Many different criteria are used to evaluate water quality in the St. Lawrence; these criteria relate to such things as the protection of aquatic life, drinking water and swimming. The relationships between the river ecosystem and the quantity of water that passes through it seem to be less well known, however. Water availability and seasonal fluctuations in water levels on the St. Lawrence are major issues that must be dealt with, particularly if inflows from the Great Lakes Basin are reduced, as most climate models predict. This may jeopardize the protection of biological resources and the maintenance of a wide variety of river uses, due to the absence of the specific water level conditions they require.

The water level subcommittee was established to increase our knowledge of the impact of water level fluctuations on the freshwater St. Lawrence ecosystem (between Cornwall and Quebec City). The committee consists of representatives of Environment Canada (the Canadian Wildlife Service, Canadian Meteorological Centre and the St. Lawrence Centre) and the Société de la faune et des parcs du Québec, who work in partnership with the university community. The committee’s objectives are to acquire the knowledge required to predict the effects of water level fluctuations and, secondly, to develop tools that integrate the responses of different ecosystem components, according to different water level fluctuation scenarios.

The subcommittee’s multidisciplinary character is one of its greatest assets. Experts from fields as wide ranging as biology, engineering, geography, sedimentology and social economics work together on projects, and in close collaboration with modelling and geographic information system specialists. Contributions from each of these disciplines are essential in establishing an integrated vision of the effects of water level fluctuations on the ecosystem.

Water level variations help to maintain and renew the wetlands along the St. Lawrence by insuring the survival of plant species specifically adapted to a regime of flooding in spring and low water levels in summer. A number of studies have been carried out on submergent and emergent vegetation to better understand wetland dynamics.

For example, the Canadian Meteorological Centre is working on a model of the biomass and species composition of submergent and emergent plant communities and their effects on currents, waves and sediments. Concurrently, the St. Lawrence Centre has been monitoring plant growth annually at a number of sites along the river since 1993. The goal of these annual studies is to determine if the low water levels observed since 1998 have resulted in the disappearance or proliferation of certain species of aquatic plants and to evaluate how quickly plant communities are adapting to various water level conditions. The study will also allow us to determine the extent to which opportunistic terrestrial plants have colonized dried-up wetlands.

Wetlands, of course, are not only intrinsically valuable but are used by a wide variety of fishes, amphibians, birds and mammals, which feed or take shelter there at various stages of their life cycle. The northern pike, one of the fish species that frequents the St. Lawrence floodplain, is being studied by the Société de la faune et des parcs du Québec and Environment Canada. The purpose of the research project is to determine how extreme water levels may modify the area of the floodplain and thus affect reproductive success and population dynamics in this species. During the study, natural and managed habitats for the main species of fish inhabiting the floodplain and river corridor (such as northern pike, yellow perch, walleye, white sucker, lake sturgeon and chubs) will also be mapped.

Lake St. Pierre is a crucial staging area for waterfowl during spring migration. Insufficient water levels may result in decreased reproductive success in some species. The Canadian Wildlife Service is carrying out a study to determine, among other things, the effects of water levels on the distribution of habitats around Lake St. Pierre and to ascertain optimum water levels for waterfowl.

Environment Canada is also conducting research on the interactions between water level variations and bank erosion on the St. Lawrence. This is a particularly complex subject, since erosion can be attributed to various factors, both natural (wind and ice) and manmade (shipping), the intensity of which varies with the season and water level conditions. Erosion is particularly severe on a number of islands between Montreal and Sorel which provide prime habitat for the river’s aquatic and terrestrial fauna.

In addition, the St. Lawrence Centre is evaluating the vulnerability of boat launches and other types of water access and pleasure boating infrastructures to water level variations. Indeed, pleasure boating is an important recreational and tourism activity in riverside communities. Due to shallow water or the proliferation of submergent aquatic plants, boat launches, piers and wharves may become unusable.

In conclusion, although only some of the projects carried out by the water level subcommittee are described here, the wide range of subjects dealt with eloquently illustrates the diversity of resources and uses that may be affected by water level fluctuations. The knowledge acquired in these projects will be used to provide data for the models. The ultimate goal of the models is to predict, based on various extreme scenarios, the effects of water level fluctuations on the components of the St. Lawrence ecosystem.

Christiane Hudon
St. Lawrence Centre
Telephone: (514) 283-6195
Email: christiane.hudon@ec.gc.ca

Marc Mingelbier
Société de la faune et des parcs du Québec
Telephone: (418) 521-3955, ext. 4486
Email: marc.mingelbier@fapaq.gouv.qc.ca

Jean Morin
Canadian Meteorological Centre
Telephone : (418) 649-6017
Email: jean.morin@ec.gc.ca