Examination of nutrient and sediment loss mitigation for farm roadway runoff on an Irish dairy farm

In Ireland, farm roadway runoff is a potential farm-scale pollution contributor of nutrients and sediments to connecting open drainage channels that pose a challenge to meeting European Union Water Framework Directive goals. To date, recommended mitigation measures such as swales, sediment ponds, bunded drains, willow beds, among others, have not been widely tested for efficiency and therefore are limiting farmers’ willingness to implement them. This study quantifies the efficiency of bespoke sediment ponds at three locations (in a treatment train with diversion bars and riparian buffers) as farm roadway runoff mitigation measures by identifying runoff connectivity to open drainage channels, co-developing and co-implementing with farmers and monitoring for efficiency in nutrient and sediment removal. The study results suggest sediment ponds are efficient for removing sediment, total suspended solids and particulate nutrients, but vary in their effectiveness in removing dissolved nutrients due to biogeochemical and hydrological processes. The study concludes that sediment ponds are efficient for reducing roadway runoff pollution to open drainage channels but need to be designed to incorporate segmentation, consider all site conditions and encourage vegetation growth for enhanced nutrient and sediment removal, which may facilitate uptake among farmers. Long-term monitoring would be required to inform maintenance procedures and scheduling. • Collaboration in mitigation selection and design encourages adoption. • Sediment trapping in ponds is determined by rainfall and contributing area. • Pond segmentation into cells enhances overall pond pollutant removal efficiency. • Considering local hydrological fluxes including springs is key to optimal removal efficiency.