A long-term copper exposure on freshwater ecosystem using lotic mesocosms - Invertebrate community responses
A lotic mesocosm study was carried out in 20 m long channels, under continuous, environmentally realistic concentrations of copper (Cu) in low, medium, and high exposure treatments (nominally 0, 5, 25 and 75 µg L-1; average measured concentrations <0.5, 4, 20, and 57 µg L -1 respectively) for 18 months. Total abundance, taxa richness and community structure of zooplankton, macroinvertebrates and emerging insects were severely affected at Cu treatment levels of 25 and 75 µg L-1. Some taxa seemed to be sensitive to Cu, i.e. gastropods such as Lymnaea spp. and Physa sp., crustaceans such as Chydorus sphaericus, Gammarus pulex and Asellus aquaticus, rotifers such as Mytilina sp. and Trichocerca sp. leeches such as Erpobdella sp. and the emergence of dipteran insects such as chironomini. Other taxa appeared to be tolerant or favoured by indirect effects, i.e. chironimidae larvae, the emergence of orthocladiinae and zooplanktoner Vorticella sp. which increased in the 25 and 75 µg L-1 treatments.
After about 8 months of Cu exposure, the macroinvertebrate community in the high treatment was decimated to the point that few organisms could be detected, with only moderate effects in the medium treatment, and very slight effects among the macroinvertebrate community in the low Cu treatment. Subsequently, most taxa in the high Cu exposure began a gradual and partial recovery. By the end of the study at 18 months, macroinvertebrate taxa richness was similar to control richness, although overall abundances remained lower than controls. After 18 months of copper exposure, a No Observed Effect Concentration at the community level (NOECcommunity) for consumers was set at 5 (4) µg L-1, with a Lowest Observed Effect Concentration (LOECcommunity) at 25 (20) µg L-1.