Burgeoning planktonic Cyanobacteria in the St. Lawrence River from Lake Ontario to 600 km downstream

Session: Harmful Algal Blooms: From Ecosystem Drivers to Ecosystem Impacts (2)

Michael Twiss, Clarkson University, Dept. of Biology & Great Rivers Center, [email protected]
Evie Brahmstedt, Clarkson University, [email protected]
François Guillmette, Centre for Research on Watershed – Aquatic Ecosystem Interactions, Université du Québec à Trois-Rivières, [email protected]
Gilbert Cabana, Universite du Quebec a Trois-Rivieres, [email protected]

Abstract

Large rivers are generally eutrophic due to natural erosive processes that define the action of rivers in watersheds but the St. Lawrence is unlike most large rivers in that it begins as a large river at the outlet of a great lake.  The river does not immediately fully mix with its tributaries but slowly entrains these waters as it flows downstream.  Thus, we hypothesize that the potamophytoplankton community in the main channel of the St. Lawrence River is influenced by the initial phytoplankton community present in the headwaters and influenced by time and (gradual) entrainment of tributary waters.  Water was collected every 12 km from Lake Ontario to just upstream of Quebec City.  Total P increased with distance downstream (154 to 2750 nM); phytoplankton biomass (1.4 to 10.5 ug chla-/L) strongly correlated to TP.  The phytoplankton community was dominated upstream by diatoms, chrysophytes and dinoflagellates but the proportion of Cyanobacteria increased (% chl-a) from 5 ± 4% to 37 ± 5% with transit downstream.  Observations support the hypothesis that phytoplankton community composition here is influenced by entrainment of nutrient-rich tributaries, including those that are impacted by agricultural and urban waste water effluent.

Twitter handle of presenter
@MTwiss