Hydropsychidae (net-spinning caddisflies) are common riffle macroinvertebrates whose larval attachment and feeding depend on stable, coarse substrate and flowing water. Fine sediment deposition can increase substrate embeddedness, reducing interstitial habitat quality, while reduced current velocity can limit food delivery and net-spinning efficiency. Hydropsychidae are among the most abundant invertebrates in the Spokane River. They can have significant ecological effects through their filtering of seston and through creating microhabitats that favor bacterial production and nutrient cycling. They are also widely used as sentinels of pollutant bioavailability. Although they are abundant in the Spokane River, their distribution in the Spokane River watershed is not documented. This study tests relationships between Hydropsychidae diversity and density and substrate embeddedness and current velocity.
We sampled benthic macroinvertebrates from sites in the Spokane River watershed during the summers of 2024 and 2025. At each site, four standardized kicknet subsamples were collected from riffles and composited into a single sample. Flow velocity was measured just above the substrate surface using a Hach 950 flow meter for each subsample. Particle sizes were characterized using the Wentworth scale and substrate embeddedness was also estimated for each subsample. We predict that Hydropsyche density will be highest in coarse, low-embeddedness substrates under moderate to high flow conditions, and lowest in embedded substrates with reduced current velocity.
Sample processing is still underway. The genera Hydropsyche and Cheumatopsyche appear to be widespread within the watershed. Preliminary results indicate that Hydropsyche were present at 9 of the 12 sampled sites within the watershed. Among sites where Hydropsyche occurred, their proportional abundance relative to the total macroinvertebrate community ranged from <1% - 40%, indicating substantial variability in dominance across sites.
Our results should clarify whether Hydropsychidae can serve as a practical indicator of fine-sediment and flow-related habitat degradation in the Spokane River watershed.