As in many coastal countries, the water supply of Quebec's coastal populations depends mainly on groundwater, whose integrity is threatened by the sea level rise and increase in marine flooding on the coastal plain. This zone is particularly vulnerable to the issue of salinization of coastal aquifers since the coastline of the south shore of the Lower St. Lawrence Estuary and Gulf. For example, in the Chaleurs Bay, relative sea level rise rates reached 7.0 mm/year between 2000 and 20143, which is significantly higher than the global average sea level rise of 3.6 mm/year reported for the period 2006–2015. In eastern Quebec, where between 30% and 50% of the inhabitants use the groundwater resource, the intrusion of saltwater into freshwater coastal aquifers poisons an essential resource. Increased chloride and sodium concentrations, as well as trace metal desorption due to ionic strength, threaten the integrity of the resource and the health of consumers. The objective of this study is to determine and mapping the actual (2022) and future (2050-2100) groundwater vulnerability to SWI under changing climate conditions at different coastal locations in the Bas-St-Laurent region. GALDIT is a diagnostic method based on the index and ranking that evaluates the vulnerability of coastal aquifers, using six parameters, that consider groundwater occurrence (G), aquifer hydraulic conductivity (A), height to groundwater-level above sea-level (L), distance from shore (D), impact of existing status of seawater intrusion (I) and aquifer thickness (T). These parameters were predicted based on the coastline retreat and seawater levels anticipated for 2050 and 2100 and surficial projection maps. The poster will present GALDIT mapping in 3 specific locations of the Bas-Saint-Laurent region where salinization still occurs (Figure 1), as well as the various validation steps carried out to validate the future GALDIT. This innovative index will significantly contribute to better protection of coastal drinking water sources from climate issues and can also be scaled up in most of Quebec's coastal communities. It could be used by local authorities and decision makers to ensure a durable use of groundwater through the protection of the most vulnerable areas.

Abstract: Flow and turbulent structures generated by the interaction of waves with arrays of vertical cylinders are investigated using large eddy simulations. Validation simulations performed with a Keulegan–Carpenter (KC) number of 20 corresponding to the laboratory experiment of Sumer et al. (J. Fluid Mech., vol. 332, 1997, pp. 41–70) show that LES predicts accurately the water surface elevations and the vertical velocity profiles at different phases of waves. High-Reynolds-number LES simulations are then conducted with 1.5 ≤ KC ≤ 30.8 to investigate the changes in the vortices and energy dissipation generated by wave-cylinder interactions. Vortices generation mechanisms vary with KC numbers, with no vortices observed at the lowest KC number (=1.5). While at the highest KC number, horseshoe vortices are present over part of the oscillatory cycle and up to three wake vortices are shed. Bed shear stresses are the highest where there are identical horseshoe vortices. In addition, the maximum bed shear stresses are commonly observed when acceleration rate of local flow is the largest in each wave cycle. This implicates that sediments would likely be resuspended before the near-bed velocity attains its maximum. Wave attenuation coefficients increase with increasing KC number and density of cylinders. The first row of cylinders facing the wave contributes the highest wave attenuation, whereas contributions from the five and further downstream rows are negligible. This observation suggests an optimized shoreline protection strategy with four-rows of mangrove planted along the shorelines.

Beaches are coastline features that offer economic benefits, ecosystem services, and natural barriers against flooding. Sustainable management of beaches requires a firm understanding of hydrodynamics and sediment transport processes. The swash zone is where breaking waves drive rapid, shallow, and intermittent flow conditions that mobilize large volumes of sediment. While the swash zone is a relatively narrow part of the nearshore region, swash zone processes determine whether the foreshore erodes or accretes. Waves commonly approach beaches at oblique angles and drive flow and sediment transport in the swash zone in both the cross-shore and alongshore directions. Most previous swash zone studies have focused solely on cross-shore dynamics. In this study, controlled laboratory experiments were conducted in a 26.0 m long, 20.6 m wide, and 1.0 m deep wave basin to investigate swash zone alongshore processes driven by obliquely incident waves. The beach consisted of fixed, smooth, concrete with a 1:10 slope. High frequency data of water depth and velocity were collected using sensors at four cross-shore locations along three different alongshore transects (see Figure 1). The experiments included a range of wave forcing conditions (wave spectra, heights, wavelengths) at different incidence angles (5,10,15 degrees) (see Table 1). An overview of the experiment and preliminary results on the relative importance of the alongshore component of near-bed velocity profiles and bed shear stress will be presented.

Along the northern coast of France, the Authie estuary is a shallow macrotidal embayment experiencing rapid infilling by sand from the English Channel. The south coast of the estuary has prograded northwards for several centuries, due to the development of an extensive intertidal and subtidal sand spit. The progressive extension of this prominent accumulation forced the main channel of the estuary to flow along the northern shore of the estuary mouth, resulting in shoreline erosion for several decades. To the south of this eroding zone, a cuspate foreland developed, forming of a series of foredune ridges. Recent morphological changes of this estuarine coast were analyzed using orthorectified aerial vertical photographs spanning from the 2005 to 2022, airborne Lidar topographic data and topo-bathymetric data of the estuary seabed. Our measurements show that the northern part of the cuspate foreland began to erode around 2005. Then, erosion continued to proceed during the following years at rates up to more than 20 m/yr after 2010, resulting in the complete destruction of the cuspate foreland by 2022, despite several shoreline protection works that were conducted in order to slow down coastal erosion.

The Bay of Sept-Îles (BSI) is a highly exploited subarctic ecosystem, home to North America's largest mineral port and aluminum smelter [1], [2]. In the context of global climate change, environmental monitoring of the BSI must be based on reliable scientific baseline science to ensure effective management and conservation of ecosystem services. Due to a lack of long-term data, the paleoceanographic approach will enable us to infer past conditions in the BSI, deduce the effects of ongoing anthropogenic and climatic pressures on the ecosystem, and explore the microbial vertical structure of the sediments. By detecting chloroplast DNA in samples from a sediment archive (sedaDNA), we were able to explore the taxonomy of photosynthetic eukaryotes using the PhytoRef database. Chaetocerotaceae, from the phylum Bacillariophyta (diatoms), are the microalgae family most abundant in the data. The complete vertical structure of bacteria and archaea was also determined using the Silva 138 database. This gradient of microorganisms can then be used to check whether signals of anthropogenic pressure or climate change are detectable. As an example, the sediments in the BSI could be contaminated with Arsenic (As) [3], as inferred by the presence of the bacterial genus Acidothermus (4 to 6cm, 7 to 8cm and 14 to 15cm), which is often associated with the presence of As in sediments [4]. Finally, with the varied ecology of bacteria, we were able to infer the depth at which sediments become anoxic. Indeed, bacteria of the order Pseudomonadales[5], a predominantly oxic order, are the main contributors up to a depth of around 9 cm, while beyond this depth, Desulfobacterales[6], a strict anaerobic order, are the main contributors (Figure 1). Our results allow us to explore the biodiversity of microorganisms that leave no visible traces in the sediment archive, and to determine whether this method is effective for environmental monitoring.

Coastal erosion is a growing concern in Quebec, where 50% of the coastline is vulnerable to erosion. Coastal erosion, a natural phenomenon, impacts the activities of coastal residents. In Quebec, the cold winter temperature freezes the soil, and thawing generally occurs in the spring when temperatures soften. The freeze-thaw cycle process makes soils vulnerable to erosion by altering their physical structure, altering their water content, density, and shear strength. Previous research indicate that soil freeze-thaw effects are some of the least understood aspects of the soil erosion process, even though freeze-thaw cycles have been investigated for decades. On the other hand, numerical modeling techniques are becoming popular engineering tools for assessing long-term shoreline recession and determining performance of innovative designs of coastal defence structures, considering projected climate change. The project’s methodology consists of three phases: first, determine the critical shear strength of frozen and thawed soils under the freeze-thaw cycle, second, couple the determined shear strength within sediment transport model and third, incorporating the effects of climate change in the model developed. The proposed research is developed based on the needs of the industry involved in the design of future infrastructure and management of existing infrastructure in the Quebec’s coastal zone.

Turbidity is a crucial aspect of water quality, particularly concerning the potential impact of suspended sediments on sensitive benthic environments. Traditional methods of measuring Suspended Sediment Concentration (SSC) involve collecting water samples and assessing particulate matter concentration. However, optical-based turbidity loggers offer a more cost-effective and high-resolution approach for long-term monitoring. This study investigates ice-free conditions in estuaries within the Northumberland Strait (Canada) through the deployment of five upward-looking Acoustic Doppler Current Profilers (ADCPs) and turbidity meters. Turbidity is a proxy for suspended sediment concentrations (SSC) and varies on daily to interannual periods. Water quality monitoring using turbidity loggers is often reported in Nephelometric Turbidity Units (NTU) and it is usual for NTU sensors to be calibrated to provide estimates of SSC by determining the relationship between the two measurements. This study outlines the methods and results of a laboratory-based protocol for finding the site-specific conversion factor for NTU to SSC at 5 water quality monitoring locations. Additionally, Drivers were identified using linear regression to model SSC variability. The findings indicate a statistically significant correlation between tidal range and SSC, discharge and log- SSC, water velocity in the 1st ADCP bin and SSC, as well as the wind speed and SSC.

Global change affects physicochemical and biological compartments of coastal ecosystems from global to local scales. However, the multiple and interacting effects makes it challenging to identify what causes ecosystem responses. In river-dominated ocean margins, marine organisms are subject to a highly variable environment in terms of e.g., water temperature, currents, salinity, river discharges, turbidity. This may affect the quantity and quality (origin, composition) of their food sources and their physiological status, which is recorded in carbon (C) and nitrogen (N) isotopic (δ13C, δ15N) and elemental ratios (C:N) of their soft tissues. Particularly, sessile filter-feeding bivalves species are particularly sensitive to changes occurring in the water column. In a multi-ecosystem study, we selected 33 sampling sites along French coastlines, distributed under the influence of large river plume gradients (from the river mouth to away from any main river-influence), or outside of any significant river influence. We analyzed δ13C, δ15N and C:N pluri-decadal trends of the bivalves Mytilus spp. and Crassostrea gigas as proxies for environmental changes over the period 1981 2021. These trends were then correlated with proxies for climate and other anthropogenic activities in order to identify whether coastal biota responded to global, regional or local effects. Our goal was to assess, through bivalve food sources and physiology, the 40-years change in river influence on the coastal areas in the era of global change. Over the four decades, bivalves δ13C significantly decreased (-0.58±0.23‰ decade-1) for 93% of the sites. Bivalves δ15N were lower close to the river mouths, and significantly decreased (-0.41±0.26‰ decade-1) for 63% of the sites. The decrease was more pronounced along the gradient of the Seine River influence, and there was no clear overall pattern among the other gradients of river influence. The C:N ratio did not exhibit significant trends but large inter-annual variability at some sites. These variations in space and changes over time will be linked to environmental datasets from global and local climate, continental inputs, coastal water chemical properties, contaminants and food sources, reflecting large, regional and local pressures of global change.

Diatoms are frequently used for paleoenvironmental studies in freshwater ecosystems, but less so in estuarine and marine environments. Sept-Îles Bay, in the Gulf of Saint-Lawrence (Québec, Canada), is the site of North America’s busiest mineral port, exposing its system to various anthropogenic pressures. The main objective of this project is to define past reference conditions for various environmental variables and assess current environmental changes in the ecosystem based on marine coastal diatom models. Diatom assemblages from surface sediments were characterized and environmental variables were measured at 35 sites along a 85km coastal transect following the 20-30 m bathymetric depth. More than 500 diatom taxa were identified and 19 surface water variables were measured (once in July 2021 and once in July 2022). Multivariate numerical methods were employed to determine the species response to the measured parameters. Turbidity, temperature, and salinity explained a significant proportion of the variation in the diatom data, leading to the development of quantitative transfer functions for these variables. Models were subsequently applied to the sedimentary diatom assemblages from a 30 cm sediment core extracted within the Bay, at a depth of 20 m. The quantitative inferences provide insight into the dynamics of past environmental changes in this high-use coastal environment. The analysis of the sediment core also revealed temporal variations in species assemblages, particularly through the industrial era. Our results offer useful knowledge on the state of variability of this region, which until recently had been little-studied, and offers a means to guide management towards sustainable development in subarctic coastal ecosystems under diverse pressures.

The Mary River Mine, an open-pit iron ore mine on Baffin Island, has been mining a high-grade iron ore deposit since 2015. Bulk carriers awaiting loading drop anchor west of Ragged Island where they discharge their ballast water and sediments. Although international and Canadian laws to limit the introduction of non-indigenous species (NIS) exist, the introduction of NIS into aquatic ecosystems via ballast discharge poses a significant threat. Here we report dinoflagellate and dinoflagellate cyst assemblages in Milne Inlet (Nunavut, Canada). Toxins produced by certain dinoflagellate species during harmful algal blooms (HABs) enter the marine food web via filter feeders where they bioaccumulate, affecting ecosystem health. Secondary and tertiary consumers are therefore susceptible to poisoning and these toxins can be fatal to humans and wildlife [1]. The risk of poisoning from HABs is particularly high for Inuit communities in the Canadian Arctic that depend on fish resources. It is therefore essential to acquire baseline information on the diversity, structure, and distribution of native dinoflagellate communities in the Canadian Arctic to detect NIS and assess the risk of HABs. A total of 39 taxa from 10 families were identified in our plankton samples. Protoperidinium pellucidum, Protoperidinium brevipes, Protoperidinium cf. mite and Tripos arcticus are the dominant species, accounting for more than 50% of the assemblages. Seven taxa produce toxins responsible for paralytic shellfish poisoning [2] (saxitoxins; Alexandrium cf. catenella), diarrhetic shellfish poisoning [3] (okadaic acid; Dinophysis acuminata, D. acuta, D. arctica and Phalacroma rotundatum) or whose effects on humans remain unknown [4], [5] (yessotoxins; Gonyaulax spinifera and Protoceratium reticulatum). We identified 18 dinocyst taxa in our sediment samples, with the assemblages being dominated by Brigantedinium spp., Islandinium minutum and Operculodinium centrocarpum. All species identified in our samples have previously been observed in this region.

Particulate organic matter (POM) is a key component of biogeochemical cycles and aquatic food webs. In estuarine systems, POM is a mixture of sources produced in-situ (e.g., phytoplankton, microphytobenthos, sewage POM) and originating from adjacent reservoirs (river, coastal systems; e.g. terrestrial POM, marine and riverine phytoplankton). POM elemental and isotopic ratios are widely used in aquatic biogeochemistry and ecology to determine the origin and even quantify, thanks to mixing models, the composition of POM. However, POM elemental and isotopic values are usually highly variable in space and time making their use often restricted to snapshot studies or requiring a dense temporal sampling strategy. Here, we propose a comprehensive study of seven temperate estuaries in France with contrasting geomorphological features and covering a wide range of environmental characteristics (flow, watershed area, eutrophication, turbidity…), to further our understanding of the dynamics and drivers of POM composition. We characterized POM elemental and isotopic composition and measured a set of environmental variables along the salinity gradient of each of these systems at either a monthly or seasonal frequency, covering at least a full annual hydrological cycle. The isotopic signature and elemental composition of primary organic matter sources was also characterized and incorporated in mixing models to quantify their relative contribution to POM. Then, the drivers of both the temporal and spatial dynamics of POM composition are determined. Typology of estuaries, based on POM composition and drivers, is put forward, differentiating three main types of estuaries. Briefly, POM composition can be stable in some estuaries, controlled by the river flow. Estuaries with high turbidity are dominated by a terrestrial source, refractory or labile. Then, estuaries with the lowest turbidities show clear seasonalities, controlled by an ambivalence between phytoplankton and terrestrial matter. Finally, the role of estuaries in transforming or transferring POM in the land-ocean continuum are discussed.