Concentrations of phosphorus (P) trapped in sediments on farm roadways surrounding fields were up to ten times more than anticipated, according to a report published by the Environmental Protection Agency (EPA).
This trapped P can remain in the ground for long periods and is released into waterways when it rains, leading to “year-round” pollution of waterways. It was previously thought that this pollution eased when cattle were wintering in sheds, the EPA said.
Concentrations of both nitrogen (N) and P in soiled run-off waters are “much higher” than previously expected, with soiled roadway run-off having a similar profile to dairy-soiled water and even cattle slurry in some cases, according to the report.
The report published as part of the EPA Research Programme 2021–2030 is based on the Roadrunner project which partners Teagasc and the University of Limerick (UL) to review mitigation measures to treat roadway run-off.
Farm roadways
Soiled waters have the highest risk of entering waterways when they drain into open ditches connected to the farmyard. There are typically 3-4 areas with direct connectivity to waters on any given farm, the project found.
The project has identified key intervention points on farmyards where water, soil and sediments can become particularly enriched with nutrients.
The following areas should be targeted to reduce the soiling of run-off waters:
- 100m radius around the farmyard;
- Underpasses;
- Waiting areas associated with underpasses;
- Water troughs situated along roadways;
- Roadway junctions or anywhere that impedes animal movement.
The EPA said that the projects findings have “direct implications” for Ireland’s Nitrates Action Programme (NAP) which states that “there shall be no direct runoff of soiled water from farm roadways to waters”.
Options to mitigate farm roadway run-off include surface profile modification to direct run-off to designated outlets, surface diversions such as grade-break diversions or open-channel drains, swales, buffer areas, and discharge points, the report states.
The project developed a farm roadway visual assessment booklet which aims to describe visual assessment indicators for identifying the extent of connectivity between roadway run-off and waters.
The handbook was co-developed with stakeholders for use by farm advisors and helps users to examine the structure and configuration of the entire roadway network and evaluate its pollution risk potential.
Other mitigation measures trialed during the project include a low-cost diversion bar which could be placed on roadways at a cost of €100 per unit. However, further validation is required, according to the report.