WINTERING CHIRONOMIDS MINE OXYGEN

Abstract

Abstract Seasonally sampled cores of burrowed sediment containing chironomid larvae were collected from Cooking Lake, Alberta, and analyzed to (1) assess and establish the typical burrowing behavior and burrow architecture of chironomid larvae; (2) record micrometer-scale geochemical profiles of O2, H2S, and pH in the uppermost sedimentary layers throughout a seasonal cycle; and (3) link changing geochemical conditions to changing burrowing behaviors. We observed that the larvae lived in soft, water-saturated sediment, maintained by open burrows accreted by the animal's mucous. Chironomid-larvae burrows were small and Y-shaped (e.g., Polykladichnus-like) or Y-shaped with basal branches (Thalassinoides-like) and were 20 cm deep. The larvae moved up and down from the oxygenated zone (“sounding” behavior) to exploit food in suboxic and anoxic sediment. Geochemical analyses showed that H2S was present in the pore waters to within 1.5 mm of the sediment-water interface during the summer, when lake-bottom algae...