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221.
Water utilities that rely on surface water may be vulnerable to future droughts and floods, a vulnerability that may be magnified by climate perturbations as well as shorter-term and, in some cases, ongoing changes in the political and regulatory environment in which utilities operate. Unfortunately, day-to-day responsibilities currently occupy most utility operators, leaving little time to plan for inherently uncertain effects. The record of actual responses to past droughts and floods can be illuminating, however, particularly when placed in the context of plausible hydrologic disruption and pressures such as population growth, floodplain development and new regulatory demands. This paper draws on interviews with water utility operators in the northwestern USA to highlight opportunities and constraints that water utilities may face vis-à-vis such disruptions. Key considerations affecting vulnerabilities include water rights, institutional barriers to efficient utility operations, hazard management policy and the fiscal status of utilities. 相似文献
222.
There have been many reports characterizing DNA from amber, which is a fossil version of plant resin. Here we report an investigation
of the effects of plant resin (from Pseudotsuga menziesii) and drying conditions on the preservation of DNA in biological tissues. We examined the degree of degradation of the DNA
by agarose gel electrophoresis of extracted DNA, by polymerase chain reaction, and by DNA sequencing. The plant resin alone
appeared to cause little or no damage to DNA. Tissue immersed in plant resin that dried rapidly (exposed to sunlight) contained
DNA with little apparent damage. Tissue immersed in the resin that was dried slowly (in shade without sunlight) contained
DNA with some degradation (3.5% nucleotide changes). The tissue that was immersed in the resin that was constantly hydrated
(by immersion in water) yielded DNA that was severely damaged (50–62% nucleotide changes). Transversions outnumbered transitions
in these samples by a ratio of 1.4 : 1. A piece of Baltic amber immersed in water for 5 days appeared to be impervious to
the water. Thus amber inclusions that initially dried rapidly have the potential to yield undamaged DNA. Those that dried
slowly may contain damaged DNA and may be unsuitable for phylogenetic and other studies.
Received: 23 March 1999 / Accepted in revised form: 16 September 1999 相似文献
223.
Kerry?L.?HowellEmail author Alex?D.?Rogers Paul?A.?Tyler David?S.?M.?Billett 《Marine Biology》2004,144(5):977-984
Zoroaster fulgens is a slope-dwelling seastar species that is distributed throughout the Atlantic Ocean. Studies into the population structure and systematics of marine animals have increasingly found that species with a reported cosmopolitan distribution are, in fact, collections of closely related cryptic or sibling species. In the Porcupine Seabight, three morphotypes of Z. fulgens can be found that have a distribution that is stratified by depth. This study investigates the genetic divergence between these morphotypes using sections of the cytochrome oxidase 1 (COI) and 16S regions of the mitochondrial genome. Bathymetrically separated morphotypes of Z. fulgens are reproductively isolated over distances of approximately 1 km while gene flow occurs among morphotypes, along isobaths, over distances of approximately 900 km. Reproductive isolation on the continental slope may have occurred as a result of selection exerted by gradients of depth-correlated physical factors, such as pressure and temperature. However, allopatric speciation with subsequent range expansion may also explain the observed patterns of genetic divergence. Further investigation of radiation within this group may provide important information on the evolution of slope species. Taxonomic revision of the genus is required.Communicated by J.P. Thorpe, Port Erin 相似文献
224.
The relationship between adaptation and mitigation in managing climate change risks: a regional response from North Central Victoria,Australia 总被引:1,自引:0,他引:1
Roger N. Jones Paul Dettmann Geoff Park Maureen Rogers Terry White 《Mitigation and Adaptation Strategies for Global Change》2007,12(5):685-712
This two-part paper considers the complementarity between adaptation and mitigation in managing the risks associated with
the enhanced greenhouse effect. Part one reviews the application of risk management methods to climate change assessments.
Formal investigations of the enhanced greenhouse effect have produced three generations of risk assessment. The first led
to the United Nations Intergovernmental Panel on Climate Change (IPCC), First Assessment Report and subsequent drafting of
the United Nations Framework Convention on Climate Change. The second investigated the impacts of unmitigated climate change
in the Second and Third IPCC Assessment Reports. The third generation, currently underway, is investigating how risk management
options can be prioritised and implemented. Mitigation and adaptation have two main areas of complementarity. Firstly, they
each manage different components of future climate-related risk. Mitigation reduces the number and magnitude of potential
climate hazards, reducing the most severe changes first. Adaptation increases the ability to cope with climate hazards by
reducing system sensitivity or by reducing the consequent level of harm. Secondly, they manage risks at different extremes
of the potential range of future climate change. Adaptation works best with changes of lesser magnitude at the lower end of
the potential range. Where there is sufficient adaptive capacity, adaptation improves the ability of a system to cope with
increasingly larger changes over time. By moving from uncontrolled emissions towards stabilisation of greenhouse gases in
the atmosphere, mitigation limits the upper part of the range. Different activities have various blends of adaptive and mitigative
capacity. In some cases, high sensitivity and low adaptive capacity may lead to large residual climate risks; in other cases,
a large adaptive capacity may mean that residual risks are small or non-existent. Mitigative and adaptive capacity do not
share the same scale: adaptive capacity is expressed locally, whereas mitigative capacity is different for each activity and
location but needs to be aggregated at the global scale to properly assess its potential benefits in reducing climate hazards.
This can be seen as a demand for mitigation, which can be exercised at the local scale through exercising mitigative capacity.
Part two of the paper deals with the situation where regional bodies aim to maximise the benefits of managing climate risks
by integrating adaptation and mitigation measures at their various scales of operation. In north central Victoria, Australia,
adaptation and mitigation are being jointly managed by a greenhouse consortium and a catchment management authority. Several
related studies investigating large-scale revegetation are used to show how climate change impacts and sequestration measures
affect soil, salt and carbon fluxes in the landscape. These studies show that trade-offs between these interactions will have
to be carefully managed to maximise their relative benefits. The paper concludes that when managing climate change risks,
there are many instances where adaptation and mitigation can be integrated at the operational level. However, significant
gaps between our understanding of the benefits of adaptation and mitigation between local and global scales remain. Some of
these may be addressed by matching demands for mitigation (for activities and locations where adaptive capacity will be exceeded)
with the ability to supply that demand through localised mitigative capacity by means of globally integrated mechanisms. 相似文献
225.
The anemone Amphianthus inornata is found at bathyal depths living on colonies of the gorgonian Acanella arbuscula. Previous studies of the morphology and reproductive stage of this anemone, during different times of the year, have indicated
that it reproduces sexually on a seasonal basis. A small proportion of the study population were also reported to be undergoing
asexual reproduction by fission. The anemone Kadosactis commensalis is also bathyal, but lives mainly on the holothurian Paroriza prouhoi. Previous morphological studies have indicated that K. commensalis is a protandrous hermaphrodite that exhibits non-seasonal sexual reproduction only. In the present study, allozyme electrophoresis
was used to examine the prevalence and genetic consequences of asexual reproduction in a population of Amphianthus inornata from 2 200 m in the Rockall Trough, North Atlantic Ocean. Genetic evidence, from five randomly selected polymorphic enzyme
loci, for asexual reproduction in this species was weak. Exact tests indicated that genotype frequencies did not differ significantly
from those expected under Hardy–Weinberg equilibrium. F
IS
(correlation of homologous alleles with reference to local population, assuming random mating) values also did not differ
significantly from zero, and observed heterozygosity (H
o
=0.446) and genotypic diversity (G
o
=17.0387) were very similar to Hardy–Weinberg expected frequencies (H
e
=0.446; G
*
e
=17.0010). Evidence suggests that the contribution of asexual reproduction to recruitment in the study population of A. inornata is low. For a single population of K. commensalis from 4 850 m on the Porcupine Abyssal Plain, North Atlantic Ocean, the hypothesis that inbreeding due to reduced occurrence
of outcrossing between anemones on a single holothurian host was examined by electrophoresis of ten randomly selected enzyme
loci. Single-locus genotypic frequencies were significantly different from expected frequencies for one locus P≤ 0.05, hexokinase-1 (Hex-1)]. F
IS
values were significantly different from zero for two enzyme loci (Hex-1 and Hex-2, P≤ 0.01 and P≤ 0.05, respectively), and the overall observed heterozygosity was lower than the expected heterozygosity (H
o
=0.125, H
e
=0.140). The hypothesis of inbreeding could not be rejected by the present study, although sample size was small (N=55), leading to possible bias in tests of significance. Genetic variation in A. inornata was higher than that recorded for most eukaryotes, although interlocus sampling error for only five loci is high. High genetic
variability has been found in other sea anemones, and has been related to high longevity and mixed reproductive modes. Genetic
variation in K. commensalis was in the higher range of that found in other eukaryotes, and is not unusual for anemones.
Received: 5 August 1996 / Accepted: 11 December 1996 相似文献
226.
227.
Production of extracellular dissolved organic substances by cultures of the marine coccolithophorid Hymenomonas carterae SMBA 254 was investigated by the 14C-tracer technique. In 4 h incubations, extracellular 14C production represented 20 to 64% of 14C incorporation into cell material for cultures nearing, or during stationary growth; for rapidly growing cultures with relatively low cell densities the 14C-production was only 4 to 10% of incorporation. Intra-and extra-cellular material was fractionated by ion-exchange membrane electrodialysis. Ionic compounds accounted for 40 to 60% of extracellular material; in contrast only 16 to 27% of intracelular metabolites were in this category. Of a range of methods which were investigated, separation of compounds by gel-filtration in conjunction with two-dimensional thin-layer chromatography proved most effective. Up to 80% of extracellular material was of less than 1 800 mol. wt and included carbohydrates and amino acids, with glutamic acid predominating. The intracellular material was more heterogeneous, with a substantially greater proportion of high molecular weight material. The quite distinct compositions show clearly that extracellular production observed in these experiments arose through excretion and was not attributable to cell lysis. 相似文献
228.
Structural marsh management, using levees and water-control structures, is used in the coastal zone for many objectives, for
example, to reduce marsh loss, to enhance waterfowl habitat, to revegetate open-water areas, and to reduce saltwater intrusion.
The literature was evaluated to categorize structural marsh management and to determine some of its effects on fishes and
crustaceans. Structural marsh management had positive effects on standing stock of most resident organisms and negative effects
on marine-transient organisms. Emigration was negatively affected for both resident and marine-transient organisms. Techniques
such as opening structures at critical migration times, designing structures that offer the greatest management flexibility,
and using structures to create a flow-through system could reduce these impacts. More effort should be put into monitoring
managed areas to determine if the objectives are being met and to evaluate the effects on fishes and crustaceans. Although
frequent manipulation could reduce these impacts, the costs and problems incurred may outweigh the anticipated benefits. 相似文献
229.
Rolando Bravo David A. Dow Jerry R. Rogers 《Journal of the American Water Resources Association》1994,30(5):891-899
ABSTRACT: The proportionality coefficient, K, and the weighing parameter, X, required for the Muskingum-Cunge Flood Routing Method are dependent on the hydraulic characteristics of the channel and the dynamic characteristic of the flood wave. This work focuses on the determination of the Muskingum-Cunge Flood Routing Method parameters for streams where measured hydrographs are not available (i.e., ungaged streams) with floods that stay within the channel banks. In the present work, a gaged creek was used and a dynamic wave was routed to test the reliability of the parameters determined through the Schaefer and Stevens technique (Schaefer and Stevens, 1978). The predicted outflow hydrographs are compared to the hydrographs obtained for the same stream determined with the Muskingum Routing option of the HEC-1 program. Cypress Creek in Harris County, Texas, was the model for this work; and the corresponding data were extracted from the Grant Road and Westfield, Texas, USGS gaging stations. 相似文献