Abundance, Distribution and Life Cycles of Midges (Chironomidae: Diptera) in an Acid Strip-Mine Lake in Southern Illinois

Abstract

The chironomid population of an acid (pH 3) strip-mine lake was studied by taking pairs of Ekman dredge samples from five stations along one transect at fortnightly to monthly intervals for 1 year; only two species were found. For Chironomus near maturus the range (and annual mean) of larval numbers in the transect were 3055 to 14,137 (X =3,936) m2, and maximum station density was 49,972 m2. Range (and annual mean) of larval biomass in the transect were 4.15 to 19.78 g m2 (X = 4.23) and maximum station biomass was 44.46 g m2 preserved wet weight. In 1977 at the deepest (8 m) station, C. nr. maturus was usually abundant, but in 1978 it was scarce or absent. Chironomus nr. maturus was univoltine, but with part of the population emerging in the autumn and part in the spring and summer. The respective numbers for Tanytarsus dendyi Sublette were 0-17,352 (2,360) and 50,105 m2; and respective weights were 0-1.20 (0.16) and 2.99 g m2. Tanytarsus dendyi was almost always scarce or absent at the deepest station. It was trivoltine; each summer generation lasted ca. 2 months. It overwintered in the egg stage or as first instar larvae. Abundance of both species was higher than for species in the same genera in most other acid and circumneutral lakes. The sparser populations in deep water in 1978 may be related to a strong stratification in which oxygen supersaturation persisted for several weeks at intermediate depths.