scholarly journals Nutrient transport pathways in the Lower St. Lawrence Estuary: seasonal perspectives from winter observations

2021 ◽  
Author(s):  
Cynthia Evelyn Bluteau ◽  
Peter S. Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay
Keyword(s):  
Vertical Mixing ◽  
Coast Guard ◽  
Tidal Mixing ◽  
Mixing Processes ◽  
Transport Pathways ◽  
Nutrient Analysis ◽  
Near Surface ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary

Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the Estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tidal-upwelling at the Head of the Laurentian Channel (HLC). During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature and near-surface water samples collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to sample in tandem with its icebreaking and ship escorting operations. This opportunistic sampling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and Gulf. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the Gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the HLC. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the Estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.

scholarly journals Winter observations alter the seasonal perspectives of the nutrient transport pathways into the lower St. Lawrence Estuary

Ocean Science ◽  
2021 ◽  
Vol 17 (5) ◽  
pp. 1509-1525
Author(s):  
Cynthia Evelyn Bluteau ◽  
Peter S. Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay
Keyword(s):  
Vertical Mixing ◽  
Coast Guard ◽  
Tidal Mixing ◽  
Mixing Processes ◽  
Transport Pathways ◽  
Nutrient Analysis ◽  
Near Surface ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary

Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tides interacting with the topography at the head of the Laurentian Channel. During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature as well as near-surface water samples collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to sample in tandem with its ice-breaking and ship escorting operations. This opportunistic sampling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and the Gulf of St. Lawrence. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the head. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.

scholarly journals Nutrient transport pathways during winter in the Lower St. Lawrence Estuary

2021 ◽  
Author(s):  
Cynthia Bluteau ◽  
Peter Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay
Keyword(s):  
Nutrient Transport ◽  
Transport Pathways ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Assessment of the Importance of Nutrient Recycling by Seabirds in the St. Lawrence Estuary

1980 ◽  
Vol 37 (4) ◽  
pp. 583-588 ◽  
Author(s):  
J. Bédard ◽  
J. C. Therriault ◽  
J. Bérubé
Keyword(s):  
Nutrient Recycling ◽  
Vertical Mixing ◽  
Nutrient Budget ◽  
Somateria Mollissima ◽  
Nutrient Regeneration ◽  
Lawrence Estuary ◽  
Nitrogenous Compounds ◽  
The One ◽  
Excretion Rates ◽  
St Lawrence Estuary

Feeding and excretion rates of the herring, great black-backed, and ring-billed gulls (Larus argentatus, L. marinus, and L. delawarensis), and of the common eider (Somateria mollissima) were measured in captive individuals and the concentration of soluble nutrients in their excreta was established.The bird population in a 30.6-km2 coastal study area varied between 2500 and 12 500 individuals between early May and mid-November. These birds excreted a seasonal total of 5.8, 4.2, and 48.1 kg-at. of soluble silicate, phosphate, and nitrogenous compounds, respectively. Such quantities, when introduced in the nutrient budget of the coastal area studied, are found to be negligible, considering the levels of nutrients generally recorded in these waters on the one hand, and the relative importance of alternate sources such as land drainage and vertical mixing on the other. Thus, the seabirds can hardly be viewed, except perhaps under the most special circumstances, as important agents in the dynamic nutrient regeneration processes of marine coastal waters of the St. Lawrence Estuary.Key words: nutrient recycling, seabirds, St. Lawrence Estuary

Mercury in Sediments and Sediment Pore Water in the Laurentian Trough

1993 ◽  
Vol 50 (8) ◽  
pp. 1794-1800 ◽  
Author(s):  
Charles Gobeil ◽  
Daniel Cossa
Keyword(s):  
Pore Water ◽  
Drainage Basin ◽  
Sediment Surface ◽  
Vertical Profiles ◽  
Sediment Pore Water ◽  
Overlying Water ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary ◽  
Dissolved Mercury

The concentration of dissolved mercury in the pore water of Laurentian Trough sediments varies between the detection limit (2.5 pM) and 64 pM, up to an order of magnitude enriched relative to the overlying water. Dissolved mercury is low near the sediment surface, increases with depth to 5 cm, and then decreases with further depth. Redistribution of remobilized mercury within the sediment column is, however, insufficient to explain the observed depth variations in mercury concentration. In the Lower St. Lawrence Estuary, the vertical profiles of mercury in trough sediments tend to be consistent with the chronology of mercury discharges from chlor-alkali plants located in the St. Lawrence drainage basin. The total amount of anthropogenic mercury in sediments deposited below the 200-m isobath in the entire lower St. Lawrence Estuary since the beginning of industrialization is estimated as 170 ± 85 × 103 kg, about six times the amount of natural mercury that has accumulated during the same period. Near the seaward end of the Trough in the Gulf of St. Lawrence, sedimentary mercury concentrations are much lower than in the Estuary, with a significant portion of the anthropogenic mercury deposited in the sediments probably coming from the atmosphere.

Classifying and combining herd surface activities and individual dive profiles to identify summer behaviours of beluga (Delphinapterus leucas) from the St. Lawrence Estuary, Canada

2018 ◽  
Vol 96 (5) ◽  
pp. 393-410 ◽  
Author(s):  
S. Lemieux Lefebvre ◽  
V. Lesage ◽  
R. Michaud ◽  
M.M. Humphries
Keyword(s):  
Surface Group ◽  
Delphinapterus Leucas ◽  
Fine Scale ◽  
Activity Data ◽  
Near Surface ◽  
Lawrence Estuary ◽  
Group Activities ◽  
Surface Activities ◽  
Herd Structure ◽  
St Lawrence Estuary

Studies of the behaviour of diving animals usually focus on either individual dives or surface group activities, but these complementary observations are seldom combined in the same study. We here study the summer (June–October) behaviour of St. Lawrence Estuary belugas (Delphinapterus leucas (Pallas, 1776)) by combining fine-scale individual diving data from 27 time–depth–speed recorder deployments (conducted in 2002–2005) with surface activity data from 1413 focal herd follows (conducted in 1991–2012). We classified 6312 dives into seven dive types based on shape and swim speed. Dives were then combined into five bout types, including three pelagic, one benthic, and one near-surface. We classified surface activities of herds into six clusters, differentiated primarily by their associated movement patterns (milling or directional) and additionally by herd structure and dispersion and occurrence of acrobatic surface events. Finally, we used herd focal follows conducted while tracking an individual beluga to relate dive and bout types to surface activities. Results indicate that milling at the surface was more frequently related to benthic dives, potentially, associated with behaviours such as benthic foraging, resting, socializing, and care of young. Directional surface movements were more frequently associated with pelagic dives likely used during pelagic foraging, exploration, and travelling.

scholarly journals Tidally induced variations of pH at the head of the Laurentian Channel

2018 ◽  
Vol 75 (7) ◽  
pp. 1128-1141 ◽  
Author(s):  
Alfonso Mucci ◽  
Maurice Levasseur ◽  
Yves Gratton ◽  
Chloé Martias ◽  
Michael Scarratt ◽  
...  
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Field Measurements ◽  
Tidal Mixing ◽  
Lawrence Estuary ◽  
Saguenay Fjord ◽  
Physical And Chemical Variables ◽  
The Difference ◽  
St Lawrence Estuary ◽  
The Impact

The head of the Laurentian Channel is a very dynamic region of exceptional biological richness. To evaluate the impact of freshwater discharge, tidal mixing, and biological activity on the pH of surface waters in this region, a suite of physical and chemical variables was measured throughout the water column over two tidal cycles. The relative contributions to the water column of the four source-water types that converge in this region were evaluated using an optimum multiparameter algorithm (OMP). Results of the OMP analysis were used to reconstruct the water column properties assuming conservative mixing, and the difference between the model properties and field measurements served to identify factors that control the pH of the surface waters. These surface waters are generally undersaturated with respect to aragonite, mostly due to the intrusion of waters from the Upper St. Lawrence Estuary and the Saguenay Fjord. The presence of a cold intermediate layer impedes the upwelling of the deeper, hypoxic, lower pH and aragonite-undersaturated waters of the Lower St. Lawrence Estuary to depths shallower than 50 m.

Summer Phytoplankton Variability in the Lower St. Lawrence Estuary

1978 ◽  
Vol 35 (9) ◽  
pp. 1171-1185 ◽  
Author(s):  
Michael Sinclair
Keyword(s):  
Species Composition ◽  
Physiological State ◽  
Light Level ◽  
Tidal Mixing ◽  
Data Series ◽  
Residual Circulation ◽  
Active Growth ◽  
Lawrence Estuary ◽  
Single Station ◽  
St Lawrence Estuary

The study involved two data series, a weekly sampling program at a single station near Rimouski from June through September, 1974, during which semidiurnal tidal effects were considered, and a 5-d survey of the lower St. Lawrence estuary during July 1975. The biomass and species composition distributions during the survey appeared to be a function of the residual circulation and mixing characteristics of the lower estuary. Active growth in phytoplankton populations was limited to a 2-mo midsummer period. The impoverishment up to late June was probably due to high turbidity, the 1% light level being about 4 m in depth, rather than due to advective flushing. Strong temporal fluctuations in water column phytoplankton biomass and production were similar to the distribution in density stratification. The confidence limits of the derived parameters [photosynthesis at light saturation normalized by chlorophyll (θ) and by carbon (μpot), and the carbon/chlorophyll ratio] were broad with respect to their seasonal range. Due to the lack of coherence in the physiological state indices considered, and the importance of species composition differences in "explaining" the observed distributions of the indices, the utility of the derived parameters as measures of physiological state of mixed populations is questioned. Key words: phytoplankton, St. Lawrence estuary, primary production, physiological state, tidal mixing

scholarly journals Near-surface real-time seismic imaging using parsimonious interferometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sherif M. Hanafy ◽  
Hussein Hoteit ◽  
Jing Li ◽  
Gerard T. Schuster
Keyword(s):  
Fluid Flow ◽  
Real Time ◽  
Temporal Resolution ◽  
Seismic Imaging ◽  
Time Lapse ◽  
Rock Properties ◽  
Recording Time ◽  
Near Surface ◽  
Arrival Times ◽  
Order Of Magnitude

AbstractResults are presented for real-time seismic imaging of subsurface fluid flow by parsimonious refraction and surface-wave interferometry. Each subsurface velocity image inverted from time-lapse seismic data only requires several minutes of recording time, which is less than the time-scale of the fluid-induced changes in the rock properties. In this sense this is real-time imaging. The images are P-velocity tomograms inverted from the first-arrival times and the S-velocity tomograms inverted from dispersion curves. Compared to conventional seismic imaging, parsimonious interferometry reduces the recording time and increases the temporal resolution of time-lapse seismic images by more than an order-of-magnitude. In our seismic experiment, we recorded 90 sparse data sets over 4.5 h while injecting 12-tons of water into a sand dune. Results show that the percolation of water is mostly along layered boundaries down to a depth of a few meters, which is consistent with our 3D computational fluid flow simulations and laboratory experiments. The significance of parsimonious interferometry is that it provides more than an order-of-magnitude increase of temporal resolution in time-lapse seismic imaging. We believe that real-time seismic imaging will have important applications for non-destructive characterization in environmental, biomedical, and subsurface imaging.

scholarly journals Benthic fluxes of dissolved organic nitrogen in the lower St. Lawrence estuary and implications for selective organic matter degradation

2013 ◽  
Vol 10 (11) ◽  
pp. 7609-7622 ◽  
Author(s):  
M. Alkhatib ◽  
P. A. del Giorgio ◽  
Y. Gelinas ◽  
M. F. Lehmann
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Nitrogen ◽  
Organic Nitrogen ◽  
Bottom Water ◽  
Estuarine Sediments ◽  
Internal Source ◽  
Lawrence Estuary ◽  
Element Partitioning ◽  
Sediment Porewaters ◽  
St Lawrence Estuary

Abstract. The distribution of dissolved organic nitrogen (DON) and carbon (DOC) in sediment porewaters was determined at nine locations along the St. Lawrence estuary and in the gulf of St. Lawrence. In a previous manuscript (Alkhatib et al., 2012a), we have shown that this study area is characterized by gradients in the sedimentary particulate organic matter (POM) reactivity, bottom water oxygen concentrations, and benthic respiration rates. Based on the porewater profiles, we estimated the benthic diffusive fluxes of DON and DOC in the same area. Our results show that DON fluxed out of the sediments at significant rates (110 to 430 μmol m−2 d−1). DON fluxes were positively correlated with sedimentary POM reactivity and varied inversely with sediment oxygen exposure time (OET), suggesting direct links between POM quality, aerobic remineralization and the release of DON to the water column. DON fluxes were on the order of 30 to 64% of the total benthic inorganic fixed N loss due to denitrification, and often exceeded the diffusive nitrate fluxes into the sediments. Hence they represented a large fraction of the total benthic N exchange, a result that is particularly important in light of the fact that DON fluxes are usually not accounted for in estuarine and coastal zone nutrient budgets. In contrast to DON, DOC fluxes out of the sediments did not show any significant spatial variation along the Laurentian Channel (LC) between the estuary and the gulf (2100 ± 100 μmol m−2 d−1). The molar C / N ratio of dissolved organic matter (DOM) in porewater and the overlying bottom water varied significantly along the transect, with lowest C / N in the lower estuary (5–6) and highest C / N (> 10) in the gulf. Large differences between the C / N ratios of porewater DOM and POM are mainly attributed to a combination of selective POM hydrolysis and elemental fractionation during subsequent DOM mineralization, but selective adsorption of DOM to mineral phases could not be excluded as a potential C / N fractionating process. The extent of this C- versus N- element partitioning seems to be linked to POM reactivity and redox conditions in the sediment porewaters. Our results thus highlight the variable effects selective organic matter (OM) preservation can have on bulk sedimentary C / N ratios, decoupling the primary source C / N signatures from those in sedimentary paleoenvironmental archives. Our study further underscores that the role of estuarine sediments as efficient sinks of bioavailable nitrogen is strongly influenced by the release of DON during early diagenetic reactions, and that DON fluxes from continental margin sediments represent an important internal source of N to the ocean.

Sign in / Sign up

Export Citation Format

Share Document