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Indicator Type: Environmental Condition
The River Nutrient Index rates river water quality based on nutrients and related variables, including phosphorus, nitrogen, pH, and dissolved oxygen, in an annual series of water samples. Data for the index are collected monthly at 24 Long-Term River Network sites (April through March).
The River Nutrient Index is a component of the general River Water Quality Index (indicator), and rates water quality as "Excellent", "Good", "Fair", "Marginal" or "Poor". Follow this link to learn more about the rating system.
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What does the indicator show?
In the 2005-2006 reporting period, the Nutrient Index ranged from marginal to excellent for major rivers throughout the province. Relative to the previous (2004-2005) reporting period, ratings improved or remained unchanged for eleven of twelve sampling sites on central and northern rivers, including the Battle, North Saskatchewan, Athabasca, Wapiti, Smoky, and Peace. For southern rivers, including the Red Deer, Bow, Elbow, Oldman, South Saskatchewan, and Milk, Nutrient Index values improved at three sites, declined at seven sites, and remained unchanged at two. Lower Index ratings for southern rivers in the current reporting period can be directly linked to unusually intense rainfall events during the summer of 2005. Heavy rainfall typically results in a higher contribution of non-point source runoff to rivers. Since this runoff is a product of overland flow, which tends to collect particulate matter, nutrients, bacteria, and other contaminants as it travels, it can lead to water quality guideline exceedances for affected rivers. Although many of the materials introduced to rivers via non-point source runoff can be attributed to human activities, most can also occur naturally in soils.
In recent years, the Nutrient Index for Long-Term River Network sites has ranged from fair to excellent. In general, water quality tends to be poorer downstream of areas with significant urban, industrial, or agricultural development. However, significant improvements have been made to water quality below major developments as a result of enhanced point source effluent control. This is reflected, in part, by improved River Nutrient Index values downstream of some of Alberta's major cities, including Calgary, Red Deer, and Edmonton.
On occasion, Index ratings for both upstream and downstream sites may be better than those for previous years at the same sites. These improved scores can be partly explained by drier climatic conditions experienced during some years. In years with lower precipitation, less rain and snowmelt result in reduced surface runoff. This, in turn, reduces movement of nutrients from the land to the river. For example, in the 2003-2004 reporting period, Index scores decreased for some rivers, such as the Oldman, due to high nutrient concentrations measured in the spring. This reflected water quality during very high river flows, influenced by increased surface runoff associated with snowmelt. In the subsequent Index period (2004-2005), lower spring nutrient concentrations were measured at the Oldman sites, resulting in higher Index scores (e.g., from “fair” in 2003-04 to “excellent” in 2004-2005 upstream of Lethbridge). Similarly, the “marginal” ratings for the Battle River in the current reporting period are largely the result of relatively high nutrient concentrations, as well as low winter dissolved oxygen concentrations.
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