Water Interaction Type Affects Environmental DNA Shedding Rates of Terrestrial Mammal eDNA Into Surface Water Bodies

The analysis of environmental DNA (eDNA) has become a non-invasive, cost-efficient, and universal biomonitoring tool, widely applied across the globe. Most eDNA research focuses on aquatic organisms in freshwater and marine environments. eDNA shedding rates are key to interpreting eDNA-based results, such as for abundance estimations or detection probabilities. Shedding rates have been estimated for several species and life stages; however, virtually all of them are aquatic. As eDNA-based biomonitoring expands to terrestrial systems, waterborne eDNA from freshwater is increasingly used to assess species presence of terrestrial mammals. When interacting with the water, terrestrial mammals deposit their DNA into the water body, with the amount deposited presumably heavily depending on the interaction type. Here we quantify eDNA shedding rates from domestic dogs during various interactions with water bodies, including “passing by”, “drinking”, “crossing through”, “standing still” and “defecating.” “Crossing through” and “defecating” had the highest DNA shedding rates (both approx. 4 × 10⁷ pg/h/ind). All direct water interactions led to eDNA shedding rates several orders of magnitude higher than those of the indirect interaction (“passing by”), resulting in higher eDNA concentrations and, consequently, higher eDNA detection probabilities. This has important implications for interpretations of eDNA-based data from such water bodies. We also highlight the high variability of eDNA concentrations across experimental replicates, which needs to be accounted for when designing eDNA sampling schemes.