Contribution of the macrobenthic compartment to the oxygen budget of a large regulated river: the Mosel

The contribution of the benthic compartment to the oxygen budget of three s ectors of the river Mosel (France, Luxembourg, Germany) was evaluated, in t erms of benthos respiration, filtration rate and sediment oxygen demand. Bo ttom substrates and benthic invertebrate communities were investigated usin g benthic dredges during six field campaigns from summer 1994 to summer 199 6. Bivalvia (Corbicula fluminalis, Dreissena polymorpha, Anodonta cygnea, U nio pictorum), Prosobranchia (Viviparus viviparus), Crustacea (Gammaridae) and Diptera (Chironomidae) were the prevailing taxa of the benthic communit y, both in density and biomass. An original method based on multivariate an alyses and a clustering approach was developed to describe the habitat mosa ic in terms of substrate-type frequencies. The biomass of each taxon was re calculated for each substrate-type. The dissolved oxygen uptake and the fil tration rate of the prevailing taxa of the benthic community were modelled using results of laboratory experiments. Both effects of water temperature and trophic level conditions were taken into account. Evaluations showed th at benthic compartment respiration processes may have reach up to 25% of th e total amount of dissolved oxygen per day, in the river Mosel. Furthermore , the macrobenthic compartment may have a great impact on phytoplankton com munities, and then on primary production, by filtration activity. Indeed, t he water volume daily filtered by filter-feeder macroinvertebrates potentia lly ranged from 26.9 to 83.8% of the total volume of a sector, in summer co nditions. Consequently, respiration and filtration activities of the benthi c compartment appear to be two important biological processes of the dissol ved oxygen budget of a large regulated river.