Ecology of a subarctic river and its associated estuary: The Great Whale River ecosystem. Christian Nozais 1 , Warwick F. Vincent 2 , Claude Belzile 3 , Michel Gosselin 3 , Philippe Archambault 3
The Great Whale River ecosystem
Christian Nozais1, Warwick F. Vincent2, Claude Belzile3, Michel Gosselin3, Philippe Archambault3
1 Département de biologie & Centre d’études nordiques (CEN), Université du Québec à Rimouski, Rimouski, Canada
2 Département de biologie & Centre d’études nordiques (CEN), Université Laval, Québec, Canada
3 Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, Canada
(5) Benthic ecosystem
The Great Whale River (GWR) in subarctic Quebec, Canada, flows 724 km from Lake Saint-Luson through Lake Bienville to the sea at Manitounuk Sound (MS). It is one of the largest rivers surrounding Hudson Bay (HB) and delivers large amounts of freshwater into it. Although its ecology has been studied over the last 40 years, there has been no published synthesis of this research. The available information is reviewed and synthesized on the following aspects of the Great Whale River and the area of southeastern Hudson Bay (SEHB) influenced by its freshwater plume: (1) distribution of salinity, water masses, freshwater discharge and ice cover; (2) distribution of carbon and nutrients; (3) plankton abundance, biomass, production and assemblages; (4) abundance, production and diversity of the sea ice ecosystem; (5) benthic abundance and diversity; (6) fish diversity; (7) marine mammals; and (8) global warming impacts on freshwater and marine environments. This synthesis may provide an ecological basis for the integrated management of the Great Whale River ecosystem, and for other rivers in the subarctic region, especially in the context of the ‘Plan Nord’ of the Quebec government.
- Very limited data in MS. Occurrence of 10 species of Chlorophyceae, 27 Phaeophyceae and 10 Rhodophyceae. However, there is a potential for 20 Chlorophyceae, 35 Phaeophyceae, and 26 Rhodophyceae all found in HB along the coast of Quebec.
- Fucus distichus: dominant species within MS.
- Overall, low phytobenthic biomass productivity and diversity within MS.
- Virtually no available published information for the GWR ecosystem.
- Occurrence of 38 species of macroinvertebrates (mainly represented by Pelecypoda and Polychaeta) at deep stations within MS.
(6) Fish diversity
MS and HB
•Occurrence of 18 fish species (belonging to 11 families) in the estuarine part of the GWR: 4 freshwater species entering occasionally brackish waters, 7 diadromous species and 7 marine species using the estuary as a nursery ground.
(1) Salinity, water masses, freshwater discharge…
•Annual discharge rate = 19.77 km3. Mean peak flow induced by meltwater = 1735.7 m3 s-1 (Day 153).
•GWR contributes about 2.8% of the freshwater inflow entering HB.
• Seasonal freshwater discharge with a high spring and autumn discharge pattern.
•A persistent plume off the GWR, ~100 km2 in summer and fall, and forming under the sea ice in winter and spring a slow-moving, 5-m thick brackish layer reaching to MS, >30 km away (2000 km2 in March).
• Ice cover of the GWR:
- 1-m thick from mid-November to late May.
- Spring break-up provides conditions of high discharge under the sea ice cover still present on HB.
(7) Marine mammals
•Occurrence of belugas in the GWR during summer.
•Presence of ringed seals and bearded seals in MS.
C. Belzile 1999
(8) Global warming impacts
(3, continued) Plankton abundance, biomass…
- Copepod biomass dominated by Calanus glacialis and Pseudocalanus minutus in spring under the ice in SEHB.
- Food sources for copepods during/after the ice algal bloom: algae growing at the ice-water interface and sedimenting algae.
- Most studies on Arctic cod (Boreogadus saida) and sand lance (Ammodytes sp.) in relation to prey density, light, temperature, and potential predator density under the ice cover during spring in SEHB.
- Success of first feeding in fish larvae = f(freshwater discharge, sea ice cover and meteorological forcing).
•A rapid change of HB and its watersheds due to global climate change.
•High rate of loss of sea ice in HB (>40% decline since 1968) and warmer air temperatures at Whapmagoostui-Kuujjuarapik.
•Earlier sea ice break-up in the offshore (ca one month).
•Earlier spring freshwater flood in the GWR (still one month before HB ice break-up).
•35% reduction in maximum sea ice thickness
Increase in irradiance at ice-ocean interface.
Decrease in the input of melt water in HB.
Potential effects on fauna and flora populations, communities and on ecosystems of the GWR and SEHB.
(2) Carbon and nutrients distribution
•Annual export of material from the GWR into HB:
- DOC: 90 000 t.
- PIM: 135 000 t.
- POM: 21 000 t.
- Typical of the oligotrophic waters of the Canadian Shield. (NO3 < 2.1 µM, dissolved reactive phosphorus <0.2 µM).
- In the plume region, strong co-variation with salinity and temperature oscillations caused by tidally driven internal waves during winter.
(4) Sea ice ecosystem
•Sea ice microalgae:
- Salinity is a major environmental driver of the distribution and abundance of algae in the ice.
- Well developed ice algal community throughout SEHB during the spring.
•Sea ice meiofauna:
- Five major faunal taxa over as well as outside the plume. Most abundant animals: nematodes.
- Total abundance between 8.3 and 9 570 ind L-1.
- Quantity/quality controlled by salinity and the presence or absence of the river plume.
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(3) Plankton abundance, biomass, production…
- Biomass remains low in GWR, with CHLa 1.2-1.6 µg L-1 in summer, 40-50% < 2 µm. The > 2 µm fraction is dominated by nanoflagellates.
- PP (MS): ca 2.5 mg C m-3 h-1; PP (SEHB): ca 35 gC m-2 a-1.