Water contamination by coliforms

Summary

• Animal manure is an important and valuable fertilizer source. However, pathogens in manure, like coliforms, can contaminate surface waters and impact environmental and human health.
• The Water Contamination by Coliforms Indicator estimates the risk that coliforms will contaminate waterways and how this risk has changed over time.
• In 2016, 3.6% of farmland was rated as having a high or very high risk of water contamination by coliforms. Areas of high risk occurred mainly in Alberta and British Columbia, primarily because of intensive cattle production.
• Between 1981 and 2016, risk did not change in most areas of Canada. However, risk increased in some areas and decreased in others because of changes in the concentration of animal production.
• In high-risk areas, the risk of water contamination by coliforms can be decreased by reducing manure per animal and by diminishing the likelihood of manure transport to waterways (for example, by preventing cattle access to waterways, reducing soil water erosion and establishing manure spreading setback distances from waterways).

Water contamination by coliforms in Canada: why does it matter?

Animal manure is an important and valuable fertilizer source. However, animal manure may also be a potential source of pathogens (harmful viruses, bacteria and protozoa). Coliforms are one type of bacteria found in all animal feces. When found in waterbodies, coliforms indicate that the water has been contaminated by fecal material.

Applying the most appropriate beneficial manure and grazing management practices is critically important for reducing environmental and water quality impacts and ensuring agricultural sustainability. Some of the consequences of water contamination by coliforms include increased water treatment costs, loss of use of recreational waters, constraints on the expansion of the livestock industry, and potentially food safety and human health effects.

It is important to understand which agricultural lands and waters are at risk of contamination by coliforms, and to understand what land-use practices can reduce or mitigate contamination. The Government of Canada must report on the risk of water contamination by coliforms on farmland. This helps the public and other countries know if Canada's farmlands are healthy and where improvements to farming practices need to be made.

What determines the risk of water contamination by coliforms?

The risk of water contamination by coliforms is determined by the estimating the amount of coliforms present in soil and the likelihood that they will move into surface waters.

Bacteria make up a large part of all types of manure. The species of bacteria vary by the type of livestock (for example, poultry, swine and cattle), manure storage and treatment, and herd health. Coliforms are found in all animal feces. They are most abundant where there is high livestock manure production. Since 1981, livestock production has become more concentrated: livestock numbers have generally increased while the number of farms has decreased to one third.

The risk of coliforms moving into waterways is highest where manure use coincides with dense water drainage networks, high surface runoff, preferential flow and soil erosion. Risk is also increased where shallow groundwater or shallow soils occur over fractured bedrock.

When spreading manure as fertilizer on cropland, weather conditions impact the risk of water contamination by coliforms. Colder weather increases coliform mortality and thus reduces coliform numbers in the soil. The risk of movement to waterbodies (and therefore risk of coliform contamination) strongly depends on how intense rainfall is during and following spreading manure.

Coliform abundance on pasture land varies throughout the year based on when livestock are on pasture. In the western provinces, some animals remain outside during winter, which makes the concentration of coliforms available for transport very high. Spring snowmelt runoff in the Prairies is often the only annual runoff, and this pasture runoff accounts for almost 90% of the risk of coliforms entering water bodies.

Risk of Water Contamination by Coliforms Indicator

The Risk of Water Contamination by Coliforms Indicator assesses the risk that fecal material from agricultural sources will contaminate surface water bodies. It also measures whether this is changing over time. It provides a tool to predict and evaluate which farm practices can be adjusted to minimize risk.

The risk of water contamination by coliforms is determined by estimating both the potential numbers of coliforms on agricultural land (coliform source) and the likelihood of their movement to surface waters (transport).

Coliform sources consider manure from four livestock types: cattle, pigs, poultry and other livestock. Coliform populations are determined for pastured and confined animals by estimating the amount of manure produced, the amount of coliform growth and the amount of coliform decay.

Coliforms from pastured-animal manure are considered to be available for transport on the same day they are produced. Coliforms from confined-animal manure are assumed to be available when spread onto fields based on the first and last day of soil freezing and on typical seeding and harvest dates.

Coliforms tend to be filtered out by soil so transport of coliforms to waterways is assumed to occur by surface flow or rapid tile drainage. The potential for coliforms to be transported to waterways considers topography, soil texture, daily precipitation, soil erosion risk and the density of surface waterbodies on the landscape.

The overall coliform load risk and risk of water contamination by coliforms are classified into in five classes: very low, low, moderate, high and very high.

The Risk of Water Contamination by Coliforms Indicator is calculated every five years. This helps to determine how the risk on farmlands of water contamination by coliforms has changed over time and identify where changes to farming practices are needed.

Risk of water contamination by coliforms in Canada: current state and change over time

Current state

Areas of intensive animal production generally have higher coliform load risk because of higher volumes of livestock manure per area.

In 2016, only 3.6% of farmland was rated at high or very high coliform load risk. These areas occurred primarily in British Columbia, Alberta and Manitoba. This was because of intensive cattle production in British Columbia's interior and Alberta; dairy production in the Fraser Valley; and pig production in Manitoba. Nova Scotia also had higher risk ratings than other eastern provinces; however, this was primarily because it has relatively little cropland (which results in a higher ratio of livestock to agricultural land). In other areas of the Prairies, risk is low to very low since agricultural land is mostly producing grain or low-intensity grassland-based beef.

In 2016, 3.5% of farmland was rated at high or very high risk of water contamination by coliforms. Areas of very high risk were located in British Columbia, Alberta, Ontario and Nova Scotia. High-risk areas were found in all provinces except Prince Edward Island and Saskatchewan. The main reasons for higher risk in these areas include: increased runoff risk due to terrain in the British Columbia interior; higher rainfall rates in Eastern Canada; and tile drainage in Ontario, Quebec and Manitoba.

Change over time

Between 1981 and 2016, the risk of water contamination by coliforms did not change for most of Canada. Where there was change, the change in risk was caused by changes to livestock populations and the redistribution of livestock to concentrated production regions. There was a slight decrease in risk in some regions (including much of Ontario) because of reductions in cattle and pig production operations. Risk increased in some areas of Western Canada (especially parts of British Columbia and Alberta) because of an increased concentration in animal production.

How can the risk of water contamination by coliforms be reduced?

For high-risk areas, the risk of water contamination by coliforms can be reduced using a number of beneficial management practices:

• Reduce the amount of manure per animal by increasing feed quality.
• Minimize the potential for soil water erosion on lands receiving manure.
• Use manure-handling practices that stabilize the waste and reduce pathogen load (for example, composting).
• Consider slope, soil moisture and climate conditions at the time of manure application.
• Establish suitable manure spreading setback distances from water bodies or streams.
• Incorporate manure into soil immediately or shortly after application.
• Discourage pastured animals from accessing streams by using fencing or providing off-site watering.
• Establish buffer strips around waterways.
• Research implementation of buffer strips with harvestable plant species such as switchgrass, shrubs and trees.

Agriculture and Agri-Food Canada's agri-environmental indicators (AEIs) provide a science-based snapshot of the current state and trend of Canada's agri-environmental performance in terms of soil quality (soil organic matter, soil erosion, soil salinization), water quality (nitrogen, pesticides, phosphorus, coliforms), air quality (particulate matter, ammonia, greenhouse gas emissions) and farmland management (agricultural land use, soil cover, wildlife habitat). While indicator results are presented individually, agro-ecosystems are complex, so many of the indicators are interrelated. This means that changes in one indicator may be associated with changes in other indicators as well.

Learn more

Risk of Water Contamination by Coliforms technical report

Related indicators

• The Nitrogen Indicator tracks the risk of water contamination from nitrogen.
• The Phosphorus Indicator examines risk to water from phosphorus.
• The Pesticide Indicator calculates the risk of water contamination from agricultural pesticides.

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