“…In three (BISO, LIRI, OBRI) of these systems, lower cumulative contaminant detections and concentrations observed in tributary samples (BISO, OBRI only) than in primary-stream samples, comparable or decreasing cumulative detections and concentrations in downstream order in primary stream samples, combined with limited road access within the study reaches (except Leatherwood Ford, BISO) are consistent with fluvial inflows from upstream external sources, as suggested in other protected-area streams in the US (Battaglin et al, 2018;Bradley et al, 2017c;Elliott and VanderMeulen, 2017;Weissinger et al, 2018), Europe (Camacho-Muñoz et al, 2010), and Africa (Gerber et al, 2016). Likewise, the presence of wastewater sources, including private residential (septic) and municipal/community wastewater treatment facilities upstream of these systems (e.g., OBRI (Guyot, 2005;Knight et al, 2014)) and generally (median exposure conditions) lower detections and concentrations of pesticides (common landscape-derived, non-point contaminants) than pharmaceuticals (common wastewaterassociated, point-source contaminants) support the importance of fluvial inflows as contaminant sources to these three study reaches. Similarly, cumulative contaminant detections and concentrations in Wekiva River samples were comparable between upstream (WEKI-1) and downstream (WEKI-2) locations and generally higher than in the tributary (WEKI-3).…”