This work is made available under the terms of the Creative Commons Attribution 4.0 International license,. Compost is often used as a soil amendment in gardens, agricultural fields, and other landscaped systems to alter soil biophysical characteristics and increase availability of valuable nutrients including nitrogen (N), phosphorus (P), and carbon (C). However, leaching of soluble nutrients from compost is of concern, particularly in wet settings, such as within green stormwater infrastructure, riparian areas, and floodplains. This research highlights the importance of saturation as an influencing factor on the nutrient leaching potential of different composts and compost-amended bioretention soils. Nutrient leaching potential was evaluated for five different compost types and two compost-amended bioretention soil mixes under increasing saturation durations, measured at 10 min, 1 day, 5 days, and 10 days of saturation. Results indicated significant increases in NH4+ concentrations in leachate for all composts and bioretention media from 10 min to 10 days. Over the same time period results showed decreases in NO3- concentrations in the leachate from all five composts, but an increase in NO3- concentration for one compost-amended bioretention media and no significant change in the other bioretention media. In response to increased saturation durations, PO43- concentrations in the leachate were found to significantly increase at each stage, from 10 min, to 1 day, to 5 days, to 10 days; overall there were higher PO43- concentrations in the leachate from the five composts than in the leachate from the two bioretention mixes
