Evaluation of the effectiveness of nature-based solutions to reduce the impact on water quality of farmyard runoff

Point source pollution from farmyard runoff can be a significant pressure on surface water quality in agricultural catchments with large uncertainty around the extent of these losses between farms and across seasons. Targeted natural-based solutions, such as willow filter beds and bunded drain systems, are currently being funded and deployed on Irish farms to intercept contaminated farmyard runoff before it enters receiving waters. However, field-based evidence of their effectiveness under variable farm management and hydrological conditions is limited.

This study presents an ongoing monitoring program aimed at (1) characterizing the physio-chemical characteristics of farmyard runoff across different farms and seasons and (2) evaluating the mitigation performance of small-scale willow filter beds (n = 6) and bunded drains (n = 2) installed on Irish farms in 2025. Water sampling consisted of monthly grab samples collected at the mitigation system inlets, internal treatment cells, and outlets, and was analyzed for pH, electrical conductivity (EC), dissolved oxygen (DO), total suspended solids (TSS), and nitrogen and phosphorus species. Sampling at the inlets allowed for the determination of physio-chemical parameters of farmyard runoff, which were also compared to the outlet values to determine the effectiveness of the mitigation systems. This abstract focuses on pH, EC, DO, and TSS data collected during the initial monitoring period from October to December 2025. Initial nitrogen and phosphorus concentration samples are currently under analysis and will be presented at the conference.

Preliminary observations indicate pronounced temporal variability in the composition of farmyard runoff, particularly in response to variability in farmyard runoff flow rates. Across the monitored farms and three sampling dates, inlet water quality exhibited substantial variability, with mean (Min-Max) TSS concentrations of approximately 120 mg L^-1 (4-320 mg L^-1), pH of 7.2 ( 5.3-9.2), EC of 900 µS cm^-1 ( 40-1860 µS cm^-1), and DO concentrations of 6 mg L^-1 ( 0.2-11.3 mg L^-1).

Early-stage analysis suggests attenuation of suspended sediment across the mitigation systems, with mean (Min-Max) outlet TSS concentrations of 60 mg L^-1 ( 0.4-174 mg L^-1), generally lower than those observed at the inlets. This reduction is accompanied by a reduction of the EC at the outlets to a mean (Min-Max) of 450 µS cm^-1 (118-1074 µS cm^-1). These patterns were most apparent during periods when flow conditions were sufficient to generate outlet discharge, enabling the comparison between inlets and outlets.

This study will continue for two years to encompass a wider range of seasonal dynamics, farmyard management conditions and additional water quality parameters, enabling a more comprehensive evaluation of farmyard runoff composition and mitigation effectiveness of these nature-based solutions as they mature.