The impact of repeated insecticidal treatments on drift and benthos of a headwater stream

Abstract

A small first-order, Appalachian Mountain stream received successive seasonal treatments with the insecticide, methoxychlor. Despite an application rate of 10 mg/1 methoxychlor for 4 hours, based on stream discharge, only a small fraction (1.6%) of the insecticide was exported to downstream reaches for a 31 h period during and following treatment. Most of the insecticide was incorporated into sediments of the streambed, which had residues ranging from 0.038 to 11.7 #g methoxychlor/g dry wt of sediments in June 1986 following treatments in December 1985 and March 1986. Despite low concentrations of methoxychlor measured in stream water (maximum = 128 #g/l) during the initial treatment, massive drift (> 950 000 organisms, and 70 g AFDM biomass) occurred from a stream area of about 144 m 2 . Numerically, collector-gatherer taxa (primarily Chironomidae) dominated drift (63 %) followed by shredders and predators; however, biomass of drift was dominated by shredders (48.9%), followed by predators and collector-gatherers. Compared with pre-treatment benthic abundances, insects were reduced by 75% following the initial treatment in December 1985, and 85% following an additional treatment in March 1986. Benthic abundances of non-insect taxa showed no significant changes. Benthic abundances of shredder, collector-filterer, and scraper functional groups exhibited significant decreases in the first month following treatment. Although benthic abundances of collector-gatherer and predator taxa were reduced by 48.6 and 40.5%, respectively, the reduction was not statistically significant because of high-sample variance. Comparisons of drift composition during the initial treatment with successive quarterly treatments (March 1986 to January 1988) reflected of ongoing pesticide disturbance of the biota as the community structure shifted from one consisting of a diverse insect and non-insect fauna toward one dominated by copepods, oligochaetes, Collembola, and chironomids.

Effects of the insecticide dursban® 4E (active ingredient chlorpyrifos) in outdoor experimental ditches: II. Invertebrate community responses and recovery

“…Given that in the 44-g/L treatment shredders were almost absent 1 year after chlorpyrifos treatment and that the most important shredders in freshwater ecosystems are usually Arthropods, this functional feeding group should be considered at least potentially susceptible to insecticide contamination (low redundancy). This is in accordance with observations of a decrease in shredder populations and breakdown of plant litter in microcosms treated with 35 g/L chlorpyrifos [27,32] and with observations by Wallace et al [33], who reported similar effects in a headwater stream treated with methoxychlor.…”

Impact of lambda-cyhalothrin on a macroinvertebrate assemblage in outdoor experimental channels: Implications for ecosystem functioning

“…Wallace et al, 1989;Sibley et al, 1991;Schulz and Liess, 1999b). Other more recent studies have found various indirect effects of pesticide exposure in addition to the more frequently used end points such as mortality or exclusion of species (Lauridsen et al, 2006;Nørum et al, 2006;Schäfer et al, 2007).…”

Secondary production of chironomid communities in insecticide‐treated and untreated headwater streams

“…Methoxychlor was applied with two hand-sprayers to the entire stream channel from the flume to the spring seeps for 4 h (December 1985) and 2 h (March, June and September 1986) at the rate of 10 mg/1 based on discharge at the flume. For more information about the treatments see Wallace et al (1989).…”