Monitoring aquatic biodiversity at scale depends on the efficient collection of environmental DNA (eDNA). However, the standard approach which actively filters liters of water often becomes slow or infeasible in turbid systems where filters clog and field logistics escalate.

In a study published in Environment International, a research team led by Prof. HE Dekui from the Institute of Hydrobiology of the Chinese Academy of Sciences showed that the water movement itself can be leveraged to improve eDNA capture. Under faster flow, passive collectors accumulate DNA quickly and can even outperform conventional filtration in running waters.

Through controlled flume experiments and field deployments across 21 sites, researchers investigated how hydrodynamic conditions govern passive eDNA sampling efficiency.

In the laboratory, researchers evaluated glass-fiber (GF) membranes as a passive eDNA sampler. They exposed GF membranes to four flow regimes ranging from stagnant conditions to high velocity, and quantified DNA accumulation using droplet digital PCR. DNA captured by the passive membranes increased with exposure time under all flow treatments, but accumulation accelerated sharply under high flow.

Using a flow-adsorption framework, researchers compared GF membranes against a commonly used 2-L filtration benchmark. At the highest velocity tested, GF samplers exceeded the 2-L filtration benchmark within 30 minutes, demonstrating that brief deployments can generate filtration-equivalent (or higher) yields when water movement increases encounter rates between DNA-bearing particles and the collector surface.

Moreover, researchers compared multiple passive substrates against filtration in natural lentic and lotic habitats. They deployed passive samplers for 24 hours across seven lentic sites and 14 lotic sites in Shennongjia National Park, Hubei Province, China, and collected paired 2-L filtration samples simultaneously.

Fish 12S metabarcoding was used to compare biodiversity recovery among methods and habitats. The results showed that across all samples, metabarcoding detected 37 fish taxa, and the overlap between passive methods and filtration was substantial, with 73% of taxa shared across all methods, indicating broad agreement in community detection.

The performance depended on flow regime. In running waters, GF membranes achieved the highest amplicon sequence variant richness and outperformed filtration. In still waters, they were broadly comparable to filtration and competitive with other passive substrates. Statistical models showed that the adsorption efficiency increased with velocity for GF, supporting the conclusion that the flow strengthens passive adsorption and boosts biodiversity recovery in lotic environments.

These findings provide guidance for the monitoring design. Short passive immersions can be sufficient in swift rivers, but longer soak times are needed in lakes and reservoirs where the flow is limited. The study positions GF-based passive samplers as a low-effort, scalable option for standardized aquatic biodiversity monitoring, especially in systems where filtration is slowed by clogging, turbidity, or logistical constraints.