FIG 1.

Map of sampling area, depicting soil pH and sample locations in a 20-km buffer surrounding the Buffalo River of Minnesota. The spatial buffer was calculated from the Buffalo River as featured in the USGS NHD (https://nhd.usgs.gov/). The Sampling Design Tool for ArcMap 10.2 (Esri) was used to produce a stratified-random spatial scheme, with strata defined based on predicted soil pH values from the USDA SSURGO database (https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/survey/). Areas of heavy urban development and open water bodies were excluded from sampling (white).