We have developed a regional mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental mercury (Hg0), divalent mercury (Hg2+), and methyl mercury (MeHg), in a five compartment environment (air, water, sediments, periphyton, and benthos). Our first objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. Our second objective was to construct a dynamic mass balance model to predict and hindcast mercury concentrations in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model in STELLA®. The inflow of mercury was the major source to this system, accounting for 0.42 mol month-1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month-1, or 63.6% of all losses, and sediment deposition was 0.12 mol month-1, or 27.3% of all losses. The dynamic mass balance model provides estimated results that are consistent with measured data and predicts historical local industrial emissions to be approximately 400 kg year-1. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates. This model is useful for predicting and hindcasting mercury concentrations in other aquatic environments because it contains the three main environmental compartments, all forms of mercury, and compartments (e.g. periphyton) not included in previous mercury multi-media models.

St. Barnabé fault, in St. Hyacinthe plain of the St. Lawrence lowlands, was postulated by Clark (1947) on his geological study of this area. Structural features of this type are of great interest to the geophysicist to establish relation between physical quantities measured at the surface and geometry of such structures. A subsurface fault can be diagnosed, under density contrast condition, with surface gravity measurements. The present detailed gravity survey was undertaken to determine if such a condition existed, to correlate geological information with gravity data, and to assess this data in terms of possible parameters of the fault structure. The field work was carried out in the summer months of 1964 with a Worden gravimeter. [...]

Certaines observations suggèrent une influence de la vallée du Saint-Laurent sur la distribution des averses à sa surface. D'autre part, depuis quelques années, les membres du "'Stormy Weather Group" ont enregistré sur films de 35-mm les échos apparaissant sur un écran de radar doté d'un indicateur panoramique à altitude constanto (IPAC). L'utilisation de ces films permet à l'auteur d'approfondir le sujet par l'identification des premiers échos et le tracé de leur trajectoire subséquente. Des dossiers, établis pour 76 premiers échos, relient ceux-ci à la surface et au profil du terrain. [...]

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We have developed a regional mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental mercury (Hg0), divalent mercury (Hg2+), and methyl mercury (MeHg), in a five compartment environment (air, water, sediments, periphyton, and benthos). Our first objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. Our second objective was to construct a dynamic mass balance model to predict and hindcast mercury concentrations in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model in STELLA®. The inflow of mercury was the major source to this system, accounting for 0.42 mol month-1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month-1, or 63.6% of all losses, and sediment deposition was 0.12 mol month-1, or 27.3% of all losses. The dynamic mass balance model provides estimated results that are consistent with measured data and predicts historical local industrial emissions to be approximately 400 kg year-1. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates. This model is useful for predicting and hindcasting mercury concentrations in other aquatic environments because it contains the three main environmental compartments, all forms of mercury, and compartments (e.g. periphyton) not included in previous mercury multi-media models.

A sequential procedure for the extraction of iron hydroxides and the associated phosphate in estuarine seston is proposed. The procedure which uses a citrate-dithionite-bicarbonate (CDB) reagent has been chosen among five commonly used methods. It makes it possible to distinguish four statistically different modes of association between P and Fe based on the (Fe/P)$ sb{ rm CDB}$ values. The extraction sequence is applied to suspend particulate matter and to surface sediments of the Saint-Lawrence Upper Estuary. The intensity and the position of the core of its maximum turbidity zone is determined by sediment exchanges between the channel and large intertidal flats. These exchanges are controlling seasonal fluctuations observed in the estuarine phosphorus geochemistry: The fresh to salt water early transition zone is the main site for the flocculation and deposition of river derived colloids, mainly as surface coating on particle, a process which results in phosphate adsorption on the suspended matter; After this process has reached equilibrium in the water column, partial desorption occurs on the flats as the particles settle temporarily in spring and summer. The P-depleted solids are returned to the estuary when the marsh vegetation is destroyed in the fall by migrating snow geese. Laboratory experiments with natural materials confirm the equilibrium level of P-adsorption observed in situ, and evidence its reversibility under the low reducing conditions typical of marsh surface sediments.

We have developed a regional mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental mercury (Hg0), divalent mercury (Hg2+), and methyl mercury (MeHg), in a five compartment environment (air, water, sediments, periphyton, and benthos). Our first objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. Our second objective was to construct a dynamic mass balance model to predict and hindcast mercury concentrations in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model in STELLA®. The inflow of mercury was the major source to this system, accounting for 0.42 mol month-1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month-1, or 63.6% of all losses, and sediment deposition was 0.12 mol month-1, or 27.3% of all losses. The dynamic mass balance model provides estimated results that are consistent with measured data and predicts historical local industrial emissions to be approximately 400 kg year-1. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates. This model is useful for predicting and hindcasting mercury concentrations in other aquatic environments because it contains the three main environmental compartments, all forms of mercury, and compartments (e.g. periphyton) not included in previous mercury multi-media models.

Note: Some illustrations out of order in manuscript.

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