Section 3: Drainage region profiles
Canada’s abundant freshwater is provided through a wide variety of ecosystems across a broad range of landscapes. These ecosystems can be large and complex, creating significant challenges in assessing how changes in land cover and climatological factors, among other drivers of change, affect the supply of freshwater.
This section provides maps, tables and charts on water supply and demand, land cover, population, nutrients and selected other factors influencing the provision of freshwaterNote 1 for each of Canada’s 25 drainage regions. Taken together, these data can help provide information on potential risks to water supply within drainage regions. See Textbox 3.1 for more information.
Drainage region profiles
Saint John–St. Croix
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Landscape modifications influence how ecosystems function and provide freshwater. Areas with more people, activities and infrastructure are generally more degraded from their natural state. Shorelines and waterways are modified by dams, culverts and diversions; roads, roofs, parking lots and other impermeable or disturbed surfaces increase runoff of sediment and contaminants into water bodies.Note 2 Some of the main factors of interest to understand this degradation include population densities, land cover and land use, and nutrient inputs.
The majority (98%) of Canada’s population is concentrated in the south of the country, with large expanses of the landscape in the central and northern portions of Canada remaining virtually uninhabited.Note 3 The St. Lawrence and Great Lakes drainage regions have the highest population densities at 59.9 and 54.7 people per square kilometre, as well as the highest proportions of built-up area at 5.0% and 3.5% (Tables A.2 and A.1).
Landscapes in the prairie drainage regions have the largest proportions of arable land and natural land used for pasture (Table A.1). Drainage regions with the highest densities of linear infrastructure such as roads, pipelines, transmission lines and railroads include the St. Lawrence, Red–Assiniboine and Great Lakes (Table A.1).
While there are many different contaminants that can have an impact on water quality, nutrient pollution is one of the most widespread issues in Canada and around the world. Much of the nitrogen and phosphorus come from commercial fertilizers and manure that run off the land into water bodies or leach into groundwater, but other major sources include wastewater and stormwater, as well as nitrogen releases to air from motor vehicle use, oil and gas production, electrical power generation and other activities.Note 4
The largest fertilizer application areas were found in the Assiniboine–Red, South Saskatchewan and North Saskatchewan drainage regions (Table A.1). Some of the highest amounts of residual soil nitrogenNote 5 or phosphorus potentially released from agricultural soilsNote 6 in 2011 occurred in areas that have historically had intensive agriculture, including parts of the Fraser–Lower Mainland, South Saskatchewan, Assiniboine–Red, Great Lakes, St. Lawrence and Maritime Coastal drainage regions (Maps 3.1 and 3.2, Table A.3).
In 2014 there were 754 thousand tonnes of nitrogen and 40 thousand tonnes of phosphorus released from industrial facilities to air, land and water across Canada (Table A.3). Wastewater discharges from industrial facilities, including wastewater treatment plants, can have varying impacts on the receiving aquatic ecosystems depending on the type of treatment, effluent quality, volume of discharge and the receiving water body. In 2012, over 3,700 wastewater systems in Canada generated an estimated 6 trillion litres of wastewater, of which over 150 billion litres may have been untreated. Of these systems, 849 were identified as needing upgrades to meet national effluent quality standards and 136 were considered high risk systems.Note 7
Turbidity measures of source water for drinking water production were highest in the Lower Saskatchewan–Nelson, North Saskatchewan and Assiniboine–Red drainage regions in the Prairies and in the St. Lawrence drainage region (Table A.3). Turbidity data collected by treatment plant operators help establish historical trends concerning source water conditions. Data on land cover and land use change in the surrounding and upstream environment can provide information on how people contribute to changing turbidity levels.
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