Precipitation effects on microbial pollution in a river: lag structures and seasonal effect modification

Area of Science:

• Environmental Science
• Microbiology
• Water Quality Management

Background:

• The Göta Älv river is a vital freshwater source for 0.7 million people in Sweden.
• Contamination stems from sewage discharge and agricultural runoff.
• Projected climate change indicates increased precipitation and heavy rainfall events.

Purpose of the Study:

• To determine how daily rainfall influences pathogen indicators in river water.
• To enhance understanding of river water quality variations.
• To discuss implications for effective risk management strategies.

Main Methods:

• Utilized 7 years of daily monitoring data for turbidity and microbial indicators (E. coli, Clostridium, coliforms).
• Applied time series regression and non-linear distributed lag models to analyze variations in relation to precipitation.
• Investigated seasonal variations in precipitation effects and compared weather station predictive abilities.

Main Results:

• Peak microbial contamination and reduced water quality typically occur 2 days post-rainfall.
• Rainfall events exceeding 15 mm/24h correlated with a threefold increase in E. coli and 30% higher turbidity.
• Precipitation showed exponential increases in indicator bacteria, with effects on turbidity diminishing during extreme rainfall.

Conclusions:

• Rainfall is a primary driver of year-round microbial risk and water quality fluctuations in the Göta Älv river.
• Heavy rainfall is a more potent indicator of fecal pollution than turbidity.
• Anticipated increases in wet weather and extreme events due to climate change will degrade water quality, necessitating enhanced pollution control measures for drinking water production.