Development of a New Laboratory Freshwater/sediment Microcosm Test

Abstract

A new laboratory freshwater/sediment microcosm test is proposed. This 2-L microcosm includes synthetic water, sediment composed of quartz sand, cellulose and fish food flakes (TetraMin®), pelagic organisms (microalgae, duckweeds, cladocerans) and benthic organisms (amphipods, chironomids). We conducted four experiments to determine conditions suitable for the development of organisms for a 4-week duration. The sensitivity of the system was then studied with a copper-spiked sediment. A TetraMin® dose of 0.4 g for 260 g sediment was found optimal to allow growth and emergence of chironomid larvae without bacterial contamination due to excess organic matter. The test with copper sulfate led to a range of effects. For concentrations higher than 10 ppm, systems were severely impaired (growth inhibition of algae and duckweeds >50%, 100% mortality within a few days for cladocerans, mortality >45% within 15 days for amphipods, 80% mortality within 15 days and no emergence for chironomids). At 10 ppm, a shift of the algal peak was observed, duckweed growth was reduced by 39%, partial mortality but no reduced reproduction was found for Daphnia magna whereas Simocephalus vetulus survived only after reinoculation on day 10. Amphipods also survived but were smaller. For chironomids, partial mortality was observed as soon as day 22 and emergence was inhibited by 50% but growth was not affected.