Evaluation of an Ion Adsorption Method to Estimate Intragravel Flow Velocity in Salmonid Spawning Gravel

Intragravel water exchange provides oxygenated water, removes metabolic waste, and is an essential factor in salmonid embryo survival. Measurements of intragravel flow velocity have been suggested as an index of gravel quality and also as a useful predictor of fry emergence; however, proposed methods for measuring velocity in gravel are problematic. We evaluate an ion adsorption technique that uses natural streamwater solute chemistry, which therefore does not require introduction of a dye or solute tracer. However, the method requires an access tube for placing an ion exchange resin bag in the substrate. Our studies suggest that the ion adsorption technique is sensitive and reproducible for measuring velocity in free‐flowing water but has little utility for measuring velocity in gravel beds. Fine sediment provided a relatively high flux density of adsorbed cations that exchanged readily with the resin, leading to spurious high apparent velocities.