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Wood Chip Bioreactors Reduce Water Nitrates Levels

Poor surface drainage and untreated runoff of nitrates from agricultural fields can lead to negative impacts on crop yields and on the structure and composition of farmland. To tackle these challenges, scientists from Agriculture and Agri-Food Canada's St. John's Research and Development Centre established four wood chip bioreactor systems to improve water drainage and protect the environment.

Bioreactors consist of a buried trench filled with wood chips through which drainage water flows before leaving the farm and entering the natural environment. The wood chips enable a process known as denitrification, in which bacteria break down the nitrates. These bacteria feed on the carbon in the wood chips and transform the nitrate from the water into nitrogen gas, which exits the bioreactor into the atmosphere.

Drainage water samples were collected from the inflow and outflow locations of each bioreactor at the St. John's Research and Development Centre. The initial results indicate a nitrate removal rate of more than 50 per cent. This promising result confirms that wood chip bioreactors can indeed reduce nitrate runoff in a cool climate. Efforts are also underway to characterize the microorganisms that are responsible for denitrification in this system.

Farmers in Newfoundland and Labrador often work with shallow, rocky soils that have poor nutrient retention and drainage. This research has the potential to protect the environment by reducing the amount of nitrate content in runoff. The study, now in its second year, will continue to characterize the nitrate removal efficiency in cool climate conditions.

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