VÉGÉTATION MACROPHYTIQUE, ENVIRONNEMENT ET QUALITÉ D'EAU DANS LE BASSIN VERSANT DU BOCQ (BELGIQUE, WALLONIE)/Macrophytic vegetation, environment and water quality in the Bocq catchment (Belgium, Wallonia)

The water and riparian vegetation of the river Bocq and its main tributaries (called Crupet stream, Leignon stream, Petit Bocq, Ri d'Vesse and Ri des Vaux) from a catchment in the south of Belgium was studied from 2009 to 2011. Fifty 100 m long sections were selected. In each section, the vegetation was described, including the anthophytes, pteridophytes, bryophytes, filamentous algae and cyanobacteria. Moreover, various mesological parameters of the stream channel and floodplain and seven chemical parameters were recorded. The statistical data analysis was conducted by means of principal component analysis and correspondence analysis. The dataset of juxtaposed floristic and mesologic tables was transformed into complete disjunctive tables and analysed using multiple factor analysis. The natural environment is responsible for an important portion of the variation in the vegetation but there is also a significant impact of human occupation and farming in the floodplain. Some species are clearly indicators of the geomorphological characteristics of the stream bed or available light, but others are also related to the discharge of domestic waste water or reflect the incidence of farms and cattle breeding. Six plant communities are described and linked to the environment and water chemistry. Algae and cyanobacteria enter several characteristic species combinations. The use of the anthophytes, bryophytes, algae and cyanobacteria as bioindicators of water quality is discussed.