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排序方式: 共有285条查询结果,搜索用时 234 毫秒
231.
Cuauhtemoc Franco Ochoa Edgar Mendoza Baldwin Rodolfo Silva Casarín Gabriel Ruiz Martínez 《洁净——土壤、空气、水》2012,40(9):920-925
Pollution, habitat modification, and species migration are some of the results of human activities on natural environments which can be mitigated or compensated with proper planning. Irresponsibility or ignorance in planning coastal projects too often produces damage to natural systems which can be unpredictable and sometimes irrevocable. The specific site analyzed in this paper is the Cuautla littoral sub‐system which was originally a lagoon that diverted river water to other lagoons and estuaries, thus irrigating the Mexican Marismas Nacionales system, in the states of Nayarit and Sinaloa, Mexico. In the 1970s social and economic considerations motivated the construction of a small breaching canal from the sea to the lagoon. The subsequent growth of this channel was unforeseen and has produced an irreversible impact not only in the sub‐system but probably in the entire area of Marismas Nacionales. A lack of understanding of the present balances in the damaged system and of the impacts the changing morphology has on future change has created the need to study this area using numerical hydrodynamic simulation. The present distribution of water in the sub‐system was established and the governing processes were detected. By means of an analytical estimation of equilibrium conditions it was found that if nothing is done, the channel will continue eroding and the ecosystem will continue to degrade. Only by understanding the dramatic perturbations caused by the construction of the channel to the hydrologic and morphologic equilibriums can there be any hope of rescuing the ecosystem, including its human activities. 相似文献
232.
Montero N Belzunce-Segarra MJ Gonzalez JL Larreta J Franco J 《Marine pollution bulletin》2012,64(1):31-39
In this contribution, the potential use of diffusive gradients in thin-films (DGTs) for the chemical evaluation of transitional water bodies within the Water Framework Directive (WFD) has been studied. The water metal concentration has been evaluated in 13 estuaries in the southeastern Bay of Biscay. The DGTs were deployed in triplicate at two stations in each estuary, delimiting the tidal influence. The DGT results were in the ranges of 2-1570 ng L(-1) for cadmium, 66-515 ng L(-1) for copper, 30-3650 ng L(-1) for nickel and 0.8-95.5 μg L(-1) for zinc. The DGTs provided reliable average labile metal concentrations in highly dynamic systems that were comparable with DGT measurements in coastal and estuarine waters worldwide. In addition, it was possible to discriminate those estuaries more susceptible to environmental impacts, being consistent with the historical contamination of each estuary. Based on the obtained results, a sampling strategy for the monitoring of transitional water bodies using DGTs is proposed. 相似文献
233.
Predicting new snow density in the Italian Alps: A variability analysis based on 10 years of measurements 下载免费PDF全文
Mauro Valt Nicolas Guyennon Franco Salerno Anna B. Petrangeli Rosamaria Salvatori Paola Cianfarra Emanuele Romano 《水文研究》2018,32(20):3174-3187
Despite its strong impact on the time evolution of the snowpack, current estimation of new snow density (ρhn) is usually accomplished either by using local empirical techniques or by assuming a constant snow density. Faced with the lack of an estimation model of ρhn valid for a wide spatial scale and supported by a suitable number of observations, this study aims to develop simple monthly linear regression models at scale of the entire Italian Alpine chain based on 12,112 snowfall observations at 122 stations, using only air temperature as predictor. Moreover, the remaining variance is investigated in both time and space, also considering some qualitative features of the snowfall events. The daily ρhn measurements present a mean value of 115 kg m?3 (105 and 159 kg m?3 for dry and wet conditions, respectively). The mean air temperature of the 24 hr preceding the snowfall event has been found to be the best predictor of the ρhn, within 31% of uncertainty. The analysis of associated residues allows supporting the idea that the adoption of a more local approach than the one analysed here is not able to substantially increase the predictive capabilities of the model. In fact, the main factor explaining the remaining variance over the air temperature is the wind, but in a complex orography, as mountain regions are, supplying realistic local wind fields is particularly challenging. Therefore, we conclude that using only the daily mean temperature as predictor is a good choice for estimating daily new snow density at scale of Italian Alpine chain, as well as at more regional scale. 相似文献
234.
New geomorphological and chronological constraints for glacial deposits in the Rivoli‐Avigliana end‐moraine system and the lower Susa Valley (Western Alps,NW Italy) 下载免费PDF全文
235.
Roberto Battiston Maria Teresa Brunetti Franco Cervelli Cristiano Fidani Mauro Menichelli 《Astrophysics and Space Science》2009,323(4):357-366
We discuss an electromagnetic sampling calorimeter for the detection of very high energy gamma-rays on the Moon, which is
based on the use of scintillating cylinders and plates imbedded in the lunar soil. The use of lunar soil as a calorimeter
radiator reduces the weight of the material to be transported to the Moon and minimises environmental impact. Plastic scintillator
bars inserted into the regolith about 1.5 m are the active elements of this instrument: at the surface, each bar is terminated
by a plastic scintillator plate to veto high energy charge particles. The readout system for the scintillator bars and plates
are based on recently developed single photon solid state detectors (Silicon Photomultiplier, SiPM), extremely compact, sturdy
and sensitive devices suited for detecting small light pulses in a space experiment. The performance of a regolith-scintillator
calorimeter is evaluated and the relevant parameters are optimised using a GEANT4 simulation. 相似文献
236.
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238.
Seoane S Garmendia M Revilla M Borja A Franco J Orive E Valencia V 《Marine pollution bulletin》2011,62(7):1484-1497
Inverted microscopy is widespread employed for the analysis of phytoplankton composition within water quality monitoring networks. However, the analysis at the lowest taxonomical level is not always required for ecological status assessment. In addition, inverted microscopy can underestimate the small phytoplankton, and not always distinguish photoautotrophic from heterotrophic cells. In this study, as alternative tools, epifluorescence microscopy and High Performance Liquid Chromatography (HPLC) were employed to characterize phytoplankton communities within waters of different trophic condition. Epifluorescence microscopy confirmed its effectiveness to count the small phytoplankton. Furthermore, significant correlations between nutrients of anthropogenic origin and nanoplankton abundances were found. However, this technique resulted very time-consuming. HPLC together with the CHEMTAX program was more appropriate than inverted microscopy, in terms of cost-effectiveness. Also, the main variability patterns observed in the phytoplankton community structure by HPLC coincided with previous findings in the study area. Nevertheless, a rapid screening at the inverted microscope is recommended. 相似文献
239.
Di Franco A Graziano M Franzitta G Felline S Chemello R Milazzo M 《Marine pollution bulletin》2011,62(5):926-933
Many human activities add new structures to the marine landscape. Despite the fact that human structures cause some inevitable impacts, surprisingly little information exists on the effects of marina on natural marine assemblages. The aim of this paper is to assess habitat-specific response of benthic sessile organisms of rocky shores in relation to the presence of a small marina. Sampling was carried out at three coastal habitats (midshore, lowshore and subtidal) by means of visual censuses adopting an after-control-impact (ACI) experimental design. It appears that the marina affects the structure and composition of benthic communities of both the midshore and the lowshore. Little effect was evident on shallow subtidal assemblage structure. The results of the present study clearly show habitat-specific responses of coastal benthic assemblages to the presence of infrastructure. 相似文献
240.
This paper presents the analysis of measurements of long waves at the harbor of Marina di Carrara, Italy. Nine pressure gauges
(eight in the inner harbor and one outside the harbor) were used to record continuously the water surface elevation, for about
3 years; incoming short waves were measured using a directional buoy at about 500 m offshore the breakwaters. The analysis
is carried out splitting the energy of the long waves into two bands, i.e., very long waves (VLW; f < 0.003 Hz) and long waves (LW; 0.003 < f < 0.030 Hz); it is found that LW energy is strongly correlated with the energy of the incoming short waves while no correlation
(or very poor) is found for VLW. During energetic sea states, surface elevation spectra of VLW and LW, normalized against
the wave energy of each frequency band, appear to be autosimilar; this suggests that the spectra of the incoming long waves
have a mostly constant shape. Simple numerical computations of harbor resonance, carried out using a mild-slope equation linearized
model, indicate that the amplification of the height of the incoming LW generated by short waves (calculated using empirical
formulae from previous researches by Melito et al. 2007) inside the harbor can be reasonably predicted using such simple approach, assuming that the LW spectra are rectangular.
The shape of the amplification diagram calculated by the numerical model shows reasonable (but not perfect) agreement with
the shape of the normalized measured spectra inside the harbor. 相似文献