Vertebrate biodiversity via eDNA at the air-water interface.

Aquatic, aerial, and terrestrial habitats exist along a continuum, with biomass and energy flows transporting genetic material across environmental boundaries. Here, we use environmental DNA (eDNA) metabarcoding to characterize genetic information exchange between water and air. From 27 paired samples collected at two urban-wildland interface sites using passive air sampling and active water filtering, we recovered 35 vertebrate taxa, with 40% detected in both media, ranging from aquatic salmon to terrestrial cottontail rabbit. Cross-medium detection probability scales with DNA abundance: logistic models identify ∼660 water reads and ∼14 air reads as 50% detection thresholds. Peaks in coho and Chinook salmon eDNA in water and air align within 24 h, demonstrating that passive air sampling reflects temporal abundance trends. Low-abundance taxa appear sporadically, reflecting stochastic behavior at low DNA concentrations, and reliable detection requires intensified sampling in the primary habitat. Together, these findings establish a unified framework for holistic vertebrate biodiversity monitoring at the land-water interface, with applications in conservation, invasive species early warning, and One Health surveillance.