Historical variability of subfossil chironomids (Diptera: Chironomidae) in three lakes impacted by natural and anthropogenic disturbances     

Vicky Tremblay  Isabelle Larocque-Tobler  Pascal Sirois 《Journal of Paleolimnology》2010,44(2):483-495

In the eastern boreal forest of Quebec, Canada, harvesting strategies try to mimic the effects of fire on forest ecosystems, assuming that both disturbances have similar impacts. However impacts of both types of perturbations on lacustrine ecosystems, especially on chironomids (non-biting midges), are still poorly understood. The objectives of this study were to determine if logging and fire resulted in chironomid assemblages significantly different than pre-disturbance states and to see if the harvesting strategy (careful logging around advanced growth (CLAAG) and buffer zones) protect lakes from logging effects in the boreal forest. Three statistical tests were used to study the difference between pre- and post-disturbance assemblages: a principal component analysis (PCA), analysis of similarity (ANOSIM) and a non-metric multi-dimensional scaling (MDS) ordination. All statistical analyses suggested that fire did not have any effects on chironomid assemblages. The PCA analysis showed that two logging events in Lac aux Huards created chironomid assemblages slightly outside the pre-disturbance variability. However, ANOSIM showed that these differences were not significant at the 0.5% level of significance. These results suggest that the presence of a buffer zone probably limited the impacts of logging on lakes in this area.  相似文献   

Albeluvisol development with time in loamy marine sediments of southern Norway     

Daniela Sauer  Isabelle Schülli-Maurer  Ragnhild Sperstad  Rolf Srensen  Karl Stahr 《Quaternary International》2009,209(1-2):31

This paper reports a study on soil development in loamy marine sediments on both sides of the Oslofjord (Vestfold, Østfold). This region has been subject to steady glacio-isostatic uplift during the whole Holocene. Hence, land surface age continuously increases from the coast inland. Several sea level curves, based on radiocarbon datings, enable estimation of land surface age for all locations. Clay illuviation starts in less than 1650 years. E horizons become lighter with age, but their lower boundary stays around 40 cm for more than 10 000 years. Albeluvic tongues develop between 4600 and 6200 years. Initially, they form along intersections of cracks. As preferential flow and leaching along the cracks continues, the tongues increase in length and width, progressively consuming the prisms between the cracks in the upper Bt horizon. The Fe_d/Fe_t ratios (weighted means of the upper meter) show a clear linear increase with soil age and may be used for “pedo-dating”, i.e. for estimating the ages of non-dated land surfaces covered with similar sediments. In contrast, the logarithmic decrease of base saturation and pH, with rapid changes in the first time but only very slight changes between 2000 and 10 000 years, makes these parameters unsuitable for “pedo-dating”.  相似文献   

Tidal sediment transport versus freshwater flood events in the Konkouré Estuary, Republic of Guinea     

Sylvain Capo  Isabelle Brenon  Aldo Sottolichio  Patrice Castaing  Patrick Le Goulven 《Journal of African Earth Sciences》2009,55(1-2):52

In comparison to their temperate counterparts, sediment processes in tropical estuaries are poorly known and especially in African ones. The hydrodynamics of such environments is controlled by a combination of multiple processes including morphology, salinity, mangrove vegetation, tidal processes, river discharge, settling and erosion of mud and by physico-chemical processes as well as sediment dynamics.The aim of this study is to understand the sediment processes in this transitional stage of the estuary when the balance between river discharges and marine processes is reversing. Studying the hydrodynamics and sediment dynamics of the Konkouré Estuary has recently been made possible thanks to new data on bathymetry, sedimentary cover, salinity, water elevations, and current velocities. The Lower Konkouré is a shallow, funnel shaped, mesotidal mangrove-fringed, tide-dominated estuary, well mixed during low river discharge and stratified during high river discharge. The Konkouré Estuary is turbid despite the small amount of terrestrial input and its residual velocity at the mouth during low river discharges, landwards for two of the three branches, suggests a landward migration by tidal pumping of the suspended particulate matter. A Turbidity Maximum Zone (TMZ) is identified for typical states of the estuary with regard to fluvial and tidal components. Suspended sediment transport during a transitional stage between the rainy and dry seasons is known thanks to current velocity and Suspended Sediment Concentration (SSC) measurements taken in November 2003. The Richardson layered number calculation assesses that turbulence is the major mixing process in the water column, at least during the flood and ebb stages, whereas stratification occurs during the slack water periods. Tidal currents generate bottom erosion, and turbulence mixes the suspended sediment throughout the water column. As a result, a net sediment input is calculated from the western Konkouré outlet for two consecutive tidal cycles. Despite the net water export, almost 300 tons per tide reach the estuary through this outlet, for a moderate river flow.  相似文献   

Effects of diuron in microcosms on natural riverine bacterial community composition: new insight into phylogenetic approaches using PCR-TTGE analysis   总被引：1，自引：0，他引：1  

Stéphane Pesce  Corinne Bardot  Anne-Catherine Lehours  Isabelle Batisson  Jacques Bohatier  Céline Fajon 《Aquatic Sciences - Research Across Boundaries》2008,70(4):410-418

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Report of the Treasurer     

Isabelle Cojan 《Sedimentology》1999,46(1):209-210

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Local Sensitivity Analysis of a Numerical Model of Volcanic Plinian Columns through Automatic Differentiation     

Isabelle Charpentier  Juan Manuel Espíndola 《Mathematical Geology》2005,37(1):95-113

Numerical simulation of geological phenomena are nowadays widely used to understand them. A good example are the numerous codes developed to model mass motion in different processes. Such models are approximations to the real phenomena because the physical conditions are simplified or because the values of the parameters intervening in the modeling are known only approximately. For this reason, an obligatory step in the application of these models is the assessment of their sensitivity to changes in the parameters. Sensitivity analysis is also required to evaluate the influence of the different input variables in the outcome of the model. In general this analysis is carried out by repeated computation of the model to different sets of input variables and settings of the model. A more fruitful procedure to carry out such analysis can be achieved by automatic differentiation. In this paper we illustrate such approach through its application to the model of an eruptive plinian column. The results of the analysis allow to assess, in a systematic and efficient manner, the relevance of the different boundary values and parameters of the model. The analysis reveals the effects on velocity, temperature, gas fraction, radius and ultimately column height, by changes in their boundary value (i.e. at the vent). The effect of changes in the value of the gas constants, density of pyroclasts and specific heat of the erupted material is also evidenced. Alternatively, the results can be regarded as a mean to estimate the values of the variables for different set of boundary values without recurring to new runs of the model. Automatic differentiation is shown to be a convenient scheme to obtain derivatives of model variables. This type of analysis forms in addition the basis for further work in inversion schemes.  相似文献   

Morphology, hydrography and sediment dynamics in a mangrove estuary: The Konkoure Estuary, Guinea   总被引：1，自引：0，他引：1  

S. Capo  A. Sottolichio  I. Brenon  P. Castaing  L. Ferry 《Marine Geology》2006,230(3-4):199-215

The Konkouré Estuary in the Republic of Guinea is a poorly understood atypical mangrove system. Sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge, morphology, salinity, erosion and deposition processes, the settling of mud, physico-chemical processes and mangrove swamps. Here we present a consistent set of data aimed at characterising the estuary and thus, increasing our understanding of tropical systems, as well as studying the impact of human intervention in the region. Water elevations, current measurements, salinity, suspended sediment concentrations, bathymetry and sediment cover are presented following a 3 year survey of the Konkouré Estuary. Here we provide conclusive evidence that the Lower Konkouré is a shallow, funnel shaped, mesotidal, mangrove-fringed, tide dominated estuary, well mixed during low river discharge. The estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides. The Konkouré Estuary has been described as hypersynchronous, and has three terminal outlets, two of which are landward-directed, attesting to a tidal pumping effect, while the third one is seaward-directed, and is controlled by the mangrove. The suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the Turbidity Maximum zone (TMZ). The location of the TMZ is river-controlled and is correlated with residual currents but not with salinity front. A dam, constructed 130 km upstream, impacts on the hydrodynamics, and reduces the salinity intrusion by about 25%. It causes an increased low river discharge whereas its efficiency over high river flows is unclear.  相似文献   

A Coastal Bay Summer Breeze Study,Part 2: High-resolution Numerical Simulation of Sea-breeze Local Influences     

Isabelle Calmet  Patrice G. Mestayer  Alexander M. J. van Eijk  Olivier Herlédant 《Boundary-Layer Meteorology》2018,167(1):27-51

We complete the analysis of the data obtained during the experimental campaign around the semi circular bay of Quiberon, France, during two weeks in June 2006 (see Part 1). A reanalysis of numerical simulations performed with the Advanced Regional Prediction System model is presented. Three nested computational domains with increasing horizontal resolution down to 100 m, and a vertical resolution of 10 m at the lowest level, are used to reproduce the local-scale variations of the breeze close to the water surface of the bay. The Weather Research and Forecasting mesoscale model is used to assimilate the meteorological data. Comparisons of the simulations with the experimental data obtained at three sites reveal a good agreement of the flow over the bay and around the Quiberon peninsula during the daytime periods of sea-breeze development and weakening. In conditions of offshore synoptic flow, the simulations demonstrate that the semi-circular shape of the bay induces a corresponding circular shape in the offshore zones of stagnant flow preceding the sea-breeze onset, which move further offshore thereafter. The higher-resolution simulations are successful in reproducing the small-scale impacts of the peninsula and local coasts (breeze deviations, wakes, flow divergences), and in demonstrating the complexity of the breeze fields close to the surface over the bay. Our reanalysis also provides guidance for numerical simulation strategies for analyzing the structure and evolution of the near-surface breeze over a semi-circular bay, and for forecasting important flow details for use in upcoming sailing competitions.  相似文献   

Assessing green gentrification in historically disenfranchised neighborhoods: a longitudinal and spatial analysis of Barcelona   总被引：1，自引：1，他引：0  

Isabelle Anguelovski  James J. T. Connolly  Laia Masip  Hamil Pearsall 《Urban geography》2018,39(3):458-491

To date, little is known about the extent to which the creation of municipal green spaces over an entire city addresses social or racial inequalities in the distribution of environmental amenities – or whether such an agenda creates contributes to green gentrification. In this study, we evaluate the effects of creating 18 green spaces in socially vulnerable neighborhoods of Barcelona during the 1990s and early 2000s. We examined the evolution over time of six socio-demographic gentrification indicators in the areas close to green spaces in comparison with the entire districts. Our results indicate that new parks in the old town and formerly industrialized neighborhoods seem to have experienced green gentrification. In contrast, most economically depressed areas and working-class neighborhoods with less desirable housing stock and more isolated from the city center gained vulnerable residents as they became greener, indicating a possible redistribution and greater concentration of vulnerable residents through the city.  相似文献   

Inclusive approaches to urban climate adaptation planning and implementation in the Global South     

Eric Chu  Isabelle Anguelovski  JoAnn Carmin 《Climate Policy》2016,16(3):372-392

As cities increasingly engage in climate adaptation planning, many are seeking to promote public participation and facilitate the engagement of different civil society actors. Still, the variations that exist among participatory approaches and the merits and tradeoffs associated with each are not well understood. This article examines the experiences of Quito (Ecuador) and Surat (India) to assess how civil society actors contribute to adaptation planning and implementation. The results showcase two distinct approaches to public engagement. The first emphasizes participation of experts, affected communities, and a wide array of citizens to sustain broadly inclusive programmes that incorporate local needs and concerns into adaptation processes and outcomes. The second approach focuses on building targeted partnerships between key government, private, and civil society actors to institutionalize robust decision-making structures, enhance abilities to raise funds, and increase means to directly engage with local community and international actors. A critical analysis of these approaches suggests more inclusive planning processes correspond to higher climate equity and justice outcomes in the short term, but the results also indicate that an emphasis on building dedicated multi-sector governance institutions may enhance long-term programme stability, while ensuring that diverse civil society actors have an ongoing voice in climate adaptation planning and implementation.

Policy relevance

Many local governments in the Global South experience severe capacity and resource constraints. Cities are often required to devolve large-scale planning and decision-making responsibilities, such as those critical to climate adaptation, to different civil society actors. As a result, there needs to be more rigorous assessments of how civil society participation contributes to the adaptation policy and planning process and what local social, political, and economic factors dictate the way cities select different approaches to public engagement. Also, since social equity and justice are key indicators for determining the effectiveness and sustainability of adaptation interventions, urban adaptation plans and policies must also be designed according to local institutional strengths and civic capacities in order to account for the needs of the poor and most vulnerable. Inclusivity, therefore, is critical for ensuring equitable planning processes and just adaptation outcomes.  相似文献