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181.
Basic principles and ecological consequences of changing water regimes on nitrogen cycling in fluvial systems 总被引:8,自引:0,他引:8
Understanding the environmental consequences of changing water regimes is a daunting challenge for both resource managers
and ecologists. Balancing human demands for fresh water with the needs of the environment for water in appropriate amounts
and at the appropriate times are shaping the ways by which this natural resource will be used in the future. Based on past
decisions that have rendered many freshwater resources unsuitable for use, we argue that river systems have a fundamental
need for appropriate amounts and timing of water to maintain their biophysical integrity. Biophysical integrity is fundamental
for the formulation of future sustainable management strategies. This article addresses three basic ecological principles
driving the biogeochemical cycle of nitrogen in river systems. These are (1) how the mode of nitrogen delivery affects river
ecosystem functioning, (2) how increasing contact between water and soil or sediment increases nitrogen retention and processing,
and (3) the role of floods and droughts as important natural events that strongly influence pathways of nitrogen cycling in
fluvial systems. New challenges related to the cumulative impact of water regime change, the scale of appraisal of these impacts,
and the determination of the impacts due to natural and human changes are discussed. It is suggested that cost of long-term
and long-distance cumulative impacts of hydrological changes should be evaluated against short-term economic benefits to determine
the real environmental costs. 相似文献
182.
The effects of nonlinear sorption and competition with major cations present in the soil solution on radioactive strontium transport in an eolian sand were examined. Three laboratory techniques were used to identify and quantify the chemical and hydrodynamic processes involved in strontium transport: batch experiments, stirred flow-through reactor experiments and saturated laboratory columns. The major goal was to compare the results obtained under static and dynamic conditions and to describe in a deterministic manner the predominant processes involved in radioactive strontium transport in such systems. Experiments under dynamic conditions, namely flow-through reactor and column experiments, were in very good agreement even though the solid/liquid ratio was very different. The experimental data obtained from the flow-through reactor study pointed to a nonlinear, instantaneous and reversible sorption process. Miscible displacement experiments were conducted to demonstrate the competition between stable and radioactive strontium and to quantify its effect on the 85Sr retardation factor. The results were modeled using the PHREEQC computer code. A suitable cation-exchange model was used to describe the solute/soil reaction. The model successfully described the results of the entire set of miscible displacement experiments using the same set of parameter values for the reaction calculations. The column study revealed that the stable Sr aqueous concentration was the most sensitive variable of the model, and that the initial state of the sand/solution system had also to be controlled to explain and describe the measured retardation factor of radioactive strontium. From these observations, propositions can be made to explain the discrepancies observed between some data obtained from static (batches) and dynamic (reactor and column) experiments. Desorbed antecedent species (stable Sr) are removed from the column or reactor in the flow system but continue to compete for sorption sites in the batch system. Batch experiments are simple and fast, and provide a very useful means of multiplying data. However, interpretation becomes difficult when different species compete for sorption sites in the soil/solution system. A combination of batches, flow-through reactor and column experiments, coupled with hydrogeochemical modeling, would seem to offer a very powerful tool for identifying and quantifying the predominant processes on a cubic decimeter scale (dm3) and for providing a range of radioactive strontium retardation factor as a function of the geochemistry of the soil/solution system. 相似文献
183.
To obtain data concerning the risk of leaching of acetochlor (2-chloro-2'-methyl-6'-ethyl-N-ethoxymethyl-acetanilide) and its major metabolites, ethanesulfonic acid (ESA) and oxanilic acid (OA), to ground water, we studied the fate of these products in two different soil types (luvisol and calcisol) under the same weather conditions. The metabolites were detected in the soils as early as 7 d after application, indicating a rapid onset of acetochlor degradation. Ethanesulfonic acid was predominant over OA in the calcisol, regardless of time or depth, whereas the ESA to OA ratio varied with both time and depth in the luvisol. The maximum depths at which they were detected were 60 to 70 and 10 to 20 cm for ESA and OA, respectively, in the luvisol, and 60 to 70 cm (maximum depth sampled) and 30 to 40 cm for ESA and OA, respectively, in the calcisol. Acetochlor was still detected in the surface layer of the two soils 344 d after its application, although the molecule was partially leached. The maximum depths at which acetochlor was detected (60-70 cm in the luvisol and 50-60 cm [maximum depth sampled] in the calcisol) were recorded during the first sampling 7 d after application. Acetochlor was not detected on later dates below the 30- to 40-cm layer in the calcisol or the 5- to 10-cm layer in the luvisol. The greater preferential flow in the luvisol, which would have favored leaching, might partially explain why the mass balances done 7 d after application were lower in the luvisol (approximately 26%) than in the calcisol (approximately 45%). 相似文献
184.
/ The management of riverine wetlands, recognized as a major component of biodiversity in fluvial hydrosystems, is problematic. Preservation or restoration of such ecosystems requires a method to assess the major ecological processes operating in the wetlands, the sustainability of the aquatic stage, and the restoration potential of each riverine wetland. We propose a method of diagnosis based on aquatic macrophytes and helophytes. Plant communities are used because they are easy to survey and provide information about (1) the origin of a water supply (i.e., groundwater, seepage, or surface river water) and its nutrient content, (2) effects of flood disturbances, and (3) terrestrialization processes. The novelty of the method is that, in contrast to available typologies, it is based on the interference of gradients resulting from several processes, which makes it possible to predict wetland sustainability and restoration potential. These predictions result from knowledge of the processes involved in terrestrialization, i.e., the influence of flood disturbances, occurrence of groundwater supplies, trophic degree, and water permanency of the habitat during a yearly cycle. The method is demonstrated on five different river systems. 相似文献
185.
Govinda R. Timilsina Christophe de Gouvello Massamba Thioye Felix B. Dayo 《Mitigation and Adaptation Strategies for Global Change》2010,15(1):93-111
Sub-Saharan Africa lags far behind other regions in terms of the implementation of Clean Development Mechanism (CDM) projects
due to several reasons. One of the reasons is a general perception that, since the region contributes very little to global
GHG emissions, it also offers few opportunities to reduce these emissions. Using a bottom-up approach, this study investigates
the technical potential of reducing GHG emissions from the energy sector in Sub-Saharan Africa through the CDM. The study
finds that sub-Saharan Africa could develop 3,227 CDM projects, including 361 programs of activities, which could reduce approximately
9.8 billion tons of GHG emissions during the CDM project cycles. The study also estimates that the realization of this CDM
potential could significantly enhance sustainable development in the region as it would attract more than US200 billion in investment and could generate US200 billion in
investment and could generate US98 billion of CDM revenue at a CER price of US$10/tCO2. Another notable finding of the study
is that the realization of this CDM potential could supply clean electricity by doubling the current capacity and thereby
providing access of electricity to millions of people in the region. However, realization of this CDM potential is severely
constrained by a number of financial, technical, regulatory and institutional barriers. 相似文献
186.
Skraber Sylvain Gantzer Christophe Helmi Karim Hoffmann Lucien Cauchie Henry-Michel 《Food and environmental virology》2009,1(2):66-76
A filtration system, based on tangential flow filtration (TFF) followed by ultracentrifugation was developed in order to concentrate
simultaneously viruses and parasites from large volumes of water. For TFF, no pre-treatment of the membrane is performed but
a post-rinsing step using high pH-beef extract-based eluant. Applying our protocol to 20 l of surface waters spiked with vaccinal
poliovirus-1, ϕX174 and MS2 bacteriophages resulted in an averaged viral recovery of 75% by TFF and 91% by ultracentrifugation
(total viral recovery of 70%). Our protocol was further applied to 31 environmental samples including surface, ground and
drinking waters from the Grand Duchy of Luxembourg in order to assess the occurrence of protozoan parasites (Cryptosporidium parvum and Giardia lamblia (oo)cysts), pathogenic viruses (enterovirus, norovirus and adenovirus) and infectious bacteriophages (somatic coliphages
and F-specific phages) in these samples. High viral recovery rates of > 70% were confirmed concentrating environmental strains
of somatic and F-specific coliphages from non-spiked surface waters. Parasites and enteric viruses were detected in 86 and
40% of the surface waters used for drinking water production, respectively. Infectious bacteriophages were isolated from all
surface waters and in two out of seven (29%) groundwaters revealing a susceptibility of the corresponding wells to viral pollution.
TFF-based method proved to be efficient for surveying the occurrence of non-bacterial pathogens such as enteric viruses and
protozoan parasites in large volumes of environmental waters. 相似文献
187.
Environmental Fluid Mechanics - For centuries, the interaction between the transport and hydrographic networks represents a significant issue in a country such as France. For example, the French... 相似文献
188.
Rubio-Gutierrez Juan Carlos Mendez-Hernández Pablo Guéguen Yann Galichon Pierre Tamayo-Ortiz Marcela Haupt Karsten Medeiros Mara Barbier Olivier Christophe 《Environmental science and pollution research international》2022,29(21):31042-31058
Environmental Science and Pollution Research - Bone mass in adulthood depends on growth and mineralization acquired during childhood and adolescence. It is well known that these stages of life are... 相似文献
189.
Metal speciation in landfill leachates with a focus on the influence of organic matter 总被引:2,自引:0,他引:2
Claret F Tournassat C Crouzet C Gaucher EC Schäfer T Braibant G Guyonnet D 《Waste management (New York, N.Y.)》2011,31(9-10):2036-2045
This study characterises the heavy-metal content in leachates collected from eight landfills in France. In order to identify heavy metal occurrence in the different size fractions of leachates, a cascade filtration protocol was applied directly in the field, under a nitrogen gas atmosphere to avoid metal oxidation. The results of analyses performed on the leachates suggest that most of the metals are concentrated in the <30 kDa fraction, while lead, copper and cadmium show an association with larger particles. Initial speciation calculations, without considering metal association with organic matter, suggest that leachate concentrations in lead, copper, nickel and zinc are super-saturated with respect to sulphur phases. Speciation calculations that account for metal complexation with organic matter, considered as fulvic acids based on C1(s) NEXAFS spectroscopy, show that this mechanism is not sufficient to explain such deviation from equilibrium conditions. It is therefore hypothesized that the deviation results also from the influence of biological activity on the kinetics of mineral phase precipitation and dissolution, thus providing a dynamic system. The results of chemical analyses of sampled fluids are compared with speciation calculations and some implications for the assessment of metal mobility and natural attenuation in a context of landfill risk assessment are discussed. 相似文献
190.
Removal of polycyclic aromatic hydrocarbons from aged-contaminated soil using cyclodextrins: experimental study 总被引:1,自引:0,他引:1
Viglianti C Hanna K de Brauer C Germain P 《Environmental pollution (Barking, Essex : 1987)》2006,140(3):427-435
The removal of polycyclic aromatic hydrocarbons (PAHs) from soil using water as flushing agent is relatively ineffective due to their low aqueous solubility. However, addition of cyclodextrin (CD) in washing solutions has been shown to increase the removal efficiency several times. Herein are investigated the effectiveness of cyclodextrin to remove PAH occurring in industrially aged-contaminated soil. Beta-cyclodextrin (BCD), hydroxypropyl-beta-cyclodextrin (HPCD) and methyl-beta-cyclodextrin (MCD) solutions were used for soil flushing in column test to evaluate some influent parameters that can significantly increase the removal efficiency. The process parameters chosen were CD concentration, ratio of washing solution volume to soil weight, and temperature of washing solution. These parameters were found to have a significant and almost linear effect on PAH removal from the contaminated soil, except the temperature where no significant enhancement in PAH extraction was observed for temperature range from 5 to 35 degrees C. The PAHs extraction enhancement factor compared to water was about 200. 相似文献