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71.
Changes in stream water quality due to logging of the boreal forest in the Montmorency Forest,Québec
Yohann Tremblay Alain N. Rousseau André P. Plamondon Denis Lévesque Marcel Prévost 《水文研究》2009,23(5):764-776
Summer stream water quality was monitored before and following the logging of 50% of the boreal forest within three small watersheds (<50 ha) nested in the ‘Ruisseau des Eaux‐Volées’ Experimental Watershed, Montmorency Forest (Québec, Canada). Logging was conducted in winter, on snow cover according to recommended best management practices (BMPs) to minimize soil disturbance and protect advance growth. A 20‐m forest buffer was maintained along perennial streams. In watershed 7·2, cut‐blocks were located near the stream network and logging was partially allowed within the riparian buffer zone. In watersheds 7·5 and 7·7, logging occurred farther away from the stream network. Observations were also made for watershed 7·3 that collected the runoff from watersheds 7·2 and 7·5, and watershed 7·6, the uproad portion of watershed 7·7. The control watershed 0·2 was contiguous to the impacted watersheds and remained undisturbed. Following clearcutting, changes in summer daily maximum and minimum stream temperatures remained within ± 1 °C while changes in diurnal variation did not decrease by more than 0·5 °C. Concentrations of NO3? greatly increased by up to 6000% and concentrations of K+ increased by up to 300% during the second summer after logging. Smaller increases were observed for Fetotal (up to 71%), specific conductance (up to 26%), and Mg2+ (up to 19%). Post‐logging pH decreased slightly by no more than 7% while PO43? concentration remained relatively constant. Suspended sediment concentrations appeared to increase during post‐logging, but there was not enough pre‐logging data to statistically confirm this result. Logging of moderate intensity and respecting established BMPs may account for the limited changes of water quality parameters and the low exceedances of the criteria for the protection of aquatic life. The proximity of the cutover to the stream network and logging within the riparian zone did not appear to affect water quality. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
72.
Hassan Er-Raioui Saida Bouzid Mohammed Marhraoui Alain Saliot 《Ocean & Coastal Management》2009,52(2):124-129
Organic geochemical study of hydrocarbon pollution of the Mediterranean coastline of Morocco (Tangier-Nador) was performed during March–April 2002. It corresponds to a preliminary work representing an initial assessment of oil contamination of Moroccan coast.Three coastal sites corresponding to Tangier, Tetouan and Nador, representing the main built-up area of this marine region, were selected for superficial sediments, water and organism sampling. Results showed high contamination levels in these three selected sites, known as the most exposed areas to urban and industrial discharges. The maximal contamination corresponding to the sum of non-aromatic (NAH) and polycyclic aromatic hydrocarbons (PAH) encountered in sediment samples was about 553 μg/g (dw). Nevertheless, even a small city agglomeration without any industrial activity showed high values reaching 370 μg/g (dw), which confirm the important hydrocarbons input coming from discharges of fishing ships and oil transporting tankers.The obtained results from this survey reflecting in part the important amounts drained via effluents toward the Moroccan Mediterranean coasts, presented to the concerned authorities drove to the realization of the project of treatment of the wastewater.They later expect to lower rates by 50%, which is still insufficient for a fragile ecosystem such as the Mediterranean and sensitive to anthropogenic effects. 相似文献
73.
74.
Copper biogeochemistry is largely controlled by its bonding to natural organic matter (NOM) for reasons not well understood. Using XANES and EXAFS spectroscopy, along with supporting thermodynamic equilibrium calculations and structural and steric considerations, we show evidence at pH 4.5 and 5.5 for a five-membered Cu(malate)2-like ring chelate at 100-300 ppm Cu concentration, and a six-membered Cu(malonate))1-2-like ring chelate at higher concentration. A “structure fingerprint” is defined for the 5.0-7.0 Å−1 EXAFS region which is indicative of the ring size and number (i.e., mono- vs. bis-chelate), and the distance and bonding of axial oxygens (Oax) perpendicular to the chelate plane formed by the four equatorial oxygens (Oeq) at 1.94 Å. The stronger malate-type chelate is a C4 dicarboxylate, and the weaker malonate-type chelate a C3 dicarboxylate. The malate-type chelate owes its superior binding strength to an -OH for -H substitution on the α carbon, thus offering additional binding possibilities. The two new model structures are consistent with the majority of carboxyl groups being clustered and α-OH substitutions common in NOM, as shown by recent infrared and NMR studies. The high affinity of NOM for Cu(II) is explained by the abundance and geometrical fit of the two types of structures to the size of the equatorial plane of Cu(II). The weaker binding abilities of functionalized aromatic rings also is explained, as malate-type and malonate-type structures are present only on aliphatic chains. For example, salicylate is a monocarboxylate which forms an unfavorable six-membered chelate, because the OH substitution is in the β position. Similarly, phthalate is a dicarboxylate forming a highly strained seven-membered chelate.Five-membered Cu(II) chelates can be anchored by a thiol α-SH substituent instead of an alcohol α-OH, as in thio-carboxylic acids. This type of chelate is seldom present in NOM, but forms rapidly when Cu(II) is photoreduced to Cu(I) at room temperature under the X-ray beam. When the sample is wet, exposure to the beam can reduce Cu(II) to Cu(0). Chelates with an α-amino substituent were not detected, suggesting that malate-like α-OH dicarboxylates are stronger ligands than amino acids at acidic pH, in agreement with the strong electronegativity of the COOH clusters. However, aminocarboxylate Cu(II) chelates may form after saturation of the strongest sites or at circumneutral pH, and could be observed in NOM fractions enriched in proteinaceous material. Overall, our results support the following propositions:
- (1)
- The most stable Cu-NOM chelates at acidic pH are formed with closely-spaced carboxyl groups and hydroxyl donors in the α-position; oxalate-type ring chelates are not observed.
- (2)
- Cu(II) bonds the four equatorial oxygens to the heuristic distance of 1.94 ± 0.01 Å, compared to 1.97 Å in water. This shortening increases the ligand field strength, and hence the covalency of the Cu-Oeq bond and stability of the chelate.
- (3)
- The chelate is further stabilized by the bonding of axial oxygens with intra- or inter-molecular carboxyl groups.
- (4)
- Steric hindrances in NOM are the main reason for the absence of Cu-Cu interactions, which otherwise are common in carboxylate coordination complexes.
75.
Jing Zhao Zewen Liao Lühui Zhang Patrice Creux Chupeng Yang Anna Chrostowska Haizu Zhang Alain Graciaa 《Applied Geochemistry》2010
Being the heaviest fraction of crude oils, asphaltenes are liable to aggregate, and other molecules in the oils can be steadily adsorbed onto, and even occluded inside the macromolecular structures of the asphaltenes. These occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes. The asphaltenes of a crude oil (ZG31) from the central Tarim Basin, NW China, were hierarchically degraded by increasing the amount of H2O2/CH3COOH to release the occluded compounds. Besides the common components, series of even numbered n-alk-1-enes and 3-ethylalkanes were detected among the occluded compounds. Comparison of the biomarker distributions and the compound-specific C isotopic results between the compounds from the maltenes and those from the occluded fraction, the ZG31 reservoir was suggested to have been charged multiple times, with different charges being derived from different strata of source rocks. 相似文献
76.
Michel Faure Alain Cocherie Eugne B Mzme Nicolas Charles Philippe Rossi 《Gondwana Research》2010,18(4):369
In France, the Devonian–Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean–Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of migmatization was not clearly settled. Eleven U–Th–Pbtot. ages on monazite and three U–Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Anglès, Vialais, Soulié) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333–326 Ma (Visean) and late granitoids emplaced around 325–318 Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560 Ma and 480 Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the “Tufs anthracifères” volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale. 相似文献
77.
HydroCube: an entity-relationship hydrogeological data model 总被引:1,自引:1,他引:0
Piotr Wojda Serge Brouyère Johan Derouane Alain Dassargues 《Hydrogeology Journal》2010,18(8):1953-1962
Managing, handling and accessing hydrogeological information depends heavily on the applied hydrogeological data models, which differ between institutions and countries. The effective dissemination of hydrogeological information requires the convergence of such models to make hydrogeological information accessible to multiple users such as universities, water suppliers, and administration and research organisations. Furthermore, because hydrogeological studies are complex, they require a wide variety of high-quality hydrogeological data with appropriate metadata in clearly designed and coherent structures. A need exists, therefore, to develop and implement hydrogeological data models that cover, as much as possible, the full hydrogeological domain. A new data model, called HydroCube, was developed for the Walloon Region in Belgium in 2005. The HydroCube model presents an innovative holistic project-based approach which covers a full set of hydrogeological concepts and features, allowing for effective hydrogeological project management. The model stores data relating to the project locality, hydrogeological equipment, and related observations and measurements. In particular, it focuses on specialized hydrogeological field experiments such as pumping and tracer tests. This logical data model uses entity-relationship diagrams and it has been implemented in the Microsoft Access environment. It has been enriched with a fully functional user interface. 相似文献
78.
Alain Dabas 《Comptes Rendus Geoscience》2010,342(4-5):370-379
Among the basic variables that characterize the thermodynamic state of the atmosphere, wind is relatively poorly observed. Surface measurements by in situ sensors are numerous, but irregularly distributed over the globe. Upper level winds are characterized by radiosoundings that are reliable and accurate, but in a very limited number due to their expensive cost. They are complemented by wind measurements performed by commercial aircrafts, but these data are mostly acquired along the major flight routes at a cruising altitude of ~10 km. Radio sondes and aircrafts leave large gaps in the observation network that have been partly complemented for 10 years by an increasing amount of wind information derived from cloud tracking in satellite images, and more recently, surface winds by scatterometers. However, the observation capacity still suffers deficiencies as there is still no information in cloud-free parts of the atmosphere, and no complete vertical profiles except for the radiosoundings. They should be overcome with the launch in 2011 of the European satellite ADM-Aeolus, a space-based Doppler lidar currently under development at the European Space Agency. 相似文献
79.
80.
Alain Tchakoutio Sandjon Armand Nzeukou Clément Tchawoua Brice Sonfack Tengeleng Siddi 《Theoretical and Applied Climatology》2014,118(1-2):319-329
In this paper, we used the Outgoing Longwave Radiation (OLR) data to compare the intraseasonal atmospheric variability patterns over Central Africa, during the last three decades. The spectral analysis indicates that for the three decades, the intraseasonal variability is dominated by 20–80 days periods band with the center near 40–50 days. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the three retained EOFs are 41.6 % for 1981–1990, 44.2 % for 1991–2000 and 42.6 % for 2001–2010. For the three decades, the three leading EOFs retained exhibit high spatial loadings over Northern Congo, Southern Ethiopia, and Southwestern Tanzania. The power spectra of the leading principal components have their peaks near 40 days for the three decades, indicating MJO signal. The PCs time series revealed that the amplitude of intraseasonal oscillations (ISO) globally decreases from decade to another. The plot of ISO and El Niño-Southern Oscillation (ENSO) indices revealed that the lowest values of ISO strength generally correspond to the relatively large values of ENSO indices and inversely. The mean ISO strength and ISO fluctuations were highest during 1981–1990, and this period also corresponds to the highest fluctuations of ENSO signal. 相似文献