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11.
Whether communities respond smoothly or discontinuously to changing environmental conditions has important consequences for the preservation and restoration of ecosystems. Theory shows that communities may exhibit a variety of responses to environmental change, including abrupt transitions due to the existence of alternate states. However, there have been few opportunities to look for such transitions in nature. Here, we examine the impact of a two-orders-of-magnitude decrease and then increase in planktivore abundance in Wintergreen lake (Michigan, USA), caused by the extinction and reintroduction of two dominant fish species (largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus). Over a 16 + yr period of slow change from high planktivory to low planktivory back to high planktivory, the zooplankton community changed smoothly and predictably between states. In years of low planktivory, the zooplankton assemblage was dominated by a single, large, cladoceran species, Daphnia pulicaria, whereas in years of high planktivory, D. pulicaria disappeared and was replaced by a suite of small-bodied cladocerans. We quantified the multivariate change in zooplankton community dissimilarity and found that community state smoothly tracked changes in planktivore density in both a forward and backward direction. Thus, there was little evidence of discontinuity in this system where transitions are strongly driven by planktivory. 相似文献
12.
Uda M Sassa S Taniguchi K Nomura S Yoshimura S Kondo J Iskander N Zaghloul B 《Die Naturwissenschaften》2000,87(6):260-263
Some of the pigments painted on the Funerary Stele of Amenemhat (ca. 2000 B.C.) exhibited at the Egyptian Museum, Cairo and
on the walls of the Tomb of Userhat (ca. 1450 B.C.), a rock-cut tomb in Thebes, Egypt, were investigated in situ using both
a convenient home-made hand-held type of X-ray diffractometer and a commercial X-ray fluorescence spectrometer in a complementary
way under touch-free conditions. CaCO3 · 3MgCO3 (huntite) was found in the white-painted parts of these two ancient monuments. An arsenic (As)-bearing phase was detected
in the yellow-painted parts of the latter monument. The occurrence of huntite in Egypt has not been reported previously.
Received: 8 October 1999 / Accepted in revised form: 10 March 2000 相似文献
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14.
Ricardo Lavandier Natalia Quinete Rachel Ann Hauser-Davis Patrick Simões Dias Satie Taniguchi Rosalinda Montone Isabel Moreira 《Chemosphere》2013,90(9):2435-2443
Polychlorinated biphenyls (PCBs) and Polybrominated Diphenyls Ethers (PBDEs) are two highly lipophilic classes of persistent organic pollutants able to resist degradation and with the ability to bioaccumulate through the food chain. In Brazil, there are still few studies on PCBs and PBDEs in aquatic organisms. In this study, we determined the levels of PBDEs and PCBs in three different fish species from the Ilha Grande Bay, located in the southern state of Rio de Janeiro, Brazil. PBDEs levels were very low, with values below the limit of quantification. PCBs concentrations ranged from 2.29 to 27.60 ng g?1 ww in muscle and from 3.41 to 34.22 ng g?1 ww in liver of the three investigated fish species. Significant positive correlations were established between PCBs concentration and fish biometric variables in mullet (length and lipid content) and a statistically significant change between seasons in croaker was observed. 相似文献
15.
Povinec PP Aggarwal PK Aureli A Burnett WC Kontar EA Kulkarni KM Moore WS Rajar R Taniguchi M Comanducci JF Cusimano G Dulaiova H Gatto L Groening M Hauser S Levy-Palomo I Oregioni B Ozorovich YR Privitera AM Schiavo MA 《Journal of environmental radioactivity》2006,89(1):81-101
A complex approach in characterisation of submarine groundwater discharge (SGD) off south-eastern Sicily comprising applications of radioactive and non-radioactive tracers, direct seepage measurements, geophysical surveys and a numerical modelling is presented. SGD fluxes in the Donnalucata boat basin were estimated by direct seepage measurements to be from 4 to 12Ls(-1), which are comparable with the total SGD flux in the basin of 17Ls(-1) obtained from radon measurements. The integrated SGD flux over the Donnalucata coast estimated on the basis of Ra isotopes was around 60m(3)s(-1) per km of the coast. Spatial variations of SGD were observed in the Donnalucata boat basin, the average (222)Rn activity concentration in seawater varied from approximately 0.1kBqm(-3) to 3.7kBqm(-3) showing an inverse relationship with salinity. The continuous monitoring carried out at the site closest to the coast has revealed an inverse relationship of (222)Rn activity concentration on the tide. The (222)Rn concentrations in seawater varied from 2.3kBqm(-3) during high tides to 4.8kBqm(-3) during low tides, thus confirming an influence of the tide on submarine groundwater discharge. Stable isotopes (delta(2)H and delta(18)O) showed that SGD samples consist up to 50% of groundwater. Geo-electrical measurements showed a spatial variability of the salt/fresh water interface and its complex transformation in the coastal zone. The presented results imply that in the studied Donnalucata site there are at least two different sources of SGD, one superficial, represented by mixed fresh water and seawater, and the second one which originates in a deeper limestone aquifer. 相似文献
16.
Albatrosses and petrels (Procellariiformes) are migratory oceanic birds of considerable conservational interest. Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were assessed in the subcutaneous fat, liver and muscle of 100 birds belonging to eight species of Procellariiformes collected during their migration period in southern Brazil, one of the most important feeding areas for these species. Although the profiles of PCBs and OCPs were similar among the individuals, with predominance of penta, hexa and heptachlorobiphenyls and p′p-DDE, organochlorine concentrations exhibited a high degree of intra-species variability. The influence of body condition during the migration period in the distribution of organochlorine contaminants was also evaluated, showing that it is a significant factor in the variation and redistribution of these compounds in the tissues of these birds. The intense use of lipid reserves associated to the contamination from organochlorine compounds could be a troubling factor for seabirds with extended breeding periods and that spend most of their lives at sea migrating long distances, such as most of Procellariiformes. Studies on contamination are necessary to improve the knowledge of the threats to these birds and their populations as well as to contribute with information about persistent organic pollutants in the South Atlantic marine environment. 相似文献
17.
Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution 总被引:2,自引:0,他引:2
Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045mM 2,4-D using O(3), O(3)/UV, UV/TiO(2) and O(3)/UV/TiO(2) systems were compared, and influence of reaction temperature on the mineralization in O(3)/UV/TiO(2) system was investigated. 2,4-D degradations by O(3), O(3)/UV and UV/TiO(2) systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O(3)/UV/TiO(2) system, and further enhancements were observed with larger O(3) supplies. The enhancements were attributed to hydroxyl radical (()OH) generation from more than one reaction pathway. The degradation and removal in O(3)/UV/TiO(2) system were very efficient with reaction temperature fixed at 20 degrees C. It was suspected that reaction temperature might have influenced ()OH generation in the system, which needs further attention. 相似文献
18.
Phytoplankton standing crop (chlorophyll a) and primary productivity were recorded, and zooplankton biomass was estimated in the two large bays of Australia, the Great Australian Bight on the south coast (December, 1965) and the Gulf of Carpentaria on the north coast (December, 1968). In the Gulf of Carpentaria, the phytoplankton standing crop (average, 27.3 mg chlorophyll a m-2) and primary productivity (average, 133.1 mg C m-2 h-1), as well as zooplankton biomass (average, 305.3 mg wet weight m-3) are much higher than in the Great Australian Bight (12.1 mg chlorophyll a m-2, 18.2 mg C m-2 h-1, 7.1 mg wet weight m-3, respectively). The unexpectedly low productivity values in the Great Australian Bight are attributable to environmental conditions of this bay, which obtains neither replenishment of nutrients from the land nor receives upwelling of deep water. 相似文献
19.
Montastraea annularis, M. faveolata, and M.␣franksi are three recently separated species that together dominate reefs of the tropical western Atlantic. Despite morphological,
life-history, ecological and genetic differences, the legitimacy of their status as separate species has been questioned.
This controversy stems from both the scarcity of unambiguous, diagnostic differences among them, and from the possibility
of extensive hybridization associated with their approximately synchronous reproduction in sympatry. Here we report on fertilization
trials and the timing of spawning, both of which suggest that the potential for hybridization may be limited. Crosses between
M. faveolata (the most genetically distinctive taxon) and the other two species were largely unsuccessful, as were selfed matings for
all three species. M. annularis and M. franksi showed no evidence of fertilization barriers, but the timing of spawning typically differed between them by 1 to 2 h. We
also found that spawning times in the field of M. annularis and M. faveolata were non-overlapping in 1995, and that the timing of spawning in M. annularis could be experimentally shifted forward by simulating earlier than natural sunsets. These findings from Panamá and Honduras,
particularly given their consistency with comparable observations and experiments elsewhere, provide evidence of reproductive
isolation and support the separate species status of these three taxa. Some hybridization may occur under natural conditions
at these sites, particularly between M. annularis and M.␣franksi. Rampant genetic interchange among these taxa in Central America seems unlikely, however, in the light of the concordant
associations between morphology, reproductive biology and other characters which are observed.
Received: 22 July 1996 / Accepted: 2 October 1996 相似文献
20.
Leonel J Taniguchi S Sasaki DK Cascaes MJ Dias PS Botta S Santos MC Montone RC 《Chemosphere》2012,86(7):741-746
Chlorinated pesticides, PCBs and PBDEs were analysed in nine blubber samples of Atlantic spotted dolphins, Stenella frontalis, incidentally captured during fishing operations in southern and southeastern Brazil between 2005 and 2007. The majority of compounds analysed were detected, suggesting widespread contamination over the region. Although the samples came from a location far from main coastal industrial areas, the results revealed an influence from such sources. Therefore, levels of PCBs (774-23 659 ng g−1 lipid wt.) and PBDEs (23-1326 ng g−1 lipid wt.) detected seem to be related to the movement of individuals throughout near-shore and offshore waters. The sample from a lactating female exhibited a lower level of contamination and a distinct pattern, indicating selective transfer favouring less lipophilic compounds. 相似文献