Examining Relationships Between Groundwater Nitrate Concentrations in Drinking Water and Landscape Characteristics to...

Area of Science:

• Environmental Science
• Hydrogeology
• Public Health

Background:

• Ingesting nitrate from drinking water is linked to adverse health outcomes, even at levels below regulatory limits.
• Groundwater is a common drinking water source, but data on nitrate patterns and concentrations are limited.
• Elevated nitrate levels in drinking water pose a significant public health concern.

Purpose of the Study:

• To map groundwater nitrate concentrations and probabilities of exceeding health-based thresholds in Michigan's Lower Peninsula.
• To identify key factors correlated with elevated groundwater nitrate levels.
• To inform strategies for identifying at-risk communities and mitigating adverse health outcomes.

Main Methods:

• Utilized an extensive dataset of over 100,000 drinking water well samples (2006-2015).
• Employed Kriging, a geostatistical method, for spatial interpolation of nitrate concentrations.
• Applied Classification and Regression Trees (CARTs) to identify variables correlated with nitrate exceedance probabilities.

Main Results:

• Mapped groundwater nitrate concentrations for 76,724 wells, revealing 13% exceeded 2 mg/L NO3-N and 2% exceeded the EPA MCL of 10 mg/L.
• CART models explained 40%-45% of variation, identifying agricultural nitrogen inputs, vulnerable soil conditions, and high aquifer recharge as critical correlated variables.
• 79% of wells had nitrate concentrations below the common detection limit (<0.4 mg/L NO3-N).

Conclusions:

• Significant portions of shallow aquifers in Michigan's Lower Peninsula exceed nitrate levels associated with adverse health effects.
• Agricultural practices, soil characteristics, and groundwater recharge rates are key drivers of nitrate contamination.
• Findings provide crucial data for targeted monitoring and risk assessment to protect public health from nitrate exposure.