Project: Effects of Climatic Conditions and Fluctuating Water Levels on St. Lawrence River Wetlands

PROJECT
Effects of Climatic Conditions and Fluctuating Water Levels on St. Lawrence River Wetlands

Program: Impacts of Level and Flow Fluctuations in the St. Lawrence River

Objectives

The aim of this project is to assess the effects of climate change, as well as fluctuating water levels and discharges on the wetlands of the St. Lawrence River, particularly their distribution, diversity and productivity.

The effects of low water levels in the river were seen in Boucherville, June 1999

Wetlands Under the Influence of Climatic and Hydrological Conditions

Wetlands are important habitats for amphibians, fish, waterfowl and mammals alike. The water levels of the St. Lawrence River have a major impact on the surface area occupied by aquatic plants, as well as their biomass and composition in these environments (Hudon 1997). Climatic and hydrological conditions, which regulate water levels, thus have a predominant influence on the characteristics of wetlands.

Plant community on Île aux Cerfeuils, in the Repentigny archipelago

Beginning in September 1998 and throughout 1999, the flow rate of the St. Lawrence River fell dramatically. This phenomenon recurred in the summer of 2001, when the water level fell to below chart datum. The decreased water level dried out the littoral area normally colonized by emergent and submergent plants, exposing vast expanses of bare mud. During the summers of 1999 and 2001, the extremely low water levels led to drought conditions that were particularly hard on riparian vegetation. Riverbeds were exposed to the chill air in fall and winter, subjecting plants to freezing and drying conditions to which they were unaccustomed.

Low levels in the St. Lawrence River at Boucherville, August 1999

Exposed Sagittaria and water lilies

Relationship between climate, water level and productivity

A thorough knowledge of the relationship between light penetration and the maximum colonization depth of macrophytes is necessary to predict the depth beyond which light is insufficient for plant growth, and to assess the surface area effectively colonized by aquatic plants. Biomass is a measure of the abundance of aquatic vegetation, either the total mass of living plant material calculated by volume (mg/L) or by surface area (mg/m²).

How do Climatic and Hydrological Conditions Affect Wetlands?

As a follow-up to the project on Temporal Dynamics of Aquatic Plant Communities in the St. Lawrence River: Short-term and Medium-term Effects of Low Water Levels, research scientists at Environment Canada are working on the present project to assess changes related to:

Species composition and distribution of plant communities;
The introduction and proliferation of plant species; and
The biomass and productivity of wetlands.

Researchers will also attempt to assess how long it takes for wetlands to recover or adapt and the state toward which plant populations evolve according to the water level conditions of the St. Lawrence River. Different mathematical models will be used to assess changes in the biomass, productivity, distribution and diversity of the wetlands of lakes Saint-Pierre and St. Lawrence; the effects of these changes on pleasure boating on Lake Saint-Louis as a function of high, medium and low water level conditions will also be examined.

Lake Saint-Pierre

Lake Saint-Louis

These results will help in integrating knowledge about plant communities (phytoplankton, periphyton, submergent and emergent plants) with knowledge about the physical environment (climate, hydrology) and chemistry (water masses) of the St. Lawrence River from a quantitative and predictive perspective. A better understanding of wetlands and of their response to environmental conditions will enable researchers to anticipate the consequences of climate change and thus better manage of the outflow from Lake Ontario to the St. Lawrence River.

Literature

Gosselain, V., C. Hudon, A. Cattaneo, P. Gagnon, D. Planas and D. Rochefort. 2005. Physical variables driving epiphytic algal biomass in a dense macrophyte bed of the St. Lawrence River (Quebec, Canada). Hydrobiologia 534: 11–22.

Hudon, C. 2004. Shift in wetland composition and biomass following low-level episodes in the St. Lawrence River: Looking into the future. Canadian Journal of Fisheries and Aquatic Sciences 61(4): 603–617.

Hudon, C. 1997. Impact of water level fluctuations on St. Lawrence River aquatic vegetation. Canadian Journal of Fisheries and Aquatic Sciences 54(12): 2853–2865.

Hudon, C., S. Lalonde, and P. Gagnon. 2000. Ranking the effects of site exposure, plant growth form, water depth, and transparency on aquatic plant biomass. Canadian Journal of Fisheries and Aquatic Sciences 57 (Suppl. 1): 31–42.

Marie-Victorin, F.E.C. 1943. La Flore Laurentienne. Third edition. Les Presses de l'Université de Montréal.