A chironomid-based model for inferring late-summer hypolimnetic oxygen in southeastern Ontario lakes

Hypolimnetic oxygen depletion has been accelerated in many lakes due to cul tural eutrophication. However, the extent and magnitude of environmental ch ange is difficult to ascertain due to the lack of historical records. Larva l Chironomidae (Diptera) are useful proxy indicators of oxygen, as they sho w a wide range of tolerances to oxygen conditions and their chitinous head capsules preserve well in lake sediments. Using paleolimnological technique s, chironomid assemblages from the surface sediments of 42 southeastern Ont ario lakes were related to environmental conditions. Hypolimnetic oxygen co nditions, measured as the average end-of-summer hypolimnetic dissolved oxyg en (AvgDO((Summ))), explained the most variation in the chironomid assembla ges, whereas dissolved inorganic carbon, the Anoxic Factor, max. depth and total phosphorus concentrations were also correlated with assemblage compos ition. Based on the relative abundances of 45 chironomid taxa, a robust, pa rtial least squares (PLS) regression transfer function for AvgDO((Summ)) wa s constructed (r(2) = 0.74, r((jack))(2) = 0.58, n = 40). This new transfer function should allow paleolimnologists to directly track past trends in h ypolimnetic oxygen levels.