Water Flow and Biofilm Cover Influence Environmental DNA Detection in Recirculating Streams.

Area of Science:

• Environmental science
• Molecular ecology
• Aquatic ecology

Background:

• Environmental DNA (eDNA) is increasingly vital for aquatic ecosystem monitoring and management.
• Understanding eDNA degradation dynamics is crucial for accurate species detection.
• Lotic (flowing) systems present unique challenges for eDNA persistence compared to lentic (still) systems.

Purpose of the Study:

• To investigate the degradation rates of fish eDNA in a controlled stream environment.
• To assess the impact of water velocity and substrate biofilm on eDNA persistence.
• To determine how eDNA fragment size influences detectability and degradation.

Main Methods:

• Experimental recirculating streams were used to simulate natural lotic conditions.
• Fish eDNA was introduced, and its concentration was monitored over approximately 10 days.
• A nested primer assay was employed to differentiate degradation across various eDNA fragment sizes.
• Variable water velocities (0.1-0.8 m s⁻¹) and biofilm coverage (0-100%) were manipulated.

Main Results:

• Biofilm presence significantly accelerated eDNA initial decay rates compared to non-flowing conditions.
• Water velocity and biofilm coverage were identified as key factors influencing eDNA persistence.
• Larger eDNA fragments (>600 bp) degraded rapidly, while smaller fragments (<100 bp) remained detectable throughout the experiment.
• Fragment size affected both degradation rate constants and long-term detectability.

Conclusions:

• Biofilm significantly enhances eDNA degradation in flowing waters, differing from lentic environments.
• eDNA fragment size is a critical determinant of its persistence and detectability in aquatic systems.
• Optimizing eDNA sampling strategies requires a thorough understanding of environmental factors controlling eDNA degradation and fragment dynamics.