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.