Benthic macroinvertebrate community response to salinization in headwater streams in Appalachia USA over multiple years

Salinization of freshwaters threatens aquatic ecosystems globally via effects that include reductions in benthic macroinvertebrate diversity. Enhanced understanding of salinity effects in freshwater ecosystems could aid mitigation efforts. Salinization effects on benthic macroinvertebrate community structure were quantified in a 4.5-year study of 25 headwater streams spanning a gradient of salinity in the central Appalachian mountains of USA. Community structure as sampled was strongly seasonal, justifying treatment of Spring and Fall data separately. Stream communities became increasingly different from reference condition as salinity increased, with stronger relationships between biota and salinity in Spring than in Fall. Intra-seasonal variation in community structure was also revealed across sampling dates. Genera of the order Ephemeroptera appeared as most sensitive to salinity, as indicated by rapid declines in richness and relative abundance as salinity increased. Plecoptera and Trichoptera richness and relative abundance metrics appeared as less sensitive to salinity, and some Plecoptera genera exhibited increased relative abundance at elevated salinity. Other community metrics were weakly associated with salinity and exhibited greater variability than Ephemeroptera metrics, suggesting that Ephemeroptera richness and relative abundance are sensitive indicators with which to gauge onset of salinity effects. Declines in richness and relative abundance of non-Baetidae Ephemeroptera were associated strongly with increasing salinity, with effects observed at specific conductance levels as low as 200 μS/cm in Spring based on seasonal discrete conductivity sampling. Chronic salinization has persistent effects on community structure over multiple years, but those effects are not uniform among taxa or consistent across seasons. Our findings suggest that effective detection of the onset of community change in salinized streams is best accomplished using Spring data and focusing on community metrics that incorporate salt-sensitive Ephemeroptera taxa.