The effect of thermal effluent, before and after macrophyte harvesting, on standing crop and species composition of benthic macroinvertebrate communities in Lake Wabamun, Alberta

Abstract

The heated area of Lake Wabamun prior to macrophyte harvesting had higher submerged macrophyte production, greater amounts of plant detritus in the sediment, and a higher standing crop of benthic macroinvertebrates than the unheated area. Species composition of the benthic macroinvertebrate community was also much different in the heated area with the warmest areas supporting a community dominated by tubificid oligochaetes (Limnodrilus hoffmeisteri and Tubifex tubifex), and the moderately heated areas supporting a community dominated by large Chironomus species (Chironomus plumosus and Chironomus atroviridis). Benthos of the unheated parts of the lake consisted mainly of smaller chironomid species such as Chironomus maturus, C. (cf.) staegeri, Polypedilum nubeculosum, Cladotanytarsus spp., and Tanytarsus spp. The heated area was subjected to mechanical macrophyte harvesting which removed the majority of the submerged macrophytes. This reduced the amount of plant detritus within the sediment and also the standing crop of benthic macroinvertebrates in the heated area. Species composition of the oligochaete-dominated community was not affected by harvesting. Species composition of the Chironomus-dominated area was greatly affected by harvesting and became more similar to that of the unheated area; densities of the large Chironomus species were reduced to low levels, while the densities of smaller chironomid species increased.