Floods and water quality in Canada: A review of the interactions with urbanization, agriculture and forestry

Water quality remains a major issue in Canada. This paper reviews recent research on the impacts of urbanization, agriculture and forestry on water quality in Canada. Specific water quality issues such as mining, sewage treatment and waste treatment are not included in this paper. For each land use, a brief summary of the dominant processes linking runoff to water quality is provided and recent findings are summarized. With respect to urbanized watersheds, the relatively large proportion of impervious areas, lower vegetation cover and the presence of high-density drainage systems alter surface water routing and timing of peak flows. High concentrations of heavy metals are considered to be the most important water quality problem in urban runoff, but nutrients, pathogens, concentration of pharmaceuticals and water temperature also often contribute. In watersheds dominated by agricultural activities, overland flow is an important vector of pollutants, but subsurface flow such as macropore and tile-drain flows also play a role in the alteration of water quality during or after high runoff events. Nutrients, pesticides, pathogens and sediments remain important topics of research in agricultural watersheds, and the modelling effort has significantly increased in the last few decades. Beneficial management practices (BMPs) are being tested and applied at a local scale, mostly on experimental watersheds. Forestry-related activities also affect water quality. In forested watersheds, studies have been ongoing for many decades, but have decreased in intensity in the last 15 years. Sediment delivery and water temperature can be strongly affected in watersheds with significant clear-cut logging and riparian buffer strips and sylviculture remain the main mitigation BMPs. There is a need for an increase in the monitoring effort for most water quality variables in Canada. The authors recommend that flow-dependent monitoring frameworks should be further developed and implemented in the future.