Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass. Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.

background

Studies on the Effects of Pollution on the Diaton Communities of the St Lawrence River Near

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

A study of the freshwater gastropods in the Saint Lawrence river near Montreal was undertaken to characterize the populations living in the benthos and on the vegetation, and to define the effects of a deterioration of water quality.

Studies on the Effects of Pollution on the Diaton Communities of the St Lawrence River Near

Citations

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Facteurs responsables de la distribution des gastéropodes dulcicoles dans le fleuve Saint-Laurent

Related Papers (5)

St. Lawrence River

St. Lawrence River basin

Water Chemistry of the St. Lawrence River

Water-Power Development of the St. Lawrence River

St. Lawrence Seaway: Navigation on Gulf of Saint Lawrence Estuary and the St. Lawrence River