Macroinvertebrate production in a headwater stream during recovery from anthropogenic disturbance and hydrologic extremes

Recovery of the macroinvertebrate community inhabiting a headwater stream (catchment 54; C54) that received 3 years of seasonal insecticide treatment was investigated. Estimates of abundance, biomass, and production in C54 during 1989 and 1990 were compared with those of a nearby undisturbed reference stream (catchment 55; C55), and those of C54 during a pretreatment year (1985). Total macroinvertebrate abundance was similar throughout pretreatment, treatment, and recovery periods of C54. In contrast, biomass and production, which decreased during treatment, increased to levels similar to those of C54 in the pretreatment year and those of the reference stream during recovery. By 1990, the functional structure of C54 was similar to that of C55 and that of C54 before the treatment. However, taxonomic and developmental stage differences within some functional groups, particularly shredders, persisted. Despite poor recovery of some larger shredder taxa, rapid recovery of a relatively small trichopteran shredder, Lepidostoma spp., contributed significantly to recovery of ecosystem processes associated with shredders. Relationships between shredder biomass and coarse particulate organic matter differed during treatment and recovery periods. Invertebrate taxa with shorter life cycles recolonized rapidly, while those with life cycles > 1 year generally displayed limited recovery. Hydrologic extremes during treatment (drought) and recovery (wet) periods affected organic matter and macroinvertebrate community dynamics in both streams, and may have influenced observed recovery patterns.