Stability and resilience in benthic macroinvertebrate assemblages Impact of physical disturbance over twenty-five years

摘要: Benthic macroinvertebrate assemblages of Bushkill Creek, Northampton County, PA were studied at the same site during 1970s (11 dates) and 1990s (8 to evaluate stability resilience. In 1970s, a Surber sampler was used, in 1990s, Hess sampler. Assemblages appeared stable over wide range environmental stresses with exception 1994–1995 when total numbers Trichoptera decreased. Taxa richness EPT indices varied little from other sampled years. By July 1996, all metrics (Trichoptera numbers, taxa richness, index, Bray-Curtis Index) resembled for lower wet weight. composition similar 1972 suggesting assemblage 25 The Trichoptera, Psychomyia (Psychomiidae) Leucotrichia (Hydroptilidae), decreased never rebounded numbers. During winter 1994, coldest temperatures greatest cumulative snowfall occurred region. These conditions probably stressed low temperatures, anchor/frazil ice break-up. then exposed four bankful floods winter/spring 1994 five 1996. Recovery time following these multiple disturbances 27 months. Previous recovery times flood considerably shorter (2–5 months). (5–9 previusly recorded) this apparently extended by physical disturbances, outside predicted range. had not been previously such severe and, therefore, extended. Despite weather conditions, recovered exhibited both resilience its return an 1970s.