What's happening in the water beneath your beach?

When we think about beach water quality, we think about whether it is safe to swim at a beach.

The water quality at a beach can become degraded due to high levels of pollutants, including nutrients such as phosphorus and nitrogen, that stimulate excessive algae growth, fecal bacteria and pathogens.

To better understand and manage beach water quality, researchers at Western University, University of Waterloo and Environment Canada are asking questions instead about the quality of water beneath your beach – the levels of bacteria and nutrients in beach groundwater and in the beach sand itself.

Why? If we want to be able to understand the nutrient and bacteria levels in the lake water, we need to understand the sources of the pollutants, and groundwater and beach sand may be an important pollutant source.

E. coli measurements in water samples from four Lake Huron beaches
CFU/100 ml = E. coli Colony Forming Units 

Research conducted at four beaches (urban and rural) on Lake Huron and Lake Ontario from May-September 2013 showed that concentrations of fecal indicator bacteria (E. coli) were significantly higher in groundwater close to the shoreline than in ankle- and waist-deep lake water (see graph).

Levels of E. coli were also found to be highest in the sand close to the shoreline rather than in offshore sediment or in the upshore sand.

Nutrient concentrations, particularly nitrate, were also elevated in the groundwater at some of the beaches, suggesting that groundwater may act as a source of nutrients to the lake.

Field research will continue in 2014 with plans to get a clearer picture of the linkages between the groundwater quality and quality of the lake water so we can generate the science needed to help improve the water quality at our beaches.