Le contrôle de la variabilité à court terme du phytoplancton estuarien: stabilité verticale et profondeur critique

1979 ◽  
Vol 36 (11) ◽  
pp. 1325-1335 ◽  
Author(s):  
L. Fortier ◽  
L. Legendre
Keyword(s):  
Water Column ◽  
Tidal Cycle ◽  
Richardson Number ◽  
Low Frequency ◽  
The Other ◽  
Critical Depth ◽  
Lawrence Estuary ◽  
Vertical Stability ◽  
St Lawrence Estuary ◽  
C Assimilation

Hourly series of summer phytoplankton biomass (ATP and chlorophyll a) and photosynthetic capacity (14C assimilation and ATP increase in saturating light) were sampled in the lower St. Lawrence Estuary during the summer of 1977. Vertical stability of the water column was estimated by the Richardson number. From the results it is concluded that the mean level of biomass is an inverse function of critical depth, likely linked to the neap-spring tidal cycle (Mf). On the other hand, the fine fluctuations of biomass and photosynthetic activity were related to vertical stability, which varies according to the semi-diurnal tidal cycle (M2). A simple model was developed on the basis of Sverdrup's critical depth, combining the M2 fluctuations in stability (degree of vertical mixing) to Mf variations in critical depth. Net biomass increases, observed in a nonturbid stabilized water column, cannot be explained by the growth rates computed from 14C assimilation, but they are consistent with the measured rates of ATP production. Spectral analyses of time series of temperature and Richardson number suggest that low frequency water column stability variations amplify the spatial heterogeneity of a reacting parameter such as phytoplankton. On the other hand, a passive scalar such as temperature does not respond to these low frequency variations of stability. It follows that the study of stability spectra may give some insight into the low frequency control of phytoplankton dynamics. Key words: phytoplankton, St. Lawrence Estuary, variability, vertical stability, critical depth, Richardson number, Kendall's cross correlation, spectral analysis

Spatial Configurations of Young Herring (Clupea harengus harengus) larvae in the St. Lawrence Estuary: Importance of Biological and Physical Factors

1985 ◽  
Vol 42 (S1) ◽  
pp. s91-s104 ◽  
Author(s):  
M. Henri ◽  
J. J. Dodson ◽  
H. Powles
Keyword(s):  
Specific Gravity ◽  
Water Column ◽  
Gravity Current ◽  
Yolk Sac ◽  
Clupea Harengus ◽  
Physical Factors ◽  
Residual Circulation ◽  
Lawrence Estuary ◽  
Clupea Harengus Harengus ◽  
St Lawrence Estuary

The phenomenon of larval retention has recently been identified as central to the structuring of herring stocks. It has been shown that retention of larval fish populations in estuaries is dependent on active vertical migration, the capacity for which develops with growth, but the present study shows that mechanisms for spatial structuring of larval herring (Clupea harengus harengus) populations act at the earliest (yolk sac and post-yolk sac) stages. The study was carried out on the Isle-Verte stock of the St. Lawrence estuary in 1981 and 1982. Length–frequencies and tide-related abundance fluctuations suggested that larvae are retained in the study area. As a result, larvae remain aggregated throughout the sampling period of approximately 1 mo. Yolk sac larvae were significantly more abundant near the bottom than in the water column, while post-yolk sac larvae were significantly less abundant in the suprabenthic layer than in the water column. Larvae, being negatively buoyant, tend to sink in slack water but are transported upwards by turbulence resulting from tidal flows. The extent of vertical transport of larvae in the water column is greatest for larvae with lesser specific gravities; specific gravity is at a maximum at hatching and decreases to a minimum at yolk sac absorption. We conclude that larval specific gravity, current velocity, and the two-layer residual circulation are the major factors causing retention and aggregation of larvae.

Mercury speciation in the Lower St. Lawrence Estuary

2000 ◽  
Vol 57 (S1) ◽  
pp. 138-147 ◽  
Author(s):  
Daniel Cossa ◽  
Charles Gobeil
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Feeding Habits ◽  
Mercury Speciation ◽  
Estuarine Sediments ◽  
Sediment Surface ◽  
Pore Waters ◽  
Mass Balance Calculation ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Mercury speciation was determined in the water column and sediment pore waters of the Lower St. Lawrence Estuary, and total Hg (HgT) was measured in seven biological species, including pelagic and demersal fish and crustaceans. In water, HgT concentrations ranged from 1.8 to 7.8 pM, with the highest levels in surface waters and the lowest in deep waters (1.8-2.9 pM). HgT concentrations in sediment pore waters were 10 times as high, with methyl mercury levels of 5.1-14.4 pM. Reactive Hg (HgR) generally accounted for around 20% of HgT in the water column and <30% in pore waters. The distribution of elemental Hg and HgR suggests that Hg(II) is reduced in surface waters and that inorganic Hg is mobilized during remineralization of organic matter at the sediment surface. In the biota, concentrations ranged between 0.05 and 0.89 nmol·g-1 (wet weight). Feeding habits and habitats account for these observations. Results suggest that the sediment is the main source of Hg contamination for the biota. A mass balance calculation showed that the Hg flux entering the lower estuary from the St. Lawrence River is equivalent to the amount buried in estuarine sediments.

scholarly journals Response of the Lower St. Lawrence Estuary to External Forcing in Winter

2006 ◽  
Vol 36 (8) ◽  
pp. 1485-1501 ◽  
Author(s):  
G. C. Smith ◽  
F. J. Saucier ◽  
D. Straub
Keyword(s):  
Low Frequency ◽  
Internal Tides ◽  
Surface Mixed Layer ◽  
Cold Intermediate Layer ◽  
Lawrence Estuary ◽  
Surface Stability ◽  
Tidal Streams ◽  
Harmonic Analyses ◽  
St Lawrence Estuary

Abstract Mostly because of a lack of observations, fundamental aspects of the St. Lawrence Estuary’s wintertime response to forcing remain poorly understood. The results of a field campaign over the winter of 2002/03 in the estuary are presented. The response of the system to tidal forcing is assessed through the use of harmonic analyses of temperature, salinity, sea level, and current observations. The analyses confirm previous evidence for the presence of semidiurnal internal tides, albeit at greater depths than previously observed for ice-free months. The low-frequency tidal streams were found to be mostly baroclinic in character and to produce an important neap tide intensification of the estuarine circulation. Despite stronger atmospheric momentum forcing in winter, the response is found to be less coherent with the winds than seen in previous studies of ice-free months. The tidal residuals show the cold intermediate layer in the estuary is renewed rapidly (14 days) in late March by the advection of a wedge of near-freezing waters from the Gulf of St. Lawrence. In situ processes appeared to play a lesser role in the renewal of this layer. In particular, significant wintertime deepening of the estuarine surface mixed layer was prevented by surface stability, which remained high throughout the winter. The observations also suggest that the bottom circulation was intensified during winter, with the intrusion in the deep layer of relatively warm Atlantic waters, such that the 3°C isotherm rose from below 150 m to near 60 m.

Characterization of the St. Lawrence Estuary's suspended matter size and composition

2020 ◽  
Author(s):  
Anne-Sophie Fabris ◽  
Pierre Larouche ◽  
Jean-Carlos Montero-Serrano
Keyword(s):  
Particle Size ◽  
Chemical Composition ◽  
Water Column ◽  
Suspended Matter ◽  
Estuarine System ◽  
Eastern Canada ◽  
Lawrence Estuary ◽  
Inorganic Matter ◽  
St Lawrence Estuary

&lt;p&gt;The St. Lawrence Estuary is a large seasonally ice-covered estuarine system in eastern Canada. The suspended particulate matter (SPM) dynamic in this estuary is strongly influenced by winds, tides, river runoff, and coastal jets. The particle size distribution (PSD) is an important property of the SPM as it may affect sinking rates, particle re-suspension and distribution of pollutants. A deeper understanding of the PSD helps to determine the vertical and horizontal fluxes of the matter in the water column.&lt;/p&gt;&lt;p&gt;Although information exists concerning the composition and the SPM dynamic in the St. Lawrence Estuary in summer, there is a lack of recent spatial and vertical characterization while no winter data is available. Thus, the purpose of this study is to better characterize the SPM particle size and sedimentological properties in the St. Lawrence Estuary during summer and winter conditions.&lt;/p&gt;&lt;p&gt;The PSD was measured using a laser diffractometer LISST-100X directly in the water column during the summer of 2010 and in the laboratory using water samples taken at discrete depths for winter 2019. X-ray diffraction and fluorescence analysis were used for the characterization of the particles&amp;#8217; mineralogical and chemical composition from which the detrital sources were evaluated.&lt;/p&gt;&lt;p&gt;Results show that SPM concentration is spatially more variable during summer than in winter. In contrast, the PSD&amp;#8217;s is inverted in winter with relatively smaller size particles upstream and larger particles downstream. The depth distribution of the PSD shows slight differences between the seasons. In summer, larger particles are mostly present at the pycnocline whereas in winter, larger particles reach deeper depths and are mostly of inorganic origin. Throughout the estuary for both seasons, particulate inorganic matter contributed the most to total SPM. The winter mineralogical and chemical composition of the SPM was similar throughout the estuary confirming previous studies indicating an origin from the Canadian Shield. Taken as a whole, this study provided valuable new information on suspended matter dynamics in a large Subarctic estuarine environment.&lt;/p&gt;

Low frequency variability in the lower St. Lawrence Estuary

1989 ◽  
Vol 47 (2) ◽  
pp. 285-302 ◽  
Author(s):  
Gordon Mertz ◽  
Mohammed I. El-Sabh ◽  
Vladimir G. Koutitonsky
Keyword(s):  
Low Frequency ◽  
Lawrence Estuary ◽  
Low Frequency Variability ◽  
St Lawrence Estuary

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.

Benthic diatom communities from two salt marshes of the St. Lawrence Estuary (Canada)

2010 ◽  
Vol 23 (4) ◽  
pp. 349-358 ◽  
Author(s):  
Michèle A. De Sève ◽  
Patrick Poulin ◽  
Émilien Pelletier ◽  
Karine Lemarchand
Keyword(s):  
Salt Marshes ◽  
Extracellular Polymeric Substances ◽  
The Other ◽  
High Marsh ◽  
Biological Index ◽  
Sediment Grain Size ◽  
Lawrence Estuary ◽  
Marsh Area ◽  
Diatom Communities ◽  
St Lawrence Estuary

Microphytobenthic diatom communities were investigated in the high and low sections of two salt marshes of the Lower St. Lawrence Estuary (eastern Canada): one featuring a sandy low marsh zone (Pointe-aux-Épinettes; PE) and one with a muddy low marsh area (Pointe-au-Père; PP). Based on diatom composition and diversity, bacterial abundance, chlorophyll-a, phaeopigments and geochemical analyses (Corg, Ntot, granulometry, extracellular polymeric substances), the PP high marsh area appeared to be singular compared to the other sampling sites. Estimated surface biomass ranged from 11 to 71 g C•m-2in the PE marsh and from 24 to 486 g C•m-2in the PP marsh. A higher diversity of diatom species was observed in the PP high marsh area with a dominance of epipelic forms, in opposition to the dominant epipsammic forms at the other sites. Statistical analyses showed that diatom density was mainly affected by nutrient availability while the relative abundance of epipelic and epipsammic species was related to sediment grain size. This study provides original data on the composition of benthic diatoms in surface sediments in St. Lawrence saltmarshes during summer time that represent the first step to the determination of the DBI (Diatom biological index) of these northern environments.

Croissance de la plie rouge (Pseudopleuronectes americanus) de l'estuaire maritime du Saint-Laurent

1985 ◽  
Vol 63 (7) ◽  
pp. 1610-1616 ◽  
Author(s):  
Robert Vaillancourt ◽  
Jean-Claude F. Brêthes ◽  
Gaston Desrosiers
Keyword(s):  
Linear Growth ◽  
Sampling Period ◽  
The Other ◽  
Pseudopleuronectes Americanus ◽  
Spawning Period ◽  
Lawrence Estuary ◽  
Growth Equations ◽  
South Shore ◽  
Males And Females ◽  
St Lawrence Estuary

A study on the growth in size and weight of the Winter Flounder, Pseudopleuronectes americanus (Walbaum), was conducted from samples collected during the summers of 1979 and 1980, in the bay of Saint-Fabien-sur-Mer (Québec) on the south shore of the Lower St. Lawrence Estuary. Age was determined by otolith readings and length–weight relationships were calculated. Linear growth equations were not statistically different for males and females. On the other hand, weight was found to be higher for females than for males of equal sizes. This relationship also varies with the sampling period, and a substantial weight increase follows the spawning period. The growth of P. americanus is slower in the estuary than in more southern areas, while the weights at equal sizes are higher. These results reflect the severe environmental conditions, which necessitate a large accumulation of food energy by the fish as reserves, to the detriment of growth.

Concentration of capelin (Mallotus villosus) in tidal upwelling fronts at the head of the Laurentian Channel in the St. Lawrence estuary

1999 ◽  
Vol 56 (10) ◽  
pp. 1832-1848 ◽  
Author(s):  
Caroline Marchand ◽  
Yvan Simard ◽  
Yves Gratton
Keyword(s):  
Tidal Cycle ◽  
High Tide ◽  
Stomach Contents ◽  
Mallotus Villosus ◽  
Lawrence Estuary ◽  
Threshold Response ◽  
Capelin Mallotus Villosus ◽  
Gut Fullness ◽  
St Lawrence Estuary ◽  
Upwelling Area

In 1994 and 1995, continuous monitoring of physical characteristics and echo integration were used to detect aggregations of capelin (Mallotus villosus) in the upper water column in relation to thermal fronts and to examine the tidal dynamics in an intense upwelling area at the head of the Laurentian Channel. During the four cruises, fish aggregations were recorded for 72% of the fronts (n = 61) resulting from the periodic upwelling of cold waters. Over the tidal cycle, only a low fish biomass was detected when the cold intermediate waters (<2°C) upwelled during high tide; 90% of the 2-year-old capelin biomass was detected in water temperatures >2°C. Capelin zooplankton prey were concentrated primarily over the deep Laurentian Channel, with very small numbers being found in the shallower areas nearby, where the fronts occurred. The prey concentrations did not increase at the fronts at any phase of the tidal cycle. The few zooplankton patches detected by the optical plankton counter did not correspond to either physical structures or fish concentrations. The gut fullness index and the stomach contents of the capelin caught in fronts did not differ from those of capelin caught elsewhere. These frontal aggregations of capelin seem therefore to be driven more by a threshold response to low temperatures than by trophic interactions based on a higher prey density.

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