Volume 15, Special Issue, 2002

FR:

Les sols exercent une multiplicité de fonctions de régulation entre l'atmosphère et les milieux aquatiques. Ceci est lié à leurs caractéristiques très variables dans l'espace, à la diversité des processus de nature physique, physico-chimique et biologique qui s'y déroulent, mais aussi à leur position d'interface entre l'atmosphère, le substrat géologique et les milieux aquatiques. Les échelles de temps qui président à sa genèse sont en général longues, du millier d'années au million d'années. Il s'agit donc d'une ressource non renouvelable à l'échelle humaine.

Les changements dans les pratiques agricoles ont profondément modifié le cycle de l'eau. Ainsi la perte de matières organiques des sols tend à amplifier l'encroûtement de surface et le ruissellement et conduit à une érosion importante des terres. Les prélèvements des cultures étant plus importants, la reconstitution de la réserve en eau des sols est souvent problématique les années sèches.

La science du sol doit fournir une réserve de connaissances dans laquelle la recherche appliquée puise des éléments d'interprétation de leur fonctionnement, et ce, afin de répondre aux besoins de l'agriculture et de l'environnement. Le sol doit alors être considéré comme un écosystème qui lui-même est une composante d'un écosystème plus vaste. Son étude nécessite de considérer une très large gamme d'échelles spatiales et d'échelles temporelles. Les évolutions des sols sont lentes et difficiles à déceler aisément. Les études sont donc complexes et nécessitent la durée. Elles permettent in fine d'évaluer les altérations possibles de ses diverses fonctions avec une estimation des risques résultant de cette altération. Ceci démontre qu'il convient de réévaluer le sol par rapport à ses fonctions environnementales, donc en ne se limitant pas à la seule fonction de production.

EN:

Soils perform a large variety of functions involved in regulation of biogeochemical fluxes between the atmosphere and the aquatic environment. Soil characteristics show significant variation spatially, in the diversity of physical, physico-chemical and biological processes. Soils also vary with respect to their location as an interface with the atmosphere, the geological substrate and aquatic environments. The time-scales governing the formation of soils are generally long, ranging from a thousands to millions of years and therefore, they are not a renewable resource from the human perspective.

The functions involved in soil regulation can be modified by various forms of stress related to farming, industrial and urban activities. In soil management, the catchment slope or watershed represents the most appropriate spatial scale for the assessment and understanding of soil distribution.. Throughout history, soil use has changed drastically depending on different environmental constraints, the available technology and the requirements of the human population. In order to manage soil, it is necessary to acquire a complete understanding of the conditions under which it has been formed. The chemical evolution of soils is related to natural processes. For example, in temperate regions, the main factor dictating soil evolution is the gradual loss of cations. These reductions in cations affect soil carbonates, which are gradually dissolved. Following the dissolution of soil carbonates, there are changes in levels of exchangeable cations, initially with the calcium found on the surface of the soil components (clay, organic matter and oxides). The soil then becomes acidic, and when the acidity becomes sufficiently low, the mineral components of the soil can be partially dissolved. Free aluminum can therefore be present in the soil and water, thus creating toxic conditions for plants (cultivated soils, forests) and to fish (pond water and river water).

Changes in soil use and the introduction of new practices often have a considerable impact on soil components and soil properties. In the soils of France today, the carbon and nitrogen balances are generally negative. This results in a widespread reduction in the levels of organic matter. Cultivated soils generally imply CO₂ emission into the atmosphere, often related to grassland cultivation and to other intensive farming practices (Arrouays et al. 1994; Rivière, 1999). Measuring and modeling the environmental balance therefore represents a major challenge both with respect to the protection of the soil environment and also with respect to understanding the global cycle of greenhouse gases such as nitrogen and carbon compounds.

The presence of contaminants and the study of their bioavailability also represent major challenges in soil research. Certain parent rocks contain a appreciable quantities of potentially toxic trace elements (Pb, Cd, Ni, Co, Cu, Zn, As). The continuous supply of substances containing pollutants results in greater inflows of trace elements than outflows. In France, there are an estimated 36,000 t/yr of copper applied to French vineyards. Regions with intensive indoor husbandry, such as Brittany, are also concerned with the addition of copper and zinc in animal diets. The supply of phosphates as fertilizers has also been a source of cadmium pollution. Urban waste is also a recent source of pollution, and the effects of air-based pollution around industrial zones needs to be taken into consideration.

Human activity affects not only the storage and transfer of water and dissolved elements, but also the aeration and temperature conditions that could impact biological activity. Although the organization of solid particles and pores is partially a result of conditions under which the soil has been formed, human activity both directly (cultivation methods, soil drainage) and indirectly (influence of plant and fauna activity) influences the physical properties of soil. For example, the general trend is for the organic matter content to decrease with an increase in soil use (ploughing of grassland). This is particularly true in the case of silty soils, which contain small quantities of clay and are thus less stable structurally and are susceptible to physical erosion. Soil chemistry also affects physical properties. For example, under slightly acidic conditions, soil particles can become highly mobile in the environment. The migration of clay from the upper soil layers to the lower layers (translocation) should not be ignored. This relative loss of clay from the surface can be observed over time as the soil becomes particularly sensitive to the effects of water (incrustation, particle suspension) and, finally, erosion and run-off occur.

Soil science must provide a reservoir of knowledge in order to increase the understanding of soil functions and to meet the needs of agriculture and the environment. The study of soil must incorporate both spatial and temporal trends, as changes are often slow and difficult to detect. This demonstrates the need to reassess soil with respect to its environmental functions, without limiting the assessment to merely the function of production.

FR:

Les pratiques de fertilisation et d'amendement peuvent contribuer à modifier profondément les propriétés des sols. Ceci est mis en évidence par le dispositif des 42 parcelles de l'INRA à Versailles qui reçoit chaque année les mêmes traitements depuis 1929. Il présente l'originalité d'être en jachère nue. Les résultats reportés ici reposent sur 16 traitements que nous comparons à une parcelle témoin. Le sol est à caractère limoneux avec 14 à 22 % d'argile. Le pH, la capacité d'échange au pH du sol (CEC_sol), et les cations échangeables ont été mesurés. Des mesures de porosité, de rétention de l'eau à différents potentiels de l'eau ont été effectuées.

Des variations considérables de pH sont observées. Les engrais ammoniacaux conduisent à des parcelles très acides (pH 3,5 à 5,0), à faible CEC_sol, essentiellement saturée par des cations aluminium. Dans les parcelles chaulées ou recevant des amendements basiques, le pH est tamponné à 8,2 par les carbonates. La CEC_sol double du sol acide au sol chaulé où elle est majoritairement saturée par du calcium échangeable. Avec les sels neutres (par exemple KCl, NaNO₃) le pH n'a pas changé et pour le témoin il a légèrement baissé. Des observations de terrain montrent que ces différents états physico-chimiques sont en relation avec les états de surface du sol et influencent la porosité du sol en profondeur.

Ainsi dans les sols des régions tempérées la CEC_sol peut doubler dans un domaine très restreint de pH (6,0 à 7,5), orientant fortement les propriétés physiques des sols.

EN:

In temperate regions, soil acidification is a real problem. The pH change causes transformations of both the chemical and physical properties of the soil. The 42 experimental plots at the Institut national de Recherche agronomique (INRA) in Versailles, France, were created in 1929. Since that time, each plot has received either fertiliser or amendments (Table 1). There are ten reference plots that have not been treated. Plots were dug up twice a year and left fallow. The results corresponding to 17 plots, 16 treated and one reference plot, are presented in this paper. The samples were collected in 1999 and compared to the 1929 soil reference. The pH was measured in water (AFNOR 1994), the cation exchange capacity (CEC) was determined at pH 7.0 (AFNOR 1994, CEC₇) and at the soil pH by the cobaltihexamine method (Ciesielski and Steckermann 1997, CEC_soil). Exchangeable cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) were measured after cobaltihexamine extraction and exchangeable aluminium by the KCl method (McLean, 1965). Water retention measurements were carried out with an apparatus developed by Tessier and Berrier (1979) and AFNOR (1996) at -10 kPa, with the Richards pressure plate cell at -1.6 kPa (Richards 1948) and with a controlled hygrometry dessicator at -107 MPa (Tessier 1984).

The average pH of the reference plot collected in 1929 was close to 6.3. In 1999, pH values ranged between 3.5 and 8.2. For plots treated with ammonium fertilisers the pH ranged from 3.5 to 5.5. In contrast, plots with basic treatment or liming had a soil pH that was close to 8.2 and was equilibrated with carbonates. Intermediate pH values (from 5.5 to 7.5) were obtained for plots treated with neutral salts such as KCl or NaNO₃, or with superphosphate.

The cation exchange capacity in soils at the reference pH (7.0) demonstrated variations in soil composition. For example, the CEC₇ varied with clay content as a function of depth or with organic matter loss or gain due to lying fallow or to manure application. When the CEC was measured at soil pH (CEC_soil), strong differences were observed. Two groups of plots can be differentiated in 1999. One ranged between 11 and 16 cmol+/kg; this range corresponded to plots with amendments or with fertilisers containing bases. A lower range of CEC_soil values (below 11 cmol⁺ /kg) was obtained with ammonium fertilisers. It is important to note that between pH=6.0 and pH=7.5 the CEC_soil doubled.

Six months after digging, the surface state of the soil was variable. Thick crusts dominated in acidic conditions, whereas the presence of dispersing cations (K⁺, Na⁺), and a smooth surface was present in soil treated with amendments. In the soil profile, bulk density increased with acidity and sodium or potassium cation concentrations. At -10 kPa, water retention measurements demonstrated that bulk density and sampling depth were linked with water retention: the higher the bulk density, the lower the water retention. At -1.6 MPa, water retention was correlated to the amount of clay and organic matter content. We also showed that the exchangeable calcium content and CEC_soil influence water retention. At -107 MPa, water retention depends on pH as well as the CEC_soil and exchangeable cation concentration.

The main purpose of this study was to show that after 70 years, plots subjected to intensive fertilisation or amendments and lying fallow (i.e., without organic matter restitution), have dramatically different soil properties. The first indicator of this evolution was pH. Ammonium fertilisers produced very acid plots (pH 3.5 to 5.0). In the presence of neutral salts (e.g., KCl, NaNO₃) and in the reference plot, the pH had decreased a little. In liming or basic treatment plots, the pH is controlled at 8.2 by carbonates. The second important factor to consider is the cation exchange capacity value. When measured at a reference pH (pH=7.0), the CEC₇ reflects the natural components present in a soil, but doesn't consider the influence of physico-chemical factors that operate in the native soil. After 70 years without organic restitution, the soil has lost approximately half of its original organic matter content, and as a result the exchangeable sites were approximately 2 cmol⁺ /kg.

The effective CEC at soil pH demonstrates the influence of pH on variable charges due to mineral constituents and organic matter. Plots with ammonium fertilisers have a low cation exchange capacity. Fertilisers with sodium and potassium cations have increased the exchangeable sodium (up to 11% of the CEC_soil) or potassium (18%) respectively. The cation exchange capacity doubled in going from acidic plots to liming plots, and in the latter the CEC is mainly saturated with exchangeable calcium.

In situ plot observations show that soil physico-chemical properties strongly influence not only soil surface state, but also soil profile porosity. Both acidification and dispersing cations are factors in soil degradation, whereas high pH values and calcium as the exchangeable cation produce strong structure stability and high porosity. It is also interesting to note that the CEC_soil can double between pH=6.0 and pH=7.5, thus influencing the physical properties of the soil. Comparing CEC₇ and CEC_soil facilitates the prediction of the effects of fertilisation and amendments on soil properties. The cation exchange capacity at soil pH can be used as an excellent indicator of soil quality.

FR:

Une méthodologie d'étude du comportement en scénario de valorisation de déchets minéraux solidifiés/stabilisés est présentée. La méthodologie est basée sur des outils expérimentaux (des tests paramétriques et des essais de simulation du scénario) et des modèles de comportement. Le cas d'un bassin de stockage d'eau construit avec un matériau contenant des résidus d'épuration des fumées d'incinération d'ordures ménagères est présenté. L'influence de la carbonatation du lixiviat par le CO₂ atmosphérique sur le relargage des éléments de constitution du matériau est étudiée. Un modèle de comportement est mis en place pour le cas étudié; il comporte trois niveaux : 1) le matériau (chimie et diffusion), 2) le lixiviat (chimie et convection), 3) l'absorption du CO₂ dans le lixiviat. Plusieurs échelles d'expérimentation (tests de laboratoire, pilote de laboratoire, pilote de terrain) ont été mises en place pour l'étude du scénario et pour la validation du modèle de comportement. Le rôle de la modélisation est mis en avant par les résultats prévisionnels des simulations. Ainsi, pour le cas étudié, la carbonatation du système diminue la concentration du plomb dans l'eau du bassin par rapport à un scénario "bassin couvert". La carbonatation ne modifie pas le relargage des éléments solubles (Na, K, Cl) et détermine la spéciation du Ca dans le bassin et à la surface du matériau.

EN:

The reuse of wastes and industrial residues should only be considered if we can assure that the environmental risks related to the planned use remain acceptable. The assessment and development of methodologies and tools used in evaluating the long-term release of pollutants from materials containing wastes is an area of research that is expanding. These methods depend on not only the characteristics of the materials (especially physical structure and composition) but also contact with both water and the reactive atmosphere.

The methodological standard ENV 12 920 is fundamental in the definition of the European approach, which involves the intrinsic and dynamic characterisation of the material/scenario couple in order to model the time-dependent source term. The main steps of the methodology are: 1) definition of the problem and the solution sought; 2) description of the scenario; 3) description of the waste; 4) determination of the influence of parameters on leaching behaviour; 5) modelling of leaching behaviour and 6) behavioural model validation.

The reuse scenario considered in the paper was a storage tank open to the atmosphere including material leaching, carbonation and contact with air. The reservoir content was composed of a mixture of hydraulic binders and air pollution control residues from a Municipal Solid Waste Incinerator. Modelling of the source term (the reservoir material) was performed in several steps ranging from the physico-chemical characterisation of the material to the validation of the proposed model by field simulation devices.

An experimental "toolbox" consisting of equilibrium dissolution tests and a dynamic leaching test was used. The experimental data supplied by the tests are the necessary input parameters for the behavioural model and give information about the release mechanisms. Identification of the main transfer mechanisms indicates that the release of soluble pollutants is the combined result of diffusional transfer of pollutants in the solution and the physico-chemical specificity of the species.

A physico-chemical and transport model has been developed for the long-term prediction of environmental leaching behaviour of porous materials containing inorganic waste solidified with hydraulic binders and placed in a reuse scenario. The model includes the source term, the leachate and the gas/liquid interface. The source term considers the main chemical equilibria (a simplified system) occurring in the interstitial water of the porous material. The consideration of the base content of the material, and the experimental determination of the solubility of heavy metals in the pore water, ensure a good representation of the metal release. The source term also includes diffusion in the porous system, which is considered the main transport phenomenon.

The leachate component considers chemical reactions that occur in the leachate. Many competitive dynamic processes (fluxes of mobile species coming from or penetrating into the material, gas absorption) take place in the leachate. Mass transport by convection of the leachate is also considered. Finally, the gas/liquid interface includes absorption with chemical reactions of carbon dioxide.

The physico-chemical parameters (initial element content, lead solubility and diffusion coefficient) of the model with respect to the source term were estimated using laboratory leaching tests. The gas/liquid mass transfer coefficient was estimated for each pilot. The simulation results agree with the two scales of experimental data: laboratory scale (volume of reservoir 80 L) and field tests (20 m³). No scale effect was observed as the intensity of the absorption phenomenon was virtually the same.

Experimental data and simulations show the main trends for the release of elements contained in the material:

1) The results obtained show that air carbonation of the leachate does not fundamentally change mass transfer mechanisms of easily soluble species (especially for alkaline metals). For these species, the use of the apparent diffusional model is a satisfactory solution for the prediction of long-term leaching behaviour.

2) The release of Ca and Pb was governed by chemical equilibria in pore water and diffusion whereas their speciation in the leachate was determined by pH and the presence of carbonate ions.

3) A carbonation front appears at the leachate/material interface and progresses into the material.

4) The target metal (lead) has a weak release (non-detectable by the analytical method used) for the study period.

5) Simulations of similar scenarios but without carbonation (a closed reservoir) predicts a higher concentration of lead than in the studied scenario.

Model estimations may be enhanced by a better knowledge of the source term (particularly the mineralogy and chemistry) and by an exhaustive listing of external factors acting in each scenario. In this study, factors such as the biological activity or temperature fluctuations were not taken into account. The general methodology used is based on several indispensable steps that lead to an environmental assessment of materials containing wastes destined for reuse scenarios. The necessary tools (experimental tests and mathematical models) are however specific for categories of materials (wastes) and types of scenarios.

A new generation of decision-making tools, based on modelling and simulation results, can complete, or even replace, the normalised procedures that mainly focus on laboratory experimental data.

FR:

Fondée sur le concept de l'écocompatibilité des déchets et élaborée à l'issue d'un programme de recherche de 5 ans, la méthode présentée nécessite une étroite collaboration entre chercheurs ou experts provenant de disciplines variées (physico-chimie, hydrogéologie, géotechnique, biologie, microbiologie,...) et travaillant sur divers milieux (déchets, sol de surface, sous-sol et eau). Elle comprend une procédure d'évaluation stricto sensu, suivie d'une procédure de décision au cours de laquelle on se prononce sur l'écocompatibilité (ou non) des scénarios de stockage ou de valorisation des déchets étudiés (ex : valorisation en technique routière). L'évaluation est effectuée selon une approche dite " en scénario ", inspirée de la norme expérimentale européenne ENV 12 920 " Caractérisation des déchets - Méthodologie pour la détermination du comportement à la lixiviation d'un déchet dans des conditions spécifiées ". Elle repose sur l'étude successive des flux de polluants émis par le dépôt ou l'ouvrage contenant les déchets (terme source), du transport de ces flux vers les milieux récepteurs (terme transport) et de l'impact des flux de polluants atteignant les milieux récepteurs (terme impact). Elle comprend une étape préalable d'analyse visant à décrire finement chacun de ces trois termes fondamentaux (source, transport et impact), de manière à identifier et à hiérarchiser les différents paramètres ayant une influence déterminante sur leur comportement. Cette analyse, qui correspond à la description du déchet et du scénario de stockage ou de valorisation des déchets, permet ensuite d'effectuer une sélection pertinente des essais à mettre en œuvre pour procéder à l'évaluation de chacun des trois termes et donc de l'écocompatibilité du scénario étudié. Les grands principes de la méthode et les principaux résultats obtenus lors du programme relatif à sa mise au point ayant fait l'objet de précédentes publications, le présent document porte sur le caractère fondamentalement pluridisciplinaire de l'application de cette méthode.

EN:

The disposal and reuse of waste (e.g., reuse of waste material for civil engineering or construction) are subjected to regulations that are mainly based on the best available technologies. They usually do not directly take into account the impact on human health and on the environment due to a lack of technical data in this field. Recent emphasis on the need to evaluate this impact has resulted in the necessity for new evaluation tools.

The ADEME (the French Agency for Environment and Energy Management) launched a research programme in 1995 called "Waste Ecocompatibility" to define a reliable methodology for measuring the impact of waste storage or reuse scenarios. This method could be used as a decision tool for environmental policy makers. It can also be used to determine what the acceptable levels of waste dumping or waste-based civil works are, while still being ecocompatible. The approach to set up this methodology is based on the concept of ecocompatibility. This is now defined as the situation where the pollutant flux from waste, either disposed of or reused, under specified conditions (physical, hydrogeological, chemical and biological conditions), is compatible with the environmental acceptance of the concerned receptor mediums. This definition integrates the evaluation of the pollutants emitted from the waste, the transport of these pollutants from the waste to the receptor media and their impact on the target receptor media.

An introduction to the research program was proposed by Mayeux and Perrodin (1996) and Gobbey and Perrodin (1999) in previous papers. The experimental sections were taken from Barna et al. (2000a), Barna et al. (2000b) and Ferrari (2000) concerning the emission pollutant term and the assessment of waste ecotoxicological properties. Experimentation dealing with the environmental impact on the soil and aquatic media was developed by Canivet (2001) and Poly (2000). This program led to an operational methodology introduced by the ADEME (2000). The general steps in conducting the ecocompatibility assessment of waste disposal or reuse scenarios are: 1) the preliminary description of the studied scenario; 2) the implementation of tests and measurements; and 3) the assessment of the global waste scenario ecocompatibility.

Ecocompatibility assessment is a multidisciplinary approach requiring researchers in biology, ecotoxicology, ecology, chemistry, hydrogeology, geology, etc. Some of them are specialists in the study of waste characterisation and waste leaching behaviour, especially with respect to investigations on long-term predictions. Researchers in charge of the impact term are skilled in the environmental impact assessment of complex effluents on soil, plants, micro-organisms, soil fauna and benthic invertebrates. In this paper, we stress the critical role of the scientific manager in the multidisciplinary work of an ecocompatibility assessment. The scientific manager must make the general problems understandable for each researcher involved. It is necessary to translate the general question into a series of specific questions related to each term of the methodology. To take advantage of a multidisciplinary study it is necessary to encourage and facilitate communication and discussion. If this is not efficient, each team will focus on its specific objective without taken into account data from the other teams. A lack of effective interactions between the involved researchers and the scientific manager will lead to a series of individual studies that are not of interest with regards to the general question. Similarly, it is essential that the various results lead to a joint discussion to draw a common conclusion.

FR:

L'exploitation du charbon dans le Nord-Pas-de-Calais (France) a engendré le dépôt d'importantes quantités de résidus miniers sous forme de terrils, essentiellement constitués de schistes houillers. Le lessivage de ces stériles par les eaux météoriques et l'oxydation des sulfures de fer contenus sont susceptibles de contribuer à l'enrichissement en sulfates et métaux associés de l'aquifère de la craie, principale ressource en eau de la région. Des analyses chimiques et isotopiques (S & C) ont été effectuées sur des prélèvements d'eau en amont et en aval hydraulique des sites d'étude ainsi que sur la fraction minérale des terrils. Afin de déterminer les modalités d'infiltration des eaux météoriques au sein des terrils, des prospections radio-magnétotelluriques, couplées à des mesures de perméabilité et de granularité ont été effectuées. Les analyses ont permis de mettre en évidence que le lessivage des terrils entraîne un flux d'ions sulfate et de carbone vers l'aquifère de la craie. L'approche géophysique a permis de mettre en évidence un phénomène d'infiltration des eaux météoriques. Elle a montré en outre l'existence de barrières de perméabilité en profondeur. Il apparaît donc que les eaux météoriques, lorsqu'elles s'infiltrent dans le terril, ne peuvent pénétrer à plus de quelques mètres de profondeur. L'existence de zones imperméables, en limitant l'infiltration des eaux en profondeur, limite également la quantité de sulfure potentiellement oxydable et donc la quantité de sulfates entraînée vers l'aquifère de la craie.

EN:

In the Nord-Pas-de-Calais region (France), coal mining activity has induced a build-up of many mine tips. The tip materials are dominantly composed of siltstones, locally rich in iron sulfide. Weathering of pyrite might be expected to release sulfate ions and associated metals within the run-off waters down to the underlying aquifer, which is composed of a thick Cretaceous chalk formation. The objectives of this study were twofold: (1) to determine the possible role of the mine tips in the sulfate mineralization of the chalk aquifer and; (2) to assess the amount of waste material that can be leached and may supply sulfate ions to the water table.

Two sites were selected for this study. Site 1 rests directly on the Senonian-Turonian chalk, whereas site 2 lies on sandy-clayey Cenozoic formations overlying the chalk formations (Figs. 1-2). Water samples were collected within the chalk aquifer (Fig. 3), which represents a free water table except for where the almost impermeable Cenozoic formations confine this table (site 2). Rock samples were collected at the surface and at a depth of <12 m at both sites. Various analyses were performed on these samples including mineralogical analyses carried out on both the bulk fraction and the clayey fraction, as well as elementary analyses of total carbon, total sulfur and CaCO₃ contents. Elemental analyses were carried out by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES: major and minor elements) or Inductively Coupled Plasma-Mass Spectrometry (ICP-MS: trace elements). Chemical and isotopic (C, S) analyses were performed on water sampled from upstream and downstream of the mine tips. In situ measurements were also carried out during sampling. Finally, to assess the degree of rainwater seeping through the coal mine tips, two radio-magnetotelluric surveys were carried out in September and November, 1999 following rainy periods. Permeability measurements and grain-size analyses of subsurface samples were also performed at site 2.

The carbon and sulfur contents showed superficial leaching on the mine tips (Fig. 4). The use of sulfur isotopes as tracers of the sulfate origin allowed identification of two sources for the two sites: a "mine tip" source with a slightly negative d³⁴ S (-2.8‰ to -3.9‰), which corresponds to the oxidation of sulfides contained by the Carboniferous shales, and another source (d³⁴ S=-20‰) corresponding to the gypsum of the Cenozoic formations, which was only present at site 2 (Figs. 5 & 6).

This study outlined different behavior for the tips of the two sites. At site 1, where there is a free water-table zone, the mine tip leachates carry sulfate ions directly to the water table, whereas in the case of a confined aquifer zone such as the one present at site 2, a proportion of the sulfate was reduced once exported to the water table (the redox potential showed negative values; Table 1). This suggestion of bacterially-mediated reduction is supported by the d³⁴ S of the sulfate content in the water table. The bacterial activity was fueled by the organic carbon release that accompanies the sulfur leaching on the mine tips. This carbon contribution was confirmed by the 14C activity that characterized the chalk aquifer waters at the upstream region of the mine tip and noticeably decreased downstream. The decrease is a result of the supply of "dead carbon" from the mine tips (Fig. 7).

The oxidation of pyrite also results in H⁺ production. However, the pH decrease observed downstream from the sites was very slight. Waters derived from leaching of the mine tip seeped through the buffered environment of the chalk aquifer. The distribution of metal content showed no surface to depth gradient for samples taken from both sites. The only evidence of "neutral acid mining drainage" (NAMD) was the sulfate amounts exported, and the increase in Mg, Ca, HCO_3- and Sr contents observed downstream from the sites (Table 2a-b).

The decrease in the apparent resistivity of radio-magnetotelluric profiles demonstrated that rain waters could deeply penetrate in some parts of the tip at site 2 (Fig. 9). Considering the constant nature of the waste material (grain size and porosity), a decrease in resistivity accompanied by an increase in conductivity between the two surveys indicated water seepage. Permeability measurements showed the occurrence of deep permeability barriers (Fig. 10), limiting not only rainwater seepage, but also the amount of mobilizable sulfide and consequently the amount of sulfates exported to the chalk aquifer. Grain size is not the only reason for the permeable or impermeable nature of waste material - the grain ordering and the compaction of levels at depth also have a role.

FR:

Les substances humiques se fixent en surface des minéraux argileux et modifient les sites d'adsorption des polluants organiques hydrophobes (POH). Parallèlement, les substances humiques dissoutes complexent les POH non ioniques selon des mécanismes de liaison réversible généralement évalués par le coefficient de partage Koc. Les solutés humiques seraient ainsi responsables du transport des POH dans les écosystèmes aquatiques par solubilisation de la fraction adsorbée sur le sédiment. Notre étude a pour objectif la quantification et la modélisation de ces phénomènes pour des composés modèles disponibles commercialement : kaolinite, pyrène et acide humique Aldrich purifié.

L'isotherme d'adsorption de l'acide humique (AH) sur la kaolinite à pH 6,5 et à force ionique 10^-2 M suit une loi de Freundlich, dont les valeurs du modèle sont K_F =0,79 et n_F =1,90. Dans les mêmes conditions expérimentales, le pyrène, composé modèle à quatre noyaux du groupe des hydrocarbures aromatiques polycycliques (HAP), semble s'adsorber en formant des microcristaux à la surface de l'argile. La présence d'acide humique fixé sur la kaolinite modifie l'adsorption du pyrène, qui se modélise par une isotherme de Freundlich de paramètres K'_F =0,30 et n'_F =2,00.

Les interactions entre le pyrène et l'acide humique dissous ont été quantifiées par spectroscopie d'extinction de fluorescence et relation de Stern-Volmer. La fraction humique dissoute non adsorbée sur le minéral argileux se caractérise par de plus fortes valeurs de Koc que l'acide humique initial (2,95.10⁵ L.kg^-1 contre 1,86.105 L.kg^-1). L'hypothèse de fractionnement des substances humiques lors de l'adsorption sur l'argile est confirmée par les variations du poids moléculaire moyen des AH, déterminé par chromatographie d'exclusion stérique, et des variations des intensités de fluorescence des fractions chromatographiées.

Les résultats obtenus pour la quantification du pyrène désorbé du solide argileux dans l'eau pure et dans une solution d'AH (50 mg.L^-1) tendent à minimiser le rôle de la matière organique naturelle dissoute dans le transfert des polluants hydrophobes du milieu solide au milieu liquide.

EN:

Humic substances become fixed to the surface of clay minerals and modify the adsorption sites of hydrophobic organic pollutants (HOP). The dissolved humic substances complex the HOP according to reversible binding mechanisms normally assessed by the Koc distribution coefficient. The humic solutes could thus be responsible of transporting HOP in aquatic ecosystems by solubilising the adsorbed fraction on sediment. Our study aims to quantify and model these phenomena using commercially available compounds:

- pyrene, a polycyclic aromatic hydrocarbon (PAH) generally used as fluorescence probe and able to bind strongly to humic acid (AH);

- a commercially available humic acid (Aldrich), with a high molecular weight and high aromaticity, which can easily adsorb onto colloidal matter and strongly bind PAH;

- kaolinite clay, a ubiquitous mineral in aquatic systems, with a particle size distribution in aqueous solution similar to that observed in lake waters.

We also have chosen physico-chemical conditions representative of freshwater: pH (6.5) and ionic strength (10^-2 M). The adsorption isotherm of the humic acid (HA) on kaolinite at pH=6.5 and at ionic strength 10^-2 M follows a Freundlich isotherm, for which model values are fixed at K_F =0.79 and n_F =1.90. The carboxylic groups of the dissolved HA, which represented more than half the total acidity, were not protonated under these conditions. Despite the negative surface charge of the particles, kaolinite was able to adsorb about 0.2 mgC.g^-1 of HA. A decrease in the solution pH occurred as the adsorbed HA quantity increased, suggesting a chemisorption of HA onto clay. The high-pressure size exclusion chromatogram (HPSEC) of the non-adsorbed HA, isolated after centrifugation of the colloidal solution, reflects the selective adsorption of the HA. The higher the molecular weight of the HA (>70 000 Da), the better the adsorption. The hypothesis of the selective adsorption of the humic substances onto clay was also confirmed by the fluorescence variations of the chromatographed fractions.

Using the same experimental conditions, pyrene seemed to adsorb and generate micro-crystals on the surface of the clay. The first part of the isotherm fits the pyrene monomer adsorption onto the hydrophobic siloxane surface of the clay. In the second part, the dramatic increase in the adsorption isotherm could be attributed to the formation of pyrene micro-crystals on the solid surface. For a residual pyrene concentration equal to 40 nmol.L-1, the PAH quantity adsorbed onto kaolinite clay (7 nmol.g^-1) was about twenty times lower than the quantity adsorbed onto montmorillonite clay (150 nmol.g^-1). This could be explained by the inaccessibility of the interlayer cavity of kaolinite to any solute.

Natural colloids are often coated by a humic layer. This coating can thus modify HOP adsorption onto the particles. The presence of humic acid fixed on kaolinite effectively modifies pyrene adsorption. This adsorption can be modelled by a Freundlich isotherm with the parameters K'_F =0.30 and n'_F =2.00. The adsorbed HA molecules seem to limit the formation of pyrene micro-crystals, even if the pyrene adsorption is not competitive with the HA fixation. Indeed, no HA desorption occurs during pyrene fixation onto the organic coated kaolinite.

The interactions between pyrene and dissolved humic acid have been quantified by extinction fluorescence spectroscopy and the Stern-Volmer relationship. The unabsorbed, dissolved humic fraction is characterised by Koc values higher than the initial humic acid (2.95 x 10⁵ L.kg^-1 compared to 1.86 x 10⁵ L.kg^-1). These two values are of the same magnitude as the published value obtained for the non-purified Aldrich HA (2.3±0.3 x 10⁵). The Koc value obtained for the non-adsorbed fraction of HA is unexpected because of the low molecular weight of these molecules. This Koc value can be related either to a better accessibility of the HA hydrophobic cavity for pyrene, or rather to a more efficient fluorescence quenching of pyrene by the humic solutes.

The dissolved humic acid may complex the non-ionic PAH according to reversible bonding mechanisms. Therefore, HA can act as a carrier of hydrophobic contaminants if it is able to desorb HOP from the surface of the particles. The results obtained for the quantification of the desorbed pyrene in pure water and in a HA solution (50 mg.L^-1) tend to minimise the role of dissolved natural organic matter in the transport of hydrophobic pollutants from the solid to the liquid medium. The values of pyrene concentration in solution obtained after 24 hours contact with kaolinite clay sorbed pyrene with pure water or with the HA solution were very low (respectively 2.4 nM and 12.9 nM) and below the water solubility of pyrene (802 nM). It has been previously demonstrated that the desorption kinetics of pyrene from quartz material are not influenced by the organic matter content of the solution (SCHMITT, 1999). Our results demonstrate that the HA content of the solution did not greatly modify the quantity of pyrene desorbed from clay minerals.

FR:

Des concentrations en P excédant le seuil d'eutrophisation sont fréquemment mesurées dans l'eau des affluents du fleuve Saint-Laurent au Québec, Canada. Un enrichissement excessif en P des sols agricoles en serait la source. Une norme relative à la saturation en P des sols a été proposée comme critère de risque de contamination en P des eaux de surface. L'objectif de ce travail est d'étudier le lien entre la richesse en P du sol et la teneur en P de l'eau de drainage dans deux agro-écosystèmes du Québec. Le bassin versant de la rivière Boyer (BVB), dominé par des sols en pente, une forte densité animale et des productions fourragères et les Basses Terres de Montréal (BTM), dominées par des sols plats utilisés pour la production intensive de maïs et une faible densité animale sont étudiés. Le degré de saturation en P des sols du BVB est de 8 à 10 % alors que celui des BTM dépasse très souvent 15 %. Le pool du P organique est plus faible dans les sols des BTM que dans le BVB. La concentration moyenne en P de l'eau de drainage est plus élevée dans les sols du BVB (171 µg L^-1) que dans ceux des BTM (98 µg L^-1). Elle est corrélée à la teneur en P extrait à l'oxalate des sols argileux et à la teneur en P soluble dans l'eau ou à l'index de sorption en P des sols grossiers. Ces relations sont plus étroites pour la couche 0-5 cm de sol que pour les couches plus profondes. Les résultats de cette étude démontrent qu'il est difficile de prédire la concentration en P de l'eau de drainage de sols contrastants. Regrouper les sols selon leur texture améliore la précision de la prédiction de la teneur en P de l'eau de drainage à partir de leurs propriétés.

EN:

Concentrations of P higher than the recognised threshold for eutrophication are often measured in the tributaries of the St. Lawrence river, Quebec, Canada. An excessive P enrichment of agricultural soils was identified as the potential cause of this phenomenon. This enrichment results in a decrease in the P sorption capacity of soils and an increased risk of P contamination of surface waters. A norm based on soil P saturation degree (DSPS) was proposed as an agro-environmental criterion to reduce this risk. Relationships between DSPS and other soil P attributes and surface runoff P concentration have been reported in the literature but not for tile-drainage water. The objective of this work is to study the relationship between soil P attributes and drainage water P in two agro-ecosystems of Quebec.

The Boyer watershed (BW), which is dominated by soils with significant slopes, a high animal density and forage production, and the Montreal lowlands (ML), dominated by flat soils, low animal density and mostly used for corn (Zea mays L.), were studied. The A, B and C horizons from soils from the BW were sampled at three locations in tile-drained fields from farms in surplus or not of manure N in regards to crop needs. Soils were sampled in the ML according to a gradient in clay content with the same procedures. Soils were characterised for their pH, particle size distribution, Mehlich 3-extractable P (P_m3) and Al, water-soluble P (P_w), organic P (Po) and oxalate-extractable P (P_ox), Al (Al_ox) and Fe (Fe_ox) contents. Grab tile-drainage samples were taken in triplicate and characterised for total (TP), particulate (PP) and dissolved reactive P (RP) and unreactive P (UP).

The soils of the BW are more acidic and have higher P retention capacities than ML soils. The Pw content of BW soils is lower than in ML ones in spite of comparable P_m3 contents. The DSPS (P_ox /Al_ox + Fe_ox) of BW soils is moderate (8 to 10 %) whereas DSPS in ML soils is often >15 %. The soil P organic pool is much smaller in the ML soils than in those from BW, probably because of more frequent tillage and lower manure C inputs.

The average P concentration (TP) in drainage water was higher in soils from the BW (171 µg L^-1) than from ML soils (98 µg L^-1). The PP was the main P fraction in drainage water from the two ecosystems. The RP was on average 44 % of TP whereas UP was much less. The TP concentration in drainage waters was higher than 0.03 mg L^-1 in most cases. The TP concentration was higher in tile-drainage waters from the BW than in the ML even though comparable P_m3 and lower DSPS were found in the BW than in ML soils. These results suggest that other criteria should be included in the prediction of the risk of P contamination of drainage waters. The results of the present study indicate that agricultural practices (crop species, manure inputs, tillage type and frequency) could have a greater influence than soil P status on the TP concentration in tile-drainage waters.

A linear correlation analysis between the logarithm of the TP (TP + 0.5) and that of the different soil P attributes indicated that TP was related to the P extracted by oxalate from clay soils and by water in coarse-textured soils. These relationships were closer in the 0-5 cm soil layer than in deeper strata. Multiple regression analysis between the logarithms of drainage water P concentrations and soil attributes revealed that, when soils were grouped by texture, the prediction of TP was much more accurate than when all soils were considered. The present regulatory approach of assessing the risk of water P contamination by using the soil P_m3 and DSPS only was inadequate in the two considered agroecosystems.

The results of this study indicate that the prediction of the drainage water P concentration with P attributes from contrasting soils is difficult. Grouping soils by texture improves the prediction of P_t from soil P attributes.

FR:

Dans un contexte de gestion intégrée de l'eau par bassin versant, on doit, avant d'implanter tout programme d'assainissement, comparer les solutions de rechange, distinguer les contributions des différentes sources de pollution aux problèmes de qualité de l'eau, et définir des objectifs environnementaux de rejet (OER) associés aux activités et aux pressions anthropiques. Dans le cas des sources de pollution d'origine ponctuelle, on détermine un OER et son risque de dépassement en fonction d'un débit d'étiage critique d'une période de retour donnée. Dans le cas de la pollution diffuse d'origine agricole, il n'existe pas de concepts similaires pour définir des OER. L'approche que nous proposons, c'est de simuler, à l'aide de chroniques météorologiques et de divers scénarios de gestion de ces rejets, les concentrations résultantes dans les cours d'eau et de calculer les probabilités de dépassement des critères de qualité de l'eau (CQE). Cette approche permet de caractériser la prise de décision pour la période de contrôle en matière du nombre moyen de jours de dépassement d'un CQE. Ceci représente une quantification plus exacte du risque car ce dernier est interprété en fonction de ce qui est mesuré en rivière, c'est-à-dire les concentrations de polluants. Dans cette étude, on illustre l'application de ce concept à partir d'un cas de figure dans le bassin versant de la rivière Chaudière (Québec, Canada) qui est simulé avec le système de modélisation intégrée GIBSI. Dans le cadre d'une analyse de scénarios de restauration des activités récréatives conduisant à des contacts directs et fréquents avec l'eau, on illustre comment on peut, en réduisant respectivement les pressions agricole et urbaine de 32 et 17%, abaisser globalement les probabilités de dépassement des critères esthétique et bactériologique de 0,32 à 0,19 et de 0,94 à 0, respectivement.

EN:

In an integrated watershed management context, the implementation of any clean water program requires the evaluation of the contribution of pollutant loads associated with wet (nonpoint or diffuse) and dry weather (point) sources to the studied water quality problem. It is also necessary to set environmental load allocations (ELA) or total maximum daily loads (TMDL) for various anthropogenic activities and to link these loads to water pollutant concentrations. The ELA or TMDL is a numerical quantity determining the maximum load of pollutants from point and nonpoint sources as well as background sources, to receiving water bodies that will meet designated water uses (e.g., swimming or fishing) in terms of water quality standards (WQS). The American Congress included a TMDL program in the Clean Water Act of 1972 (US EPA, 1997; 1999). The outcome of the TMDL program corresponds to the drafting of a watershed management plan (NOVOTNY, 1999).

Estimation of ELA from point sources is generally based on simultaneous occurrence of severe low flows and maximum daily loads. The ensuing risk of not meeting WQS is usually linked to the inverse of the return period of the design flow. Meanwhile, estimation of ELA from diffuse sources, and associated environmental risks, is not as well established since diffuse sources of pollution generally occur during important runoff events and strongly depend on land use and management practices. These wet weather loads may be allocated using continuous hydrological modelling. Simulation results can then in return be used to link ELA from point sources and diffuse sources to pollutant concentrations and, for a given time period (e.g., summer), to evaluate the probabilities (namely the risks) of exceeding WQS designating the water use.

The objective of this study was to present, using the integrated modelling system GIBSI (VILLENEUVE et al., 1998b; MAILHOT et al.,1997), this new approach to assess the risk associated with the establisment of ELA from point and diffuse sources. A case study on the Chaudière River watershed (Quebec, Canada) was defined and simulations were performed (scenarios A-E). The case study focussed on determining whether WQS defining the designated recreational use of water requiring direct and prolonged contact were attainable. Untreated municipal waste waters from a small town (St. Martin) and nonpoint source pollution were responsible for impairment of the studied river segment. Water contaminants considered were fecal coliforms (FC) and phosphorus (P).

Two base case scenarios, A and C, were simulated using four years (1982-1985) of meteorological data to illustrate the degraded bacteriological and aesthetic conditions of the river segment due to dry and wet weather sources, respectively. Dry weather sources were assumed to solely contribute to the bacteriological impairment. Meanwhile, both wet and dry weather sources were assumed to contribute to aesthetic impairment. Scenario B was defined to examine the impact of constructing a waste water treatment plant (WWTP) for the town of St. Martin on the bacteriological conditions. Scenarios D and E were elaborated to quantify the impact of both reducing diffuse and point source loads on aesthetic conditions, respectively. For scenario C, on average 31 kg P/ha were applied on cultivated land according to local fertilization calendars. Similarly, the fertilization rate for scenarios D and E was on average 13 kg P/ha. The design stream flow for ELA from point sources was a₃₀ Q₅ (30-day low flow, 5-year return period) and estimated at 6.05 m³ /s for the studied river segment. It is noteworthy to mention that for the 1982-1985 summers (June 21 through September 20), simulated daily stream flows exceeded the design flow 31, 62, 19 and 2 times and that 150, 48, 348, and 270 Mm³ of water flowed through the studied river segment, respectively. This means the 1983 meteorological series was three times as dry as that of 1982 despite the fact it was the latter that produced the₃₀ Q₅. The ELA from both point and diffuse sources for the river segment receiving the St. Martin's effluent and the studied river segment were 0.75*10¹² UFC and 11.21 kg P and 1.05* 10¹² UFC and 15.68 kg P, respectively.

For scenario A, simulation results showed that respectively 94% and 14% of the time, the bacteriological (WQS_FC < 200 UFC/100 ml) and aesthetic (WQS_P < 0,03 P mg/l) WQS were not met over the summer season of the four-year meteorological series. Similarly, for scenario C, the simulation results indicated that 32% of the time, the aesthetic WQS was not achieved. Dry weather sources, namely WWTP and wet weather sources, namely agricultural runoff, accounted for P loads. During the driest summer, dry weather sources accounted for 63% of the P loads. For the other summers, wet weather sources accounted for 71, 88, and 78% of total P loads. For scenario B, simulation results showed that the bacteriological WQS was met 100% of the time. Meanwhile, scenario D was designed to see whether a 27% reduction of the agricultural nonpoint source load could alone restore the aesthetic properties. The simulation results showed an improvement as the probability of exceedence dropped from 0.32 to 0.27. This probability was further lowered to 0.19 when St. Martin's waste waters were treated using aerated lagoons and dephosphotation. This corresponded to an additional 17% abatement of the dry weather sources loads (scenario E).

It is noteworthy that this study did not specifically attempt to specify the reasons why WQS were not met, whether it was due to low stream flows or large point or nonpoint sources loads although the integrated modelling system allows for this. Also, this study did not attempt to determine impacts of local management scenarios instead of a systematic reduction though GIBSI also allows for this. However, this study clearly illustrated how the proposed methodology, which is rooted in a risk assessment approach based on evaluation of the probability of exceeding WQS, is well suited to characterise ELA for various anthropogenic activities. Indeed, simulation results clearly demonstrated the benefits of assessing independently the impacts of ELA from point and diffuse sources on the attainability of a designated water use. It is believed that this type of ELA assessment approach will facilitate communication with stakeholders. Ideally, these exceeding probabilities should be evaluated using long meteorological series (e.g., 30 years).

FR:

Le programme d'assainissement des eaux de Québec (PAEQ), mis en place à la fin des années 1970, s'est d'abord attaqué au problème de la pollution ponctuelle d'origine urbaine. Plusieurs stations de traitement des eaux usées municipales ont été construites dans le cadre de ce programme réduisant de façon importante les charges de polluants d'origine urbaine. La question demeure toutefois de savoir dans quelle mesure les charges urbaines rejetées avant et l'après l'instauration de ce programme peuvent entraîner des dépassements de différents critères de l'eau. La présente étude a pour objectif d'examiner cette problématique pour le bassin versant de la rivière Chaudière en utilisant le système de modélisation intégrée GIBSI (Gestion Intégrée par Bassin versant à l'aide d'un Système Informatisé). Deux scénarios d'assainissement urbain ont été examinés, l'un représentatif de la période avant la mise en place du programme, le début des années 1980, et un autre représentatif de la période plus récente. Deux chroniques météorologiques ont été utilisées (années 1983 et 1994). L'estimation des probabilités de dépassement de différents critères de l'eau montre une nette réduction de ces probabilités après mise en place du programme. Pour la DBO₅ et l'azote total, les charges urbaines rejetées actuellement n'entraînent pas de dépassement des critères de qualité de l'eau pour les deux années retenues. Toutefois, les résultats montrent que les charges en phosphore total d'origine urbaine peuvent à elles seules entraîner des probabilités de dépassement importantes lors d'étiage.

EN:

In 1978, the Québec Government put in place a provincial municipal clean water program, referred to as the Programme d'assainissement des eaux du Québec (PAEQ), to restore the province's rivers to their natural state. The program focussed primarily on the problem of municipal waste loads and, hence, a large number of wastewater treatment plants (WWTP) were constructed during the 1980's and the 1990's. At the beginning of the 1980's, only a few percent of the population had their waste water treated, but this figure had increased to over 95% by 1997 (Figure 1). In the Chaudière river watershed, this program resulted in the construction of more than 35 WWTP over an 18-year period. Although an impressive effort was devoted to reduce municipal waste loads, a question remains: how does this reduction translate into terms of overall improvement of water quality at the watershed level?

The Chaudière river watershed was considered for this application. This watershed covers an area of 6682 km2 and is located south of Quebec City. Land use is dominated by forest (62%) followed by agricultural land (33%), urban area (3.6 %), and water (1.7 %). The total population in 1996 was 173129 and was mainly located in the northern part (i.e., the downstream region) of the watershed. A total of 44 municipal point loads were identified (see Figure 2 and Table 1), most of them corresponding to WWTP. Characteristic data on municipal WWTP for year 1995 were obtained from the Quebec Department of the Environment (MINISTERE DE L'ENVIRONNEMENT ET DE LA FAUNE DU QUEBEC, 1997) and used to estimate average concentrations of total phosphorus and the biological oxygen demand (BOD). Data included affluent and effluent concentrations at various WWTP. Since no data were available for nitrogen, a concentration of 40 mg-N/l was used (TCHOBANOGLOUS et SCHOEDER, 1985; NOVOTNY et CHESTERS, 1981). Nitrogen removal efficiency for different types of treatment was estimated from available data compiled by the Environment Quebec (Table 2). An average, per capita, daily wastewater volume of 0.73 m³ was derived. This large value indicates a large infiltration capacity in the sewer network and, on average, a poor structural state.

Results were analysed at four locations distributed along the river. These points corresponded to the locations of the four major water quality monitoring stations (Figure 3). Total annual loads within the sub-watersheds defined by these points were estimated (Table 3). Affluent characteristics were considered for the simulation of the pre-PAEQ period. Figure 4 represents the evolution of total phosphorus loads at station 2340012 (water intake for the town of Charny, the most downstream point). It shows that an important reduction occurred in 1986. For the same sub-watershed, the overall reduction for the 1982-1999 period was 38% for total phosphorus, 37% for total nitrogen and 83% for BOD.

Assessment of the impact of the PAEQ was done using the integrated modelling system GIBSI ("Gestion Intégrée par Bassin versant à l'aide d'un Système Informatisé") (ROUSSEAU et al., 2000; MAILHOT et al., 1997 ; VILLENEUVE et al., 1998). Only pollutant loads originating from sewer networks were considered; pollutant loads from industrial plants not connected to a municipal sewer network were not considered in this study. Similarly, diffuse sources of pollution from urban area or agricultural land were not taken into account. Two scenarios were considered: a first scenario associated with the 1983 year corresponding to the pre-PAEQ period; and a second scenario associated with the 1994 year describing the post-PAEQ period (following load reductions). Two hydrological reference years were also selected, namely, years 1983 and 1994. The former corresponded to a significantly drier year than the latter. At station 2340012 (Charny water intake), this difference was even more pronounced when considering that the cumulative summer flow was 6.9 times larger in 1994 than in 1983. Four simulations corresponding to different combinations of representative municipal waste loads and meteorological conditions were performed (Table 5).

Simulation results at the four control points were compared with water quality standards (WQS) for total phosphorus (0.03 mg-P/l, aesthetic WQS for prevention of eutrophication in rivers) and BOD (3 mg-BOD₅ /l, sanitary WQS for domestic use of water requiring disinfection treatment only). The probabilities of exceeding these WQS were defined (equation 1) as the number of days (daily computational time step) where simulated values exceeded a given value (complementary cumulative distribution function). Table 8 introduces annual probabilities of exceeding WQS at the four control points and for the different simulations whereas Table 9 introduces those for the summer period. At station 2340012 (Charny water intake), for hydrological year 1994, a comparison of pre- and post-PAEQ conditions for total phosphorus shows that post-PAEQ condition lowered the number of days exceeding WQS by 49. Similar reductions were reached at the other control points. For the 1994 summer period, the reduction was not as pronounced since the probability of exceeding WQS was 0.24 for pre-PAEQ situation and it decreased to 0.21 for the post-PAEQ condition. These probabilities worsened under the 1983 summer conditions as concentrations exceeded the WQS 98% of the time at station 2340014.

FR:

Les échanges en surface dans le Modèle de Chimie Transport (MCT) multi-échelles MOCAGE de Météo-France comprennent à la fois les flux d'émissions et de dépôt sec d'espèces gazeuses. Une interface 2D a été développée entre MOCAGE et le modèle de prévisions météorologiques opérationnel français ARPEGE dans le but de calculer des flux à la surface réalistes

Pour les émissions, un inventaire global est employé pour le moment; cet inventaire a été construit essentiellement à partir des inventaires des programmes IGAC/GEIA (International Global Atmospheric Chemistry / Global Emission Inventory Activity) et EDGAR (Emission Database for Global Atmospheric Research qui ont des résolutions temporelles annuelles, sai-sonnières ou mensuelles et une résolution spatiale de un degré.

Le dépôt sec d'espèces gazeuses, y compris l'ozone, le dioxyde de soufre, les composés azotés, les composés organiques à longue et à courte durée de vie, a été paramétrisé selon [Wesely, 1989]. Le modèle calcule la vitesse de dépôt à partir de valeurs de trois résistances en série, les résistances aérodynamique, laminaire et de la surface. Ces résistances sont calculées en utilisant les champs de surface d'ARPEGE. Les champs liés à la végétation, tels l'indice foliaire, sont prescrits avec une résolution de un degré sur le globe et de cinq minutes sur l'Europe. Un certain nombre de modifications a été apporté à la paramétrisation de [Wesely, 1989], par exemple pour la formulation de la résistance stomatale et celle de la résistance de surface sur les surfaces mouillées. Les valeurs calculées de vitesse de dépôt ont été comparées à des observations et leurs distributions spatiales et temporelles ont été analysées sur deux saisons opposées (hiver et été, sur les différents domaines de MOCAGE, de résolution allant de 2 degrés pour le globe à 0.25 degrés pour la France.

EN:

Surface exchanges considered in the MOCAGE multiscale Chemistry and Transport Model (CTM) of Météo-France include both emissions and dry deposition of gaseous species. To compute realistic time-dependent fluxes at the surface, a 2D interface between MOCAGE and ARPEGE, the French operational numerical weather prediction model, was developed.

With regard to emissions, a default global inventory is presently employed. Built mainly from the IGAC/GEIA (International Global Atmospheric Chemistry / Global Emission Inventory Activity) and the EDGAR (Emission Database for Global Atmospheric Research programs, this inventory has an annual, seasonal or monthly temporal resolution, and a degree-by-degree spatial resolution.

Dry deposition of gaseous species, including ozone, sulfur dioxide, nitrogen-containing com-pounds, long-lived and short-lived intermediates organic compounds, were parameterised ac-cording to [Wesely, 1989]. The model calculates dry deposition velocities from three resistances in series: aerodynamic, laminar, and surface. These resistances are computed using the surface fields obtained from the analyses or forecasts of ARPEGE. Vegetation fields such as the Leaf Area Index are prescribed with a one-degree spatial resolution at the global scale, and a five-minute resolution over Europe. A number of modifications was incorporated into the original surface resistance scheme (e.g., the formulation of stomatal resistance and surface resistance over wet surfaces. Calculated dry deposition velocities were compared to observations, and the spatial and temporal distributions were analysed for two different seasons (summer and winter) using the varions MOCAGE domains of varying resolutions (from 2 degrees over the globe to 0.25 degrees over France).

FR:

Ces travaux s'inscrivent dans le cadre du programme national de MEsure des Retombées Atmosphériques (MERA). Ils portent sur la recherche de l'origine des précipitations collectées entre 1997 et 1999 dans trois (Morvan, Iraty, Le Casset) des onze stations du réseau MERA localisées en différents points du territoire français. Deux méthodes statistiques ont été utilisées dans cette étude. Les régions à l'origine des fortes concentrations mesurées au site récepteur ont d'abord été déterminées à l'aide d'un modèle (méthode de Seibert) combinant les mesures réalisées sur site et les rétrotrajectoires de masses d'air puis, dans un second temps les différents profils de transport atmosphérique, leur fréquence et concentrations associées ont été évaluées à l'aide d'une classification par Nuées Dynamiques (méthode K-means/distance Euclidienne simple) des rétrotrajectoires de masses d'air. Le test de Kruskal-Wallis a été utilisé pour vérifier si les médianes des concentrations associées à chaque classe sont statistiquement différentes. L'étude réalisée à Iraty (Pyrénées) et au Casset (Alpes) a montré que ces deux stations sont influencées différemment du Morvan. Plus exactement, ces deux sites ne sont pas, ou pratiquement pas, influencés par les zones d'Europe centrale ou du Nord-Ouest fortement émettrices de SO2, de NOx et de NH₃. Seul le pH des précipitations collectées à Iraty semble dépendre des émissions de SO2 et de NOx d'une de ces zones. Iraty et le Casset sont très influencées par les émissions anthropiques et par les poussières d'origine terrestres en provenance d'Afrique du Nord. Néanmoins, les niveaux de concentrations mesurés dans les flux en provenance d'Afrique du Nord sont similaires pour Iraty, le Casset et le Morvan (sauf en ions calcium, pour lequel le Casset et Iraty montrent de fortes concentrations). Une autre région européenne peut influencer les niveaux en composés acidifiants mesurés au Casset, il s'agit de l'Italie et de la zone localisée au niveau de l'ex-Yougoslavie. Mais, les niveaux de concentrations qui en résultent sont faibles par rapport à ceux mesurés dans certains flux arrivant au Morvan.

EN:

The chemistry of precipitation in France was examined using data from the French atmospheric deposition network (MERA). In order to examine the source-receptor relationships responsible for acid rain at three background sites in France, a receptor-oriented model was applied to the precipitation data collected from 1997 to 1999. This methodology combined precipitation and chemical data with air parcel backward trajectories to establish concentration field maps of likely contributing sources. Then, a clustering technique using partitioning methods (K-means/Euclidian distance) was performed to backward trajectories and the distributions of mixing samples associated with backward trajectories in each cluster were compared. The Kruskal-Wallis test was used to verify that the concentration medians associated with each cluster were statistically significant. The results of this study demonstrated that two stations (Iraty and le Casset) were not influenced by the same sources as Morvan. Specifically, these sites were less influenced by high emissions from Central or Northwestern Europe when compared to Morvan. Only the pH seemed under the influence of SO₂ and NOx emissions from one of these areas. Iraty and Le casset are very influenced by anthropogenic emissions and the crustal sources around the Mediterranean Basin and North Africa. Other European areas (e.g. Italy) can influence the concentrations recorded at Le Casset but the levels of concentration are lower than those measured at Morvan.

This paper represents a complete statistical analysis of wet-only deposition chemistry data for three stations (Iraty, Le Casset and Morvan). Two statistical methods were used in this study. In order to examine the source-receptor relationships responsible for acid rain at these three background sites in France, a receptor-oriented model was applied to the precipitation data collected from 1997 to 1999. This methodology combined chemical data with air parcel backward trajectories to establish concentration field maps of likely contributing sources. This receptor-oriented model was developed by Seibert and it assumes that if a trajectory endpoint falls in a grid cell (i,j), the air mass is assumed to collect components emitted in this cell and once the components are incorporated, they are transported along the trajectory to the receptor site. This model doesn't take into account the atmospheric diffusion and the removal mechanisms occurring during the trajectory from the sources to the receptor. Finally, a concentration field map for the selected species was calculated taking into account all grid cells. For mapping, the grid cells counting fewer than 10 endpoints were not taken in consideration because the confidence of their results was considered too low. The role of three-dimensional backward trajectories is fundamental, so we used three different information sources: the French Institute of Meteorology, Météo-France; the British Atmospheric Data Centre (BADC); and the Atmospheric Environment Service Long Range Transport model of Air Pollution (AES-LRTAP), Canada. These trajectory models were compared for different chemical species. All data were projected in the EMEP grid (150 x 150 km) for establishment of the concentration field map. A clustering technique by partitioning methods (K-means/Euclidian distance) was performed on backward trajectories and the distributions of mixing samples associated with backward trajectories in each cluster were compared. The Kruskal-Wallis test was used to verify that the median concentrations associated with each cluster were statistically significant.

The results of this study for Morvan determined five classes of backward trajectories associated with the precipitation collected at this station located in the centre of France. The fluxes from SW and WSW sectors contribute for 52% of events, while the fluxes of NW and E contribute for 31% of events but are mainly responsible for high concentrations of sulphates, nitrates, ammonium and hydronium ion. Regions found to be responsible for rain events coincide with European regions known for their high anthropogenic emissions of SO₂ and NOx (Great Britain, North of France, Belgium, The Netherlands and the North of sea).

The results for Iraty (South of France) yielded five classes of backward trajectories associated with the precipitation collected in this station. The fluxes from W sectors (NNW, NW, W and WSW) were responsible for 71% of events, while the flux of S (low wind) was responsible for 29% of events but is mainly responsible for high concentrations of sulphates, nitrates, ammonium and calcium. High concentrations of hydronium ion were identified in the NNW sector.

The results for Le Casset (East region and mountainous) gave four classes of backward trajectories associated with the precipitation collected in this station. The fluxes from W and WSW sectors were responsible for 35% of events, while the flux of SSW was responsible for 43% and the flux from the SE was responsible for 22% of events. This last sector was mainly responsible for high concentrations of sulphates, nitrates, ammonium and calcium. The concentrations measured at this station were low. Regions found to be responsible for rain events coincide with southern and eastern areas known for their high anthropogenic emissions of SO₂ and NOx (north Africa, northern Italy, Yugoslavia).

All these results demonstrate that the Iraty and Le Casset stations were not influenced by the same sources as Morvan. Specifically, these sites were less influenced by the high emissions from central or northwestern Europe than Morvan. Only the measurement of pH seemed to be under the influence of SO₂ and NOx emissions of one of these areas. Iraty and Le Casset were very influenced by the anthropogenic emissions and the crustal sources around the Mediterranean Basin and North Africa. Other European areas (e.g., Italy) can influence the concentrations recorded at Le Casset but the levels were lower than those measured at Morvan. A relation between sulphates, nitrates and ammonium was identified for Morvan and Le Casset. This observation suggests that aerosol transport of NH₄ HSO₄, (NH₄)₂ SO₄ and NH₄ NO₃ is occurring.

FR:

La volatilisation du mercure des surfaces vers l'atmosphère et les dépôts atmosphériques du mercure sont des phénomènes importants dans la dynamique globale du mercure. Les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent sont variables dans le temps et dans l'espace. Bien que le modèle de la double couche montre que la grande partie des écosystèmes aquatiques sont en sursaturation par rapport à la constante d'Henry, des observations in situ, à l'aide de techniques de chambre à flux, montrent que des dépôts gazeux sont également possibles. Les dépôts gazeux du mercure dans l'écosystème lac Ontario/fleuve Saint-Laurent oscillent entre 0 et 4,66 ng/m²/h alors que les valeurs de volatilisation varient entre 0 et 9,28 ng/m²/h. Globalement, la volatilisation médiane du mercure est de 0,77 ng/m²/h alors que le dépôt gazeux médian est d'environ un ordre de grandeur inférieur (0,075 ng/m²/h). En été, l'ensemble des dépôts atmosphériques du mercure semble être mis à contribution lors de la volatilisation du mercure au-dessus des sols. Il semble que la majeure partie de cette volatilisation serait en fait de la ré-émission du mercure vers l'atmosphère. En hiver, seule la portion gazeuse des dépôts de mercure semble être ré-émise vers l'atmosphère. Plusieurs observations dans un marécage fluvial du lac Saint-Pierre (baie Saint-François) montrent que les flux de volatilisation du mercure sont supérieurs en période sèche qu'en période inondée (0,83 vs. 0,52 ng/m²/h). Ainsi, en période d'inondation le mercure réactif disponible pour la volatilisation serait en compétition avec les mécanismes responsables pour la méthylation du mercure (bio-disponible) et/ou la formation du sulfure de mercure (inerte sous forme de cinabre). Cet article a pour objectifs de présenter et discuter les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent.

EN:

This paper presents and discusses mercury surface-atmosphere gas exchange in Lake Ontario/St. Lawrence River ecosystem. Atmospheric sources are recognised to be significant in the cycling of global mercury. Being volatile in its elemental and dimethylated forms, mercury is distributed worldwide. The dominant form of mercury in the atmosphere is gaseous elemental mercury (Hg°) (~ 98%). Cycling of atmospheric mercury proceeds by gas exchange, particle settling or by rain scavenging. Wet and particle Hg deposition mainly involves the oxidised form, i.e. the Hg(II) species, which is relatively immobile. Chemical, photolytic or biological reduction to the elemental form can increase the mobility of mercury.

Transport of mercury from bodies of water to the atmosphere (volatilisation) and atmospheric deposition are significant components for mercury budgets in lakes and rivers. The large majority of aquatic ecosystems studied so far have been found to contain dissolved gaseous mercury at concentrations that were supersaturated relative to the equilibrium values predicted by Henry's law. Evasion of elemental mercury was suggested to occur over the ocean and from inland waters but was only measured directly in a few cases. A few instances of net deposition were observed over inland waters. The dynamic aspect of mercury exchange has to be explored for a better understanding of mercury behaviour in the environment. Part of this understanding can be achieved by quantifying the rate of exchange or fluxes between compartments.

Until recently, mercury fluxes were quantified by estimations using mathematical models or by measuring the mercury accumulation in biological, soil and sediment samples. It is only in the last few years that technical improvements have allowed a more or less direct measurement of mercury fluxes between air/soil and air/water compartments. One of these methods is the dynamic flux chamber, which is a simple and relatively reliable technique. Total Gaseous Mercury (TGM) analysis in this study was achieved with an automatic analyser (Tekranâ 2537A). Briefly, the analytical train of this instrument is based on amalgamation of mercury onto a pure gold surface followed by a thermo-desorption step and analysis by Cold Vapour Atomic Fluorescence Spectrophotometry (CVAFS) (l=253.7 nm). Dual cartridge designs allowed alternate sampling and desorption, resulting in continuous measurements of mercury in the air stream. Both modelling and dynamic flux chamber methods are reported in this paper. The former technique was applied along cruises on Lake Ontario and the Upper St. Lawrence River whereas the latter was applied at various stationary locations along the St. Lawrence River (e.g., pasture, water, wetlands and snow surfaces). The dynamic flux chamber used was built in our laboratory. The chamber consists of a hemispheric stainless steel bowl coated with Teflon®. The open area of the chamber is 0.13 m² and its volume is 10 L. The flow rate into the chamber is 0.09 m³/h. The measurement of mercury in the inlet and outlet air sample ports is achieved by the mercury analyser. A peripheral device using a solenoid valve directs the sample to a specific cartridge of the analyser. Hence, the analyser does sequential measurement of the ports. The mercury gas exchange fluxes across the interfaces (surface-atmosphere) (ng/m²/h) are computed using the mass balance of mercury within the flux chamber.

Mercury flux across the water surface was modelled using a two-layer model. The two-layer model is a convenient but not necessarily a mechanistically accurate model, which depends on empirical relationships reported for other chemicals. The model is based on the saturation of mercury within the layers with respect to Henry's law and the overall mass transfer coefficient (air and water). Since Henry's law for mercury is high, most of the resistance to gas exchange lies in the water film (> 99%). There are two main conditions required to apply the model: (1) the chemical does not undergo any reaction within the layers; and (2) the concentrations at the boundaries of the layers are kept constant long enough that the concentration profile reaches a steady state. The model was applied to estimate the mercury flux (ng/m²/h) during cruises on Lake Ontario and the St. Lawrence River. Mercury surface-atmosphere gas exchanges in Lake Ontario/St. Lawrence River ecosystem vary in space and time. Gaseous mercury deposition in Lake Ontario/St. Lawrence River ecosystem varied between 0 and 4.66 ng/m²/h whereas mercury evasion varied between 0 and 9.28 ng/m²/h. Overall, the median mercury evasion value is 0.77 ng/m²/h which is one order magnitude larger than median deposition (0.075 ng/m²/h). In summertime, total deposition flux over soil surface is counterbalanced by mercury re-emission flux. However, during wintertime, only dry deposition over snow surface is counterbalanced by volatilisation. Hence, mercury snow deposition during wintertime might have a huge impact on the ecosystem especially during the springtime through the influence of the melt water on aquatic biota. Many mercury gas exchange observations in fluvial wetlands in the Lake Saint-Pierre (baie Saint-François) suggested larger emissions over dry wetland than flooded wetland (0.83 vs. 0.52 ng/m²/h). Hence, flooded wetlands offered conditions that contributed to competition between mercury volatilisation and methyl mercury formation or immobilisation as mercury sulphide (cinnabar).

FR:

Cet article discute des aspects chimiques et physiologiques du devenir des composés organométalliques chez les organismes aquatiques et est basé sur les résultats de travaux ayant porté sur la pharmacocinétique et l'organotropisme du tributylétain (TBT) et du méthylmercure (MeHg) ingérés avec la nourriture chez deux prédateurs benthiques : la plie canadienne (Hippoglossoides platessoides) et le crabe des neiges (Chionoecetes opilio). Les principales observations ont été les suivantes;

- 1^o l'efficacité d'assimilation (EA) du MeHg est élevée (ca. 90 %) et il est lentement (t₀.95 " 40 d) et uniformément distribué dans l'organisme de la plie et du crabe,

- 2^o la demie-vie biologique du MeHg est beaucoup plus longue que celle du TBT (t₀.5 " 600 d et 50 d, respectivement), et ce pour les deux espèces,

- 3^o la plie canadienne assimile moins efficacement le TBT que le crabe des neiges (EA=47 % et 92 %, respectivement),

- 4^o le TBT est rapidement (t₀.95=7 d) et uniformément distribué dans l'organisme de la plie canadienne, alors que chez le crabe des neiges une faible fraction de la dose de TBT administrée avec la nourriture est retrouvée dans les tissus autres que l'hépatopancréas.

Certaines de ces observations peuvent être conciliées en tenant compte des propriétés physiques et chimiques du TBT et du MeHg, tels que l'encombrement stérique, la stabilité en milieu biologique, et l'affinité pour certains ligands biologiques. Cependant, des facteurs physiologiques doivent être invoqués pour concilier d'autres observations, comme l'étendue et la vitesse de la distribution du TBT chez la plie canadienne comparativement au crabe des neiges. Par exemple, bien que le TBT soit métabolisé au niveau hépatique chez les deux espèces, la structure du système dans lequel le TBT est distribué diffère fondamentalement. Ainsi, chez la plie canadienne, une importante proportion du TBT absorbé est distribuée à l'ensemble de l'organisme sans être capté par le foie, site de métabolisation, alors que chez le crabe la totalité du TBT absorbé doit d'abord traverser le site de métabolisation, l'hépatopancréas, avant d'être distribué au reste de l'organisme. Dans ce dernier cas, ceci peut avoir pour résultat de limiter le transfert du TBT vers les tissus autres que l'hépatopancréas. Ces résultats montrent que les facteurs ayant une influence dominante sur le transfert trophique et le devenir des organométaux chez les prédateurs benthiques peuvent différer selon le composé considéré; du fait de sa stabilité, le devenir du MeHg semble être presqu'exclusivement contrôlé par ses propriétés chimiques, alors que dans le cas du TBT ce sont les 'propriétés physiologiques' des organismes considérés qui ont une plus grande influence sur son devenir.

EN:

It is well known that the physical and chemical characteristics of an organometal determine its fate within a given aquatic organism. The extent of uptake and the body distribution of a given organometal can vary greatly from one animal species to another. However, the effects of both chemical and physiological factors have rarely been considered simultaneously. This paper presents the results of a study on the pharmacokinetics and tissue distribution of dietary [¹¹³Sn]tributyltin (TBT), and [²⁰³Hg]methylmercury (MeHg) in a coastal benthic fish, the American plaice (Hippoglossoides platessoides), and a coastal benthic crustacean, the snow crab (Chionoecetes opilio). The main observations were:

- the assimilation efficiencies (AE) of MeHg for the plaice and the snowcrab were high (88% ± 8 and 94% ± 4, respectively), and it was slowly and uniformly distributed within the body of both American plaice and snow crab (t₀.95=35 ± 4 d and 42 ± 38 d, respectively);

- the biological half-life of MeHg was longer than that of TBT (t₀.5 " 600 d and 50 d, respectively) for both species;

- the assimilation efficiency of TBT was lower for the plaice than for the crab (47% ± 7 and 92% ± 12, respectively);

- TBT was rapidly (t₀.95=7 ± 2 d) and uniformly distributed in the American plaice, whereas only a minor fraction of the dose administered to snow crab reached tissues other than the hepatopancreas.

These observations can be explained if physical and chemical properties of TBT and MeHg are taken into account, as well as the physiological properties of the two organisms. Chemical factors can explain some of the differences observed. For example, the lower AE values of TBT compared to MeHg in the American plaice may be due to steric factors. The much longer half-life of MeHg is due to its higher stability in biological media compared to TBT. The high affinity of MeHg for sulfhydryl groups, that are ubiquitous in living tissues, is most likely responsible for its uniform distribution in the body of both American plaice and snow crab. However, physiological factors must be considered to explain the more uniform and faster rate of distribution of TBT in the American plaice, when compared to the snow crab. Though hepatic metabolism of TBT occurs in both species, the physiological systems of the plaice and the snowcrab are fundamentally different. Fish are characterised by a mammillary structure (peripheral compartments connected in parallel to a central one), whereas crustaceans are characterised by a caternary structure (compartments connected in series only to their nearest neighbours) (see below). In the American plaice, binding of TBT to plasmatic proteins likely prevents its efficient removal from blood by the liver, resulting in a large proportion of the TBT dose being distributed throughout the body.

In the snow crab, TBT must first go through the site of metabolism before diffusing into the hemolymph for subsequent distribution to other tissues. This may limit the transfer of TBT or its metabolites to tissues other than the hepatopancreas. These results suggest that there are different factors influencing the fate of organometals ingested by benthic predators. Because of its stability, it appears that the fate of MeHg is almost exclusively controlled by its chemical properties (i.e., its exceptional affinity for SH groups). In contrast, the physiological properties of the organisms appear to be a more important determinant of the fate of TBT. These observations illustrate the need to consider the trophic transfer of organometals from a multidisciplinary point of view.