Progress in understanding the chemical stratigraphy of metals in lake sediments in relation to acidic precipitation

At the beginning of the reproductive season corixids were excluded from several small-sized rock-pools by netting carried out repeatedly at 5 d intervals. In control pools corixid populations were allowed to develop normally. Changes in the bottom fauna, consisting of chironomid larvae were followed by repeated sampling.When corixids were excluded, the density of chironomid larvae remained at a relatively high level, the total biomass (as organic carbon) was 1.5–4.5 g m^–2 (the midsummer median 2.83 g m^–2). When corixids were present, the chironomid biomass fell to 0.1–1.0 g m^–2 (median at the time of peak corixid biomass was 0.52 g m^–2). The largest chironomid larvae tended to disappear first and ultimately only small larvae were present. When corixids were removed, the density of chironomid larvae returned to the level of the experimental pools in about two weeks.