Concentrations and transport of trace metals in the St. Lawrence River

Samples of raw water were collected in the St. Lawrence River during six sampling trips from August 1990 to April 1992. Water samples were analyzed for both dissolved and particulate phases for five trace metals. Partition coefficients (Kd) and metal fluxes were calculated in order to determine metal transport. A mass balance equation was used for the determination of the major metal sources to the St. Lawrence River and an estimation of metal loadings to the estuary was made. Average dissolved metal concentrations were found to be Cd 10 ng/L, Co 74 ng/L, Cu 64 ng/L, Fe 69 µg/L and Mn 700 ng/L. Particulate concentrations were (in µg/g) 1.68 for Cd, 31 for Co, 73 for Cu, 25 mg/g for Fe and 1.69 mg/g for Mn. Co, Fe and Mn were transported essentially in the particulate phase while Cd and Cu were predominantly found in the dissolved phase at 56% and 48% of the total metal concentration respectively. Log Kd values varied from 5.1 (for Cu) to 6.8 (for Mn). In the dissolved phase the major sources were found to be the Great Lakes and the Ottawa River whereas in the particulate phase Québec tributaries appear to be the most important. Industrial inputs are quite important in both the dissolved and the particulate phases for Cd, whereas other sources are very variable, especially for the dissolved phase.     

Physically Based Groundwater Vulnerability Assessment Using Sensitivity Analysis Methods

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability assessment considered here is based on the calculation of sensitivity coefficients for a user‐defined groundwater state for which we propose several physically based indicators. Two sensitivity analysis methods are presented: the sensitivity equation method and the adjoint operator method. We show how careful selection of a method can significantly minimize the computational effort. An illustration of the general methodology is presented for the Herten aquifer analog (Germany). This application to a simple, yet insightful, case demonstrates the potential use of this general and physically based vulnerability assessment method to complex aquifers.     

Small scale study of groundwater flow in a fractured carbonate-rock aquifer at the St-Eustache quarry, Québec, Canada

A small-scale hydrogeological study was conducted in a fractured carbonate-rock aquifer located in a quarry to relate groundwater flow to the fracture network. The field study in the St-Eustache quarry, which integrates structural surveys, well logging and hydraulic tests, showed that the most important features that affect groundwater flow in the sedimentary aquifer are high hydraulic conductivity horizontal bedding planes. Vertical fractures are abundant in the quarry and throughout the region, but they have a minor effect on groundwater flow. To have a significant impact on the flow regime and lead to vertical groundwater flow, the permeability of all vertical joints need to be enhanced compared to what was generally observed at the site. Such an increase in permeability could potentially occur where dissolution and fracturing is more intense or at stress release locations such as near the surface in the quarry.     

Assessment of paleo-recharge under the Fennoscandian Ice Sheet and its impact on regional groundwater flow in the northern Baltic Artesian Basin using a numerical model

The study investigates the mechanism of glacial meltwater recharge under the Fennosciandian Ice Sheet during the last glacial maximum (LGM) and its impact on regional groundwater flow in the northern Baltic Artesian Basin (BAB) in Estonia and Latvia. The current hypothesis is that a flow reversal occurred in the BAB due to subglacial recharge during the LGM. This hypothesis is supported by an extensive dataset of geochemical and isotopic measurements in the groundwater of northern Estonia, exhibiting significant depletion in δ¹⁸O with respect to modern precipitation. To verify the consistency of this hypothesis and better understand groundwater flow dynamics during the LGM period, a numerical model is developed for this area. Two cross-sectional models have been created across the northern BAB, in which groundwater flow and the transport of δ¹⁸O have been simulated from the beginning of the LGM to present-day. Several simulations were performed with different subglacial boundary conditions, to investigate the uncertainty related to subglacial recharge of meltwater during the LGM and the subsequent flow reversal in the northern BAB. Several simulations provide a satisfying fit between computed and observed values of δ¹⁸O, which means that the hypothesis of subglacial recharge of meltwater is consistent with δ¹⁸O distribution. The numerical model suggests that preservation of meltwater in northern Estonia is controlled by confining layers and the proximity to the outcrop area of aquifers, located in the Gulf of Finland. The results also suggest that glacial meltwater has been preserved under the Baltic Sea in the Gulf of Riga.     

The geoarchaeology and traditional knowledge of winter sod houses in eastern Hudson Bay,Canadian Low Arctic

A multidisciplinary study was undertaken at the Qijurittuq Site (IbGk‐3) on Drayton Island in Low‐Arctic Quebec (Canada) to document the relationships between climatic, environmental, and cultural changes and the choice of Thule/Inuit dwelling style in the eastern Arctic. Several marine terraces were ¹⁴C‐dated with shells in order to reconstruct the area's uplift (glacioisostatic rebound) curve. Plant macrofossil analysis of peat was conducted to reconstruct past vegetation and, indirectly, past climate. Archaeological surveys and excavations characterized the structure of subterranean sod houses at the Qijurittuq Site and were supplemented with open interviews with Inuit elders for a better understanding of site location and the use of household space. The sites selected for habitation were well‐drained sandy marine terraces in a valley sheltered from prevailing winds. Sod houses were in turn made possible by the abundance of driftwood on the island and the presence of nearby peatland. Thule/Inuit people used semi‐subterranean houses rather than igloos at the Qijurittuq Site during the dry, cold conditions toward the end of the Little Ice Age. Stable environmental conditions and food supply during winter possibly explain the use of those semipermanent houses on Drayton Island. However, it does not exclude the use of igloos during short expeditions on ice. © 2011 Wiley Periodicals, Inc.