Progress in scientific studies of groundwater in the hydrologic cycle in Canada, 2003-2007

Canadian Water Resources Journal, Summer, 2009 by Masaki Hayashi, Garth van der Kamp

Introduction

Canadian hydrologists have a long-standing tradition of making fundamental contributions to the science of groundwater as it relates to the hydrologic cycle, such as the concept of nested flow systems (Teth, 19e3), physically-based distributed hydrological models (Freeze and Harlan, 1969; Freeze, 1974) and tracerbased hydrograph separation (Sklash and Farvolden, 1979). Since groundwater science has a wide variety of applications in diverse fields of knowledge, it is impractical to cover all aspects of Canadian groundwater research in a short review. Therefore, the scope of this paper is limited to scientific studies of groundwater in the context of the hydrologic cycle, excluding those studies that are primarily focused on groundwater contamination, water resource evaluation, and other engineering aspects of groundwater. The objective is to identify recent trends and to highlight the progress made in Canada during 2003-2007 as part of the overall summary of Canadian hydrology in 2003-2007, prepared by the Canadian National

Committee for the International Association of Hydrological Sciences. As such, the paper is not meant to be a complete review of all relevant studies. Compendiums of progress summaries of this kind have previously been published for other aspects of Canadian hydrological research in 2000 and 2005 (e.g., Buttle et al., 2005; Price et al., 2005), but these did not include a report specifically dealing with groundwater research.

To achieve the objective within the limited time and resources available, we sent a request to 24 hydrogeologists in different regions across Canada in May 2007, asking them to send us their contributions and also forward our request to other hydrogeologists in their region and organizations. It is estimated that our request was received by well over 100 hydrogeologists across Canada from universities, government organizations, and the consulting community. Contributions were received from 20 hydrogeologists. These were supplemented by our own knowledge of the recent literature and suggestions made by the reviewers. The following review is primarily based on refereed journal papers, although some conference proceedings and technical reports are cited as appropriate. Upon examining numerous papers, common themes (see below) were found in many of the papers, which represent the recent trends in Canadian groundwater research in the context of the hydrologic cycle.

Interaction between Groundwater and Surface Water

The interaction between groundwater and surface water is a focal point of groundwater hydrology. The number of researchers studying groundwater-surface water (GW-SW) interaction has been increasing over the past decade. Interests in GW-SW interaction are partly driven by practical needs to understand the effects of contaminated groundwater discharging into surface water and the extraction of groundwater from aquifers connected to rivers. It is also driven by ecohydrological interests, such as the role of groundwater in maintaining aquatic habitats. The increased research activity in GW-SW interaction is consistent with the international trends. Over the past decade, it has been widely recognized that the sustainable management of groundwater requires the consideration of groundwater contributions to streamflow, which maintain the baseflow and support the ecological function of streams (NeffetaZ, 2005).

Aquifers in fluvial deposits adjacent to streams are considered under the influence of surface water and are used by many municipalities in Canada as water supply source, prompting studies to understand the effects of pumping on river flow regime and on the quality of surface water as it is filtered through the sediments before reaching the well. The Fredericton Aquifer underlying the St. John River in New Brunswick is an example of a fluvial aquifer recharged by the infiltration of riverwater. Geophysical studies revealed that the river was recharging the aquifer through an irregular-shaped permeable "window" where the aquitard between the river bed and the aquifer had been removed by erosion (Al et al., 2005; Dawe and MacQuarrie, 2005). Infiltration of river water with high dissolved organic carbon was causing reductive dissolution of manganese in the aquifer, indicative of the complex geochemical nature of GW-SW interactions (Petrunic et al., 2005).

It has been recognized that the discharge and recharge of groundwater through streambeds is highly variable even over a small scale, which leads to the necessity of 'mapping' groundwater flux with sufficient detail. In addition to geophysical methods (Al et al., 2005), streambed temperature can be used as an effective tool to delineate zones of discharge and recharge. For example, Conant (2004) mapped groundwater discharge zones in the Pine River in Ontario as the zones of relatively low temperature in summer and high temperature in winter, and showed that the geological variation at depths plays a key role in determining the occurrence of discharge zones. Similar principles were used by Alexander et al. (2003) in a section of the Catamaran Brook in New Brunswick, where upland recharge in a clear-cut patch was contributing to groundwater discharge into the streambed. They found that the water temperature in the streambed (i.e., the hyporheic zone) was more strongly influenced by the temperature of groundwater at depth than by air temperature. Bustros-Lussier and Robin (2007) used a drag probe to map water temperature and electrical conductivity at the sediment-water interface in rivers near Ottawa, Ontario and detected the areas of high groundwater discharge.