Fate and transport of environmental DNA: mapping the knowns and unknowns

The use of environmental DNA (eDNA) in routine biomonitoring is transforming our ability to detect and quantify aquatic species. However, translating these indirect molecular detections into ecological insight requires understanding how long eDNA persists and how it moves through the environment. Here, we present a systematic mapping review of the controls on eDNA fate and transport and provide the most comprehensive synthesis to date of mechanistic evidence across aquatic systems. Drawing on over 200 manuscripts, we introduce the concept of the eDNA profile, defined by state, molecular properties, and molecular origin, as a unifying framework for interpreting why eDNA signals differ across environments and taxa. Where eDNA profile has been quantified, source, state, particle size, fragment length, and molecular origin measurably alter decay and transport, confirming that different eDNA forms experience distinct fates and movement distances within aquatic systems. Using this lens, we then synthesize the evidence for the effects of abiotic factors, biotic factors, and transport on eDNA fate. For abiotic factors, we find that temperature, pH, nutrients, suspended particles, substrates, dissolved organic matter, and dissolved oxygen measurably modulate eDNA decay, whereas light exposure (UV and visible light) and salinity show weak or no direct effects across studies. For biotic factors, we conclude that microbial activity, extracellular enzymes, and biofilms are likely major drivers of eDNA degradation, although the identities, functions, and dynamics of responsible communities are poorly resolved. Finally, we show that transport patterns differ strongly among aquatic systems, with depth-structured and short-range signals common in lakes, highly variable downstream distances in rivers that depend on discharge and eDNA particle size, and longer potential transport in coastal and open-ocean systems that often still yield predominantly local signals. In these advective environments, robust interpretation commonly requires coupling eDNA observations with hydrological and oceanographic circulation models. Finally, we highlight three priorities for a predictive framework: (1) explicitly resolve eDNA profiles, (2) isolate the causal mechanisms that govern decay and removal, and (3) identify which microbes and microbial processes drive degradation across environments. Our goal is to integrate the field, highlight critical gaps, and ultimately advance the interpretation of eDNA-based detections for biodiversity monitoring.