Road Deicing Salt Application Reduces Ephemeroptera, Plecoptera, and Trichoptera Richness in Northeastern U.S. Stream Systems

This study investigates road deicing salt chloride loading effects on sensitive stream macroinvertebrate assemblages within the context of stream ecology and freshwater ecotoxicology, an area of growing scientific importance given its implications for road maintenance policy reform and stream water quality standard development for chloride. Using standardized kick-net macroinvertebrate sampling combined with continuous conductivity monitoring and watershed chloride mass-balance modeling, we examine chloride ion toxicity disrupting osmoregulation and reducing EPT taxa sensitive to ionic stress in 64 headwater stream reaches across 32 paired watersheds in four northeastern states drawn from first- and second-order headwater streams in suburban and rural watersheds of New York, Vermont, New Hampshire, and Massachusetts. Results indicate that EPT taxon richness declines significantly at mean annual chloride concentrations above 35 mg/L, with a 58.4% reduction in richness at the highest-exposure sites compared to reference streams (p < 0.001), with 58.4% as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to stream ecology and freshwater ecotoxicology and carry actionable implications for the design of programs and policies targeting road maintenance policy reform and stream water quality standard development for chloride.