Christiane Hudon

Environment and Climate change Canada · Water Science and technology

Measuring freshwater submerged aquatic vegetation (SAV) biomass at large spatial scales is challenging, and no single technique can cost effectively accomplish this while maintaining accuracy. We propose to combine and intercalibrate accurate quadrat-scuba diver technique, fast rake sampling, and large-scale echosounding. We found that the overall...

Large rivers can retain a substantial amount of nitrogen (N), particularly in submerged aquatic vegetation (SAV) meadows that may act as disproportionate control points for N retention. However, the temporal variation of N retention in large rivers remains unknown since past measurements were snapshots in time. Using high‐frequency plants and NO3⁻...

Measuring freshwater submerged aquatic (SAV) biomass at large spatial scales is challenging and no single technique can cost effectively accomplish this while maintaining accuracy. We propose to combine and intercalibrate accurate quadrat-scuba diver technique, fast rake sampling and large scale echosounding. We found that the relationship between...

Ecological subsidies have been hypothesized to be key factors affecting the dynamics of the recipient ecosystems. We assessed the impact of the flood regime on the assimilation of a trophic subsidy produced in the floodplain of a large fluvial lake, Lake Saint-Pierre (Quebec, Canada) on five invertivore littoral fish species (yellow perch (Perca fl...

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 Québec lakes distributed ov...

A time-series (1990–2013) of classified vegetation cover maps was produced for Netley-Libau Marsh, a 26,000 ha coastal wetland on Lake Winnipeg, to assess its current status and verify earlier trends of emergent vegetation loss. Open water area in the marsh was measured from late-summer Landsat images for 20 years; three classes of vegetation types...

Benthic cyanobacterial mats occurring in the St. Lawrence River fluvial lakes Saint-Louis and Saint-Pierre are dominated by Microseira (Lyngbya) wollei which produce several cyanotoxins including LWTX-1 that is characteristic of Microseira wollei. This cyanotoxin is not only present in the filaments forming benthic mats, but was also measured in th...

Submerged aquatic vegetation (SAV) is considered an important driver of the zooplankton community, owing to the refuge offered by its structural complexity. However, non-destructive in situ approaches to assess quantitatively the features of SAV beds and their effects on zooplankton community are still lacking. This study aims to: 1) estimate SAV c...

This study examines the temporal and spatial variability of the floodplain trophic contribution to the fish community of Lake Saint-Pierre, a large (≈ 300 km²), shallow (≈ 3 m) widening of the St. Lawrence River (Québec, Canada). We hypothesized that floodplain contribution to fish diet would be maximal during the early growing period following the...

Aquatic plants (macrophytes) are known to affect flow dynamics, contributing to flow resistance. Most studies on flow‐vegetation interactions are performed in laboratory flumes and focus on the flow field around plants, with little research at the level of vegetation patches in large aquatic ecosystems. In most hydrodynamic models, increased drag d...

Temporal changes (1970–2016) in St. Lawrence River wetlands were assessed between Cornwall and Québec (≈400 km) to assess wetland response to cumulative anthropogenic pressures in the watershed. Emergent wetlands area and biomass of submerged aquatic vegetation (SAV) were contrasted among five regions subjected to sharply different water level/disc...

Temporal changes (1970–2016) in St. Lawrence River wetlands were assessed between Cornwall and Québec (≈400 km) to assess wetland response to cumulative anthropogenic pressures in the watershed. Emergent wetlands area and biomass of submerged aquatic vegetation (SAV) were contrasted among five regions subjected to sharply different water level/disc...

Increased flux of carbon and nutrients from human activities in river basins were linked to acidification and deepwater hypoxia in estuaries and coastal areas worldwide. Annual loads (1995–2011) of suspended particulate matter (SPM), dissolved organic carbon (DOC), total nitrogen (TN) and total phosphorus (TP) were assessed at the Lake Ontario inle...

The mechanisms controlling phytoplankton biomass and composition in the lower reach of the eutrophic Rivière Yamaska were studied over six consecutive summers characterized by high (2008–2009) and low (2012–2013) discharge conditions. In the lower river reach, low river discharge favoured planktonic blooms dominated by centric diatoms, in contrast...

Freshwater molluscs can be affected by various environmental and anthropogenic pressures, which consequently determine their distribution, richness, and abundance in freshwater ecosystems. The objectives of this study were to determine the relative influence of water quality, exposure to wind, and emersion on the composition, diversity, and abundan...

Wetlands of a large fluvial lake in the St. Lawrence River (Québec, Canada) were visited during 3 years (2004–2006) to collect macroinvertebrates across the belt of emergent vegetation. We tested the hypothesis that hydrology, river landscape, and local environment would explain variations in macroinvertebrates. The 66 taxa collected lake-wide comp...

The influence of environmental factors controlling the biomass of submerged aquatic macrophytes, cyanobacterial mats, and epiphyton was examined at three nested spatial scales within the St. Lawrence River: (1) along a 250-km-long upstream–downstream river stretch, (2) among three fluvial lakes located within that river stretch and (3) within each...

The concentration of the saxitoxin analogue LWTX-1 was quantified in samples of the benthic filamentous cyanobacterium Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck collected in two fluvial lakes of the St. Lawrence River (Canada) over the 2006–2013 period. The study was aimed at documenting the spatial (between fluvial lakes, between sites w...

The performance of various algal indices to document improvements in water quality across a low nutrient concentration gradient was assessed during 2 years in the St. Lawrence River.

We investigated the ecological role of Lyngbya wollei (Farlow ex Gomont, comb. nov.) cyanobacterial mats in aquatic ecosystems, especially as a food source and shelter for the amphipod Gammarus fasciatus (Say). For this, we offered amphipods a choice between mats of L. wollei and either chlorophytes (Spirogyra, Rhizoclonium) or an artificial mat m...

Aquatic vegetation (AV) is an important component of aquatic system, affecting habitat carrying capacity and fish productivity. By modulating habitat complexity, AV has the potential to influence the early ontogenetic stages of many fish species. However, understanding how variations in AV abundance influence fish distribution and abundance at the...

Harmful proliferations of the mat-forming cyanobacterium Lyngbya wollei are increasingly reported in North American lakes, springs, and reservoirs. We examined the hypothesis that currents generated by waves and river flow control spatial and temporal variations of L. wollei biomass in a large river system. We measured L. wollei biomass together wi...

We experimentally assessed the mechanisms underlying the reduction in gastropod abundance in areas dominated by the filamentous, toxin-producing cyanobacterium Lyngbya wollei, which has replaced the large beds of Vallisneria americana in some areas of the St. Lawrence River. We hypothesized that the reduction in gastropod abundance was due to adult...

Aquatic vegetation (AV) is an important component of aquatic system, affecting habitat carrying capacity and fish productivity. By modulating habitat complexity, AV has the potential to influence the early ontogenetic stages of many fish species. However, understanding how variations in AV abundance influence fish distribution and abundance at the...

The St. Lawrence River (SLR) is the second largest waterway in North America. The discharge of the City of Montreal wastewater treatment plant (WWTP) represents the largest volume of treated wastewaters being released into the river. It also ranks as the largest sewage treatment plant of its kind in North America. Over the last decade, intensive mu...

Submerged aquatic vegetation (SAV) creates functional habitats for aquatic organisms in both marine and freshwater ecosystems. By structuring habitats (fragmentation, patch size, complexity), SAV influences prey–predator interactions, population dynamics, community structure and ecosystem functioning. In freshwater ecosystems, the loss of SAV beds...

The filamentous cyanobacterium Lyngbya wollei (Farlow ex Gomont) comb. nov. forms dark green to black mats on the bottom of rivers and lakes. Benthic mats often remain inconspicuous until they float to the surface because of trapped gas bubbles or until high winds and wave action dislodge and wash mats ashore. Mats induce dark, anoxic conditions co...

The use of sulfonylurea herbicides (SU) has increased greater than 100 times over the past 30 years in both Europe and North America. Applied at low rates, their presence, persistence and potential impacts on aquatic ecosystems remain poorly studied. During late-spring to early fall in 2009–2011, concentrations of 9 SU were assessed in two agricult...

Filamentous green algae (FGA) often proliferate in nutrient-rich rivers under low flow conditions. We assessed the hydrological and meteorological variables controlling the occurrence and composition of FGA in Lac Saint-Pierre (LSP), the largest of the St. Lawrence River fluvial lakes. We hypothesized that, under nutrient-rich conditions, hydrology...

SynonymsNutrient enrichmentDefinitionThe word “eutrophication” has its root in two Greek words: “eu” which means “well” and “trope” which means “nourishment.” The modern use of the word eutrophication is related to inputs and effects of nutrients (nitrogen and phosphorus) in aquatic systems (Nixon 1995).The process of eutrophication manifests itsel...

Lyngbya wollei is a toxin-producing cyanobacterium, forming mats of filaments that proliferate in rivers, lakes, and springs in North America. We determined its distribution over a 250 km stretch of the St. Lawrence River (SLR; Quebec, Canada) to elaborate predictive models of its presence and biomass based on chemical and physical characteristics....

We assessed the relative magnitude of various factors (year, preservation method, continent, investigator, and taxonomic level) affecting prediction of invertebrate dry mass (DM) in light of the variability of assessments of invertebrate density. We developed 34 length (L)–DM relationships for Oligochaeta and 17 freshwater invertebrate families bel...

Submerged aquatic vegetation (SAV) constitutes a major component of fish habitat, providing support for epiphytes and invertebrates as well as shelter from predators. The effects of wetland epuration from a mesotrophic to a nearly oligotrophic state were examined over a 15 km long reach of the St. Lawrence River under the direct influence of major...

Different abundance indices of American eel (Anguilla rostrata LeSueur) in the lower St. Lawrence River (SLR), eastern Canada, over the past 50 years were assessed to determine the effect of hydro-climatic factors on the species decline. Daily catches at commercial weirs and at an experimental fishery were used to model the long-term trend in eel a...

The presence of cyanotoxins in benthic Lyngbya wollei algae samples collected in a fluvial lake along the St. Lawrence River, Canada, was investigated using a multi-toxins method. Hydrophilic interaction liquid chromatography (HILIC) and reverse phased liquid chromatography (RPLC) were coupled to triple quadrupole mass spectrometry (LC-QqQMS) for q...

The physical structure of submerged aquatic plant communities differentially influences the availability of light and substratum in the water column and, thus, the functional role of epiphytes growing on macrophytes. We examined the depth distribution of photosynthesis and respiration of epiphyte communities within macrophyte stands of contrasting...

The physical events and changes of abundance of freshwater and marine organisms were documented daily at the mouth of the Great Whale River to a distance of about 5 km in the freshwater plume extending in Hudson Bay. For the 2-wk period before, during, and after the ice breakup, water flow and concentration of coarse (>500 μm) particulate organic m...

The sensitivity of Vallisneria americana Michx. as an indicator species of metal concentrations was assessed through the examination of its spatial (between- and within-site) and temporal (short- and long-term) variability. Eight macrophyte beds located in the St. Lawrence and Ottawa rivers were selected to contrast metal concentrations found in pl...

The egg development index, dry weight, and energy content were measured on eggs from 148 ovigerous female lobsters (Homarus americanus) caught off îles de la Madeleine (Québec). Two modes of embryonic development were observed at stages 3 and 8 (Perkins. 1972. Fish. Bull. 70: 95–99). Stage 3 predominated among females of 71–82 mm and stage 8 among...

Density, biomass and size structure were closely related to the coarseness of the bottom. Density and biomass were greater and mean size was larger on algae-covered boulders than on bare stones. Postlarval and juvenile lobsters were most numerous on shallow rocky bottoms where high densities (0.8-3.8 ind. m-2) of small lobsters (mean size from 23.8...

The carapace length of the three planktonic larval and one postlarval stages of Homarus americanus was measured for larvae collected off îles de la Madeleine over three summers. Mean larval size did not vary between years or locations around the islands. The size of stages I and II remained constant throughout the summer, but after molting into sta...

In the Canadian eastern Arctic, the catches of common species of decapods and fish in bottom trawls reveal a continuum of increasing species richness and abundance in an easterly direction through Hudson Strait. Species richness is greatest in Ungava Bay, where Arctic and Labrador Sea components of the fauna coexist. Over the study area, species co...

This study characterizes the seasonal anadromous movements of a brook charr population and compares its biological and energetic characteristics with charr spending summer in freshwaters. Downstream movements monitored at a counting fence over 3 yr were most intense in spring but occurred until fall and were positively correlated with rapid increas...

The vertical distribution and diet of shrimp (Pandalus montagui) were investigated using a multistage plankton sampler (BIONESS) and were compared with those of shrimp captured on the bottom using a trawl. Massive nocturnal vertical migrations of shrimp were observed in association with intense pelagic feeding activity. The sex ratio, size frequenc...

Abundance and spatial distribution of the larvae of the American lobster (Homarus americanus), the common rock crab (Cancer irroratus), and the toad crab (Hyas spp.), were monitored weekly during the summer of 1980 at a grid of 12 stations located in Baie de Plaisance. Following a period of winds ≥ 30 km∙h−1 shifting from the north to the southeast...

American lobster (Homarus americanus) landings per unit of habitat, calculated for 25 statistical districts (SD) of Atlantic Nova Scotia (N.S.), were consistently higher in northern Cape Breton (SD 1–7) and southwestern N.S. (SD 32–34) than from the eastern (SD 15–18) and southern (SD 22–31) shores. Analyses suggest that changes in lobster populati...

The initial phases of subtidal and intertidal community development were observed using scanning electron microscopy on samples from plastic panels immersed monthly in the St. Lawrence Estuary.Bacteria and diatom populations were quantitatively evaluated on samples collected from May to November, 1978. The pattern of immersion and/or periodical eme...

Settled larvae of Balanus crenatus were collected at Pointe Mitis, in the St. Lawrence Estuary, Quebec. Four substrata were sampled and observed using scanning electron microscopy (SEM): shells of Mytilus edulis, fronds of Fucus evanescens, and laminated panels immersed for periods of 4 and 8 wk. Following this treatment, 23 variables describing th...

Historical records of average seasonal water levels in the St. Lawrence River over the past 80 years reveal cyclic variations of up to 1 m above (1976) and 1 m below (1965) present levels. These variations are probably related to climatic conditions in the basin. Over the same period, the vertical range of seasonal water levels decreased from 2.2 t...

Consistent differences in physical, chemical, and biological characteristics were observed along a transversal river section located 2 km downstream of the confluence of the Ottawa and the St. Lawrence rivers. Phytoplankton sampled at stations subject to the influence of the St. Lawrence River had a lower biomass, smaller cell volume, lower chlorop...

The maximum depth of macrophyte colonization and depth distribution of macrophyte biomass were assessed over 3 years, in late summer, at six sites in the St. Lawrence River and two sites in the Ottawa River (Lake des Deux Montagnes). Maximum depth of submerged plant colonization could be predicted from the light extinction coefficient (r2 = 0.82) a...

The annual load and the composition of material exported to the coast of Hudson Bay were characterized and modelled over the hydrological cycle of the Great Whale River. Annual exportations of particulate inorganic matter (PIM), particulate organic matter (POM), and dissolved organic carbon (DOG) to Hudson Bay were estimated at 135 000, 21 000, and...

Greenland cod populations near Wemindji, eastern James Bay, were studied in 1987 and 1988 to describe the species' general ecology and life-history characteristics. During the summer, they principally occupied shallow (2–5 m) coastal waters. This habitat was characterized by a belt of eelgrass (Zostera marina) at depths of 1–3 m, salinities between...

Proliferations of filamentous chlorophytes and mats of cyanobacteria (hereafter termed metaphyton) are increasingly observed in rivers, lakes, wetlands, and estuaries undergoing eutrophication, but their contribution to invertebrate production and overall ecological significance remains poorly understood. In Lake Saint-Pierre, a shallow widening of...

The epiphytic cyanobacterium Gloeotrichia pisum forms spherical colonies embedded in a gelatinous matrix that is attached to submerged aquatic vegetation. In surveys of 2 fluvial lakes of the St. Lawrence River conducted in 2006-2007, we examined its growth conditions and diazotrophic ability in conjunction with the biomass and condition (carbon (C...

Primary production, planktonic respiration, bacterial abundance, and chlorophyll a were measured in the epilimnion of two Canadian Shield lakes and in two large rivers to establish their metabolic balance and to contrast oligotrophic and oligo-mesotrophic systems. Pronounced diel respiration cycles were observed in all systems, with a minimum in th...

The implications for fish populations of long- (multi-decadal, 1919–2007), medium- (inter-annual) and short- (seasonal, daily) term variations in water temperatures and levels were examined in the St. Lawrence River (SLR). The effects of the seasonal thermal regime of the SLR and its tributaries on the thermal budgets of resident and migrating fish...

L'expansion des colonies de Phragmites australis a été suivie entre 1980 et 2002 sur sept séries de photographies aériennes et d'images satellitaires couvrant les Grandes Battures Tailhandier (îles de Boucherville, fleuve Saint-Laurent, Québec, Canada). En 23 ans, la superficie occupée par la graminée s'est accrue de façon exponentielle, passant de...