Conclusions
Environmental DNA exists in a mixture of different states (e.g.,
dissolved, particle-adsorbed, intra-cellular and organellar) and each
state is expected to have a specific decay rate that depends on the
complex interplay of varied environmental parameters. Our effort to
provide a comprehensive review of the parameters affecting
state-dependent eDNA decay rates and the mechanisms involved have
yielded some important insights. Notably, water chemistry and suspended
mineral particles likely affect conversion of eDNA among states and
persistence of eDNA states in the water column. However, the eDNA
literature contains inconsistently reported metadata and sometimes
conflicting results, thus further study of how environmental parameters
affect eDNA state conversion and decay in aquatic environments is
needed. Improving our understanding of these issues will require a
concerted effort by the scientific community to collect more
comprehensive and consistent metadata on environmental conditions at the
time of sampling. It will also require the implementation of analytic
eDNA controls during sample collection, preservation, extraction and
analysis to better understand eDNA state conversion and decay in aquatic
environments. This represents a crucial research agenda for the field,
given the shift toward using eDNA as a tool to support management
decisions pertaining to invasive alien species, species at risk and
other valued ecosystem component species.