Distribution patterns of macrobenthic species in relation to organic enrichment within aquaculture earthen ponds   总被引：1，自引：0，他引：1  

Carvalho S  Barata M  Pereira F  Gaspar MB  Cancela da Fonseca L  Pousão-Ferreira P 《Marine pollution bulletin》2006,52(12):1573-1584

The relationship between organic enrichment and macrobenthic colonization patterns was investigated during an 8-month period in Diplodus sargus (white seabream) production ponds. A stratified sampling design was applied and each pond was divided into three zones: water entrance (WE); central (C); and automatic feeder zones (AF). Generally, the number of species and Shannon–Wiener diversity increased from the WE to the AF zone. Abundance did not present a clear trend. The recently developed marine biotic index (AMBI) was applied and showed to be sufficiently robust to discriminate, within a relatively small area, differences in macrobenthic communities due to organic enrichment. Nevertheless, caution is advised when applying this index or others based on ecological group’s assignment, as the classification of a certain area may differ when allocating a certain species to an unsuitable group. This is particularly evident when common species are involved.  相似文献   

Erratum to: The earth system model of intermediate complexity CLIMBER-3α. Part I: description and performance for present-day conditions     

Marisa Montoya  Alexa Griesel  Anders Levermann  Juliette Mignot  Matthias Hofmann  Andrey Ganopolski  Stefan Rahmstorf 《Climate Dynamics》2010,34(1):151-151

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Do photosynthetic bacteria have a protective mechanism against carbonate precipitation at their surfaces?     

Raul E. Martinez  Emmanuel Gardés  Jacques Schott 《Geochimica et cosmochimica acta》2010,74(4):1329-109

Closed reactor kinetic experiments, SEM and TEM imaging, EDX analyses, and zeta potential measurements were used to assess the existence of metabolic process protecting cyanobacteria against carbonate mineralization on their surfaces. Carbonate precipitation rates measured at pH of ∼8.2 and 23 °C in initially supersaturated solutions in the presence of active Synechococcus sp. and Planktothrix sp. correspond closely to those measured in analogous inorganic control experiments. TEM imaging and EDX analysis indicates the absence of Ca²⁺ on active Synechococcus sp. and Planktothrix sp. surfaces. Electrophoretic measurements of active cyanobacteria surfaces demonstrate development of a positive surface potential on active Synechococcus sp. and Planktothrix sp. cyanobacteria at pH 8-10. This positive charge was suppressed by the presence of 1 mM HCO₃⁻ but enhanced by increasing aqueous Ca²⁺ concentration in the fluid phase. These observations suggest the existence of a mechanism, based on the metabolic maintenance of a positive surface charge at alkaline pH, protecting active cyanobacteria against Ca²⁺ adsorption and subsequent carbonate precipitation on their surfaces.  相似文献   

Allochthonous subsidies of organic matter across a lake–river–fjord landscape in the Chilean Patagonia: Implications for marine zooplankton in inner fjord areas     

Cristian A. Vargas  Rodrigo A. Martinez  Valeska San Martin  Mauricio Aguayo  Nelson Silva  Rodrigo Torres 《Continental Shelf Research》2011,31(3-4):187-201

Ecosystems can act as both sources and sinks of allochthonous nutrients and organic matter. In this sense, fjord ecosystems are a typical interface and buffer zone between freshwater systems, glaciated continents, and the coastal ocean. In order to evaluate the potential sources and composition of organic matter across fjord ecosystems, we characterized particulate organic matter along a lake–river–fjord corridor in the Chilean Patagonia using stable isotope (δ¹³C) and lipid (fatty acid composition) biomarker analyses. Furthermore, estimates of zooplankton carbon ingestion rates and measurements of δ¹³C and δ¹⁵N in zooplankton (copepods) were used to evaluate the implications of allochthonous subsidies for copepods inhabiting inner fjord areas. Our results showed that riverine freshwater flows contributed an important amount of dissolved silicon but, scarce nitrate and phosphate to the brackish surface layer of the fjord ecosystem. Isotopic signatures of particulate organic matter from lakes and rivers were distinct from their counterparts in oceanic influenced stations. Terrestrial allochthonous sources could support around 68–86% of the particulate organic carbon in the river plume and glacier melting areas, whereas fatty acid concentrations were maximal in the surface waters of the Pascua and Baker river plumes. Estimates of carbon ingestion rates and δ¹³C in copepods from the river plume areas indicated that terrestrial carbon could account for a significant percentage of the copepod body carbon (20–50%) during periods of food limitation. Particulate organic matter from the Pascua River showed a greater allochthonous contribution of terrigenous/vascular plant sources. Rivers may provide fjord ecosystems with allochthonous contributions from different sources because of the distinct vegetation coverage and land use along each river’s watershed. These observations have significant implications for the management of local riverine areas in the context of any human project that may modify terrestrial habitats as well as the productivity, food webs, and community structure of rivers, lakes, fjords, and the coastal ocean in the Chilean Patagonia.  相似文献   

Particle‐scale effects on global axial and torsional interface shear behavior          下载免费PDF全文

A. Martinez  J.D. Frost 《国际地质力学数值与分析法杂志》2017,41(3):400-421

An extensive literature on the shear behavior of continuum–particulate interfaces has been developed during the last four decades. However, relatively limited work regarding the behavior of interfaces under different loading conditions has been published. This paper presents a discrete element modeling study, along with comparisons from experimental data, of interface behavior under axial and torsional drained loading conditions. Detailed studies allow for links between micro‐scale particle behavior and observed global response to be developed and for the latter to be evaluated in light of particle–particle and particle–continuum interactions. The results of this study indicate that axial and torsional interface shear induce inherently different loading conditions, as shown by the different failure envelopes, stress paths, and induced soil volume changes and deformations. Furthermore, the results presented in this paper indicate that particle‐level mechanisms, such as particle rotations and contact slippage, play different roles in axial and torsional shear. Coordination number, polar histograms, particle displacements, particle rotations, and local void ratio measurements provide further insights into the fabric evolution, loading conditions, and failure mechanisms induced by these two shear modes. This study expands the current understanding of interface behavior and discusses potential improvements to geotechnical systems that leverage the characteristics of different imposed loading conditions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Prediction of groundwater‐induced flooding in a chalk aquifer for future climate change scenarios          下载免费PDF全文

Joaquin Jimenez‐Martinez  Martin Smith  David Pope 《水文研究》2016,30(4):573-587

Current climate change models for the southeast UK predict changing rainfall patterns, with increased incidence of extreme events. The chalk aquifer in the UK and northern France is susceptible to groundwater‐induced flooding under such conditions. In this methodological study we apply a frequency domain analysis approach to the chalk aquifer to derive a transfer function between effective rainfall and groundwater level from 7 years of monitoring data from the North Heath Barn site, near Brighton. The derived transfer function was calibrated and validated against monitoring data and then used to predict groundwater level for rainfall models for high, medium and low emission scenarios from the UKCP09 database. The derived transfer function is most closely comparable to the linear aquifer model, despite evidence for both matrix and fracture or karst water flow in the chalk, with transmissivity and unconfined storativity at the catchment scale of 1548 m² day^?1 and 1.6 × 10^?2. The application of the transfer function to UKCP09 rainfall data suggests that groundwater‐induced flooding may be about four times more frequent by 2040–2069 compared with 1961–1990 and seven times more frequent by 2070–2099. The model data also suggest an increase in the duration of groundwater minima relative to the reference period. Compared to deterministic modelling which requires detailed knowledge of aquifer heterogeneity and processes, the transfer function approach, although with limitations, is simpler, incorporating these factors into the analysis through frequency and phase coefficients, and thus may have the potential for groundwater risk assessment in other areas. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

The role of ground reference data collection in the prediction of stem volume with LiDAR data in mountain areas     

Michele Dalponte  Cristina Martinez  Mirco Rodeghiero  Damiano Gianelle 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):787-797

Ground reference data collection represents an important element in the prediction of stem volume with LiDAR-derived variables, and at present it is the most expensive part of such analyses. In this paper two aspects of ground reference data collection were analyzed: (1) the positioning error of the ground plots; and (2) the optimal number of training plots. A system for the prediction of stem volume at area-based level was adopted. LiDAR data were preprocessed and 13 variables describing both height and coverage were extracted. Models were defined using a stepwise ordinary least square (OLS) regression. Three experiments were conducted: (i) the role of the plots positioning error on prediction accuracy; (ii) the influence of random downsampling of plot numbers on prediction accuracy; and (iii) the influence of a stratified downsampling of plot numbers on prediction accuracy based on LiDAR-derived variables. A dataset comprising 799 ground plots was used. They were distributed throughout a mountainous area in the Southern Alps, where the presence of a complex landscape increases the uncertainty of the Global Positioning System (GPS) accuracy, and where a large variety of tree forest species and climatic environments make it necessary to have a large number of sample plots for accurate characterization of the study area. All the experiments provided important indications for LiDAR based forest inventories: the GPS error did not significantly influence the prediction accuracy and it was possible to reduce the number of training samples without compromising the generalization ability of the prediction model. Leading on from these findings, a new ground sampling protocol based on genetic algorithms was proposed. The new protocol allowed us to obtain promising results for the considered dataset: using only 53 training plots, instead of 534 in the original dataset, we obtained the same results for the validation set. These results, obtained in a complex mountainous area, are representative of Alpine environments and allow us to infer that similar (or better) results could also be obtained within non mountainous areas.  相似文献   

Winter and summer characterization of biogenic enantiomeric monoterpenes and anthropogenic BTEX compounds at a Mediterranean Stone Pine forest site     

Wei?Song  Jonathan?WilliamsEmail author  Noureddine?Yassaa  Monica?Martinez  José?Antonio?Adame?Carnero  Pablo?J.?Hidalgo  Heiko?Bozem  Jos?Lelieveld 《Journal of Atmospheric Chemistry》2011,68(3):233-250

Measurements of biogenic gases including enantiomeric monoterpenes and isoprene, and anthropogenic gases such as benzene, toluene, ethylbenzene, ortho-, meta- and para- xylene (BTEX) compounds were made by GC-MS in November and December 2008 within a stone pine (Pinus pinea L) forest located on the Southwest coast of Spain (37.10°N, 6.70°W). Mixing ratios of the biogenic species were found to be low (mean circa 10 pptv) consistent with previously observed low wintertime regional forest emission rates. In contrast, anthropogenic species were significantly higher (mean 10–156 pptv), the dominant emissions originating from the city of Huelva and associated petrochemical activities, located 25 km north west of the measurement site. In wintertime the monoterpene (?)-α-pinene was found to be in slight enantiomeric excess over (+)-α-pinene at night but by day the measured ratio was closer to one i.e. racemic. Samples taken the following summer in the same location showed much higher monoterpene mixing ratios and revealed a strong enantiomeric excess of (?)-α-pinene. This indicates a strong seasonal variance in the enantiomeric emission ratio which is not manifested in the day/night temperature cycles in wintertime. Mixing ratios of the xylene isomers (meta- and para-) and ethylbenzene, which are all well resolved on the beta-cyclodextrin column, were exploited to estimate average OH radical exposures to VOCs from the Huelva industrial area. These were compared to empirical estimates of OH based on JNO₂ measured at the site. The deficiencies of each estimation method are discussed.  相似文献   

Impacts of wildfire and post-fire land management on hydrological and sediment processes in a humid Mediterranean headwater catchment     

João Pedro Nunes  Léonard Bernard-Jannin  María Luz Rodríguez-Blanco  Anne-Karine Boulet  Juliana Marisa Santos  Jan Jacob Keizer 《水文研究》2020,34(26):5210-5228

The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the north-western Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was ploughed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail. Results show that the fire led to a notable impact on sediment processes during the first two post-fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment-limited sediment yield before the fire, to transport-limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality.  相似文献   

Cosmology and VHE gamma ray astrophysics: connections and perspectives     

Manel Martinez 《Astrophysics and Space Science》2007,309(1-4):477-485

The observation of the universe in the VHE gamma ray domain with the new generation of Cherenkov Telescopes is producing new measurements with a direct implication for cosmology. The present results and the future prospects will be discussed.   相似文献