WATER QUALITY – Health Scores

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.