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71.
Van Campenhout K Bervoets L Blust R 《Environmental pollution (Barking, Essex : 1987)》2007,145(3):905-914
The impact of several factors on the assimilation efficiency (AE) of Cd and Zn from food in the common carp (Cyprinus carpio) was studied. Tested prey species were midge larvae (Chironomus riparius), zebra mussels (Dreissena polymorpha) and oligochaetes (Tubifex tubifex). The Cd load of the larvae did not affect the Cd AE in the carp. The Zn AE however, was negatively related to the Zn load of the prey. Food quantity and starvation of the carp did not significantly affect the Cd AE. For Zn, a significant decrease in AE was found when carp were fed ad libitum. Decreasing the temperature from 25 degrees C to 15 degrees C did not influence the Cd AE, while for Zn a significant decrease of the AE was measured. Carp assimilated Cd from both zebra mussels and oligochaetes with a significantly lower efficiency in comparison to the midge larvae, although Zn AEs was prey independent. 相似文献
72.
Differential responses of the freshwater wetland species Juncus effusus L. and Caltha palustris L. to iron supply in sulfidic environments 总被引:1,自引:0,他引:1
Van der Welle ME Niggebrugge K Lamers LP Roelofs JG 《Environmental pollution (Barking, Essex : 1987)》2007,147(1):222-230
Sulfur pollution can lead to serious problems in freshwater wetlands, including phosphorus eutrophication and sulfide toxicity. We tested the effects of anaerobic iron-rich groundwater discharge in fens, simulated by iron injection, on two characteristic species (Juncus effusus and Caltha palustris) in a sulfidic environment. Biomass production of C. palustris roots showed an optimum response to the combined addition of iron and sulfide, with highest values at intermediate concentrations of both substances. Iron deficiency apparently occurred at low iron concentrations, while at high iron concentrations, growth was decreased. For J. effusus, in contrast, no toxic effects were found of both iron and sulfide. This could be explained by larger radial oxygen loss (ROL) of J. effusus and could not be explained by differences in phosphorous concentrations. The results of our experiments confirm that iron-rich groundwater discharge has the potential to affect vegetation composition through toxicity modification in sulfidic environments. 相似文献
73.
Work teams are being utilized more frequently to give organizations access to the broader knowledge and skill base of employees, as well as to provide for adaptive, efficient decision‐making. In teams, we argue that constructive confrontation norms are an important contingency variable in the relationship between mental model similarity and decision quality. Mental model similarity helps team members understand one another's perspectives and reduces the likelihood of conflict. Accordingly, mental model similarity improves decision quality. When strong norms of constructive confrontation are in place, however, teams are in a better position to reap the benefits of conflict (greater diversity of inputs) without experiencing its negative consequences. Thus, when constructive confrontation norms are strong, less mental model similarity (i.e., more diversity of perspectives) is likely to improve decision quality. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
74.
Various developmental stages (early larvae to adults) of Euphausia superba have been collected in different seasons in the Weddell Sea, the Lazarev Sea and off the Antarctic Peninsula to investigate
the role of lipids and fatty acids in the life cycle of the Antarctic krill. The total-lipid data for E. superba exhibited seasonal variations, with low lipid levels in late winter/early spring and the highest levels in autumn. Seasonal
changes were most pronounced in the immature and adult specimens, increasing from about 10% lipid of dry mass to more than
40%. The fatty-acid compositions of the younger stages were dominated by 20:5(n-3), 22:6(n-3) and 16:0. These are typical
phospholipid fatty acids, which are major biomembrane constituents. The phospholipid composition was similar in the older
stages. With increasing storage of triacylglycerols in the lipid-rich immature and adult stages, the fatty acids 14:0, 16:0
and 18:1(n-9) prevailed, comprising about 70% of total triacylglycerol fatty acids. The trophic-marker fatty acids 16:1(n-7)
and 18:4(n-3), indicating phytoplankton ingestion, were less abundant. They reflected, however, the dependence of the larvae
on phytoplankton as well as the seasonal changes in algal composition. The generally close linear relationships between fatty
acids and lipid suggest that the fatty-acid compositions of the collected specimens were largely independent of the respective
developmental stage, season and region. The linear fit indicates that triacylglycerol accumulation started at a level of about
5% of total lipid. Considering the various overwintering scenarios under discussion, the life cycle and reproductive strategies
of krill are discussed in the context of the lipid metabolism and fatty-acid composition of E. superba. Lipid production is effective enough to accumulate large energy reserves for the dark season, but E. superba does not exhibit the sophisticated biosynthetic pathways known from other Antarctic euphausiids and copepods. Although important,
lipid utilisation appears to be just one of several strategies of E. superba to thrive under the extreme Antarctic conditions, and this pronounced versatility may explain the success of this species
in the Southern Ocean.
Received: 16 June 2000 / Accepted: 18 December 2000 相似文献
75.
Juvenile and adult marine organisms differ in their morphology, chemistry, physiology, behavior, and ecology. Because juvenile
algae are thinner, smaller, and have more delicate tissues than adults, they are often assumed to be more susceptible to grazers.
We examined within-species food preferences of four common generalist herbivores for juvenile and adult tissues of eight common
brown algae in two-choice laboratory food-preference experiments. Our results showed that juvenile algae did not tend to be
a preferred food of herbivores. Juvenile tissues were significantly preferred over adult tissues in only four of the 32 combinations
of algae and herbivores tested. In 12 experiments, adult tissues were preferred over juvenile tissues, and no choice occurred
in the remaining 16 experiments. When sea urchins exhibited a preference, it was always for adult tissues. The other three
herbivores, an isopod and two snails, were more variable in their choices, sometimes preferring juveniles, sometimes adults,
and sometimes having no preference. We measured nitrogen and phlorotannin concentrations in adult and juvenile seaweeds to
see whether these parameters were correlated with herbivore food preferences. Nitrogen levels were similar in juveniles and
adults of three algal species and were higher in juveniles of two. Phlorotannin levels were higher in juveniles of four species
and lower in juveniles of one. The other three species showed no differences in phlorotannin levels. Phlorotannin concentrations
decreased with increasing juvenile size in three species and increased with increasing size in one species. Neither nitrogen
nor phlorotannin concentrations explained overall herbivore food preferences for algae of different stages. Our results suggest
that preferences of certain grazers for juvenile algae are not as strong as previously assumed and are dependent on herbivore
species. Preferences between juveniles and adults are likely to be determined by a combination of morphological and chemical
features of the tissues and the unique responses of herbivore species to those features.
Received: 10 April 2000 / Accepted: 19 November 2000 相似文献
76.
A distinct smell of dimethylsulfide (DMS) was noted at the edge of the intertidal mudflat of Marennes-Oléron Bay, at the
French Atlantic coast, where dense populations of the marine flatworm Convoluta roscoffensis Graff (Platyhelminthes: Turbellaria) were present. DMS is the cleavage product of dimethylsulfoniopropionate (DMSP). DMSP
was shown to be present in high amounts in sediment containing the flatworm as well as in axenic cultures of the symbiotic
alga Tetraselmis sp. that was isolated from the flatworm. In untreated sediment samples containing C. roscoffensis the concentration of DMS was as high as ∼55 μmol l−1 sediment, and in samples that were fixed with glutaraldehyde the concentration of DMS was even three orders of magnitude
higher (∼66 mmol l−1 sediment). This rapid cleavage of DMSP to DMS in fixed samples was unexpected. Pure DMSP was stable in glutaraldehyde, and
it was therefore concluded that a DMSP-lyase was responsible for cleavage in the field samples. The isolated symbiotic alga,
Tetraselmis sp., did not show DMSP-lyase activity, indicating that DMSP-lyase may have been present in the flatworm, although the role
of bacteria could not be excluded. The Chl a-specific DMSP content of C. roscoffensis (∼200 mmol g−1) was much higher than that of Tetraselmis sp. (∼30 mmol g−1). Possibly, DMSP was not only present in the symbiotic alga, but was also incorporated in the body tissue of the flatworm.
It remains unclear what the function of DMSP is in C. roscoffensis. In Tetraselmis sp., but not in C. roscoffensis, DMSP increased with increasing salinity. It was concluded that salinity probably does not play an important role in the
dynamics of DMSP and DMS in sediment containing C. roscoffensis.
Received: 21 January 2000 / Accepted: 29 August 2000 相似文献
77.
78.
Human population growth in coastal areas continues to threaten estuarine ecosystems and resources. Populations of Crassostrea virginica have declined across the USA due to water quality degradation, disease pressure, alteration of habitat, and other changes related to anthropogenic impacts. Metals that may be present in estuarine habitats can bioaccumulate in oysters, with potential consequences to the health of oysters and humans consumers. This study (1) evaluated the occurrence and relationships of metal concentrations in oyster tissue versus estuarine sediments, (2) examined oyster tissue concentrations in relation to state water quality designations, and (3) evaluated the potential risk for humans from oyster consumption related to metal concentrations from harvestable waters. Results indicated metal concentrations in sediments and oysters along coastal South Carolina remain low compared to other areas and that concentrations in oyster tissue and adjacent sediments were not highly correlated with each other. However, high concentrations of some metals occurred in oysters sampled from areas designated as Approved for Harvesting. This is important because most harvest area designation systems rely on regular bacterial monitoring when evaluating the safety of consumption. Others safety measurements may be necessary as part of routine monitoring. 相似文献
79.
80.
Hirokazu Ozaki Thi Kinh Co Anh Kha Le Viet Nu Pham Van Be Nguyen Mitsunori Tarao Huu Chiem Nguyen Viet Dung Le Hieu Trung Nguyen Masaki Sagehashi Sachi Ninomiya-Lim Takashi Gomi Masaaki Hosomi Hideshige Takada 《Environmental monitoring and assessment》2014,186(2):845-858
In this study, we focused on water quality in an urban canal and the Mekong River in the city of Can Tho, a central municipality of the Mekong Delta region, southern Vietnam. Water temperature, pH, electrical conductivity, BOD5, CODCr, Na+, Cl?, NH4 +?N, SO4 2??S, NO3 ??N, and NO2 ??N for both canal and river, and tide level of the urban canal, were monitored once per month from May 2010 to April 2012. The urban canal is subject to severe anthropogenic contamination, owing to poor sewage treatment. In general, water quality in the canal exhibited strong tidal variation, poorer at lower tides and better at higher tides. Some anomalies were observed, with degraded water quality under some high-tide conditions. These were associated with flow from the upstream residential area. Therefore, it was concluded that water quality in the urban canal changed with a balance between dilution effects and extent of contaminant supply, both driven by tidal fluctuations in the Mekong River. 相似文献