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171.
The distribution and intensity of hypoxia (low dissolved oxygen) in estuaries is increasing worldwide due to cultural eutrophication.
This study quantifies the strength of associations between the duration of diel-cycling severe hypoxia (≤2 mg O2 l−1) in bottom water (∼15 cm above bottom) of a shallow (<2 m) coastal lagoon estuary (Delaware, USA) and abiotic environmental
variables (water temperature, insolation, tide, streamflow, and wind) and predicts the duration of severe hypoxia given different
combinations of these variables. The intensity and spatial extent and dynamics of diel-cycling severe hypoxia events were
defined. Vertical variability in dissolved oxygen (DO) concentration during the daytime was also determined. During the summers
of 2001–2005, bottom DO data were collected for periods of weeks to months at multiple sites using automated sondes. Multiple
linear regression (MLR) and regression tree analysis (RTA) were used to determine the relative importance of the environmental
variables in predicting the number of hours of severe hypoxia per day. Key findings of the study were that severe hypoxia
events of minutes to hours in duration occurred frequently in all four tributaries sampled, primarily between 0200 and 1000
hours. Severe hypoxia duration and diel-cycling amplitudes of DO concentration increased in the up-tributary direction. Hierarchically,
the duration of severe hypoxia was influenced mostly by the mean daily water temperature, then by preceding days’ total insolation,
percentage of morning hours (02:00 to 10:00 a.m.) ebb tide, and daily streamflow. Collectively, the variables examined by the MLR and the RTA approaches accounted for 62%
and 65% of the variability in the duration of severe hypoxia, respectively. RTA demonstrated that daily mean water temperature
above 26.3°C and previous day’s total insolation below 13.6 kW m−2 were associated with the longest lasting severe hypoxic events (9.56 h). The environmental variables and combinations of
conditions that modulate or augment diel-cycling hypoxia presented in this paper enhance understanding of this widespread
and growing phenomenon and provide additional insight regarding the extent to which it can impact food webs in very shallow
estuarine waters that often serve as nursery habitat. 相似文献
172.
Yong Wang Qi-Long Miao Chong-Yi E Jian-Kang Han Yuan-Yuan Ding 《Environmental Earth Sciences》2010,60(6):1257-1266
The δ18O data obtained from an 18.7 m ice core drilled in Chongce Ice Cap at an elevation of 6,530 m a.s.l. in the West Kunlun Mountains
on the northern Tibetan Plateau show a strong correlation with the summer temperature of the middle to upper troposphere over
the mid-high latitudes of Eurasia. Based on this, the δ18O record can be used as a proxy of the June–September mean temperature of the mid-upper troposphere (MUT) from 1903 to 1992.
The time span of the ice core record is much longer than the meteorological data available only after 1948. Using the empirical
mode decomposition method (EMD), the δ18O record is decomposed into various frequency components and compared with the solar irradiance variations of the same period.
The results show that (1) The June–September mean temperature of the MUT over Eurasian mid-high latitudes is completely decomposed
into four IMF (intrinsic mode function) components and an increasing trend. (2) Solar irradiance is decomposed into the Schwabe
cycle, the Hale cycle, the Gleissberg cycle, and an increasing trend. (3) The correlation coefficients between the June and
September mean temperatures of the MUT over Eurasian mid-high latitudes and solar irradiance on the longer timescales (at
least more than 11-year) show the significant correlations; their phase changes are basically identical in general, and (4)
the 11-year Schwabe cycle exists in the June–September mean temperature of the MUT over Eurasian mid-high latitudes during
most of the time from 1903 to 1992, and only in the two high-temperature phases (1929–1944 and from 1975 to the present) may
global warming disturb this relation. A full understanding of this phenomenon would shed insight into the potential consequence
of global warming on the MUT. 相似文献
173.
This study uses radiometric analysis (210Pb and 137Cs) of short sediment cores with high-resolution sampling (1-cm interval) to trace sedimentation rates in the Nile Delta lagoons,
particularly since completion of the Aswan High Dam in 1964. A declining trend in 210Pbex as calculated by the CIC model is clearly identified in about 10 cm of the upper-core sediments from the lagoons of Manzala
and Edku, accompanied by two spikes of 137Cs in cores from the lagoons of Burullus and Edku. These findings illustrate average post-dam sedimentation rates ranging
from 0.22 to 0.27 cm a−1 in the lagoons, in contrast with those found previously based on low-resolution sampling. The lower sedimentation rates in
the lagoons are a consequence of a dramatic reduction in riverine sediment load to the coastal area as a result of the damming.
Although widespread erosion occurs along the open estuarine coast, the lagoon setting remains calmer than before due to coastal
diking and freshwater regulation in the delta plain in the past decades. This provides the possibility of continuously preserved
radiometric records in the less-bioturbated lagoon sediments. Dating individual layers using the CRS model has revealed increasing
sedimentation rates in Manzala and Burullus since the 1980s, which can largely be explained as a consequence of the reduction
in lagoon area due to intensifying reclamation. The post-dam sedimentation in the shrinking lagoons may have some adverse
ecological consequences due to finer sediment’s affinity with pollutants. These findings would shed light on the environmental
conservation and socioeconomic development in the Nile Delta region. 相似文献
174.
YU Shanshan KONG Xiaoyu LI Yulong XU Hui 《中国海洋大学学报(英文版)》2007,6(2):187-192
The complete mitochondrial cytochrome oxidase subunit Ⅱ (COⅡ) gene of Penaeinae shrimp Fenneropenaeus chinensis was cloned and sequenced. The gene is 688 bp in length and codes for 229 amino acids. It shows 83.2%, 87.0% and 83.8% sequence similarity to Marsupenaeus Japonicus, Penaeus monodon and Farfantepenaeus notialis, respectively. The A+T content of the whole gene and that at the third position of codons are 64.7% and 78.2%, respectively. The phylogenetic relationship between F. chinensis and three other species representing genera Farfanatepenaeus, Marsupenaeus and Penaeus was analyzed. Results showed that the genetic distances among the four taxa ranged from 0.144 0 to 0.200 5, exceeding those estimated with COⅠ and partial 16S rRNA gene sequences among Marsupenaeus, Litopenaeus and Melicertus, and being therefore larger than the value among subgenera. It has been suggested that the COⅡ gene has a faster evolutionary rate than that of the COⅠ gene and partial 16S rRNA gene and could be used for phylogenetic analysis at genus or species level. The results of the present study indicated that Farfantepenaeus, Fenneropenaeus, Marsupenaeus and Penaeus are at a higher phylogenetic level than subgenus, which supports the opinion of the elevation of phylogenetic status of the four subgenera to genus level. 相似文献
175.
John Clinton Aldo Zollo Alexandru Marmureanu Can Zulfikar Stefano Parolai 《Bulletin of Earthquake Engineering》2016,14(9):2441-2458
European researchers and seismic networks are active in developing new approaches to earthquake early warning (EEW), implementing and operating test EEW systems, and in some cases, offering operational EEW to end users. We present the key recent developments in EEW research in Europe, describe the networks and regions where EEW is currently in testing or development, and highlight the two systems in Turkey and Romania that currently provide operational systems to a limited set of end users. 相似文献
176.
The tracking performance of a Phase Lock Loop (PLL) is affected by the influence of several error sources. In addition to thermal noise and dynamic stress error, oscillator phase noise can cause significant phase jitter which degrades the tracking performance. Oscillator phase noise is usually caused by two different effects: Allan deviation phase noise is caused by frequency instabilities of the receiver's reference oscillator and the satellite's frequency standard. It can be termed as system-inherent phase noise and is relevant for both static and dynamic applications. “External” phase noise, however, is caused by vibration and is a major problem for dynamic applications. In the context of this paper, both types of phase noise will be modeled and the resulting integrals will be evaluated for PLLs up to the third order. Besides, phase jitter induced by thermal noise and signal dynamics will also be discussed, thus providing all necessary formulas for analyzing the performance of a phase lock loop in case of different forms of stress. Since the main focus is centered on the effects of oscillator phase noise, the overall PLL performance is graphically illustrated with and without consideration of oscillator phase noise. © 2002 Wiley Periodicals, Inc. 相似文献
177.
Climate change caused by carbon emissions continuously threatens sustainable development. Due to China’s immense territory, there are remarkable regional differences in carbon emissions. The construction industry, which has strong internal industrial differences, further leads to carbon emission disparity in China. Policymakers should consider spatial effects and attempt to eliminate carbon emission inequality to promote the sustainable development of the construction industry and realize emission reduction targets. Based on the classic Markov chain and spatial Markov chain, this paper investigates the club convergence and spatial distribution dynamics of China’s carbon intensity in the construction industry from 2005 to 2014. The results show that the provincial carbon intensity in the construction industry is characterized by “convergence clubs” during the research period, and very low-level and very high-level convergence clubs have strong stability. Moreover, the carbon intensity class transitions of provinces tend to be consistent with that of their neighbors. Furthermore, the transition of carbon intensity types is highly influenced by their regional backgrounds. The provinces with high carbon emissions have a negative influence on their neighbors, whereas the provinces with low carbon emissions have a positive influence. These analyses provide a spatial interpretation to the “club convergence” of carbon intensity. 相似文献
178.
By using sonar imaging, this paper presents a new algorithm for the clustering of seabed types based on the self-organizing feature maps (SOFM) neural network. The theory as well as data processing is studied in detail. Some valuable conclusions and suggestions are given 相似文献
179.
Xianyu Kong Xiurong Han Min Gao Rongguo Su Ke Wang Xuzhao Li Wei Lu 《中国海洋大学学报(英文版)》2016,15(6):1014-1020
With the global ban on the application of organotin-based marine coatings by the International Maritime Organization, the development of environmentally friendly, low-toxic and nontoxic antifouling compounds for marine industries has become an urgent need. Marine microorganisms have been considered as a potential source of natural antifoulants. In this study, the antifouling potential of marine dinoflagellate Amphidinium carterae, the toxic and red-tide microalgae, was investigated. We performed a series of operations to extract the bioactive substances from Amphidinium carterae and tested their antialgal and antilarval activities. The crude extract of Amphidinium carterae showed significant antialgal activity and the EC50 value against Skeletonema costatum was 55.4 μg mL?1. After purification, the isolated bioactive substances (the organic extract C) exhibited much higher antialgal and antilarval activities with EC50 of 12.9 μg mL?1 against Skeletonema costatum and LC50 of 15.1 μg mL?1 against Amphibalanus amphitrite larvae. Subsequently, IR, Q-TOFMS, and GC-MS were utilized for the structural elucidation of the bioactive compounds, and a series of unsaturated and saturated 16- to 22-carbon fatty acids were detected. The data suggested the bioactive compounds isolated from Amphidinium carterae exhibited a significant inhibiting effect against the diatom Skeletonema costatum and Amphibalanus amphitrite larvae, and could be substitutes for persistent, toxic antifouling compounds. 相似文献
180.
ZHENG Xiaodong XIAO Shu WANG Zhaoping WANG Rucai 《中国海洋大学学报(英文版)》2007,6(4):393-397
The secretion function of mantle is closely related to shell formation in some bivalves and gastropods. Up to now, few researches have been reported for cuttlebone formation in the class Cephalopoda. In this study, the structure and secretion function of cuttlebone sac of the golden cuttlefish Sepia esculenta was analyzed using the histological and histochemical methods. The results showed that high and columnar cells located in sac epithelium, and flat cells existed near the base membrane. A lot of fibroblasts were found in the lateral mantle collective tissue. Some mucus, mucopolysaccharide and alkaline phosphatase (ALP) were found in the sac. The ultrastructural characteristics of Quasi-connective-tissue-calcium cells (QCTCC) were observed using a transmission electron microscope (TEM). The relationship between cuttlebone sac secretion function and shell formation was discussed. 相似文献