Etude quantitative du benthos d'une rivière de Belgique : l'Ourthe liégeoise

Abstract

The biocoenotic structure of macroinvertebrates in the Ourthe river is similar in each rapid station (R) above and below a town, but there are more individuals per square meter and the "standing-crop" is always higher in the stations lying below the towns (above Hamoir: 111 kg/Ha and below Hamoir: 228 kg/Ha ) . These different values for standing crop in the rapid stations could be due to sewage which contains organic matter.At every slow and deep station (B), the biocoenosis is always poor and the biomass is very low (B<sub>2<sub/> : Esneux: 21 kg/Ha). The markedly different values for standing crop between rapid stations (R) and slow deep stations (B) could be due to the depth (1,5 - 3 m in B stations). In the deep stations, the primary production on the substratum is lower than in rapid stations (R); it follows that secondary biomass is lower.In investigating the pattern of spatial distribution of ten species, the distribution of Lumbriculus variegatus, Erpobdella octoculata, Glossiphonia complanata, Gammarus pulex, Notidobia ciliaris, etc. was seen to be clumped at every station.The results of the statistical study show that the different population densities of Lumbriculus variegatus, Glossiphonia complanata, Ancylus fluviatilis, Theodoxus fluviatilis, Gammarus pulex and Notidobia ciliaris are not statistically significant.The populations densities of Erpobdella octoculata and Hydropsyche sp. are statistically higher in the below town stations. These different values of density and biomass may be explained primarily by trophic factors, without denying the importance of other influences.The results of this study provide an illustration of the value of statistical methods in a study of the benthos of a river.