Removal is Mediated by Decomposing Leaf Litter in Streams Running Title: Stream eDNA Removal Mediated by Leaf Litter

Abstract

Understanding what controls eDNA removal from the water column remains a critical challenge for interpreting eDNA results in flowing waters. Allochthonous organic matter inputs represent an important seasonal change in stream ecosystems. In smaller, headwater streams, leaf litter accumulation and decomposition modify biotic and abiotic conditions that may influence eDNA removal. We conducted experimental releases of Common Carp (Cyprinus carpio) and Steelhead Trout (Oncorhynchus mykiss) eDNA in recirculating mesocosms to explore how leaf litter density and decomposition stage might influence eDNA removal. We found that leaf density had no significant effect on eDNA removal rates, but removal rates for smaller eDNA particles (0.4–1.2 μm) were 74% higher in mesocosms with biofilm-colonized leaves relative to those with “fresh” leaves. In contrast, we found no significant difference in removal rates between colonized and uncolonized leaves for larger eDNA particles (>1.2 μm). Overall, eDNA removal rates were higher for smaller eDNA particles, particularly in the presence of biofilm-colonized leaves, implying a biological mechanism for eDNA removal from the water column. These results suggest that seasonal leaf litter can affect the fate of eDNA particles and may assist in interpreting eDNA data in natural systems.