Impacts of Urban Land Use

Rideau Canal, OttawaWhen converted from its natural condition, urban land use can cause several impacts on the downstream water body. These impacts include eroding natural streambanks, water quality, elimination of groundwater recharge and its implications on stream baseflows, and the presence of persistent contaminants from urban non-point sources.

Another important impact of urban areas to the hydrologic cycle is the effect of impermeable surfaces. The built-up nature of the city means that asphalt and concrete replace the soil, buildings replace trees, and the catch basin and storm sewer have replaced the streams of the natural watershed. Impermeable surfaces such as roads, sidewalks, driveways and buildings do not allow water to pass through them so it can not infiltrate into the soil. Instead water flows quickly over these surfaces as runoff. Runoff is water that runs along the surface of the ground into nearby stormsewers or directly into water bodies. When water flows as runoff, it picks up oil, salt, dog poop, pesticides and a host of other pollutants. Most of the pollutants that reach our river arrive through runoff. However, modern stormwater management practices can mitigate some of the potential damage on surface water resources.

Adapted from Environment Canada's The State of Canada's Environment Report

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Impacts of Industrial Land Use

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Impacts of Agricultural Land Use

Farmland applications of pesticides and fertilizers can contaminate surface waters if applied too generously. Manure, fertilizers and sewage are major sources of nitrogen, phosphorus and bacteria contamination in surface waters. Water supplies contaminated with manure contain fecal coliform bacteria, such as E. Coli. Other disease-causing microorganisms such as Cryptosporidium and Giardia in drinking water can pose a threat to public health and that of livestock.

Added nutrients from sewage, manure, and fertilizer runoff can also lead to eutrophication, causing algae and pond scum, which interfere with water use for fisheries, recreation, industry, agriculture and drinking.

This type of water pollution can be reduced through best management practices to protect water quality.

Pesticides, sediments and pharmaceuticals in runoff water from urban and rural land use may also affect water quality.

Agriculture accounts for 9% of total water withdrawals. The water is mainly used for irrigation, but also for livestock watering. Because of the high rate of evapouration from agricultural fields, irrigation is a highly consumptive use (i.e. very little of the water withdrawn for irrigation is returned to its source).

More efficient irrigation methods help to conserve water, and more accurately matching fertilizer and manure application rates to crop requirements also help to reduce surface water contamination.

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Adapted from Statistics Canada's Human Activity and the Environment, p164; and the Alberta Government's Impact of Land Use on Water.

Impacts of Commercial Forestry

Undisturbed forests efficiently cycle water, with very small losses to surface and groundwaters. Streams draining undisturbed forest generally have high water quality with low concentrations of dissolved nutrients and suspended sediments.

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Adapted from Freshwater website's The Role and Contribution of Natural Resources Canada, Water Issues and Forests