Bioassays using the midge Chironomus riparius and the zebra mussel Dreissena polymorpha for evaluation of river water quality

To evaluate if the water quality of the river Meuse affects macrofauna species, the impact of water from this river on two representative species was tested under controlled conditions. Short-term bioassays with reference populations of the midge Chironomus riparius and the zebra mussel Dreissena polymorpha were performed simultaneously, using growth and filtration rate as sublethal parameters, respectively. Filtration rates of mussels seemed to be slightly inhibited by Meuse water in 1994 and 1995, although this was only significant in the first year. Apparently, although this species is inhabiting the river Meuse, the water quality still causes sublethal effects. In contrast to the mussel, midges were less sensitive to Meuse water in laboratory experiments; growth inhibition was never observed, while in some experiments growth was even enhanced. In the period of testing, it was not possible to relate effects on macrofauna species in laboratory tests to individual substances in polluted river systems. Because the response of the test species was marginal, it is recommended to include more sensitive species as tested in the present study, especially in view of a general improvement of the water quality in the river Meuse.