Figure 1.
Distribution of water masses and sampling sites (1–51) for the St.Lawrence River.
The study area is located from Cornwall to Île-aux-Coudres. Transect numbers (1–16) are indicated in circles. (A) Fluvial section including Lake Saint-François (LSF), Lake Saint-Louis (LSL), the fluvial reach (FR) and Lake Saint-Pierre (LSP). (B) Fluvial estuary (FE) and the estuarine transition zone (ETZ).
Table 1.
Riverscape characteristics of the physical discontinuity zones (PDZs): Lake Saint-François (LSF), Lake Saint-Louis (LSL), fluvial reach (FR), Lake Saint-Pierre (LSP), fluvial estuary (FE), and the estuarine transition zone (ETZ).
Figure 2.
Distribution of water column depth, mean depth and water flow as a function of distance.
(A) is sounded and smoothed depths, (B) is mean depth (volume/area), and (C) represents water flow from Cornwall to Île-aux-Coudres. Vertical lines are the boundaries of the physical discontinuity zones (PDZs): Lake Saint-François (LSF), Lake Saint-Louis (LSL), fluvial reach (FR), Lake Saint-Pierre (LSP), fluvial estuary (FE) and estuarine transition zone (ETZ).
Table 2.
Prediction of color ratios based on the given scenarios.
Table 3.
Best models (Δi AIC≤2) in the prediction of the cyanobacteria/eukaryote (cyano/euk) ratio using color ratios, Kd(PAR), and nutrient variables.
Figure 3.
Distribution of environmental variables as a function of distance.
(A) is DOC, (B) is turbidity, (C) is aCDOM, (D) is transmittance, (E) is SRP, and (F) is temperature from Cornwall to Île-aux-Coudres for the north, central, and south water masses. Vertical lines are the boundaries of the physical discontinuity zones (PDZs): Lake Saint-François (LSF), Lake Saint-Louis (LSL), fluvial reach (FR), Lake Saint-Pierre (LSP), fluvial estuary (FE), and the estuarine transition zone (ETZ).
Figure 4.
1% penetration depth of blue, green, red, and PAR wavebands for the central water mass.
The study area islocated from Cornwall to Île-aux-Coudres. At the upper right, 1% penetration depth of PAR for the north, central, and south water masses as a function of distance.
Figure 5.
Relationships between the color ratios and inherent optical properties of the water column.
Relationships between blue/red ratio and (A) aCDOM and (B) transmittance. Relationships between the green/red ratio and (C) aCDOM and (D) transmittance.
Figure 6.
Distribution of color ratios and phytoplankton as a function of distance.
(A) is blue/red, (B) is green/red, and (C) is cyanobacteria/eukaryote ratios from Cornwall to Île-aux-Coudres for the north, central, and south water masses. Vertical lines are the boundaries of the physical discontinuity zones (PDZs): Lake Saint-François (LSF), Lake Saint-Louis (LSL), fluvial reach (FR), Lake Saint-Pierre (LSP), fluvial estuary (FE), and the estuarine transition zone (ETZ).
Figure 7.
Distribution of phytoplankton and Chl a as a function of distance.
(A) is <20 µm phytoplankton, (B) is Chl a, (C) is picocyanobacteria, (D) is nanocyanobacteria, (E) is picoeukaryotes, and (F) is nanoeukaryotes from Cornwall to Île-aux-Coudres for the north, central, and south water masses. Vertical lines are the boundaries of the physical discontinuity zones (PDZs): Lake Saint-François (LSF), Lake Saint-Louis (LSL), fluvial reach (FR), Lake Saint-Pierre (LSP), fluvial estuary (FE), and the estuarine transition zone (ETZ).
Figure 8.
Directional graph representing the connectivity process of the SLR riverscape between Cornwall and Ile-aux-Coudres (ETZ).
Numbers in circles represent sampling sites.
Figure 9.
Variation partitioning between spatial and environmental models.
(A) is the cyanobacteria/eukaryote ratio, (B) is Chl a, (C) is picocyanobacteria, (D) is nanocyanobacteria, (E) is picoeukaryotes, and (F) is nanoeukaryotes. The shaded area represents the environmental variation once the spatial influence has been removed.
Figure 10.
Relative importance of each independent variable for the models with color ratios.
Data represents the despatialized environmental fraction for the models with the blue/red and green/red ratios. (A) cyanobacteria/eukaryote ratio, (B) Chl a, (C) picocyanobacteria, (D) nanocyanobacteria, (E) picoeukaryotes, and (F) nanoeukaryotes.
Figure 11.
Conceptual model of the St. Lawrence riverscape’s structure and functioning.
The degree ofconnectivity and thus transfer of material between habitats in the SLR is determined by the spatial structure of the tributary network and morphology of the riverscape (Fig. 11 panel A). The matter transported by the tributary network interacts with the receiving river’s morphological characteristics (e.g. shape and mean depth), which ultimately redistribute the transported matter in a given direction. The structure of the drainage network is the dominant factor in determining physical heterogeneity through the water mass distribution and the type and amount of injected material on a multikilometer scale (Fig. 11 panel B). This induces the formation of distinct water masses with contrasting underwater light characteristics (Fig. 11 panel B). Ultimately, this optical heterogeneity acted as an important driver in the distribution of the phytoplankton community structure (Fig. 11 panel C).