Biotic impoverishment and trichoptera loss in a Pennsylvania trout stream: Benthic macroinvertebrate assemblages over 43 summers

Abstract

Abstract Benthic macroinvertebrates (BMI) are valued as proxies for water quality. Over 43 years, BMI samples were collected in the summers from Bushkill Creek Northampton County, PA. from the same site. The Bushkill is a high-quality cold water trout stream formerly surrounded by agricultural fields and forests, but the area is becoming increasingly urbanized. Data collected over the period indicate that BMI assemblages have undergone considerable changes. Despite no detectable change in water quality, taxa richness, total abundance, and wet weight (mg) have all decreased (p < 0.01). The Hydropsychidae (Trichoptera) family and Psychomyia (-Trichoptera: Psychomyiidae) have declined significantly (p < 0.01). At the same time, two BMI genera, Gammarus (Crustacea: Amphipoda) and Hydroptila (Trichoptera: Hydroptilidae), have increased modestly. Bray–Curtis Community Similarity indices demonstrate that 2015 assemblages were different from those in 1973. Possible explanations for these trends are stresses from land use changes and/or regrowth of riparian vegetation. These results suggest that although water pollutants are often considered when BMI assemblages change, land use and riparian zone changes are also of concern.