Suspended Materials Affect Particle Size Distribution and Removal of Environmental DNA in Flowing Waters

Environmental DNA (eDNA) in aquatic systems is a complex
mixture
that includes dissolved DNA, intracellular DNA, and particle-adsorbed
DNA. Information about the various components of eDNA and their relative
proportions could be used to discern target organism abundance and
location. However, a limited knowledge of eDNA adsorption dynamics
and interactions with other materials hinders these applications.
To address this gap, we used recirculating stream mesocosms to investigate
the impact of suspended materials (fine particulate organic matter,
plankton, clay, and titanium dioxide) on the eDNA concentration and
particle size distribution (PSD) from two fish species in flowing
water. Our findings revealed that eDNA rapidly adsorbs to other materials
in the water column, affecting its concentration and PSD. Nonetheless,
only particulate organic matter affected eDNA removal rate after 30
h. Moreover, we observed that the removal of larger eDNA components
(≥10 μm) was more strongly influenced by physical processes,
whereas the removal of smaller eDNA components was driven by biological
degradation. This disparity in removal mechanisms between larger and
smaller eDNA components could explain changes in eDNA composition
over time and space, which have implications for modeling the spatial
distribution and abundance of target species and optimizing eDNA detection
in high turbidity systems.