Warming increases environmental DNA (eDNA) removal rates in flowing waters

The use of environmental DNA (eDNA) for aquatic conservation is emerging, but its value is limited by our understanding of how environmental factors like temperature impact eDNA persistence. Although elevated temperatures are known to increase eDNA decay in lakes and ponds, no studies have experimentally explored the effect of temperature on eDNA fate in flowing waters where physical removal could obscure the effect of temperature on decay rates. We compared eDNA removal rates in n=12 indoor, recirculating mesocosms under varying water temperatures (20, 23, 26°C) and found that, for small eDNA particles (0.2-1.0μm), removal rates were higher at the warmest temperature (Tukey’s post hoc, p ≤0.03) while removal rates were consistent across temperatures for larger eDNA particles (>1.0μm, Tukey’s, p<0.05). Consequently, smaller eDNA particles were removed faster than larger particles (>1.0μm) at 26 and 23°C (Tukey’s, p<0.001) compared to 20°C (Tukey’s, p=0.01), resulting in an increase in the proportion of the eDNA sample made up of small particles with downstream transport for the two warmer temperatures (beta linear model, p<0.001). This suggests eDNA removal in streams reflects a complex interplay between physical trapping and microbial degradation influenced by temperature. Consequently, differences in temperature between geographic locations, seasons, and climates could impact the fate and interpretation of eDNA, even in flowing waters where physical removal contributes substantially to eDNA fate.