Phytoplankton of the canalized Scarpe River downstream from the Douai sewage treatment plant

The phytoplankton and physicochemistry of the canalized lower Scarpe River in northern France were studied from April 1992 to October 1993. The phytop lankton was dominated by diatoms in spring and autumn and by chlorophytes i n summer. There was' an irregular occurrence of cyanophytes, which characte rized a eutrophic river environment. Certain centric diatoms typical of eut rophic environments (Srephonodiscus hantzschii, Cyclostephanos dubius), whi ch were present in a high proportion in 1992, were replaced in 1993 by othe r species characteristic of moderate to large size rivers (Asterionella for mosa, Aulacoseira granulata). The seasonal variation observed on the lower Scarpe River was similar to that of the large European rivers. Changes in c ertain chemicals and the phytoplankton community indicated some improvement in river water quality subsequent to the start-up of a new sewage treatmen t facility in 1992.