Environmental Conditions Influence eDNA Persistence In Aquatic Systems

Environmental DNA (eDNA) surveillance holds great promise for improving species conservation and management.  However, few studies have investigated eDNA dynamics under natural conditions, and interpretations of eDNA surveillance results are clouded by uncertainties about eDNA degradation.  We conducted an experiment to explore how environmental conditions influence eDNA degradation.  Previous studies have reported macrobial eDNA persistence ranging from less than 1 day to over 2 weeks, with no attempts to quantify factors affecting degradation.  Using quantitative PCR to observe Common Carp (Cyprinus carpio) eDNA degradation in laboratory mesocosms, we found that logistic regression models accurately predicted detection vs. non-detection over time.  After 47 hours, qPCR was more likely not to detect target eDNA than to positively detect it.  Meanwhile, target eDNA concentration followed a pattern of exponential decay.  Contrary to our expectations, eDNA degradation rate declined as biochemical oxygen demand, chlorophyll, and total eDNA concentration increased.  Our results help explain the widely divergent previously published estimates for eDNA degradation.   Consideration—and quantification where possible— of the influence of local environmental conditions on eDNA degradation rates will improve interpretation and comparison among eDNA surveillance efforts.