IMPACT OF FRESH-WATER ON A SUB-ARCTIC COASTAL ECOSYSTEM UNDER SEASONAL SEA-ICE (SOUTHEASTERN HUDSON-BAY, CANADA) .2. PRODUCTION AND EXPORT OF MICROALGAE

In the under-ice plume of the Grande riviere de la Baleine (Great Whal e River) and offshore waters of southeastern Hudson Bay (Canada), seve ral environmental factors influence the distribution, growth, taxonomi c composition and sedimentation of algae found in the sea ice, at the ice-water interface and in the underlying water column. During the spr ing and early summer, these factors include: salinity of bottom ice, w ater turbidity, nutrients and vertical stability of the water column. In the present study, relationships between three predictor variables (water salinity, river runoff and seasonal air temperature index) and biological variables are used to assess the impact of freshwater on pr oduction and export of microalgae. Relationships are derived from exis ting data, which were collected between 1978 and 1990. Correlations wi th water salinity are positive for some variables (salinity of bottom ice, phosphate, ammonium, Sigma N:Si, and algae in bottom ice and at t he interface) and negative for others (coefficient of light attenuatio n, silicate, Sigma N:P, Sigma Si:P and water column phytoplankton). Us ing together salinity and the seasonal index leads to improved proport ions of explained variance for nitrate, ammonium, Sigma N:P and phytop lankton. The amount of sedimenting algae is positively correlated with runoff, and chemical composition (C/N) of the sedimenting material is negatively correlated with salinity. The empirical relationships are applied to the results of a model of river plume dynamics, for three r unoff conditions. Seasonally averaged total Chl. a concentrations, der ived from the model, are higher for maximum river runoff than for mean or minimum conditions. This is because, in the studied environment, a real concentrations of phytoplankton are higher than those of ice alga e, especially under condition of maximum runoff.