Advection of freshwater phytoplankton in the St. Lawrence River estuarine turbidity maximum as revealed by sulfur-stable isotopes

Factors Determining the Location of the Chlorophyll Maximum and the Fate of Algal Production within the Tidal Freshwater James River

“…Prior studies have concluded that CHLa maxima in some estuaries arise through retention of exogenous phytoplankton because abundance cannot be explained by local growth where turbidity is high (Cole et al 1992;Lapierre and Frenette 2008). Our metabolism data suggest that is not the case in the tidal freshwater segment of the James River Estuary.…”

“…Circulation patterns in some estuaries are characterized by a surface layer of lowsalinity water flowing seaward over a bottom layer of higher salinity water moving landward. Hydrodynamic entrapment occurs as dense particles sink into the landward bottom current (Moon and Dunstan 1990;Simons et al 2006;Lapierre and Frenette 2008). Where CHLa maxima co-occur with the estuarine turbidity maximum, retention has been invoked as a mechanism to explain high phytoplankton abundance despite low light availability (Cole et al 1992;Kocum et al 2002;Muylaert et al 2005).…”

Relating RNA:DNA ratio in Eurytemora affinis to seston fatty acids in a highly dynamic environment

“…This calanoid copepod plays an important role in the trophic dynamics of the St. Lawrence upper estuary where it feeds on phytoplankton (Winkler et al 2003), mainly freshwater species advected from upstream (Lapierre & Frenette 2008), as well as on aggregates and attached bacteria (Zimmermann-Timm 2002, Martineau et al 2004). E. affinis is amongst the major prey items for anadromous fish larvae (Winkler et al 2003, Barnard et al 2006, such as Microgadus tomcod and Osmerus mordax, which may colonize downstream environments later in their ontogenic cycle.…”

“…Finally, the seston from brackish waters (Group B) integrated the signal of hydrodynamic mixing and was mainly composed of 16:1n7 and 18:0, dominant FAs in fresh and saline waters, respectively. Comparatively, Lapierre & Frenette (2008) reported the percent occurrences of the major phytoplankton genera sampled in summer 2006 in the St. Lawrence ETZ at Stns 46 (freshwaters), 48 (brackish waters) and 50 (saline waters). Diatoms and cyanophytes dominated the phytoplankton community structure at all sites, but no distinct longitudinal pattern was evidenced throughout the ETZ, as the abundance of diatoms and cyanophytes did not show any significant variations from Stns 46 to 50.…”

“…Interestingly, on the basis of sulfur-stable isotopic ratios from planktonic algae, Lapierre & Frenette (2008) reported that high concentrations in chl a within the St. Lawrence ETZ are related to the advection and retention of freshwater algae (mainly diatoms and cyanophyceae) rather than to in situ primary production. In the context of hydrological connectivity within the St. Lawrence River, the ETZ may therefore be viewed as a receptacle in which seston of high nutritional quality, mostly associated with freshwater diatoms advected from upstream, mixes with seston of lower quality originating from the tidal flow of saline waters.…”