendency to accumulate (210)Po over (210)Pb, while in the rest of species; this ratio is less than unity. 相似文献
109.
A watershed disturbance index developed by the USDA Forest Service called equivalent roaded area (ERA) was used to assess
the cumulative effect from forest management in California's Sierra Nevada and Klamath mountain ranges. The basins' ERA index
increased as logging and road-building occurred and then decreased over time as management ceased and vegetation recovered.
A refinement of the standard index emphasized disturbances in sensitive, near-channel areas, and evaluated recovery periods
of 20, 30, and 50 years. Shorter recovery periods yielded better correlations between recovering forest systems and aquatic
response than the longer recovery period, as represented by ERA and diversity or dominance, respectively. The refined ERA
index correlated more closely with macroinvertebrate dominance and diversity information that was available for part of the
study period. A minimum ERA threshold of 5% was detected, below which no effect to the macroinvertebrate community was observed.
Above this threshold, elevated ERA values were associated with a decline in macroinvertebrate diversity and an increase in
dominance of the top five taxa. Use of an ERA technique that emphasizes near-channel areas and biological thresholds would
contribute to the Forest Service's implementation of ecosystem management. 相似文献
110.
Evaluating Flow Metric‐Based Stream Classification Systems to Support the Determination of Ecological Flows in North Carolina 下载免费PDF全文
Michele C. Eddy Jennifer Phelan Lauren Patterson Jessie Allen Sam Pearsall 《Journal of the American Water Resources Association》2017,53(1):30-41
Hydroecological classification systems are typically based on an assemblage of streamflow metrics and seek to divide streams into ecologically relevant classes. Assignment of streams to classes is suggested as an initial step in the process of establishing ecological flow standards. We used two distinct hydroecological river classification systems available within North Carolina to evaluate the ability of a hydrologic model to assign the same classes as those determined by observed streamflows and to assess the transferability of such systems to ungaged streams. Class assignments were examined by rate of overall matches, rate of class matches, spatial variability in matches, and time period used in class assignment. The findings of this study indicate assignments of stream class: (1) are inconsistent among different classification systems; (2) differ between observed and modeled data; and (3) are sensitive to the period of record within observed data. One clear source of inconsistency/sensitivity in class assignments lies with the use of threshold values for metrics that distinguish stream classes, such that even small changes in metric values can result in different class assignments. Because these two hydroecological classification systems are representative of other classification systems that rely on quantitative decision thresholds, it can be surmised that the use of such systems based on stream flow metrics is not a reliable approach for guiding ecological flow determinations. 相似文献