Component Level Scores
The overall Water Quality Component health score is the average of three water quality input scores.
What does the Water Quality score show?
The Water Quality Component Health Score reflects the influence of three major watershed scale input indices.
- Non-Point Sources: Chemicals associated with agriculture and runoff from impervious surfaces in riparian areas.
- Localized Pollution Sources: Combined value for localized pollution risk factors.
- Water Quality Assessment Index: Percentage of assessments that fail to meet water quality standards relative to the total number of assessments for each watershed.
In general, the scores are lower across the southern half of Minnesota indicating a higher risk to water quality. This part of the state has potential for impacts from both agricultural production and expanding urban areas.
Northern Minnesota generally has higher scores. While this indicates the presence of fewer risk factors, these locations may also experience significant water quality problems from a single impactful pollution source.
MPCA Water Quality Data provides a list of resources for reviewing information and impacts from a wide range of pollution sources. The MPCA Groundwater Atlas has extensive information for investigating site level impacts.
Creating the Index
- Input Data
Three major watershed scale health scores (Non-Point Sources, Presence of Localized Pollution Sources, Water Quality Assessments) were combined into one mean (average) Water Quality Component Health Score for each watershed.
Data inputs for each health score:
Impervious Land Cover Satellite Data (U of MN, 2000)
Chemical and Nutrient application rates (National Ag. Statistics Service, 2007)
200m Riparian Zone based on MDNR Streams and Lakes data
Presence of Localized Pollution Sources:
Potential Contaminant Sites (MPCA, MES Sept, 2014)
Superfund Sites (MPCA, MES July 2008) Score under revision, 2020
Minnesota County Feedlot Inventory (November, 2014)
Mines of Minnesota (MDNR, Lands and Minerals, 2008)
Water Discharge Permits (MPCA, January, 2009)
County Well Index, Domestic Wells (MDH, 2008)
Stream and Lake WQ Assessment Database (MPCA, April 2016)
- Mean Water Quality Health Rankings
Three water quality index values were combined into one mean (average) water quality score for each watershed.
Water Quality Input Scores:
Localized Pollution Source Index
Non-Point Source Index
WQ Assessment Index
- Interpreting Results
The Localized Pollution Source Index illustrates the challenge of combining five different localized pollution source scores. The results show low scores (poor health/high risk) for populated areas due to the density of many types of potential contaminant sites, painting an overly optimistic picture for out-state Minnesota. For out-state watersheds with high (good) scores, it is very important to view each type of localized pollution source to determine its potential for concern in a particular watershed. A higher score may indicate fewer risk factors, but these locations may also experience significant water quality problems from a single impactful pollution source. The MPCA Water Quality Data provides a list of resources for reviewing information and impacts from a wide range of pollution sources. The MPCA Groundwater Atlas has extensive information for investigating site level impacts.
The Non-Point Source Index reflects the pattern of intense land use alteration that has occurred across much of the southern half of Minnesota, as well as the Red River Valley. This index combines an estimate of agricultural chemical application with the amount of impervious surfaces near water bodies. This combination of agricultural and developed land uses is reflected in the low scores for mixed use areas and high scores for less densely populated regions.
The Water Quality Assessment Index has low scores for the Red River Basin and the Minnesota River Basin. Higher scores are found in the Upper Mississippi Basin and in the extreme northeast and southeast. Low scores for the Water Quality Assessment Index in northern watersheds is due to impairments for mercury found in many northern lakes. This mercury is carried into Minnesota on air currents, primarily from western coal burning facilities. Impairments in the south are primarily due to turbidity (sediment in water), and nutrients.
The combined Water Quality Mean Health Score masks some of the variation found in each individual index, but serves to illustrate an overall gradient in results by basin and region. The combined Water Quality Health Score shows a pattern of slightly higher results in the north, declining toward the south and along the western border. Generally, the lower combined scores reflect landscapes with intense land use change and a greater presence of risk factors. The lowest mean scores are in the Minnesota River Basin, particularly the watersheds near the Iowa border.
- Future enhancements
Each of the data input scores could be enhanced and updated to create a more accurate combined water quality health score.
The Localized Source Index could weight different localized sources by their relative impact. Sources in outstate Minnesota could be scored differently to show trends away from the metropolitan areas.
The Water Quality Assessments Index could be updated as more assessments are completed to provide comparable results as a more consistent level of data collection is completed across the state.
The Non-Point Index could be improved with better information on the location of chemical applications to agricultural lands.