Impact of hydropower complex implantation on primary production of the Estuary of the romaine river, Québec, Canada

Hydro-Québec is constructing a hydroelectric complex that include four powerhouses and reservoirs on Romaine river situated on the North shore of the St-Lawrence Gulf. The Romaine estuary is characterized by two distinct areas, the first one is very shallow (<1,5 m) close to the mouth of the river and well influenced by Romaine river discharges. The second area, Mingan channels, is deeper (up to 100 m) with cold saline waters and is strongly influenced by tides cycles.

Anticipated changes in the estuary related to the reservoirs creation were documented during Environmental Impact Assessment (EIA) and covered salinity, benthic and eelgrass communities, sedimentation as well as primary production. In the present study, we compare primary production and physico-chemistry during ice-free season before (2013) and after (2015) the first of four powerhouse and reservoir creation. The monitoring program rely on two instrumented fixed buoys that continuously record sub-surface water temperature, salinity, turbidity, nitrates, O₂, CO₂ and chlorophyll a on a 20 minutes interval. The program also includes monthly vertical profiles realised at 10 stations and an extensive monitoring of the Romaine freshwater plume propagation with more than 300 profiles. Phytoplankton and zooplankton samples were collected for counting and taxonomical analysis. Our results show that although present in the Mingan channel, turbid freshwaters from the Romaine river only represent a small fraction of the whole system which tend to be dominated by marine waters inputs and tides cycles. In the study area, primary production appears to be controlled primarily by temperature followed by nutrients inputs. We will present detailed results on reference conditions and from the first of four year of environmental follow-up.