Vertebrate Biodiversity via eDNA at the air-water interface

Although aquatic, aerial, and terrestrial habitats are often treated as separate ecological systems, these environments exist along a continuum of connectivity: flows of biomass and energy routinely create linkages across water and air, blurring traditional boundaries. Here, we use eDNA sequencing to illustrate and quantify the movement of trace genetic information between water and air. We collected 27 paired air-and-water samples from two urban-wildland interface sites using passive air sampling and active water filtering. Metabarcoding with the MiFish-U 12S marker recovered 35 vertebrate taxa, 40% of which were detected in both water and air, ranging from the strictly aquatic salmon to wholly terrestrial cottontail rabbit. This reciprocal relationship suggests that eDNA pools form within each partition (water or air), with the probability of transfer governed by DNA concentration. In this view, detecting aquatic eDNA in the air is not contamination or stochastic noise but an expected, repeatable phenomenon. Logistic models confirm that higher abundance in one medium predicts spillover into the other. For instance, peaks in Coho and Chinook salmon eDNA align within 24 hours, demonstrating that passive air sampling reflects the temporal abundance trends of the most common aquatic species. In contrast, low-read-abundance taxa appear only sporadically, implying that rare detections are the first to drop out of cross-medium transfer and therefore demand intensified sampling in their primary habitat. Together, our findings bridge the conventional separation of aquatic and airborne eDNA and establish a unified, non-invasive framework for holistic vertebrate monitoring at the land-water interface. This approach offers transformative potential for conservation, invasive-species early warning, and One Health surveillance.