Zooplankton are relevant indicators of changes in lake water quality, used for monitoring the response of aquatic ecosystems to the combined effects of declining acidic deposition and rising air temperatures. First, the current landscape was defined from the recent (2017) spatial patterns of zooplankton communities in 73 Quebec lakes distributed over an 800-km SW–NE gradient, spanning a wide range of water quality, climate, and morphometric characteristics. On a large scale, we identified among-lake clustering of three types of zooplankton assemblages and variation in species composition at fine scale between lake pairs. Dissimilarity in zooplankton assemblages among lake pairs were best correlated (r > 0.400, p < 0.001) with their difference in air temperature, pH, and calcium, reflecting spatial gradients in climate and lake acid–base status. Second, to examine long-term response in the zooplankton community, we compared acidification indicators and abundance of taxa for a subset of 19 lakes sampled in 1982 and 2017. Despite an average threefold drop in sulfate concentration, changes in calcium and pH were relatively small, and consequently, no major changes in zooplankton assemblages were detected since 1982.
Municipal wastewater treatment plant (WWTP) effluents are significant sources of organic and inorganic pollutants to aquatic ecosystems. Several studies have shown that the health of aquatic organisms can be adversely impacted following exposure to these complex chemical mixtures. The objective of this study was to examine the effects of in situ exposure in the St. Lawrence River (QC, Canada) of juvenile yellow perch (Perca flavescens) to a major WWTP effluent. Perch were caged at a reference site in the St. Lawrence River and downstream of a WWTP effluent-influenced site for one, three, and six weeks. Fish kept in controlled laboratory setting were also examined at the beginning of the experiment to evaluate the potential effect of caging on fish. Liver metabolites and gill oxidative stress biomarkers as well as body condition of perch were investigated at four time points (zero, one, three, and six weeks). Nitrogen (δ15N) and carbon (δ13C) stable isotopes as well as tissue concentrations of halogenated flame retardants and trace metals were also analyzed. Results indicated that body condition of perch caged in the effluent increased after three and six weeks of exposure compared to that of reference fish. Perch caged at the WWTP effluent-influenced site also had higher muscle δ13C and slightly depleted muscle δ15N after three and six weeks of exposure, suggesting differences in sewage-derived nutrient assimilation between sites. Concentrations of Σ34 polybrominated diphenyl ether (PBDE) were 2-fold greater in perch exposed downstream of the WWTP compared to those caged at the reference site. Metal concentrations in kidney of perch after three weeks of exposure were significantly lower at the effluent-influenced site. Kidney concentrations of Cd, Cu, Se, As, Zn and Fe were, however, higher after six weeks of exposure, supporting that metal accumulation is time- and element-specific. The metabolomes of perch from the effluent-influenced and reference sites were similar, but were distinct from the laboratory control fish, suggesting a caging effect on fish. Seven liver metabolites (glucose, malate, fumarate, glutamate, creatinine, histamine, and oxypurinol) were significantly more abundant in perch from cages than in the laboratory control perch. The combination of metabolomics and physiological variables provides a powerful tool to improve our understanding of the mechanisms of action of complex environmental pollutant mixtures in wild fish.
La végétation aquatique submergée (VAS) joue plusieurs rôles écologiques cruciaux et offre des services écosystémiques inestimables aux sociétés humaines. Cependant, une tendance mondiale montre un déclin de la VAS, généralement causé par la hausse des matières en suspension et des nutriments dans l’eau. L’étude de la VAS du lac Saint-Pierre de 2002 à 2021 a permis de documenter l’occurrence et la composition en espèces de cette végétation. La probabilité d’observer de la VAS aux différentes stations d’échantillonnage est passée de 75 % en 2002 à 20 % en 2021. Ce déclin de la VAS est accompagné d’un changement de composition de la communauté végétale principalement attribuable à la diminution de la vallisnérie d’Amérique ( Vallisneria americana ). Un potentiel refuge photique associé à la masse d’eau translucide des Grands Lacs supporterait le développement de la VAS dans le lac Saint-Pierre. Toute intervention réduisant la dispersion de cette masse d’eau dans le lac Saint-Pierre devrait être évitée. Des actions de gestion visant l’amélioration de la qualité de l’eau du lac Saint-Pierre et ses tributaires, en réduisant notamment la turbidité, sont nécessaires afin de protéger et de restaurer cette réserve mondiale de la biosphère de l’UNESCO.
Total gaseous mercury (TGM) air‐water flux measurements were taken using a dynamic flux chamber (DFC) coupled with a gaseous mercury (Hg) analyzer at the Bay St. François (BSF) wetlands (Quebec, Canada) in summer 2003. The measured TGM fluxes over water exhibited a consistent diurnal pattern, with maximum emissions during daytime and minimum fluxes occurring at night. Pearson correlation analysis showed that solar radiation was the most influential environmental parameter in TGM air‐water exchange. Significant correlations were also found between TGM fluxes and 1 hour time‐lagged water temperature, indicating the enhancement of fluxes by bacterial activities or chemical reactions. The concentrations of dissolved gaseous mercury (DGM) in water were measured during the 2003 sampling period and indicated that DGM was always supersaturated, which implied that the water body acted primarily as a source of mercury to the atmosphere. Several empirical models of mercury air‐water gas exchange were developed and evaluated. Compared to the published models, these proposed models were capable of producing good results, leading to a better agreement between the measured and modeled fluxes (improvements by 48–98%). Among these empirical models, the ones linking TGM fluxes with net radiation were superior because of their strong predictive capability. Two preferred models were selected for air‐water TGM flux estimation from Lake St. Pierre's surrounding wetlands. These two models yield a mean emission of 0.19–0.24 kg mercury during May–September each year from 1999 to 2003.
