Large Fluvial Lake Research Articles

Fish responses to underwater sounds depend on auditory adaptations: An experimental test of the effect of motorboat sounds on the fish community of a large fluvial lake.

Freshwater fishes exhibit a wide range of auditory adaptations and capabilities, which are assumed to help them navigate their environment, avoid predators, and find potential mates. Yet, we know very little about how freshwater environments sound to fish, or how fish with different auditory adaptations respond to different soundscapes. We first compiled data on fish hearing acuity and adaptations and provided a portrait of how anthropogenic sounds compare to natural sounds in different freshwater soundscapes. We then conducted a sound-enrichment field experiment at Lake Saint Pierre, a large fluvial lake in Canada, to evaluate the effect of motorboat sound exposure on the fish community by looking at the extent to which changes in species abundances were linked to auditory adaptations. Data compilation showed that the hearing acuity of most species overlaps with a wide range of ambient and anthropogenic underwater sounds while the field experiment showed that species with more specialized auditory structures were captured less often in sound-enriched traps, indicating avoidance behavior. Our findings highlight the importance of considering species' sensorial adaptations when evaluating the community-scale effects of anthropogenic sounds on the fish community, especially at low levels of anthropogenic activity.

Hydrological control of a floodplain subsidy to littoral riverine fish

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 flavescens), pumpkinseed (Lepomis gibbosus), bridle shiner (Notropis bifrenatus), golden shiner (Notemigonus crysoleucas), and banded killifish (Fundulus diaphanus)). We hypothesized that the incorporation of floodplain-derived carbon into fish biomass and individual fitness would increase in years with higher magnitude and longer duration floods. Studying four consecutive years with contrasting spring-flood events, we used a stable isotope mixing model to estimate floodplain contribution, and linear mixed models to analyze the impact of hydrology on floodplain contribution and fish body condition. Floodplain and main river’s invertebrates exhibited statistically distinct isotopic ratios (t test: p value < 0.001). Floodplain contribution and body condition were positively correlated with flooding intensity and duration for all species. Body condition was positively correlated with the assimilation of floodplain-subsidy for golden shiner and banded killifish. Our study identified flooding intensity as a main driver influencing the assimilation of floodplain-derived carbon by littoral fish and their fitness in a large river ecosystem.

Submerged aquatic vegetation cover and complexity drive crustacean zooplankton community structure in a large fluvial lake: An in situ approach

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 cover and complexity using subaquatic upward photographs (SUP) and 2) analyse the relationship between SAV variables and crustacean zooplankton composition and functional diversity (FD). SAV biomass and zooplankton were sampled at 52 stations in a large fluvial lake. Two metrics based on SUP were used to quantify SAV cover and complexity: 1) the percentage of the underwater landscape occupied by SAV (PLAND: SAV cover), and 2) its perimeter-area fractal dimension (PAFRAC: SAV complexity). Zooplankton composition and functional diversity were estimated based on crustacean species assemblages and functional traits. We used linear models to describe the relationships between SAV indices, environmental variables and zooplankton abundance, biomass and FD. SUP was an effective method to estimate in situ SAV cover and complexity. PLAND and PAFRAC were positively related to SAV biomass and zooplankton abundance, yielding a non-destructive assessment of the SAV-zooplankton relationships. Our study partially supports the habitat complexity-ecological niche availability hypothesis, as SAV cover and complexity influenced zooplankton functional groups and diversity indices. However, water transparency and depth also had important effects in interaction with PLAND and PAFRAC, and it remains difficult to fully disentangle the effects of SAV complexity from SAV cover on crustacean zooplankton community structure.

Mercury and selenium distribution in key tissues and early life stages of Yellow Perch (Perca flavescens)

Whereas early life stages are usually considered as particularly sensitive to both organic and inorganic contaminants, field studies assessing contaminant bioaccumulation in these stages are scarce. Selenium (Se) is thought to counteract Hg toxic effects when it is found at Se:Hg molar ratios above 1. However, the variation of this ratio in key fish tissues of different early life stages is mostly unknown. The present study therefore aimed to assess Hg and Se content in gravid female tissues (gonads, muscle, liver, gut, and brain) and different life stages (egg masses, newly hatched larvae (NHL), larvae and juvenile) of Yellow Perch (YP) in a large fluvial lake (Lake Saint-Pierre, Québec, Canada). Se:Hg molar ratios were measured for each compartment in order to fill associated knowledge gaps. Total Hg (THg) and methylmercury (MeHg) concentration varied between tissue according to the following trend: Muscle > Liver > Gut > Brain > Gonads. During YP early life stages, MeHg values increased according to an ontogenetic pattern (mg/kg dw) (mean ± SEM): Egg masses (0.01 ± 0.002) < NHL (0.015 ± 0.001) < Larvae (0.14 ± 0.01) < Juveniles (0.18 ± 0.01). Se concentrations in different YP tissues showed the following trend (mg/kg dw) (mean ± SEM): Gut (3.6 ± 0.1) > Liver (2.5 ± 0.1) > Gonads (1.92 ± 0.06) > Brain (1.26 ± 0.03) > Muscle (1.23 ± 0.06). In YP early life stages, Se concentrations were highest in NHL (3.0 ± 0.2), and then decreased as follows: Egg masses (2.8 ± 0.1) > Larvae (1.37 ± 0.04) > Juveniles (0.93 ± 0.05). Se:Hg molar ratios varied considerably and were systematically above 1. This is the first study to simultaneously report Hg and Se bioaccumulation through fish life cycle.

A three‐dimensional numerical model investigation of the impact of submerged macrophytes on flow dynamics in a large fluvial lake

Abstract 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 due to plants is modelled by increasing the Manning's n roughness coefficient. The objectives of this study were to: (1) develop a three‐dimensional hydrodynamic model (Delft3D) applicable to large water bodies including a novel approach to represent macrophyte resistance (modified k‐ε turbulence closure model); and (2) compare the modelled flow with field measurements for different vegetation configurations and patch arrangements. Work was carried out in Lake Saint‐Pierre, a large fluvial lake of the St Lawrence River in Québec, Canada. Results showed a marked increase in residence time in the zone affected by macrophytes when using the modified k‐ε turbulence closure model compared to the Manning's n approach, particularly near the bed. An improved agreement with field measured depth‐averaged velocity is obtained with this novel approach (correlation coefficient of 0.80 compared to 0.46 with Manning's n only). In addition, a good fit was obtained between vertical velocity profiles modelled and measured in the macrophyte zone. Sensitivity analysis revealed that the additional drag due to plants was closely associated with plant height, but that plant density played only a minor role in retarding velocities. These findings indicate that it is possible to accurately quantify both the horizontal and vertical flow modulations resulting from submerged vegetation in large fluvial systems. Considering that the Delft3D model is capable of approximating measured velocity magnitude, preserving the logarithmic shape throughout the water column and reaching near‐zero velocities without increasing the roughness coefficient, we recommend this modelling approach for future research on the impact of macrophytes on flow at the scale of vegetation patches in large water bodies comparable to Lake Saint‐Pierre.

Modeling the effective spawning and nursery habitats of northern pike within a large spatiotemporally variable river landscape (St. Lawrence River, Canada)

AbstractSpawning and nursery habitats are often spatially disjunct as a consequence of specific life history stage habitat requirements and spatiotemporal habitat changes. Nevertheless, free‐swimming larvae originating from spawning habitats must reach productive nurseries to maximize survival. We examined spawning and nursery habitats of northern pike (Esox lucius) over the past 50 yr to investigate how habitat connectivity and hydrological variability interact to alter the distribution of effective spawning habitat. Habitat models coupled to a least‐cost approach were developed to quantify connectivity between habitats in two contrasting regions of the St. Lawrence River (Canada): a riverine corridor lake (~ 46 km) and a large fluvial lake (~ 48 km). Our simulations demonstrate that depending on hydrological conditions, between 3% to 51% of spawning habitat used by adults in the riverine corridor, and 22% to 90% in the lake, allowed larval survival up to the fifth week of development. Although rapid dewatering of spawning habitat is responsible for most spawning losses in the fluvial lake, increasing water currents were responsible for dispersing larvae away from suitable habitats in the riverine corridor. However, stable hydrological conditions led to spatial overlapping of spawning and nursery habitats favoring larval survival and growth. In addition, downstream larval dispersal by low water currents allowed larvae to reach spatially disjunct nursery habitat, especially in the lake. Our results indicate that despite the vast areas of potentially suitable habitats provided by large vegetated floodplains of fluvial lakes, the effective spawning habitats favoring early‐life recruitment are much more heterogeneous and variable both spatially and temporally.

Molluscan assemblages under multiple stressors in a large fluvial lake

Molluscan assemblages under multiple stressors in a large fluvial lake

Effects of hydrological regime, landscape features, and environment on macroinvertebrates in St. Lawrence River wetlands

Wetlands of a large fluvial lake in the St. Lawrence River (Quebec, 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 comprised a few abundant but widespread groups (Malacostraca, Oligochaeta, Chironomidae, and Mollusca). Between 2004 and 2006, total abundance at 5 sites monitored annually fell by one order of magnitude, and taxa richness decreased from 19 to 12 taxa. Proportion of amphipods (Gammaridae) dropped sixfold whereas proportion of annelids (Oligochaetes) rose ninefold. The impoverishment of macroinvertebrates coincided with low summer water levels in 2005 and 2006, resulting in the periodic emersion of up-slope sites. Spatial differences in macroinvertebrate communities were less important than inter-annual differences, owing to large variability among sites. Patterns in macroinvertebrate communities were related to water depth, vegetation, and local changes in sediments (31% of variance explained). Gammaridae (Malacostraca) were strongly associated with down-slope sites, whereas Oligochaeta (Annelida) dominated in up-slope sites. Inter-annual changes in water level had major effects on macroinvertebrate communities in Lake Saint-Pierre, above and beyond other environmental variables.

Wave exposure and current regulate biomass accumulation of the benthic cyanobacteriumLyngbya wolleiin a large fluvial lake

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 with meteorological, physical, and chemical variables during 2009–2011 at 10 sites along a gradient of exposure to current and wind in Lake Saint-Louis, a large (148 km2) fluvial lake of St Lawrence River. Where water chemistry was conducive to L. wollei growth, wave exposure and current velocity controlled spatial and temporal biomass variations. Biomass increased from May to November and persisted during winter. Interannual variations were primarily controlled by river flow (water level), and high spring discharge dislodged mats from the previous growing season. Under climate-change scenarios, anticipated declines in water level and rising storm intensity may lead to an increase in the areas colonized by L. wollei, more frequent than present-day episodes of mat disruption, water-use impairment, and beach fouling.

Spatio-temporal variations in biomass and mercury concentrations of epiphytic biofilms and their host in a large river wetland (Lake St. Pierre, Qc, Canada)

Within wetlands, epiphytes and macrophytes play an important role in storage and transfer of metals, through the food web. However, there is a lack of information about spatial and temporal changes in their metal levels, including those of mercury (Hg), a key priority contaminant of aquatic systems. We assessed total mercury (THg) and methylmercury (MeHg) concentrations of epiphyte/macrophyte complexes in Lake St. Pierre, a large fluvial lake of the St. Lawrence River (Québec, Canada). THg and MeHg concentrations were ten fold higher in epiphytes than in macrophytes. THg concentrations in epiphytes linearly decreased as a function of the autotrophic index, suggesting a role of algae in epiphyte Hg accumulation, and % of MeHg in epiphytes reached values as high as 74%. Spatio-temporal variability in THg and MeHg concentrations in epiphytes and macrophytes were influenced by water temperature, available light, host species, water level, dissolved organic carbon and dissolved oxygen.

What controls distribution of larval and juvenile yellow perch? The role of habitat characteristics and spatial processes in a large, shallow lake

The goal of this study was to determine the relative contribution of environmental and spatial processes governing the distribution of larval and juvenile yellow perch (Perca flavescens) in two shallow embayments of a large fluvial lake on the St. Lawrence River system. We tested the hypotheses that: i) larval distribution is not related to habitat characteristics, presumably due to their relatively low swimming capacity, whereas ii) these environmental variables drive juvenile distribution, reflecting a more active habitat selection. This study is one of the first attempts to partition the relative roles of environmental and spatial factors in shaping the distribution of a freshwater fish through its early ontogeny. We show that larvae were not spatially aggregated within the embayments and that habitat characteristics, mainly related to aquatic vegetation, played an important role in explaining their distribution. In contrast, juvenile abundances were not significantly related to habitat characteristics, despite being spatially structured over multiple scales. Contrary to our predictions, habitat association was stronger for larvae than for juveniles which were aggregated independent of habitat characteristics. Increased swimming capacities may thus facilitate the aggregation of juveniles rather than strengthening their association with habitat, at least at the scales considered here (ca 3km2). These results shed a new light on the factors governing larval and juvenile yellow perch distribution, suggesting that active habitat choice might begin earlier than previously thought.

Hydrological control of filamentous green algae in a large fluvial lake (Lake Saint-Pierre, St. Lawrence River, Canada)

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 and climate would be the main drivers of FGA occurrence and composition. We tested this hypothesis during the 2005 growing season, by fortnightly sampling at 7 stations within Anse-du-Fort, a 9km2 LSP embayment chronically exposed to the inflow of two tributaries draining farmland. Cladophora was the prevalent genus (89% occurrence), but Oedogonium, Hydrodictyon, and Spirogyra were at times dominant. Hydrological (depth, water level change) and meteorological variables (hours of sunshine, wind velocity) were the best predictors of FGA occurrence (r2=0.55), but no water quality variable was significant in any model. The generality of our findings was then assessed using lake-wide FGA occurrence from surveys conducted over 6years (2000–2001 and 2005–2008) of widely different hydrological and climatic conditions. Years of low water levels (2001 and 2007) coincided with early occurrence, highest prevalence and longest seasonal FGA persistence. Validation of model predictions using remote sensing images yielded a 74% success rate in forecasting FGA. We identified a water level limit for FGA occurrence (<4.07m above sea level). This limit provides a simple operational guideline for managers, improving our ability to predict FGA proliferation under increasingly low discharge and warming climatic conditions forecasted for the St. Lawrence River.

A mechanistic‐based framework to understand how dissolved organic carbon is processed in a large fluvial lake

Lay AbstractDissolved organic carbon (DOC) is a fundamental component of the biogeochemical cycling of nutrients in aquatic ecosystems and is the main carbon source supporting bacterial production. The efficiency at which heterotrophic (nonphotosynthetic) bacteria convert this substrate into biomass depends mainly on the quality of DOC in the water column. DOC is constantly processed through various physical, chemical, and biological mechanisms that operate simultaneously and alter its quality. It is paramount to understand how these different processes interact to drive the fate of DOC in aquatic ecosystems. Based on field data collected in a large fluvial lake, we developed and validated a mechanistic model that provides a framework to understand the relative contribution of the main processes involved in both labile (DOCL) and semilabile (DOCSL) DOC pool kinetics. The model revealed that during the downstream flow, each category of DOC pool was processed differently by bacteria: DOCL was preferentially used for biomass production, whereas DOCSL completed bacterial carbon demand. Our results also suggest that a decrease in DOCL abundance will further determine the intake of DOCSL.

Variability in nitrogen content of submerged aquatic vegetation: utility as an indicator of N dynamics within and among lakes

Submerged aquatic vegetation (SAV) may serve as an integrative proxy of spatial and temporal nitrogen (N) availability in aquatic ecosystems as plants are physiologically capable of storing variable amounts of N. However, it is important to understand whether plant species behave similarly or differently within and among systems. We sampled different SAV species along a nutrient gradient at multiple sites within several lakes to determine variability in C:N ratios and % N content among species, among plants of the same species at a single site, among sites and among lakes. Species respond differently suggesting that not all plant types can be used universally as nutrient proxies. The greatest variability in % N and C:N ratios for Valliseneria americana was observed among lakes whereas for Elodea canadensis it was among sites within a lake and among plants within a site. This suggests that V. americana could be a particularly useful indicator of N availability at larger spatial scales (regional and within a large fluvial lake) but that E. canadensis was not a particularly useful proxy.

Influence of functional feeding groups and spatiotemporal variables on the δ15N signature of littoral macroinvertebrates

The δ15N trophic enrichment in littoral food webs is not well known despite the importance of macroinvertebrates in lacustrine energy fluxes. We wanted to assess the influence of functional feeding group (grazer, collector, shredder, predator, predator–hematophagous, predator–sucker) and spatiotemporal variables (year, month, station of sampling) on littoral macroinvertebrate δ15N signatures. For 2 years, during the plant growth period phytophilous littoral macroinvertebrates were sampled in Lake St. Pierre, a large fluvial lake of the St. Lawrence River, Quebec, Canada. The δ15N analyses showed that station was the most important factor for explaining δ15N variation, followed by sampling month and functional feeding group. The organisms sampled in the stations of the south shore, which experienced greater macrophyte abundance, slower currents, and stronger NO3 depletion exhibited higher δ15N values than those sampled on the north shore. Grazer-to-predator δ15N enrichment valued 1.6‰, which is inferior to the 3.4‰ generally admitted in food-web research. Shredders exhibited the lowest δ15N values and predators–hematophagous the highest. δ15N signature of invertebrates increased 3‰ through the summer between May and September. Only samples collected within a short period should be pooled to avoid an error value equivalent to one trophic level (1.6) enrichment. Furthermore, it is recommended not to pool macroinvertebrate samples collected at stations with differing watershed land uses.

Biomass and composition of macroinvertebrate communities associated with different types of macrophyte architectures and habitats in a large fluvial lake

The influence of macrophyte habitat and architecture on macroinvertebrate biomass, abundance, and richness was investigated in Lake St. Pierre, a large fluvial lake of the St. Lawrence River (Quebec, Canada). A lake-wide estimate of macroinvertebrate biomass associated with different macrophyte habitats was also calculated in order to assess the quantitative effects of vegetation changes on macroinvertebrate communities. For two years during the ice-free period, phytophilous macroinvertebrates were sampled in macrophyte beds comprising more than ten species of plants and three habitats (emergent, floating-leaved, submerged), and in three submerged macrophyte architectures based on plant morphology (simple, intermediate, and complex). Invertebrate sub-samples were classified into four functional groups (detritivore, grazer, crawling predator, diving predator). Biomass and density of invertebrates were expressed per unit of plant dry weight. The main findings are that macroinvertebrate biomass, abundance and richness were significantly greater in submerged than in emergent and floating-leaved habitats. However, macrophytes with a complex architecture did not host significantly greater macroinvertebrate biomass than plants with a simpler architecture. This could be related to substrate preferences of herbivores (mostly Gastropoda) toward the tape grass Vallisneria americana. Differences in macroinvertebrate abundance and biomass were found between the two years associated with variations in the river water level. During the year with average water level, total macroinvertebrate biomass was 16 % greater than in the year with a lower water level. We conclude that a reduction in the water level of Lake St. Pierre, predicted to occur with climate change, could lead to a decrease in benthos biomass which constitutes a crucial food source for fish. © E. Schweizerbart'sche Verlagsbuchhandlung 2008.

Using the landscape morphometric context to resolve spatial patterns of submerged macrophyte communities in a fluvial lake

This study investigates the spatial heterogeneity of macrophyte communities in a fluvio-lacustrine landscape. We analysed the importance of the geomorphological point/bay pattern in structuring aquatic plant assemblages inside a 20-km-long littoral segment of a large fluvial lake. The abundance of 21 macrophyte species was surveyed in 232 quadrats along 24 transects perpendicular to the lakeshore. Two contrasting plant communities were identified, corresponding to the bay and point morphology of the study zone: a bay community characterized by Chara sp. and a point community dominated by Butomus umbellatus f. vallisneriifolius, Vallisneria americana, Potamogeton richardsonii and Myriophyllum sp. We subsequently investigated the spatial patterns within the bay and point communities. From a dataset containing local environmental variables, landscape morphometric descriptors, and spatial geographical positions of the sampling sites, variation partitioning of the species abundance table showed that more than two-thirds of the explained variation was spatially structured. Around half of the spatially structured variation was due to the spatially structured environment. We identified important broad-scale patterns in the vegetation correlated to the local environmental variables, mainly depth and sediment richness. The remaining half of the spatially structured variation in the aquatic plant communities was explained by the landscape morphometric context; shoreline complexity of the bay or point, relative width, duration of wind exposure, and fetch were the landscape descriptors explaining most of this variation. Our results indicate that the landscape morphometric context can resolve as much spatial patterning as environmental variables and should be considered when studying a large lake ecosystem.

RNA/DNA ratio and total length of yellow perch (Perca flavescens) in managed and natural wetlands of a large fluvial lake

RNA/DNA ratios and total lengths were compared to determine growth patterns of age-0 yellow perch (Perca flavescens) in managed and natural habitats of a large fluvial lake (Lake Saint-Pierre, St. Lawrence River, Quebec, Canada) over seasonal and yearly temporal scales. In 2002, the RNA/DNA ratio responded to degree-days accumulated over periods of 7–8 days before sampling, while in 2003, no relationship with temperature was established. The growth patterns obtained each year probably reflect indices responding to different limiting variables. In 2002, temperature would have been limiting, whereas in 2003, other factors such as prey availability, food quality, and competition may have influenced growth. In addition, the discrepancy between total length and RNA/DNA ratio observed in 2003 may reflect a differential time of response to limiting variables. These results together show that the two indices reflect growth at different time scales and suggest that their combination can help identify shifts between limiting environmental variables. Also, growth in managed wetlands during springtime was systematically superior to that in the natural environment, supporting the contention that managed wetlands are highly productive habitats. In natural habitats, growth rates were higher on the south shore by summer, which is consistent with the established north-south productivity gradient in Lake Saint-Pierre.

Changes in the spectral and chemical properties of a water mass passing through extensive macrophyte beds in a large fluvial lake (Lake Saint-Pierre, Québec, Canada)

Large fluvial lakes, as part of river corridors, are recognized as spatially heterogeneous ecosystems. Due to their shallowness, the littoral zone of these lakes occupies a large proportion of their surface and is extensively covered by macrophytes that are known to affect their physical, chemical and biological environments in various ways. This study documents the small-scale (5 km) bio-optical variations associated with the longitudinal passage of a water mass through macrophyte beds during their maximal growth season. The utilization of a 2D hydrodynamic model allowed us to establish hydrological connectivity between stations within the beds, and thus to identify longitudinal heterogeneity along the macrophyte beds. Significant changes in the inherent properties of the water were observed along the upstream-downstream gradient. Due to their effects on hydrodynamics, macrophytes were responsible for a decrease in particles and dissolved organic carbon (DOC) resulting in an increasing penetration depth of ultraviolet (UV) and photosynthetically active radiation (PAR). Along the transect, chromophoric dissolved organic matter (CDOM) decreased more rapidly than DOC resulting in a decrease of the CDOM to DOC ratio. The observed changes in the DOC pool may be explained by the constant input of non-chromophoric DOC from macrophyte leachates and exudation within the bed and/or the photochemical and microbial degradation of CDOM. The implication of such small-scale heterogeneity on Lake Saint-Pierre productivity is discussed.

An evaluation of approaches used to determine the distribution and biomass of emergent and submerged aquatic macrophytes over large spatial scales

We compared the performance of various approaches to determine the distribution and biomass of submerged and emergent aquatic plants in a large fluvial lake. Three empirical models linking local macrophyte biomass to single and multiple environmental variables were applied in a GIS-framework to estimate the spatial distribution and biomass of aquatic macrophytes in Lake St. Pierre, a large (300 km 2), shallow (mean depth: 3 m) and complex widening of the St. Lawrence River (Quebec, Canada). The resulting maps and emergent and submerged macrophyte distributions obtained independently by remote sensing and echo sounding techniques were compared to field data collected in 2000. Maps derived from echo sounding, from a biomass versus depth regression and from a four-variable model (i.e. exposure to wind and waves, plant growth form, water depth and transparency) were the most accurate (55–63% overall agreement with field data). Remote sensing techniques were the least accurate for determining underwater macrophyte distribution in Lake St. Pierre due to the limitations of image-based methods for detecting submerged aquatic vegetation in coloured, turbid waters. This study demonstrates that environmental models in combination with GIS can be used to estimate aquatic macrophyte distribution over larger spatial scales and to examine potential change in macrophyte growth form assemblages arising from different environmental conditions.