摘要 :
The diurnal vertical migrations of smelt (Osmerus eperlanus), larvae of phantom midge (Chaoborus fiavicans) and cladoceran zooplankton in eutrophic Lake Hiidenvesi were studied in order to clarify the factors behind the low zoopla...
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The diurnal vertical migrations of smelt (Osmerus eperlanus), larvae of phantom midge (Chaoborus fiavicans) and cladoceran zooplankton in eutrophic Lake Hiidenvesi were studied in order to clarify the factors behind the low zooplankton biomass. In the study area, an oxygen minimum occurred in the metalimnion in the' 10-15 m depth. No diurnal fluctuations in the position of the minimum were observed. Cladocerans inhabited the epilimnion throughout the study period and their vertical movements were restricted to above the thermocline and above the oxygen minimum. C. fiavicans conducted a diurnal migration. During the day, the majority of the population inhabited the 12 -15 m depth just in the oxygen minimum, while during darkness they were found in the uppermost 8 ill. Smelts started ascending towards the water surface before sunset and reached the uppermost 3 m around 23:00. During daytime, the majority of smelts inhabited the depth of 7-9 m, where the water temperature was unfavourably high for them (18 °C). Smelts thus probably avoided the steep oxygen gradient in the metalimnion, whereas Chaoborus used the oxyg~n minimum as a refuge against predation. Those smelts that were found in the same water layers as Chaoboru~ used the larvae as their main prey. The metalimnetic oxygen minimum thus seemed to favour the coexistence of vertebrate and invertebrate predators, leading to a depression of cladoceran zooplankton.
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摘要 :
Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is
related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris
(C. vulgaris) ...
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Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is
related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris
(C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed
by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and
normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then
stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant
effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the
lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L,
3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon
(DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days,
respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial
degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were
found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence
intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The
increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of
HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the
release of IOM during the development of MOM.
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摘要 :
Most of the reservoirs or lakes will form a metalimnetic oxygen minimum (MOM) with the characterization of a substantial fraction of dissolved oxygen (DO) depleted below the epilimnion. The effect of intracellular organic matter (...
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Most of the reservoirs or lakes will form a metalimnetic oxygen minimum (MOM) with the characterization of a substantial fraction of dissolved oxygen (DO) depleted below the epilimnion. The effect of intracellular organic matter (IOM) of algal cells transformed under MOM conditions is completely different from that of the original IOM on water quality. In this study, the IOM changes of Microcystic aeruginosa under different MOM conditions and its related disinfection by-products formation potentials (DBPFPs) were investigated by changing the pres-sure and DO concentration of MOM. Total Fmax increased slightly and then decreased under different pressure conditions, finally decreasing by no more than 22.0%. Under aerobic condition, dissolved organic carbon (DOC) and total Fmax decreased significantly, and decreased by 60.4% and 38.8% within the first 2 days. The results of specific UV absorbance (SUVA) and UV250/UV365 indicated that aromatic compounds and average molecular weight of IOM were gradually increased under different MOM conditions. The total DBPFPs increased firstly and then decreased under different pressure conditions, and finally decreased by 26.2%-33.1%. The decrease of total DBPFPs was significantly higher under aerobic condition than that under anoxic condition, which finally decreased by 64.5%. Redundancy analysis showed that the fluorescence parameter (protein-like and humic-like fluorescence) could be expected as an index to predict the DBPFPs. Moreover, the results revealed that with the decrease of DO, the activity and diversity of natural microbial consortium decreased, which prevented the further degradation and utilization of organic matter by natural microbial consortium. Therefore, lower DO was a key player for the deterioration of water quality under MOM conditions.
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摘要 :
The metalimnetic oxygen minimum (MOM) is a common anaerobic phenomenon that occur between 5.00 and
40.00 m of reservoirs. Amino acids (AAs) are widely found in water, but their change in MOM remain unclear. In
this study, four A...
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The metalimnetic oxygen minimum (MOM) is a common anaerobic phenomenon that occur between 5.00 and
40.00 m of reservoirs. Amino acids (AAs) are widely found in water, but their change in MOM remain unclear. In
this study, four AAs with different side chain groups were selected to explore the change of their samples and
related disinfection by-products formation potential (DBPFPs) under MOM condition. The results showed that
the final degradation rate of dissolved organic carbon and dissolved organic nitrogen of four AAs samples were
11.71%-59.87% and 26.50%-100.00% under MOM condition. Aspartic acid samples were the easiest to be
degraded, whereas glycine samples were the opposite. While the total fluorescence intensity increased by
6.30%-113.40% for the appearance of tryptophan-like substance. The total DBPFPs of glutamic acid, arginine
and aspartic acid samples were finally decreased by 4.73%, 8.00% and 98.88% (glycine sample increased by 2.30
times). Compared with the surface condition, the degradation of AAs samples and the change of DBPFPs were
significantly inhibited under MOM condition. In addition, the diversities of bacterial communities were significantly reduced under MOM condition, which was very unfavorable to the degradation of AAs samples, and
in turn affected the control of DBPs and deteriorated the water quality.
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摘要 :
Dissolved oxygen (DO) dynamics of a temperate drinking water reservoir in the Harz Mountains (Germany) were investigated over a time period of 18 months. Via depth profiles in a fortnightly sampling resolution we were able to trac...
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Dissolved oxygen (DO) dynamics of a temperate drinking water reservoir in the Harz Mountains (Germany) were investigated over a time period of 18 months. Via depth profiles in a fortnightly sampling resolution we were able to trace DO and temperature dynamics including the formation and breakdown of a Metalimnetic Oxygen Minimum (MOM) by means of DO concentration, saturation patterns and stable isotope ratios of dissolved oxygen (expressed as δ~(18)O_(DO)). Over the evaluation period, 19.4 % of the samples collected had δ~(18)O_(DO) values compatible with atmospheric equilibration (+ 24.6 ‰ ± 0.4 ‰). With values smaller and larger than this threshold, the remaining δ~(18)O_(DO) values showed that 40.8 % of our samples were dominated by photosynthesis and 39.8 % by respiration. From December to April the reservoir was mixed and DO consumption by respiration exceeded production via photosynthesis. During stratification period, quantification of respiration/photosynthesis rates (R/P) confirmed the epilim-nion as a photosynthetic (i.e. net-autotrophic) environment while the hypolimnion was heterotrophic and dominated by respiration at various degrees. Samples of the MOM zone showed the highest R/P ratios and had among the most positive δ~(18)O_(DO) signals caused by respiration. This study showed that combinations of DO concentrations and their isotope ratios are promising to quantify critical zones of respiration and photosynthesis in aquatic environments.
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