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1.
In the last decade, green Noctiluca scintillans with its symbiont and other dinoflagellates such as Cochlodinium polykrikoides, Prorocentrum micans and Scrippsiella trochoidea have become the dominant HABs, partially replacing the previously dominant diatoms and red Noctiluca scintillans, especially during the northeast monsoon. Fish kills in the Sea of Oman are linked to a slow seasonal decline in oxygen concentration from January to November, probably due to the decomposition of a series of algal blooms and the deep, low oxygen waters periodically impinging the Omani shelf. In the western Arabian Sea, cyclonic eddies upwell low oxygen, nutrient-rich water and the subsequent algal bloom decays and lowers the oxygen further and leads to fish kills. Warming of the surface waters by 1.2 °C over the last 5 decades has increased stratification and resulted in a shoaling of the oxycline. This has increased the probability and frequency of upwelling low oxygen water and subsequent fish kills.  相似文献   

2.
The occurrence of biomarker variations linked to environmental factors makes it difficult to distinguish the effect of pollution. In an attempt to evaluate spatial and seasonal effects of environmental parameters on biomarker responses, mussels Mytilus edulis chilensis coming from an aquaculture farm were transplanted to several points within Ushuaia Bay (Beagle Channel) for 6 weeks in summer and winter. Activities of superoxide dismutase, catalase, glutathione-S-transferase and levels of lipid peroxidation were measured in gills and digestive gland. Cu, Zn, Fe, Cd and Pb concentrations were also assessed. Results indicated a significant effect of seasons on biological responses as well as in metal bioaccumulation showing the influence of natural factors such as dissolved oxygen, temperature and food availability. The interdependence of those environmental factors is important for the homeostasis of thermoconformers, especially regarding their oxidative metabolism and should also be taken into consideration to distinguish natural from pollution-induced variations.  相似文献   

3.
A model framework is presented for simulating nitrogen and carbon cycling at the sediment–water interface, and predicting oxygen consumption by oxidation reactions inside the sediments. Based on conservation of mass and invoking simplifying assumptions, a coupled system of diffusive–reactive partial differential equations is formulated for two-layer conceptual model of aerobic–anaerobic sediments. Oxidation reactions are modeled as first-order rate processes and nitrate is assumed to be consumed entirely in the anoxic portion of the sediments. The sediments are delineated into a thin oxygenated surface layer whose thickness is equal to the oxygen penetration depth, and a lower, but much thicker anoxic layer. The sediments are separated from the overlying water column by a relatively thin boundary layer through which mass transfer is diffusion controlled. Transient solutions are derived using the method of Laplace transform and Green’s function, which relate pore-water concentrations of the constituents to their concentrations in the bulk water and to the flux of decomposable settling organic matter. Steady-state pore-water concentrations are also obtained including expressions for the extent of methane saturation zone and methane gas flux. A relationship relating the sediment oxygen demand (SOD) to bulk water oxygen is derived using the two-film concept, which in combination with the depth-integrated solutions forms the basis for predicting the extent of oxygen penetration in the sediment. Iterative procedure and simplification thereof are proposed to estimate the extent of methane saturation zone and thickness of the aerobic layer as functions of time. Sensitivity of steady-state solutions to key parameters illustrates sediment processes interactions and synergistic effects. Simulations indicate that for a relatively thin diffusive boundary layer, d, oxygen uptake is limited by biochemical processes inside the sediments, whereas for a thick boundary layer oxygen transfer through the diffusive boundary layer is limiting. The results show an almost linear relationship between steady-state sediment oxygen demand and bulk water oxygen. For small d methane and nitrogen fluxes are sediment controlled, whereas for large d they are controlled by diffusional transfer through the boundary layer. It is shown that the two-layer model solution converges to the one-layer model (anaerobic layer) solution as the thickness of the oxygenated layer approaches zero, and that the transient solutions approach asymptotically their corresponding steady-state solutions.  相似文献   

4.
The variation of the point-defect concentrations with oxygen partial pressure, PO2, and temperature are derived for forsterite, Mg2SiO4, and Mg-rich olivine (Mg,Fe)2SiO4 assuming the cation/cation ratios are fixed. These dependencies differ from the open-system situation in which matter is easily transferable between forsterite or olivine and other solid phases. The details depend on whether the cation/cation ratio is exactly stoichiometric, or, if non-stoichiometric, the nature of the majority defects at precise oxygen stoichiometry. One generality which emerges is that regardless of the cation/cation stoichiometry the dominant defects in forsterite at low PO2 are free electrons, Mg and Si interstitials; at high PO2 the majority defects are holes, Mg and Si vacancies. In Mg-rich olivine the same defect species exist at the extremes of oxygen partial pressure with the exception of trivalent Fe on Mg sites replacing holes. At low PO2, therefore, both behave as n-type conductors. The models also suggest that in the PO2 range around precise oxygen stoichiometry the electrical conductivity in both materials can be a complex function of PO2.  相似文献   

5.
The Ponto–Caspian amphipod Pontogammarus robustoides was introduced into Lithuanian inland waters more than 50 years ago and is now among the most successful local crustacean invaders. Existing as an oxyphilic species in its native range, in Lithuania it managed to establish in some lentic eutrophic waters facing long-term hypoxic conditions under winter ice cover, or shorter periods of hypoxia during the warm season. Recently, it has been observed to be further expanding in such waters. The aim of this study was to explore the possible divergence in anaerobic metabolism among introduced populations facing different selective pressures. A closed-bottle experiment was conducted using individuals from three Lithuanian lentic water bodies of different trophic status: mesotrophic, eutrophic and hypertrophic. Severe hypoxia was gradually reached, after which lactate dehydrogenase activity was significantly higher in amphipods from eutrophic and hypertrophic, than from mesotrophic environments, and was well correlated with trophic status of inhabited environments as assessed by chlorophyll a concentration. These findings suggest a physiological acclimation response to oxygen deficiency faced by the species in some environments in the northern invaded range, which may have a genetic background. Such resistance to oxygen deficiency may expand the environmental niche and promote species’ spread into previously unsuitable habitats, which may pose a threat to native species residing in refuges that are currently free of the invader.  相似文献   

6.
Self-diffusion of oxygen in a natural phlogopite mica (annite 4%) has been measured under hydrothermal conditions at 2000 bars pressure and from 500 to 800°C using water enriched in18O. Diffusional transport is dominantly parallel to the c crystallographic axis. A linear Arrhenius plot was obtained with a pre-exponential term = (1.03 ± 0.38) × 10?9cm2sec?1 a and an activation energy of 29 ± 2kcal/g-atom O. The difference in transport rate between oxygens in the OH groups and those in tetrahedral sites is small to non-existent unless the OH oxygens diffuse much more slowly than the other oxygens, which we consider unlikely. A typical phlogopite crystal, 0.2 mm thick by 1 mm across will lose radiogenic argon faster than it will exchange oxygen at temperatures above 435°C, but the reverse holds at lower temperatures if the diffusion mechanism can be extrapolated to temperatures below 500°C. Such a crystal will lose only 5% of its argon if held at 380°C for 1 m.y., but could exchange 27% of its oxygen in that time. The rate at which phlogopite will undergo deformation by diffusional creep does not appear to be controlled by oxygen diffusion.  相似文献   

7.
The shallow water shrimp Palaemon adspersus was exposed to 200, 100 and 0 ppb WSF of crude oil for 14 days after which the oxygen consumption rate was measured in a closed chamber with an electrode. Previous work has shown a changed oxygen consumption rate in animals exposed to WSF in concentrations 100 to 1000 times the concentrations used in the present experiments. The oxygen consumption rate was also significantly increased by the low concentrations used in the present work.Although the oxygen consumption rate was significantly increased, as an effect of WSF-pollution, the method is very time-consuming.  相似文献   

8.
Response of 12 urban lakes with different trophic states in Beijing to variations of meteorological factors was studied in this research. Monthly water quality parameters, including total nitrogen (TN), total phosphorus (TP), chlorophyll a, chemical oxygen demand (COD), biological oxygen demand (BOD), dissolved oxygen, and water temperature, were analyzed from 2009 to 2011. Results indicated that TN in the urban lakes did not exhibit significant response to meteorological variations owing to relatively lower TN concentration in the urban soil. For the highly eutrophic lakes, TP, chlorophyll a, COD, and BOD were positively correlated with precipitation, and negatively correlated with wind speed (p < 0.05). Chlorophyll a showed significant positive correlation with TP and temperature. Moreover, the abrupt increase of TP occurred in spring, which was associated with higher temperature induced internal phosphorus loading. On average, temperature/precipitation and wind speed/sunshine duration contributed to 10.7–43.8 and 8.3–19.2 % of the variations in water quality. In contrast, lakes with mesotrophication/light eutrophication did not show significant sensitivity to meteorological variations owing to their better buffer capacity and regulation effect of algae growth. Beijing is undergoing increased temperature and heavy rainfall frequency as well as decreased wind speed during the past five decades; the above results infer that water quality of most urban lakes of Beijing is becoming worse under this climate change trend. This study suggested that urban lakes with different trophic states will respond differently to global climate change, and highly eutrophic lakes might face big challenges of water quality deterioration and algae bloom.  相似文献   

9.
The hyporheic interstitial provides habitat for many different organisms – from bacteria to burrowing invertebrates. Due to their burrowing and sediment reworking behaviour, these ecosystem engineers have the potential to affect hyporheic processes such as respiration and nutrient cycling. However, there is a lack of studies that characterize the interactions between bioturbators, physico-chemical habitat properties and microbial communities in freshwater substrates. In a standardized laboratory experiment, we investigated the effects of three functionally different bioturbators, duck mussels (Anodonta anatina, Linnaeus 1758), mayfly nymphs (Ephemera danica, Müller 1764) and tubificid worms (Tubifex tubifex, Müller 1774), on the physico-chemical conditions and bacterial communities in hyporheic substrates. We hypothesized that different invertebrates distinctly alter habitat conditions and thus microbial community composition, depending on the depth and the manner of burrowing. A. anatina and E. danica caused an increase in interstitial oxygen concentration, whereas strong declines in oxygen concentration and redox potential were detected in the T. tubifex treatment. These effects on physico-chemical habitat properties were even detectable in open water. Mussels and tubificid worms also significantly influenced the composition of bacterial communities in the hyporheic zone. A loss or replacement of bioturbators in stream ecosystems due to anthropogenic habitat alterations is expected to result in shifts in microbial community compositions, with effects on nutrient fluxes, pollutant degradation and benthic food webs. An understanding of the effects of functionally different native and invasive bioturbators is crucial to predict changes in stream ecosystem functioning.  相似文献   

10.
Fine structured multiple-harmonic electromagnetic emissions at frequencies around the equatorial oxygen cyclotron harmonics are observed by Van Allen Probe A outside the core plasmasphere(L~5) off the magnetic equator(MLAT~.7.5°)during a geomagnetic storm. We find that the multiple-harmonic emissions have power spectrum density(PSD) peaks during 2–8equatorial oxygen gyroharmonics( f ~ n fO+, n=2–8), while the fundamental mode(n=1) is absent, implying that the harmonic waves are generated near the equator and propagate into the observation region. Additionally, these electromagnetic emissions are linearly polarized. Different from the equatorial noise emission that propagates considerably obliquely, these emissions have moderate wave normal angles(approximately 40°–60°), which predominately increase as the harmonic number increases.Considering their frequency and wave normal angle characteristics, it is suggested that these multiple-harmonic emissions play an important role in the dynamic variation of radiation belt electrons.  相似文献   

11.
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12.
Analysis of the physical, chemical and biological parameters assessing water quality in Harris Neck estuary indicated that the average dissolved oxygen level was 8.6 mg/L, it maintained moderate levels of total dissolved nitrogen (2.7-4.6 mg/L) and total dissolved phosphorous (<0.05 mg/L), chlorophyll a was above 5.0 μg/L and it is contaminated with low levels of fecal bacteria. Bifidobacterium adolescentis, a putative marker of human fecal pollution, was detected once at stations 3 and 5. Overall the Harris Neck water quality analyses indicated a relatively pristine and a healthy functioning marine environment.  相似文献   

13.
Respiration rates (mg O2 g?1 AFDW h?1) of Leuctra hippopus, Sericostoma personatum, Helodes minuta, Gammarus pulex and Asellus aquaticus were studied across an oxygen gradient at 2.8 and 6.3 °C, corresponding to an expected 3.5 °C increase in Danish winter stream temperature. Species were selected from the Danish Stream Fauna Index (DSFI), representing an expected hierarchy of tolerance towards water quality degradation. We expected that low-ranking, tolerant species (i.e. indicators of bad water quality) would have the capacity to regulate their oxygen uptake relatively independently of oxygen availability (oxy-regulators) and high-ranking, sensitive species (i.e. indicators of good water quality) would be less able to do so (oxy-conformers). For all species respiration rate was higher (although non-significantly) at 6.3 °C. The species’ oxy-regulatory capacity did not consistently reflect their DSFI ranking. As expected, and in accordance with its DSFI ranking, A. aquaticus had the highest oxy-regulatory capacity with the ability to regulate O2 uptake until an oxygen saturation of only 20%, which did not change with increasing temperature, emphasizing the robustness of A. aquaticus towards changes in the environment. S. personatum, H. minuta and G. pulex revealed no oxy-regulatory capacity. In contrast, the plecopteran L. hippopus did display an unexpected oxy-regulatory capacity. Though an increase in temperature changed L. hippopus’ capacity to oxy-regulate (the critical limit increased from 32.5 to 43.5% oxygen), respiration rates did not change significantly in spite of the temperature increase. This result contradicts the general belief that stoneflies, because of their affinity to well oxygenated habitats, are conformers. Our findings call for further studies on the respiratory conformer–regulator concept and its role as an eco-physiological trait for bio-assessment.  相似文献   

14.
Carbonate cement is the most abundant cement type in the Fourth Member of the Xujiahe Formation in the Xiaoquan-Fenggu area of the West Sichuan Depression. Here we use a systematic analysis of carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and enclosure homogenization temperatures to study the precipitation mechanism, pore fluid evolution, and distribution of different types of carbonate cement in reservoir sand in the study area. Crystalline calcite has relatively heavy carbon and oxygen isotope ratios(δ13C = 2.14‰, δ18O = -5.77‰), and was precipitated early. It was precipitated directly from supersaturated alkaline fluid under normal temperature and pressure conditions. At the time of precipitation, the fluid oxygen isotope ratio was very light, mainly showing the characteristics of a mixed meteoric water-seawater fluid(δ18O = -3‰), which shows that the fluid during precipitation was influenced by both meteoric water and seawater. The calcite cement that fills in the secondary pores has relatively lighter carbon and oxygen isotope ratios(δ13C = -2.36‰, δ18O = -15.68‰). This cement was precipitated late, mainly during the Middle and Late Jurassic. An important material source for this carbonate cement was the feldspar corrosion process that involved organic matter. The Ca2+, Fe3+ and Mg2+ ions released by the clay mineral transformation process were also important source materials. Because of water-rock interactions during the burial process, the oxygen isotope ratio of the fluid significantly increased during precipitation, by about 3‰. The dolomite cements in calcarenaceous sandstone that was precipitated during the Middle Jurassic have heavier carbon and oxygen isotope ratios, which are similar to those of carbonate debris in the sandstone(δ13C = 1.93‰, δ18O = -6.11‰), demonstrating that the two are from the same source that had a heavier oxygen isotope ratio(δ18O of about 2.2‰). The differences in fluid oxygen isotope ratios during cement precipitation reflect the influences of different water-rock interaction systems or different water-rock interaction strengths. This is the main reason why the sandstone containing many rigid particles(lithic quartz sandstone) has a relatively negative carbon isotope ratio and why the precipitation fluid in calcarenaceous sandstone has a relatively heavier oxygen isotope ratio.  相似文献   

15.
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16.
Hypoxia associated with eutrophication is a potential threat to the Chinese horseshoe crab Tachypleus tridentatus which inhabits intertidal sand flats in Asia. This study investigated the effect of dissolved oxygen level (DO) (6, 4 and 2 mg O2 l−1) on the physiological energetics in the juvenile T. tridentatus. They were exposed to various oxygen levels for three days and then transferred to normoxia for three days to examine the recovery from low oxygen stress. Feeding rate, respiration rate and scope for growth were reduced at lower DO levels while absorption efficiency and excretion rate were independent of DO levels. Although full recovery of the physiological responses and scope for growth from hypoxis stress was observed when normoxia resumed, their long term survival in suboptimal habitats with frequent occurrence of hypoxia deserves a close monitoring as hypoxia may be even more common in future in a warming world.  相似文献   

17.
Summary: In the control of the discharge of a large-scale sewage treatment being under enlargement it was repeatedly pointed out that the oxygen saturation of the water in the treated sewage channel at the mouth of the main water occasionally was much lower than 50 %, contrary to the demands of the public inspection of waters. The results of the oxygen input capacity investigated by oxygen measurements on the falls of the 17.5 km stretch of flow indicate a total of 2.67 t/d. For lack of information on the diffusing and biogenic oxygen input an oriented balance about the budget of the water in the treated sewage channel was made. From the resulting oxygen depletion of the sediment of only 1.8 t/d as well as from energy-related considerations concerning the oxygen input by falls, technical alterations and arrangements for the protection and improvement of the water in the treated sewage channel were derived. By this it is guaranteed that the oxygen content of the treated channel-water at the mouth of the main water does not decrease below 6.0 mg/l also during the daily periods of higher discharges of treated sewage waters.  相似文献   

18.
In this study we compare the organic geochemistry of fossil and modern Glycymeris shells. Amino acids were preserved within the shells. The amino acid content of the shells was similar at all the sites studied. Amino acid racemization and epimerization of Glycymeris shells are suitable techniques for dating Pleistocene raised marine deposits. As reported in other studies, we found that isoleucine epimerization analysis has a greater capacity to discriminate between sites of different age than glutamic acid and aspartic acid. However, particular constraints regarding the use of amino acid dating concern intrashell variability, so to avoid divergent results, it is necessary to sample the same part of the shell, namely the complex cross lamellar region near the umbo. The dating of high-energy coastal marine deposits calls for extensive field work in order to ensure the collection of a large number of samples in order to obtain robust results and reject spurious values. Shell accumulations on the shore-line are conditioned by several factors. The high coefficients of variation for epimerization values and their distribution pattern can be attributed mainly to time-linked taphonomical processes (time-averaging) that gave rise to the shell-bearing bed. However, reworking from former highstand sea level deposits, which usually occupy higher topographic levels, is not a common occurrence. Therefore, as a result of time-averaging and post-depositional processes, it is difficult to identify substages in stacked shell beds in raised beach deposits belonging to the same marine oxygen isotope stage by means of amino acid racemization/epimerization.  相似文献   

19.
During the past decades, major anthropogenic environmental changes occurred in Lake Victoria, including increased predation pressure due to Nile perch introduction, and decreases in water transparency and dissolved oxygen concentrations due to eutrophication. This resulted in a collapse of the haplochromine cichlids in the sub-littoral waters of the Mwanza Gulf in 1986–1990, followed by a recovery of some species in the 1990s and 2000s, when Nile perch densities declined. We studied two data sets: (1) haplochromines from sand and mud bottoms in the pre-collapse period; (2) haplochromines from sub-littoral areas during the pre-collapse, collapse and recovery periods. Water over mud is murkier and poorer in oxygen than water over sand, and differences in haplochromine communities in these natural habitats during the pre-collapse period may predict the effects of anthropogenic eutrophication during the collapse and recovery periods. In the pre-collapse period, haplochromine densities over sand and mud did not differ, but species richness over sand was 1.6 times higher than over mud bottoms. Orange- and white-blotched colour morphs were most common at the shallowest sand station. More specifically, insectivores and mollusc-shellers had higher numbers of species over sand than over mud, whereas for mollusc-crushers no difference was found. Laboratory experiments revealed that mollusc shelling was more affected by decreased light intensities than mollusc crushing. During the pre-collapse period, spawning occurred year-round in shallow areas with hard substrates and relatively clear water. In deeper areas with mud bottoms, spawning mainly occurred during months in which water clarity was high. No effects of hypoxia on spawning periods were found. It follows that clearer water seems to support differentiation in feeding techniques as well as year-round spawning, and both may facilitate species coexistence. Water clarity is also known to be important for mate choice. These observations may explain why, since the decline of Nile perch, haplochromine densities have recovered, the numbers of hybrids increased and species diversity in the current eutrophic sub-littoral waters has remained 70 % lower than before the environmental changes.  相似文献   

20.
The oxygen isotope composition of bone and tooth phosphate of 50 fox specimens and 30 reindeer specimens from various locations with different climatic and environmental conditions was measured. The existing relationship between these values and the mean oxygen isotope composition of local meteoric water has been calculated. In the case of foxes, specimens belonging to two genera (Vulpes and Alopex) and three different species were measured. The samples fit a straight line whose equation can be used for paleoclimatological studies either in Arctic or in temperate regions. For reindeer (Rangifer), a relatively large range of isotopic values was obtained from each location, suggesting imperfect equilibrium conditions with environmental water. The calculated equation can be used for semi-quantitative information on local paleowaters at high latitudes only.  相似文献   

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