Nitrate

What is Nitrate?

Nitrate is a naturally-occurring nitrogen compound. It may be present in surface water from a number of sources including runoff from agricultural lands where manure and/or chemical fertilizers have been applied and the discharge of treated sewage from municipal wastewater treatment plants. Nitrate is an important plant nutrient but too much can contribute to eutrophication – excessive growth of aquatic plants and algae. Nitrate is also a concern for drinking water supplies as high levels of nitrate can be toxic.

During colder months, biological processes in the river slow down considerably, reducing the uptake of nitrogen and keeping the potential for elevated nitrate concentrations high. Large runoff events may also have the potential to export large quantities of nitrate to receiving streams and rivers.

GRCA Nitrate Sensors

The GRCA monitors, assesses and reports on regional and watershed water quality conditions to support conservation authority, municipal and provincial decision making. The GRCA operates two nitrate sensors, one at the Bridgeport Water Quality (WQ) station and one at the Brant WQ station. These sensors allow for continuous readings of nitrate levels in the river but are less accurate than in-house spectrophotometry and accredited laboratory testing. The GRCA sensors use an optical lens and a factory-calibrated relationship between the absorption of UV light by nitrate molecules and the concentration of nitrate passing through the sensor’s lenses. During high-flow events, the water is very turbid (murky) and this decreases the accuracy of the optical sensors. As such, the nitrate concentration readings from the GRCA sensors can over-estimate the actual nitrate concentration in the river, particularly during high-flow events.

The GRCA’s nitrate sensors are intended to track overall trends, and to inform public utility and operating authorities when nitrate concentrations are increasing, which could trigger the utility or operating authority to increase the frequency of their sampling program.

The GRCA nitrate sensor readings are not intended to be used for operational or regulatory decision making, but rather as a tool for early detection of increasing trends.