Aitazaz A. Farooque

Riparian buffers protect surface water from diffuse pollutants, mitigating sediment, nutrient, and chemical losses from agricultural landscapes. Prince Edward Island, Canada, has legislated 15‐m riparian buffers, yet stream contamination from agriculture remains widespread. The Soil and Water Assessment Tool and Riparian Ecosystem Management Model were used to simulate 12 years of nutrient and sediment loads from five potato Hydrologic Response Units in the Dunk River watershed on PEI and evaluate water quality impacts of 30 m three‐zone buffers incorporating shrub willow relative to existing 15 m grass and forest buffers and assess optimal buffer width. Willow buffers (30 m) removed 49.9 T ha −1 year −1 sediment, 18.5 kg ha −1 year −1 total N (TN) and 7.8 kg ha −1 year −1 total P (TP). This was 5.6% and 4.1% more sediment and TP than existing 15 m grass buffers and 7.5%, 12.6%, and 16.8% more sediment, TP, and TN than existing 15 m forest buffers. Willow buffers removed significantly more particulate contaminants than forest and significantly more soluble than grass. Optimal willow buffer width downslope of potato fields was 40 m. Overall, incorporating shrub willow and/or riparian widening can have considerable water quality benefits, particularly in regard to sediment retention, and maximize both soluble and particulate pollutant removal on PEI.