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Nutrient cycling in roadside ditches and lawns

 

Roadside ditches are common strategies for preventing roads from flooding, but they can lead to downstream water quality issues, including nutrient pollution. Grassed ditches may have beneficial nutrient removal processes occurring, but conditions promoting nutrient removal could also drive greenhouse gas production.

In the November–December 2016 issue of the Journal of Environmental Quality, researchers report on a field study in a suburban watershed in upstate New York where they compared nutrient cycling processes in grassed roadside ditches to those in adjacent lawns. 

Roadside ditch

The team found that the ditches had high potential denitrification, a biological process that removes excess nitrate, though very wet ditches also had high emissions of methane, a potent greenhouse gas. Lawns, especially those which were fertilized by homeowners, had overall greater emission of greenhouse gases due to their much greater area and greater rates of nitrous oxide and carbon dioxide efflux relative to ditches.

Reducing fertilizer application to lawns can reduce excess nutrients available for transformation into greenhouse gases or runoff into ditches. Managers can utilize grassed ditches for their potential to reduce nitrogen pollution, particularly by controlling residence time of stormwater to promote denitrification but minimize methane emissions. 

Read the full paper in JEQ.  Free preview Dec 9 - Dec16