Spatio-temporal changes in totally and enzymatically hydrolyzable amino acids of superficial sediments from three contrasted areas     

Antoine Grémare  Dimitri Gutiérrez  Jean Michel Amouroux  Gilles Vétion 《Progress in Oceanography》2005,65(1):89-111

Spatio-temporal changes in totally and enzymatically hydrolyzable amino acids (THAA and EHHA) and EHAA/THAA ratios of superficial sediments were assessed during 1997-1999 in three areas (i.e., the Gulf of Lions, the Bay of Biscay, and Central Chile) differing in their primary productivity. In all three areas, and even off Central Chile where a strong El Niño event took place during 1997-1998, spatial changes were always much greater than temporal ones. The factors affecting the spatial distributions of amino acid concentrations differed among areas. In the Gulf of Lions, sediment granulometry was apparently the most important driving force of THAA, EHAA, and EHAA/THAA, and there was no marked difference between stations located on the open slope and those in submarine canyons. Conversely, in the Bay of Biscay, there were clear differences between the stations located off Cap-Breton, on the open slope, and those in the Cap-Ferret canyon; the latter two featuring lower EHAA and THAA but higher EHAA/THAA. This pattern is likely to result from the predominance of different sources of organic matter and especially from the importance of continental inputs to the Cap-Breton canyon. Off Central Chile, amino acid concentrations and ratios were both maximal around 100 m depth, probably reflecting the interaction between the primary productivity gradient and the presence of an oxygen minimum zone (OMZ) reducing the degradation of sedimentary organics. When comparing the average values collected in the three areas studied, THAA and EHAA were highest in Central Chile, intermediate in the Bay of Biscay and lowest in the Gulf of Lions. EHAA/THAA ratios were also highest in Central Chile but were lowest in the Bay of Biscay. Differences between the Gulf of Lions and the Bay of Biscay could have been affected by sampling design. In Central Chile, the use of labile organic carbon to total organic carbon (C-LOM/TOC) and EHAA/THAA as indices of organic matter lability led to very similar results. This was not the case in the Bay of Biscay. It is therefore argued that the use of C-LOM/TOC should be restricted to highly productive areas.  相似文献   

Limiting similarity, niche filtering and functional diversity in coastal lagoon fish communities     

David Mouillot  Olivier Dumay  Jean Antoine Tomasini 《Estuarine, Coastal and Shelf Science》2007,71(3-4):443-456

The fundamental idea behind the study of biodiversity patterns is the presumed connection between the shape of species assemblages and the functional ways in which they are organized, this functional organization referring to how species are related to one another, as competitors or members of a web of interactions and to how species are facing similar environmental constraints. Amongst the different facets of biodiversity, functional diversity is certainly a key for ecosystem processes in coastal areas. However, surprisingly, patterns of functional diversity have received little attention until now. After presenting a common framework linking functional diversity patterns to species coexistence theories, the aim of our study was twofold: (1) to seek assembly rules in brackish lagoon fish communities drove by functional traits. To this aim we used null models to examine the influence of two opposing forces acting on community structure: interspecific competition that might prevent the coexistence of the most similar species, and environmental filters that might result in the most similar species to coexist. (2) To seek relationships between fish functional diversity and environmental gradients, if any. Fish sampling was carried out in two coastal lagoons where stations differ considerably in terms of physicochemical parameters. Using morphological functional traits, functional diversity of fish communities was estimated using two recently published indices as well as a new proposed index. Firstly our study was not able to demonstrate a limitation of similarity in coexisting lagoon fishes due to interspecific competition. Conversely our results support the niche filtering hypothesis preventing species too dissimilar from one another to co-occur at the same station. Secondly, salinity was positively related to the functional diversity of fishes in both lagoons suggesting that within species assemblages near the channel species are less redundant than at stations far from the channel where species tend to be functionally similar (benthic and eating zooplankton).  相似文献   

Field data analysis and application of a complex water column biogeochemical model in different areas of a semi-enclosed basin: towards the development of an ecosystem management tool     

Petihakis G  Triantafyllou G  Pollani A  Koliou A  Theodorou A 《Marine environmental research》2005,59(5):493-518

The Pagasitikos gulf ecosystem is studied through the analysis of experimental field data acquired during several monitoring projects and the application of a complex biogeochemical model. The gulf was separated into three different parts (internal, top central-external, bottom central-external) according to the patterns exhibited by the key ecosystem indicators. Unlike other semi-enclosed gulfs Pagasitikos can be characterised as meso-oligotrophic undergoing periods of P or N limitation. Although the signal of nutrient inputs is not very clear in the field data, their importance is assessed through simulation. Increased phosphate concentrations either due to mixing or due to anthropogenic activities can result in phytoplanktonic blooms with significant contribution by diatoms. The effect of hydrodynamic patterns on primary production has been demonstrated through ecosystem modeling indicating that due to long stratification periods, all nutrients released through the benthic regeneration are trapped in the deeper layers, developing a microbial food web. However when the thermocline erodes nutrients find their way up in the upper layers of the euphotic zone and the system turns into more classical type with primary producers growing significantly faster.  相似文献   

Evaporation from boreal reservoirs: A comparison between eddy covariance observations and estimates relying on limited data     

Judith Fournier  Antoine Thiboult  Daniel F. Nadeau  Nikki Vercauteren  François Anctil  Annie-Claude Parent  Ian B. Strachan  Alain Tremblay 《水文研究》2021,35(8):e14335

Hydrological models used for reservoir management typically lack an accurate representation of open-water evaporation and must be run in a scarce data context. This study aims to identify an accurate means to estimate reservoir evaporation with simple meteorological inputs during the open-water season, using long-term eddy covariance observations from two boreal hydropower reservoirs with contrasting morphometry as reference. Unlike the temperate water bodies on which the majority of other studies have focused, northern reservoirs are governed by three distinct periods: ice cover in the cold season, warming in the summer and energy release in the fall. The reservoirs of interest are Eastmain-1 (52°N, mean depth of 11 m) and Romaine-2 (51°N, mean depth of 42 m), both located in eastern Canada. Four approaches are analysed herein: a combination approach, a radiation-based approach, a mass-transfer approach, and empirical methods. Of all the approaches, the bulk transfer equation with a constant Dalton number of 1.2 x 10⁻³ gave the most accurate estimation of evaporation at hourly time steps, compared with the eddy covariance observations (RMSE of 0.06 mm h⁻¹ at Eastmain-1 and RMSE of 0.04 mm h⁻¹ at Romaine-2). The daily series also showed good accuracy (RMSE of 1.38 mm day⁻¹ at Eastmain-1 and RMSE of 0.62 mm day⁻¹ at Romaine-2) both in the warming and energy release phases of the open-water season. The bulk transfer equation, on the other hand, was incapable of reproducing condensation episodes that occurred soon after ice breakup. Basic and variance-based sensitivity analyses were conducted, in particular to measure the variation in performance when the bulk transfer equation was applied with meteorological observations collected at a certain distance (~10–30 km) from the reservoir. This exercise illustrated that accurate estimates of open water evaporation require representative measurements of wind speed and water surface temperature.  相似文献   

Performance comparison of two biotic indices measuring the ecological status of water bodies in the Southern Baltic and Gulf of Lions   总被引：1，自引：1，他引：0  

Fleischer D  Grémare A  Labrune C  Rumohr H  Berghe EV  Zettler ML 《Marine pollution bulletin》2007,54(10):1598-1606

Two biotic indices, ATZI Marine Biotic Index (AMBI) and Benthic Quality Index (BQI) have been recently introduced within the EC Water Framework Directive to assess the quality of marine habitats: both are based on sensitivity/tolerance classification and quantitative information on the composition of soft-bottom macrofauna. Their performance, especially with regard to sampling effort was assessed based on two data sets collected in Southern Baltic and one from the Gulf of Lions Mediterranean. AMBI was not affected by sampling effort but BQI was. Two modifications were proposed for BQI (i.e., BQI) (1) the removal of the scaling term (i.e., BQI(W)), and (2) the replacement of the scaling term by different scaling term (i.e., BQI(ES)). Both modified BQIs were largely independent of sampling effort. Variability was slightly lower for BQI(W) than for BQI(ES). BQI was highly correlated with BQI(W) and with BQI(ES) both in the Southern Baltic and in the Gulf of Lions. However, the proportions of stations, which were not attributed the same ecological quality status (EcoQ) when using BQI and its two modified forms were always high. Differences in ecological classification were mostly due to the scales used to infer EcoQ. Based on this study we recommend to use BQI(ES) in future studies because it apparently constitutes the best compromise in (1) being independent of sampling effort, (2) limiting the variability in computation in relation with sampling effort, (3) being correlated with BQI and corresponding EcoQ.  相似文献   

Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean)     

Bigot L  Conand C  Amouroux JM  Frouin P  Bruggemann H  Grémare A 《Marine pollution bulletin》2006,52(8):865-880

Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refineries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injection. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most prominent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic content over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macrofaunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportunistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment.  相似文献   

Three-Dimensional Electron Density from Tomographic Analysis of LASCO-C2 Images of the K-Corona Total Brightness     

Richard A. Frazin  Philippe Lamy  Antoine Llebaria  Alberto M. Vásquez 《Solar physics》2010,265(1-2):19-30

We present the first quantitative three-dimensional (3D) tomographic reconstructions of electron density from coronagraph measurements of the K-corona’s total brightness (B) made by LASCO-C2 on SOHO. This is possible because new calibrations of the LASCO-C2 images in both polarized brightness (pB) and B have now been made for the entire mission. The B and pB reconstructions are compared, and the differences are explained in terms of line of sight weighting functions in Thomson scattering. We conclude that the LASCO-C2 B archive, which is vastly larger than the pB archive, will be a very valuable resource for determining the 3D electron density throughout the SOHO mission which started taking data in 1996.  相似文献   

Jurassic Amber in Lebanon     

Dany AZAR  Raymond GèZE  Antoine El-Samrani  Jacqueline Maalouly  André NEL 《《地质学报》英文版》2010,84(4):977-983

<正>Reports of amber predating the Lower Cretaceous are unusual and scarce;they mostly refer to amber pieces of millimetric dimension.In the present study,we report the discovery of 10 new outcrops of Jurassic amber in Lebanon.Some of these had large centimetric-sized pieces of amber.The new localities are described,amber is characterized,and its infrared spectra given.Although the new Jurassic amber yielded to date no more than fungal inclusions,this material is significant and promising.The discovery of several Jurassic outcrops provides crucial information on the prevailing paleoenvironment of that time.  相似文献   

Boundary layer evolution over a large and broad mountain basin     

A. G. Triantafyllou  C. G. Helmis  D. N. Asimakopoulos  A. T. Soilemes 《Theoretical and Applied Climatology》1995,52(1-2):19-25

Summary In this study observations of the vertical structure of the Atmospheric Boundary Layer (ABL), recorded at a broad mountainous valley are presented. The vertical profiles of temperature, wind speed and direction up to a height of about 800 meters over the valley bottom have been measured and the temporal evolution of ABL structure of the area has been studied. Specifically, the mechanism of nocturnal inversion destruction during morning hours has been studied, which is of major importance in the study of the dispersion of air pollutants over the area. These observations suggest that the break up of nocturnal inversion during morning hours is mainly caused by a combined mechanism, the build up of the Convective Boundary Layer (CBL) and the presence of upslope winds, resulting to a continuous descent of the top of the nocturnal inversion.With 5 Figures  相似文献   

Diagenesis and the reconstruction of paleoenvironments: A method to restore original δO values of carbonate and phosphate from fossil tooth enamel     

Antoine Zazzo  Christophe Lécuyer  Simon M.F. Sheppard  André Mariotti 《Geochimica et cosmochimica acta》2004,68(10):2245-2258

Intra-tooth δ¹⁸O variations within the carbonate (δ¹⁸Oc) and phosphate (δ¹⁸Op) components of tooth apatite were measured for Miocene and Pliocene hypsodont mammals from Afghanistan, Greece and Chad in order to evaluate the resistance of enamel to diagenetic alteration. Application of water-apatite interaction models suggest that the different kinetic behaviours of the phosphate-water and carbonate-water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra-individual variations are considered. Selective alteration of the oxygen isotope composition from the carbonate component of Afghan and Greek enamels suggests inorganic isotopic exchange processes. Microbially-induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from Chad, in association with extensive recrystallization. In Chad, δ¹⁸Op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis. Mass balance calculations using average carbonate content in enamel as a proxy for recrystallization, and the lowest δ¹⁸Op value of dentine as a proxy for the isotopic composition of the diagenetic fluid, indicate that diagenesis can alter δ¹⁸Op by as much as 3‰ in some enamel samples. This diagenetic alteration is also responsible for a decrease in intra-individual variations of up to 1‰ in affected specimens. The effects of diagenesis on δ¹⁸Op values of fossil enamel are not systematic, however, and can only be estimated if sequential δ¹⁸Op and δ¹⁸Oc analyses are performed on fossil enamel and dentine. Reconstruction of large temporal- or spatial-scale paleoclimates based on δ¹⁸Op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects.  相似文献