Severe Hypoxia in the Lower St-Lawrence Estuary: causes et impacts

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of Earth and Planetary Sciences McGill University

Sundby/ISMER; Philippe Archambault/ISMER; Anne de

Gobeil/INRS-ETE; Yves Gélinas/Concordia; Roxane

Benoit, Constance Guignard, Benoit Thibodeau,

Majeau-Bettez, Philippe Benoit, Geneviève

Preston, Sergei Katsev, Suzanne Dufour, Stelly

1 Severe Hypoxia in the Lower St-Lawrence Estuary: causes et impacts Alfonso Mucci Dept. of Earth and Planetary Sciences McGill University Collaborators: Denis Gilbert/DFO; Bjorn Sundby/ISMER; Philippe Archambault/ISMER; Anne de Vernal/UQAM; Yves Gratton/INRS-ETE; Charles Gobeil/INRS-ETE; Yves Gélinas/Concordia; Roxane Maranger/UdeM; Morizt Lehmann/Basel Phillipe Benoit, Constance Guignard, Benoit Thibodeau, Pascale Collin, Erika Warnatzsch, Guillaume Majeau-Bettez, Philippe Benoit, Geneviève Bernier, Cédric Magen, Claudia Campeau, Gwen Preston, Sergei Katsev, Suzanne Dufour, Stelly Lefort, Gwennaelle Chaillou, Stéphanie Ringuet, Audrey Limoges, Véronique Gauthier, Acknowledgements: Captains and crew of the R/V Alcide C. Horth, Coriolis II and Marion Dufresne, as well as NSERC.

2 Centre Saint-Laurent, Environment Canada St-Lawrence drainage basin

3 Strait of Belle-Is Cabot Strait

5 Anticosti Channel Esquiman Channel Tadoussac Rimouski Trois-Pistoles Cabot Strait

6 R/V ALCIDE C. HORTH

7 R/V CORIOLIS II

12 Vertical profile measured in the middle of the Laurentian Channel across from Rimouski. 0 IML , 07-NOV :47: th (m) Dep Oxygen saturation (%) Temperature ( C) Salinity Density σ (kg m -3 ) t

13 Three-layer estuarine circulation Lower St- Lawrence Estuary Atlantic Gulf of St-Lawrence Continental Shelf Surface Layer Intermediate (Cold) Layer (<0 C) Dep pth (m) Deep Layer (S= T= 2-5 C) TADOUSSAC CABOT STRAIT Distance from Quebec City (km)

15 Monitoring the State of the St-Lawrence River/Estuary Nicolet, QC June 13-14, 2006

16 Winkler oxygen titrations Sampling

17 Winkler oxygen titrations Claudia Campeau The Chemists work! Gwen Preston

18 One hundred and eleven point calibration of the Seabird SBE-43 oxygen sensor (July, 2003)

19 Study Area, September 2002 Gulf of St-Lawrence & Laurentian Channel Lower St-Lawrence Estuary (LSLE)

20 Dissolved O 2 (µmol/l)survey, September Longitudinal section along the deepest part of the Laurentian Channel m 200 m 300 m

21 Oxygen saturation along the Laurentian Channel % saturation = ([O 2 2] meas /[O 2 2] sat ) * 100

22 HYPOXIA Severe hypoxia is a condition that occurs when dissolved oxygen falls below the level (62.5 μm = 2 mg l -1 20% saturation) necessary to sustain most animal life.

23 Lethal [O 2 ] for 96-hour exposures Species LC 05 LC 50 Temp. (% satur.) (% satur.) ( C) (C) Cod (Gadus Morhua) (Plante et al., 1998) 28 % 21 % 2and6 Flounder comm.) 19 % 13 % 6

24 Chesapeake Bay Map of anoxic bottom waters

25 The Baltic Sea (July and August 2000)

26 Gulf of Mexico Hypoxic zone: 8000 to km 2

27 Three-layer estuarine circulation Lower St- Lawrence Estuary Atlantic Gulf of St-Lawrence Continental Shelf Surface Layer Intermediate (Cold) Layer (<0 C) Dep pth (m) Deep Layer (S= T= 2-5 C) TADOUSSAC CABOT STRAIT Distance from Quebec City (km)

28 25% 55% 70%

29 Dissolved O 2 in the Lower Estuary, z 300 m Slope = -1μM (±0.2) /yr Anoxia in 2060? Gilbert et al., Limnol. Oceanogr. (2005)

30 Factors responsible for the development of hypoxia Change in the properties of the waters at the edge of the continental shelf that supply the deep waters to the Laurentian Channel. An increase in bottom oxygen demand resulting from increases in the flux of terrigenous and/or marine organic matter to the seafloor in the Laurentian Channel. (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) O HCO NO 3- + H 3 PO H 2 O H + A decrease in the landward advection velocity in the bottom water

31 Three-layer estuarine circulation Lower St- Lawrence Estuary Atlantic Gulf of St-Lawrence Continental Shelf Surface Layer Intermediate (Cold) Layer (<0 C) Dep pth (m) Deep Layer (S= T= 2-5 C) TADOUSSAC CABOT STRAIT Distance from Quebec City (km)

32 T,S,σ t, O 2 saturation in the bottom water of the LSLE ?? Gilbert et al., Limnol. Oceanogr. (2005)

33 Time series on the kg m -3 potential density surface in Cabot Strait.

34 Contours of potential density from Cabot Strait to Rimouski Gilbert et al., Limnol. Oceanogr. (2005)

35 Linear regression between water temperature and DO concentration on the kg m -3 potential density surface in Cabot Strait. Slope = ± 6.5 μm C -1 at the 95% significance level Gilbert et al., Limnol. Oceanogr. (2005)

36 Long-term mean temperature, salinity and DO saturation estimated on the kg m -3 potential density surface. Gilbert et al., Limnol. Oceanogr. (2005)

37 Water mass sources % Labrador/28% WC Atlantic % Labrador/47% WC Atlantic Gilbert et al., Limnol. Oceanogr. (2005)

38 Implications of 1.65 C warming in the LSLE μm C -1 x165 C 1.65 = -40 ± 11 μm or -6.0% C -1 x 1.65 C = -9.9 ± 3.3% Observed oxygen decline from 1930s to period: -65 μm Conclusion: we can account for one half to two thirds of the decline in oxygen concentration, but must still account for the remaining ~ μm decline.

39 Factors responsible for the development of hypoxia Change in the properties of the waters at the edge of the continental shelf that supply the deep waters to the Laurentian Channel. An increase in bottom oxygen demand resulting from increases in the flux of terrigenous and/or marine organic matter to the seafloor in the Laurentian Channel. A decrease in the landward advection velocity in the bottom water

41 Box corer

42 Box-corer and recovered interface

45 Erika Warnatzsch Audrey Limoges

46 Sub-sampling the box-core Geneviève Bernier

47 Lisa Barazzuol Sub-sampling the box-core under an inert (N 2 ) atmosphere

48 Porewater extraction Geneviève Bernier

51 Multi-corer

53 Calypso piston core on the R/V Marion Dufresne II

54 R/V Marion Dufresne II

60 Position of Calypso (MD-99/2220) and box cores (AH-00/2220) taken in the LSLE

61 Organic carbon content and δ 13 C in a composite sequence (box core AH and upper part of MD ) Flux ~ 100gC/m 2.a Depth (cm) Flux ~ 25gC/m 2.a 580 ± 50 BP Thibodeau, de Vernal and Mucci (2006; Mar. Geol. 231: 37-50) Blue : Box core (50 cm) Red : Calypso core (~35 m)

62 Organic carbon content & Corg:N molar ratio Marine Terrestrial Thibodeau, de Vernal and Mucci (2006; Mar. Geol. 231: 37-50)

63 Sedimentary organic carbon isotopic signature Terrestrial Marine ~1970 First occurence of the pollen Ambrosia Thibodeau, de Vernal and Mucci (2006; Mar. Geol. 231: 37-50)

64 δ 13 C( ) ) Dep pth (cm ~1970 ~1940 Thibodeau, de Vernal and Mucci (2006; Marine Geology) Abundance of dinocysts (cysts/cm 3 )

65 Benthic foram distribution and assemblages Thibodeau, de Vernal and Mucci (2006; Marine Geology)

66 EUTROPHICATION Excess nutrient supply and organic matter respiration 106 HCO NO 3- + H 3 PO H 2 O H (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) O 2

67 Centre Saint-Laurent, Environment Canada St-Lawrence drainage basin

68 Phosphate and nitrate fertilizer sales in Quebec 1961 to 2002 Source: Agriculture et Agroalimentaire Canada

69 Impact of hypoxia on the benthic community in the LSLE scallops Sea fan 70 m depth near the head of the Laurentian Trough at Tadoussac 310 m depth near Rimouski Photos from: P. Archambault/ISMER-UQAR

70 Conclusions DO levels in the bottom waters of the LSLE decreased by 50% since the early1930 s Most of this decline can be attributed t to a reduction in the westward transport of Labrador Sea water on the southern edge of the Grand Banks of Newfoundland, possibly linked to a larger scale change in ocean circulation and global warming (e.g., NAO). Increased accumulation and respiration of terrestrial and marine organic matter (i.e, eutrophication) at or near the sediment-water interface since European settlement has also contributed to the decline in DO concentrations.

Salinity distribution in the Oceans

Salinity distribution in the Oceans Average practical salinity of open ocean waters 34.72 http://eps.mcgill.ca/~courses/c542/ 1/58 Salinity distribution in the Oceans Factors that control seawater salinity: