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821.
Richard H. McCuen Walter J. Rawls 《Journal of the American Water Resources Association》1979,15(1):88-93
ABSTRACT: The literature abounds with procedures for estimating the magnitude and frequency of floods at ungaged locations. Unfortunately, the large number of available procedures creates an awesome task for potential users of sorting and selecting a method for immediate use. The objectives of this paper are to present (1) criteria that are necessary to evaluate the usefulness of hydrologic procedures, (2) to present a classification system for categorizing the multitude of procedures that are available, (3) to summarize the findings of the literature review, and (4) to make recommendations on reporting of flood frequency estimation procedures on ungaged watersheds. 相似文献
822.
Ronald M. North Walter P. Neely 《Journal of the American Water Resources Association》1977,13(5):995-1005
ABSTRACT: Three basic principles of responsibility have influenced the Federal/non-Federal cost sharing rates for water resources programs (1) full payment by beneficiaries (2) exclusive Federal assumption of costs and (3) joint Federal/non-Federal sharing. The efforts to determine appropriate cost sharing rates have resulted in several hundred complex arrangements involving contributions, user charges and direct sales based on many variations of payment terms. This basic present value model was developed to determine the non-Federal cost shares which are expected to be paid for 32 different functional purposes emanating from Federal water resources programs and projects for both implementation and OMR stages. The model introduces the concept of a composite (implementation plus OMR) cost share as a focus developing appropriate cost sharing rates for the private, public and mixed outputs produced through public water resources investments. The model can be used as a focus for policy decisions on cost sharing which seek to achieve consistent and equitable cost shares for purposes provided while maintaining an efficient allocation of resources within water programs. 相似文献
823.
Walter H. Corson 《The Environmentalist》2002,22(1):67-82
Indirect, unpriced environmental and social costs of human activities in the United States amount to several trillion dollars each year. By accounting for these costs and shifting some of the tax burden from work to waste, it would be possible to protect the environment and benefit society and the economy. 相似文献
824.
Ingrid Langer Doris Krpata Walter J. Fitz Walter W. Wenzel Peter F. Schweiger 《Environmental pollution (Barking, Essex : 1987)》2009,157(10):2871-2877
The effect of increasing soil Zn concentrations on growth and Zn tissue concentrations of a metal-accumulating aspen clone was examined in a dose–response study. Plants were grown in a soil with a low native Zn content which was spiked with Zn salt solutions and subsequently aged. Plant growth was not affected by NH4NO3-extractable soil Zn concentrations up to 60 μg Zn g?1 soil, but it was completely inhibited at extractable concentrations above 90 μg Zn g?1 soil. From these data an effective concentration of 68.5 μg extractable Zn g?1 soil was calculated at which plant growth was reduced by 50%. The obtained information on toxicity threshold concentrations, and the relation between plant Zn accumulation and extractable soil Zn concentrations may be used to assess the suitability of the investigated Populus canescens clone for various phytoremediation strategies. The potential risk of metal transfer into food webs associated with P. canescens stands on Zn-polluted sites may also be estimated. 相似文献
825.
Walter R. Tschinkel 《Behavioral ecology and sociobiology》1998,43(4-5):247-257
Many benefits and risks of cooperative colony founding (pleometrosis) have been identified, but rarely have the proximate
factors that lead to association been considered. This study examined the choices queens make during the first few hours after
mating, and some of the correlates of those choices. Queens had a strong affinity for preformed holes in the soil and readily
used these as their initial founding chambers. This affinity was so strong that in a field experiment, the dispersion pattern
of preformed holes controlled the final dispersion of colony-founding queens. Attraction to partially formed holes is thus
an important cause of pleometrosis. The excavation of complete founding chambers incurred no measurable cost on the subsequent
reproductive output of queens, suggesting that the primary benefit of using preformed holes is to remove the queen quickly
from exposure to predation and desiccation. In the field, pairs of queens offered five equivalent preformed holes in soil
were more likely to share the same hole if the holes were shallow and close together. In these experiments, queens modified
preformed soil holes so that the test holes were no longer equivalent, causing the choice of queen and hole to become confounded.
Laboratory experiments in plaster arenas with unmodifiable holes confirmed the field experiments: queens were more likely
to share a hole when the holes were shallow than when they were deep. Because queens entering adequately deep holes seldom
reemerged, this suggested that the likelihood of sharing increased with increasing contact between queens, that is, when queens
were readily and frequently detected. Such contacts will also predict the future competitive environments to be experienced
by incipient colonies, and may temper the tendency of queens to associate. However, experiments in which queens were exposed
to high and low densities before pairing in the choice arenas failed to show an effect on the choice to join the resident
queen. Queens that joined a resident queen differed in their robustness from queens that did not join. Queens choosing their
own partners did no better reproductively than those assigned partners at random. Overall, this study suggests that (1) newly
mated queens are under strong selection to leave the soil surface and do so by using any available holes, whether dug by another
queen or of some other origin; (2) they are attracted to other queens, and are more likely to cofound as contact with the
potential cofoundress becomes more frequent and (3) they choose whether or not to cofound partly on the basis of their own
reproductive characteristics.
Received: 20 November 1997 / Accepted after revision: 14 March 1998 相似文献
826.
The effects of ultraviolet radiation (UVR 280–400 nm) on the germination of Porphyra
haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released
conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when
UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division
of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area,
and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis,
enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such
sporelings. We also tested the effects of solar UVR on the growth of P.
haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis
of the species, but on the other hand, sporelings of P.
haitanensis are more sensitive to UV-B radiation than juveniles. 相似文献
827.
828.
829.
Walter Wheaton Dimmick †‡ Michael J. Ghedotti † Michael J. Grose † Anne M. Maglia † Daniel J. Meinhardt † and David S. Pennock 《Conservation biology》1999,13(3):653-660
Abstract: Conservation biology is linked inextricably with systematic biology. The principles of systematic biology, however, have not been integrated completely into the practice and principles of conservation biology. Systematists have recognized for some time that a number of evolutionary processes lead to the diversification of lineages. Yet some present units of conservation, such as the evolutionarily significant unit ( Waples 1991), primarily emphasize only one of these processes, adaptation. Allopatric speciation produces biodiversity without requiring any adaptive shift (and consequent adaptive differences between daughter species), so definitions of conservation units that emphasize adaptation may underestimate biodiversity. We estimated the frequency of different modes of speciation for three groups of vertebrates. The frequency of allopatric speciation varies among these groups, but is an important type of speciation in two of the three groups studied. Our results, and the results of other published studies of the frequency of modes of speciation, demonstrate that any unit of conservation defined solely in terms of adaptation is likely to underestimate biological diversity. 相似文献
830.
The concept of sustainable development (SD) has highly been debated since it was presented 25 years ago, with ‘hard science’ approaches on one side and more process-oriented approaches on the other side. Academic teaching in SD has emerged in response to this in very different contexts, partly mirroring this academic debate. Some master’s programmes in SD take a strong science approach, while other programmes focus on the process of implementing sustainability projects, sometimes connected with forms of action research and teaching. In this article, we identify diverse views on the concept of SD as well as views on most relevant modes of teaching. We discuss core competencies required for sustainability professionals in their working practices and we organise them in three main clusters: Know, Interact and Be (KIB). The article presents the results of a worldwide survey, which addresses these visions on the concept of SD, the capabilities needed for ‘sustainable development professionals’ and the teaching approach needed. The analysis is based on the responses of 54 lecturers and 287 students active in 34 SD master’s programmes on all continents. The results of this worldwide survey are discussed. We observe in practice some gaps between preferences and practice. Looking at what both lecturers and students see as essential topics to address, some topics get relatively less attention (like the population issue). The identified core competencies (KIB) are supported and all addressed in practice, while the ‘Be’ competencies receive relatively less attention. Suggested consequences for academic teaching include a further matching of programmes with perceived needs and bridging the gap between the experienced teaching approaches in practice with such identified needs. 相似文献