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.