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701.
长江干流不同江段鱼卵及仔鱼漂流特征昼夜变化的初步分析 总被引:2,自引:0,他引:2
根据2007~2009年在长江干流的泸州、珞璜、宜都、武穴4个江段分别采集的数据,对这些江段鱼卵及仔鱼漂流特征的昼夜变化规律进行初步分析。结果显示,长江上游泸州江段和珞璜江段鱼卵及仔鱼昼夜漂流密度有一定差异,但不显著;长江中游宜都江段,鱼卵漂流密度在昼夜时间上有显著性差异(〖WTBX〗n=38,p〖WTBZ〗=000),表现为6〖DK〗∶00的平均漂流密度13.02 ind./100 m3明显大于18〖DK〗∶00的密度3.28 ind./100 m3,仔鱼夜间漂流密度明显大于白天,于22〖DK〗∶00达到高峰值;武穴江段仔鱼漂流密度在昼夜时间上有显著性差异(〖WTBX〗n=62,p〖WTBZ〗=000),8〖DK〗∶00的平均漂流密8621 ind./100 m3明显大于18〖DK〗∶00的密度4485 ind./100 m3。不同物种的鱼卵及仔鱼漂流密度亦呈现出一定的昼夜差异,宜都江段贝氏〖FK(W*5/5。1〗〖PS黎明政造字2.EPS;%84%84,BP〗〖FK)〗,草鱼和银鲴鱼卵主要分布在白天,鳙、鲢等种类分布在夜间;另外,鳙、银鮈、铜鱼和翘嘴鲌等多数种类的仔鱼仅在夜间有分布,而飘鱼属的种类主要分布在白天。通过采集到鱼卵发育期推算,四大家鱼、贝氏〖FK(W*5/5。1〗〖PS黎明政造字2.EPS;%84%84,BP〗〖FK)〗、银鲴和翘嘴鲌的繁殖时间主要集中在夜间,而花斑副沙鳅和鳊全天均有繁殖 相似文献
702.
Climate change and human disturbance drive catchment erosion and increase riverine sediment load sensitively in small and
medium-sized watersheds. This is not always true in large basins, where aggregation and buffering effects have dampen the
ability to determine the driving forces of sedimentation. Even though there are significant responses to sedimentation in
large river basins, it is difficult to get a precise quantitative assessment of specific drivers. This paper develops a methodology
to identify driving forces that change suspended sediment load in the Upper Yangtze river. Annual runoff and sediment load
data from 1954 to 2005 at the Yichang gauging station in the Upper Yangtze basin, daily precipitation data from 60 meteorological
stations, and survey data on reservoir sediment were collected for the study. Sediment load/rainfall erosivity (S/R), is a
new proxy indicator introduced to reflect human activities. Since the mid-1980s, S/R in the Upper Yangtze has dramatically
declined from 0.21 to 0.03 (×1010 t ha h MJ−1 mm−1), indicating that human activity has played a key role in the decline of the suspended sediment load. Before the mid-1980s,
a higher average S/R is attributed to large-scale deforestation and land reclamation. A significant sediment decrease occurred
from 1959 to 1961 during an extreme drought condition, and an increase in sedimentation in 1998 coincided with an extreme
flood event, which was well recorded in the S/R curve. This indicates that the S/R proxy is able to distinguish anthropogenic
from climate impacts on suspended sediment load, but is not necessarily indicatory in extreme climate events. In addition,
typical drivers of riverine sediment load variation including soil conservation projects, reservoirs construction, and land
use/cover change are discussed. 相似文献
703.
Dechlorination of PCBs in the simulative transformer oil by microwave-hydrothermal reaction with zero-valent iron involved 总被引:1,自引:0,他引:1
The conventional hydrothermal reaction with iron powder, NaOH and H2O as reactants was reported to occur at temperature above 423 K, and iron oxides (Fe3O4 and NaFeO2) and hydrogen were produced. In this study, microwave heating was adopted to take the place of conventional heating to induce the hydrothermal reaction. Under microwave irradiation, NaOH and H2O absorbed microwave energy by space charge polarization and dipolar polarization and instantly converted it into thermal energy, which initiated the hydrothermal reaction that involved with zero-valent iron. X-ray diffraction (XRD) analysis found Fe3O4/NaFeO2 and confirmed the occurrence of microwave-induced hydrothermal reaction. The developed microwave-hydrothermal reaction was employed for the dechlorination of PCBs. Hexadecane containing 100 mg L−1 of Aroclor1254 was used as simulative transformer oil, and the dechlorination of PCBs was evaluated by GC/ECD, GC/MS and ion chromatography. For PCBs in 10 mL simulative transformer oil, almost complete dechlorination was achieved by 750 W microwave irradiation for 10 min, with 0.3 g iron powder, 0.3 g NaOH and 0.6 mL H2O added. The effects of important factors including microwave power and the amounts of reactants added, on the dechlorination degree were investigated, moreover, the dechlorination mechanism was suggested. Microwave irradiation combined with the common and cheap materials, iron powder, NaOH and H2O, might provide a fast and cost-effective method for the treatment of PCBs-containing wastes. 相似文献
704.
Adverse effects of manufactured nickel oxide nanoparticles on the microalgae Chlorellavulgaris were determined by algal growth-inhibition test and morphological observation via transmission electron microscopy (TEM). Results showed that the NiO nanoparticles had severe impacts on the algae, with 72 h EC(50) values of 32.28 mg NiOL(-1). Under the stress of NiO nanoparticles, C. vulgaris cells showed plasmolysis, cytomembrane breakage and thylakoids disorder. NiO nanoparticles aggregated and deposited in algal culture media. The presence of algal cells accelerated aggregation of nanoparticles. Moreover, about 0.14% ionic Ni was released when NiO NPs were added into seawater. The attachment of aggregates to algal cell surface and the presence of released ionic Ni were likely responsible for the toxic effects. Interestingly, some NiO nanoparticles were reduced to zero valence nickel as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The maximum ratios of nickel reduction was achieved at 72 h of exposure, in accordance with the time-course of changes in soluble protein content of treated C. vulgaris, implying that some proteins of algae are involved in the process. Our results indicate that the toxicity and bioavailability of NiO nanoparticles to marine algae are reduced by aggregation and reduction of NiO. Thus, marine algae have the potential for usage in nano-pollution bio-remediation in aquatic system. 相似文献
705.
The residual levels and dissipation rate of trichlorfon, and its degradation product, dichlorvos, in cabbage crops and the soil in which these were grown, were determined by gas chromatography at two geographically distant experimental sites, one in Kunming and one in Beijing, China. Trichlorfon was applied at two dosages (900 g ai ha−1 and 1350 g ai ha−1). Maximum final residues of trichlorfon in soil and cabbage were 1.23 mg kg−1 and 1.81 mg kg−1 respectively at Kunming, and 0.35 mg kg−1 and 0.70 mg kg−1 respectively at Beijing. However, the final residues of dichlorvos in both cabbage and soil was only 0.04 mg kg−1 at Kunming, and only 0.03 mg kg−1, or “not detectable”, at Beijing. The mean half-life of trichlorfon in cabbage was 1.80 d with a dissipation rate of 90% over 5 d, while that in soil was 3.05 d with a dissipation rate of 90% over 14 d at one experimental site. The dissipation rates of trichlorfon and its degradation product dichlorvos at the two experimental sites were different, suggesting that degradation of these pesticides was affected by local soil characteristics and climate. When applied at both the recommended dosage and at 1.5 times this, no detectable residues of either trichlorfon or dichlorvos were found in soil or cabbage at harvest. Although trichlorfon can easily degrade into dichlorvos, which is highly toxic to humans and other animals, the observed low residual levels of dichlorvos suggest that trichlorfon is safe when applied at the recommended dosage. 相似文献
706.
Several classes of oxidative enzymes have shown promise for efficient removal of endocrine disrupting compounds (EDCs) that are resistant to conventional wastewater treatments. Although the kinetics of reactions between individual EDCs and selected oxidative enzymes are well documented in the literature, there has been little investigation of reactions with EDC mixtures. This makes it impossible to predict how enzyme-mediated treatment systems will perform since wastewater effluents generally contain multiple EDCs. This paper reports pseudo-first order rate constants for a model oxidative enzyme, horseradish peroxidase (HRP), during single-substrate (k1) and mixed-substrate (k1-MIX) reactions. Measured values are compared with literature values of three Michaelis-Menten parameters: half-saturation constant (KM), enzyme turnover number (kCAT), and the ratio kCAT/KM. Published reports had suggested that each of these could be correlated with HRP reactivity towards EDCs in mixtures, and empirical results from this study show that KM can be used to predict the sequence of EDC removal reactions within a particular mixture. We also observed that k1-MIX values were generally greater than k1 values and that compounds exhibiting greatest estrogenic toxicities reacted most rapidly in a given mixture. Finally, because KM may be tedious to measure for every EDC of interest, we have constructed a quantitative structure-activity relationship (QSAR) model to predict these values. This model predicts KM quite accurately (R2 = 89%) based on two molecular characteristics: molecular volume and hydration energy. Its accuracy makes this QSAR a useful tool for predicting which EDCs will be removed most efficiently during enzyme treatment of EDC mixtures. 相似文献
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