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The Indo-Pacific oyster Chama pacifica Broderip, 1835 (Mollusca, Bivalvia, Chamidae) is rarely found in the Northern Red Sea reefs of Eilat (Gulf of Aqaba), where it is outnumbered by its indigenous congener, Chama savignyi Lamy, 1921. The influx of Eritrean biota from the Red Sea into the Mediterranean Sea via the Suez Canal has led to the formation of massive Chama oyster beds along the Eastern Mediterranean shore. However, unlike the Northern Red Sea, the Eastern Mediterranean Chama beds are dominated by C. pacifica oysters, whereas C. savignyi is absent from this region. In an attempt to understand this difference in their respective distribution, the reproductive biology of both species was compared. Histological analysis of the male and female gonads, monitored monthly from March 2009 to August 2010 in both regions, revealed a similar reproductive cycle, comprising six stages: onset of gametogenesis, advanced gametogenesis, ripe, ready to spawn, spent and sexual rest. Female gonads demonstrated an additional, seventh stage – restoration, coinciding with inferred spawning of ripe gametes. Both species were found to be dioecious spawners, with a single, annual, temperature-dependent inferred spawning period. Chama pacifica was found to reproduce efficiently in maximal Mediterranean seawater temperatures not experienced by the Northern Red Sea Chama populations. This study demonstrates the high invasive potential of an oyster species despite its rarity in its source region. 相似文献
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Yosef Ashkenazy Martin Losch Hezi Gildor Dror Mirzayof Eli Tziperman 《Climate Dynamics》2013,40(7-8):1803-1817
Sea ice has been suggested, based on simple models, to play an important role in past glacial–interglacial oscillations via the so-called “sea-ice switch” mechanism. An important requirement for this mechanism is that multiple sea-ice extents exist under the same land ice configuration. This hypothesis of multiple sea-ice extents is tested with a state-of-the-art ocean general circulation model coupled to an atmospheric energy–moisture-balance model. The model includes a dynamic-thermodynamic sea-ice module, has a realistic ocean configuration and bathymetry, and is forced by annual mean forcing. Several runs with two different land ice distributions represent present-day and cold-climate conditions. In each case the ocean model is initiated with both ice-free and fully ice-covered states. We find that the present-day runs converge approximately to the same sea-ice state for the northern hemisphere while for the southern hemisphere a difference in sea-ice extent of about three degrees in latitude between the different runs is observed. The cold climate runs lead to meridional sea-ice extents that are different by up to four degrees in latitude in both hemispheres. While approaching the final states, the model exhibits abrupt transitions from extended sea-ice states and weak meridional overturning circulation, to less extended sea ice and stronger meridional overturning circulation, and vice versa. These transitions are linked to temperature changes in the North Atlantic high-latitude deep water. Such abrupt changes may be associated with Dansgaard–Oeschger events, as proposed by previous studies. Although multiple sea ice states have been observed, the difference between these states is not large enough to provide a strong support for the sea-ice-switch mechanism. 相似文献
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Eran Halfi Dror Paz Kyle Stark Uri Yogev Ian Reid Michael Dorman Jonathan B. Laronne 《地球表面变化过程与地形》2020,45(14):3510-3524
The monitoring of bedload flux under flash flood conditions has been successfully achieved since 1992 using slot samplers in the semiarid Nahal Eshtemoa. In the present study, a surrogate bedload monitoring technique - the Japanese plate microphone - has been deployed and calibrated against data from the slot samplers. Since a slot sampler has a sensitivity threshold that becomes especially important when transport rates are low, different averaging periods should be considered for high and low fluxes. In order to overcome the deficiencies of time-based aggregation used hitherto, we have developed a new method involving mass aggregation and commensurably variable intervals, thereby enabling a more accurate analysis and optimizing the bedload sampler's capabilities. The data derived with this new method has then been utilized to calibrate the Japanese plate microphone. The Eshtemoa is an ephemeral gravel bed channel with a high proportion of fine gravel (< 0.02 m); for these conditions, acoustic sensors have not been calibrated as yet. Two multiple linear regression models incorporating the effect of median bedload grain size on pulse rate have been established to predict bedload flux and cumulative transported bedload mass. The coefficients in these models are statistically significant. Good predictions are obtained for bedload flux (adj. r2 = 0.83) and for cumulative bedload mass (adj. r2 = 0.98) during flood recession. Overall, the multiple linear regression models, used in conjunction with the mass aggregation method of estimating bedload flux, suggest that field calibration of acoustic devices is feasible under these conditions for ca. 90% of the duration of bedload transport. © 2020 John Wiley & Sons, Ltd. 相似文献
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This study traces both the long-term deterioration of the ground water supply in two neighboring villages that had relied
upon cesspits/cesspools for waste disposal, as well as the subsequent progressive improvement to original water quality levels.
The rapid improvement is attributed to the replacement of the cesspits by a central sewage disposal network. In each of the
villages of Kefar Bara and Kefar Kassem, a single, relatively deep, community well supplies drinking water. These wells were
drilled into the underlying carbonate Judea Group aquifer that initially provided very high quality potable water. Over time,
large increases in the nitrate contamination, reaching to as high as 67 mg/L nitrate, paralleled the population growth. The
higher dissolved nitrate concentrations were also marked by enrichments in the δ15 N (approximately +8 ‰(air)) values above those of the surrounding and regional uncontaminated background δ15 N values (in the range of +3 to +6 ‰ (air)). Within several years after the cesspit disposal was terminated the nitrate values declined to concentrations that were
reported (approximately 25 mg/L-NO3) decades prior, when the water quality monitoring had just commenced. This study demonstrates not only how water quality
can degrade but also how it can be restored once the problem is identified and countered. This simple method of ameliorating
a water quality problem that was tending towards reaching serious proportions would seem to be quite efficacious for any area
lacking economic alternative water resources. 相似文献
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Oxytetracycline (OTC) is an antibiotic that is regularly added to fish ponds used in industrial- scale fish-farming along
the Mediterranean coast of Israel. It is not found in unpolluted water. The ponds are constructed upon porous sands that are
also the host rock of the local aquifer. These ponds leak. Monitoring for OTC was carried out in a fish pond and three surrounding
water wells that exploit the local aquifer. The local groundwater is composed of the native groundwater and the leakage additions.
Two wells, P-204 P-205 are used to insure that the water levels in the ponds are maintained. A frequently pumping well, M-2,
is located closest to the main source of OTC input at pond B. It is used to supply drinking water and OTC was found in it.
This contaminant is related to leakage from the nearby fish pond. OTC is generally assumed to be immobile and effectively
removed by soil and sediments. In this case, continuous leakage of the pond has created preferential saturated flow paths
that bring the contaminants directly to groundwater, bypassing the immobilizing sorption processes that usually take place
in the unsaturated zone. In the absence of such conduits OTC is effectively excluded from reaching other producing wells. 相似文献
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Barak Herut Efrat Shoham-Frider Nurit Kress Ulrich Fiedler Dror L. Angel 《Marine pollution bulletin》1998,36(12):994-1003
The main aim of this study was to assess the hydrogen peroxide (HP) production rates (HPPR) related to anthropogenic pollution in coastal waters by laboratory and field experiments. HPPR's were assessed by simultaneous measurements of HP concentrations, cumulative solar UV irradiation and dissolved organic matter (DOM) fluorescence in the seawater samples at clean and polluted sites in the Mediterranean, Red and the Baltic Seas. The natural HP concentrations at all sites (8–100 nM) fall within the normal range recorded elsewhere, and follows a diurnal pattern. The polluted stations in the Mediterranean and Baltic Seas showed higher HPPR (3.2–16.6 nM m2 W−1 h−1) than the clean stations, while in the Red Sea no significant differences were found because the station that was considered a priori polluted was actually rather clean (2–3 nM m2 W−1 h−1). Laboratory experiments demonstrated that HPPR was positively linearly correlated to DOM fluorescence, however, this relationship was not found in the natural seawater samples examined in the field. The lack of relationship between HPPR and DOM in the field was attributed to enzymatic breakdown of HP as observed in dark decay experiments. HP dark decay rates were highest in polluted stations, probably due to larger bacterioplankton populations in these samples. Moreover, the HP dark decay rates were much lower in filtered than in non-filtered samples. Sun incubation of filtered (0.2 μm) seawater samples were performed to assess whether elimination of particles would yield higher HPPRs than in non-filtered samples. In the Baltic Sea (low UV irradiation) HPPR was higher in the filtered samples, while at sites with relatively high UV irradiation (Mediterranean and Red Seas), filtration of seawater did not stimulate HPPRs, probably due to UV-damage to planktonic microorganisms. 相似文献
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