خيارات البحث
النتائج 1511 - 1520 من 4,309
Coastal debris survey in a Remote Island of the Chilean Northern Patagonia النص الكامل
2017
Perez-Venegas, D. | Pavés, H. | Pulgar, J. | Ahrendt, C. | Seguel, M. | Galbán-Malagón, C.J.
Global marine litter pollution is increasing dramatically, and oceanic islands are one of the most vulnerable ecosystems due to their high debris accumulation rate compared to continental sites. Remote areas, such as inhabited islands, represent a perfect study case to track marine debris sources, due to the assumed low rates of local production of debris. Guafo Island is one of the largest islands of the Chilean Northern Patagonia and is considered a remote zone. The accessible coast of Guafo Island was monitored during four austral summers revealing higher levels of marine debris accumulation than continental Chile. Plastic was the most abundant type of debris constituting 50% of the total litter monitored. Our results suggest that most of the plastic identified is likely to be related to local fisheries activities. Mitigation measures including collaboration among fishing communities and scientists could contribute to reduce the coastal debris pollution in remote areas.
اظهر المزيد [+] اقل [-]Ignitability of crude oil and its oil-in-water products at arctic temperature النص الكامل
2017
Ranellone, Raymond T. | Tukaew, Panyawat | Shi, Xiaochuan | Rangwala, Ali S.
A novel platform and procedure were developed to characterize the ignitability of Alaska North Slope (ANS) crude oil and its water-in-oil products with water content up to 60% at low temperatures (−20–0°C). Time to ignition, critical heat flux, in-depth temperature profiles were investigated. It was observed that a cold boundary and consequent low oil temperature increased the thermal inertia of the oil/mixture and consequently the time to sustained ignition also increased. As the water content in the ANS water-in-oil mixture increased, the critical heat flux for ignition was found to increase. This is mainly because of an increase in the thermal conductivity of the mixture with the addition of saltwater. The results of the study can be used towards design of ignition strategies and technologies for in situ burning of oil spills in cold climates such as the Arctic.
اظهر المزيد [+] اقل [-]Analysis of bloom conditions in fall 2013 in the Strait of Hormuz using satellite observations and model simulations النص الكامل
2017
Zhao, Jun | Temimi, Marouane | Al Azhar, Muchamad | Ghedira, Hosni
In this study an algal bloom event in fall 2013 in the Strait of Hormuz was thoroughly investigated using satellite remote sensing and hydrodynamic modeling. The motivation of this study is to deduce ambient conditions prior to and during the bloom outbreak and understand its trigger. Bloom tracking was achieved by sequential MODIS imagery and numerical simulations. Satellite observations showed that the bloom was initiated in late October 2013 and dissipated in early June 2014. Trajectories of bloom patches were simulated using a Lagrangian transport model. Model-based predictions of bloom patches' trajectories were in good agreement with satellite observations with a probability of detection (POD) reaching 0.85. Analysis of ancillary data, including sea surface temperature, ocean circulation, and wind, indicated that the bloom was likely caused by upwelling conditions in the Strait of Hormuz. Combined with numerical models, satellite observations provide an essential tool for investigating bloom conditions.
اظهر المزيد [+] اقل [-]Marine litter abundance and distribution on beaches on the Isle of Rügen considering the influence of exposition, morphology and recreational activities النص الكامل
2017
Hengstmann, Elena | Gräwe, Dennis | Tamminga, Matthias | Fischer, Elke Kerstin
The abundance, weight and composition of marine debris were determined at the northwest coast of the Isle of Rügen in 2015. A total number of 1115 macrolitter items were registered, resulting in an abundance of 304±88.96 items per 100m of beach length and therefore being greater than the abundances found for other beaches at the Baltic Sea. Macrolitter items were predominantly composed of plastic, on average 83%. The four beaches under investigation have different exposition as well as touristic levels. The differing influence of wind and water currents as well as recreational activities on the macrolitter at these beaches was detectable. The distribution of items within a beach segment was analyzed by implementing D-GPS and drone aerial photography. The results of this analysis suggested that the identity of the substrate as well as the presence of vegetation are both major influencing factors in the macrolitter distribution.
اظهر المزيد [+] اقل [-]Effectiveness of a chemical herder in association with in-situ burning of oil spills in ice-infested water النص الكامل
2017
van Gelderen, Laurens | Fritt-Rasmussen, Janne | Jomaas, Grunde
The average herded slick thickness, surface distribution and burning efficiency of a light crude oil were studied in ice-infested water to determine the effectiveness of a chemical herder in facilitating the in-situ burning of oil. Experiments were performed in a small scale (1.0m2) and an intermediate scale (19m2) setup with open water and 3/10, 5/10 and 7/10 brash ice coverages. The herded slick thicknesses (3–8mm) were ignitable in each experiment. The presence of ice caused fracturing of the oil during the herding process, which reduced the size of the herded slicks and, as a consequence, their ignitability, which in turn decreased the burning efficiency. Burning efficiencies relative to the ignited fraction of the oil were in the expected range (42–86%). This shows that the herder will be an effective tool for in-situ burning of oil when the ignitability issues due to fracturing of the oil are resolved.
اظهر المزيد [+] اقل [-]A short note on a present-day benthic recovery status in the formerly heavily polluted Idefjord (Sweden/Norway) النص الكامل
2017
Polovodova Asteman, Irina | Nordberg, Kjell
Idefjord (Skagerrak, North Sea) has had a long pollution history due to a heavy exposure to effluents from sawmills and pulp and paper industry, which had a detrimental effect on fjord life. Earlier we presented a paper on the pollution history and benthic recovery in the fjord by studying sediment geochemistry (TOC and heavy metals) and benthic foraminifera in the sediment cores taken in the inner and the outer Idefjord. At that stage the foraminiferal (~benthic recovery) record was limited to years 2000 (inner fjord) and 2002 (outer fjord), in contrast to pollutant data reaching all the way up to 2014. In this short note we extend the foraminiferal record to year 2014 and fill the gap in the benthic recovery in the inner and the outer fjord over the last 12years. The results show that both inner and outer fjord inlets currently undergo a steady benthic recovery reflected in comeback of transitional and pre-pollution benthic foraminiferal species after 2000–2002 and towards 2014. The recovery is also supported by increasing faunal diversity, low dominance and since 2000–2002 re-appearance of calcareous foraminiferal species (Bulimina marginata, Elphidium spp., Epistominella vitrea, Hyalinea balthica and Lagena spp), which all disappeared during the period of maximum effluent discharges. At the same time, detection of opportunistic newcomers (e.g. Stainforthia fusiformis) and persisting absence of some transitional species such as Ammoscalaria tenuimargo suggests a recolonization by foraminiferal population with a different species composition as compared to the original pre-pollution community either due to changed environmental conditions or/and increased competition.
اظهر المزيد [+] اقل [-]Dramatic increase in mud distribution across a large sub-tropical embayment, Moreton Bay, Australia النص الكامل
2017
Lockington, James R. | Albert, Simon | Fisher, Paul L. | Gibbes, Badin R. | Maxwell, Paul S. | Grinham, Alistair R.
Major flood events can dramatically alter the coastal sediment environment. This study established the current sediment distribution in a large sub-tropical embayment, Moreton Bay, Australia, and examined the effect of three recent floods on modifying this distribution. In 2015, surface sediment samples were collected from 223 sites across the study area and analysed for particle size distribution with the resultant sediment distribution mapped. In addition, sampling of flood waters during two major events in 2011 and 2013 was undertaken and particle size distribution of suspended sediment was determined. Data was compared to the result of an earlier large-scale survey completed in 1970, with three large flood events occurring between the two surveys. The sediment environment has undergone a dramatic change with muddy sediments now covering an estimated area of over 860km2, more the double the area found in 1970. Mud is now the dominant sediment type within Moreton Bay.
اظهر المزيد [+] اقل [-]A new method to calibrate Lagrangian model with ASAR images for oil slick trajectory النص الكامل
2017
Tian, Siyu | Huang, Xiaoxia | Li, Hongga
Since Lagrangian model coefficients vary with different conditions, it is necessary to calibrate the model to obtain optimal coefficient combination for special oil spill accident. This paper focuses on proposing a new method to calibrate Lagrangian model with time series of Envisat ASAR images. Oil slicks extracted from time series images form a detected trajectory of special oil slick. Lagrangian model is calibrated by minimizing the difference between simulated trajectory and detected trajectory. mean center position distance difference (MCPD) and rotation difference (RD) of Oil slicks' or particles' standard deviational ellipses (SDEs) are calculated as two evaluations. The two parameters are taken to evaluate the performance of Lagrangian transport model with different coefficient combinations. This method is applied to Penglai 19-3 oil spill accident. The simulation result with calibrated model agrees well with related satellite observations. It is suggested the new method is effective to calibrate Lagrangian model.
اظهر المزيد [+] اقل [-]Distribution, enrichment and source of heavy metals in Rizhao offshore area, southeast Shandong Province النص الكامل
2017
Song, Hongying | Liu, Jinqing | Yin, Ping | Zhang, Yong
50 surface sediments were collected from Rizhao offshore area to determine heavy metals (Cu, Pb, Zn, Cr, Cd, As, Hg) pollution. High heavy metal values were located near the two ports in the north and south study areas, which was consistent with the distribution of fine-grained sediments. According to threshold effect level (TEL) and probable effect level (PEL), Cu and As had occasionally adverse biological effects on the aquatic ecosystems. The enrichment factor (EF) values showed that most of the study area was moderate or moderately severe enrichment for As, and minor enrichment for Pb, but Hg was only moderately enriched in the river estuaries. The sources of Cu, Zn and Cr were mainly influenced by natural weathering processes via the river inputs, whereas Pb, Cd and As were mainly derived from anthropogenic sources. Hg may have both natural and anthropogenic sources.
اظهر المزيد [+] اقل [-]Nervous system disruption and swimming abnormality in early-hatched pufferfish (Takifugu niphobles) larvae caused by pyrene is independent of aryl hydrocarbon receptors النص الكامل
2017
Itoyama, Tatsuya | Kawara, Moe | Fukui, Makiko | Sugahara, Yuki | Kurokawa, Daisuke | Kawaguchi, Masahumi | Kitamura, Shin-Ichi | Nakayama, Kei | Murakami, Yasunori
Pyrene, a member of the polycyclic aromatic hydrocarbons (PAHs), contributes to abnormality in the size of the brain and the swimming behavior of pufferfish (Takifugu niphobles) larvae. We hypothesized that the aryl hydrocarbon receptor (AHR) may mediate pyrene-induced toxic effects because AHR is assumed to be a candidate for the downstream target of PAHs in many cases. To identify the contribution of AHR on developing pufferfish, we performed exposure experiments using β-naphthoflavone, an agonist of AHR. We found that the toxic effects of pyrene and β-naphthoflavone in pufferfish larvae are fundamentally different. Pyrene specifically induced problems in the developing midbrain and in swimming behavior, while β-naphthoflavone affected the heartbeat rate and the size of the yolk. These results suggest that the behavioral and morphological abnormality caused by pyrene exposure is mediated by an AHR-independent pathway. Alternatively, defects caused by pyrene may be attributed to the inhibition of the FGF signal.
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