Bacterial Index
(Updated March 2011)
Rivers are an important source of water for agricultural use and are popular for recreational activities. Bacterial contamination of these water bodies may pose a risk to human, animal, and ecosystem health.
The presence of fecal coliform bacteria or Escherichia coli in a water supply suggests that the water may have been recently contaminated with the fecal material of humans or animals. This can be associated with improper or inadequate sewage treatment, overflow of municipal sewage systems, urban runoff, or other point and non-point sources of bacteria, such as livestock operations. Not only does this represent a potential health risk, but it may also indicate concurrent contamination with other waterborne pollutants.
What does the indicator show?
The River Bacterial Index describes river water quality based on the number of bacteria detected at selected sites in the province's six major river systems. The index evaluates bacterial densities through an annual series of water samples. These are collected monthly at 28 provincial Long-Term River Network sites from April to March.
The River Bacterial Index is a component of the general River Water Quality Index. It rates water quality as "Excellent", "Good", "Fair," "Marginal" or "Poor" based on the presence and abundance of bacteria.
Rating System
The River Bacterial Index formula incorporates two factors representing key aspects of water quality:
- Frequency: the number of times bacterial density in these samples exceeds a guideline
- Amplitude: the extent to which the guideline is exceeded
The result is a number between zero and 100, where 100 represents the best quality relative to objectives. The numbers are further divided into fivecategories:
- Excellent (96-100) - Objectives almost always met
- Good (81-95) - Objectives occasionally not met, but usually by small amounts
- Fair (66-80) - Objectives sometimes not met by moderate amounts
- Marginal (46-65) - Objectives often not met, sometimes by large amounts
- Poor (0-45) - Objectives almost always not met by large amounts
General reductions in the number of bacteria detected in provincial rivers during 2008-2009 led to improvements in the indicator, relative to the previous reporting period (2007-2008). Although Bacterial Index results were quite variable among sites during 2008-2009, improvements in several ratings were evident. All but two sites on northern Alberta rivers – including the Battle, North Saskatchewan, Athabasca, Smoky, Wapiti, and Peace – received ratings of “good” to “excellent”. One site on each of the Battle and Wapiti Rivers was rated as “fair” and “marginal”, respectively.
Southern Alberta rivers (Red Deer, Elbow, Bow, South Saskatchewan, Oldman, Milk) demonstrated considerable improvements over the previous reporting period. Monitoring stations generally achieved higher Bacterial Index ratings, with six sites rated as “excellent”, six as “good”, and one as “fair”. None were rated as “marginal” or “poor”.
Overall, 18 monitoring stations received higher Bacterial Index ratings than they did in the previous (2007-2008) reporting period. Three stations remained unchanged, while six sites showed lower results. One new monitoring station on the Red Deer River was added to the Long-Term River Network program during 2008-2009.
Decreases in Bacterial Index ratings are frequently linked to precipitation events and the resulting surface runoff. Overland flow resulting from precipitation tends to collect nutrients, bacteria, and other potential contaminants, all of which are eventually deposited into receiving rivers and lakes. Although many of these contaminants occur naturally, others may be related to human activities on the landscape. In either case, increased introduction of these substances to rivers will generally lead to lower index ratings.
Upgrades to municipal wastewater treatment processes in major urban centres, such as Calgary (1997), Red Deer (1999) and Edmonton (1998), generally led to rapid improvements in water quality downstream of these cities. Enhanced wastewater treatment tends to reduce bacteria and nutrients released into rivers. As a result, Bacterial Index ratings downstream of all three cities showed improvement after the late nineties. More recent declines in Bacterial Index ratings suggest that non-point sources of bacterial contamination, such as increased agricultural development, may impact water quality in some areas. Human population growth may also be a significant factor; ongoing and future enhancements to wastewater treatment facilities will help address issues of this nature.
What actions are being taken?
A number of natural and human factors can influence index values, including the volume of river flow, climatic conditions, the degree of development along a given river, non-point sources of runoff (such as agricultural fields), and point source discharges of effluent into rivers.
Alberta's Water for Life strategy considers all of these factors in its watershed approach to protect water quality and aquatic ecosystems. In keeping with this approach, continuous improvements to river water quality are being pursued through upgrades to municipal wastewater treatment facilities and infrastructure, enhanced land use and watershed management practices, and various other means.
