The July 1996 flash flood in the Saguenay region (Quebec). 1. Impact on the water column of the Baie des Ha!Ha! and the Saguenay Fjord

A flash flood, which occurred in July 1996 in the Saguenay area (Quebec), t ransported millions of tons of sediment to the upstream section of the Sagu enay Fjord and the Baie des Ha! Ha! in a few days. This first article repor ts the physical, chemical, and biological observations obtained for the wat er column in September 1996 and August 1997 and attempts to define indicato rs that can adequately characterize the effects of the flood on the water c olumn. The chemical composition, the abundance, and the distribution of sus pended particles clearly show the influence of the flood on the composition of particles in the water column of the bay and the fjord 2 months and eve n 1 year after the flood. However, biological indicators such as the abunda nce and the distribution of phytoplankton and zooplankton species determine d in September 1996 are only slightly different between the Bay and the Fjo rd and show little difference with preflood data. The zooplankton physiolog ical state appears to be a very good indicator of the health of the whole p elagic ecosystem.