eDNA Transport in Streams with Coarse Sediment Beds

Environmental DNA (eDNA) has emerged as a non-intrusive tool to identify species in aquatic habitats. Because eDNA is transported in the environment, knowing where it originates remains a challenge in flowing systems. eDNA is a heterogeneous mixture of particulate organic matter that can be filtered out of the water column by the bed sediment. Even though a few studies have measured eDNA transport parameters in flowing waters, they have used unknown quantities found in nature or in fisheries. Here, we conducted experiments in an artificial laboratory channel with a coarse sediment bed to measure eDNA filtration coefficients and predict the breakthrough behavior downstream. We injected known quantities of ground Atlantic Salmon (Salmo Salar) in a horizontal flume (10 m long, 0.3 m wide) with a 10 cm deep overlaying flow with a 1 L/sec discharge. We sampled the water column at four locations at plateau and measured the filtration coefficients as the slope of the (logged) concentration data vs downstream distance. We used the measured filtration coefficient to predict the breakthrough behavior at a location downstream and showed good agreement between the predicted and observed concentrations over time. We were able to measure filtration rates at low, environmentally relevant concentrations. Our results indicate that even at low concentrations, efficient eDNA filtration in stream-sediments may limit the distance eDNA travels downstream. Finding eDNA at a location in a lotic system could thus indicate the presence of the target species within a limited range.