Ginette Méthot

Macroinvertebrate community as a biological indicator of ecological and toxicological factors in Lake Saint-François (Québec).

To assess the potential of the macroinvertebrate community for monitoring variation in the environmental quality of large rivers, the response of littoral macrobenthos in Lake Saint-François, a fluvial lake of the St Lawrence River (Québec) are described. First, the composition of total macroinvertebrate communities and important taxonomic groups as well as the biotic ICI-SL index in 16 littoral stations varying in sedimentology, water chemistry and contamination are described to define indicator species groups and environmental quality ranks. Thereafter, the relative contribution of ecological and toxicological factors in explaining the variation observed in macroinvertebrate assemblages and biotic index were quantified using partial canonical correspondence analysis. Cluster analyses based on taxonomic composition separated five groups of stations where macroinvertebrate assemblages varied in density, composition and tolerance to pollution. The ICI-SL biotic index varied from 7.2 to 27.2 with a mean value of 19 +/- 6. The ICI-SL values determined for the macroinvertebrate communities in Lake Saint-François did not reflect an important deterioration in environmental quality, and there was some agreement between the environmental quality ranking of the stations expressed either by the ICI-SL index or the community cluster analysis. Water conductivity and phosphorus concentration, followed by macrophyte types (Chara, Ceratophyllum) and sediment grain size, were the most significant ecological variables to explain variation in macroinvertebrate communities and derived ICI-SL index in Lake Saint-François. Among the toxicological factors, metals in water (Fe, Cr, Pb, Mn, Zn) and sediment (Mn, Pb, Se), as well as the composite indices of metal and organic contamination (water CI, sediment CI, sediment total PAHs) were the most important factors. The contamination factors selected in our models represented contaminant sorption processes rather than direct toxicological effects. The lack of clear relationships between contaminants and macroinvertebrate variables reflected the relative low level of contamination in the stations sampled in Lake Saint-François. There were some interactions between toxicological and ecological variables that should be considered in the planning of sampling and interpretation of biomonitoring studies. However, the large amount of unexplained variance (49.2-86.6%) in the CCA models underlined the limitations of the use of the indices of macroinvertebrate community structure that were assessed in this study for biomonitoring purposes in the absence of a contrasting pollution gradient.

Epiphyte size and taxonomy as biological indicators of ecological and toxicological factors in Lake Saint-François (Québec)

To assess the potential of the epiphyton community for monitoring spatial and temporal variations in the environmental quality of freshwater ecosystems, this paper describes the response of epiphytons to ecological and toxicological factors in Lake Saint-François, a fluvial lake of the St. Lawrence River (Québec). First, community descriptions and biotic indices based on size structure and on taxonomic composition were compared to test if size could usefully describe epiphyton response to environmental factors. Secondly, the relative contribution of ecological and toxicological variables in explaining the variation observed in epiphyton was quantified. A size-based approach classified the sites similarly to taxonomic analysis, but a larger portion of variance in size could be explained indicating a stronger relationship with environmental factors. Among both taxonomy and size-based biotic indices, the slope of the normalized size spectra performed best in terms of total explained variance. There were strong interactions between toxicological and ecological variables. These interactions should be considered in the planning and interpretation of biomonitoring studies. In such surveys, samples should be collected at sites with similar ecological characteristics: for example, the same macrophyte type and sediment texture. Interpretation of the data should consider the possible covariance of toxicological and ecological variables.

Macroinvertebrate size–mass relationships: how specific should they be?

Abstract.  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 belonging to Mollusca, Crustacea, and Insecta. Comparison of our predicted DM for reference-size individuals with values from 120 other published equations revealed that 31% of predicted values were within our 95% CI and 73% were within a 2× DM range (i.e., between 0.5× and 2×). Interannual differences in exponent (slope) or scale factor (intercept) of L–DM relationships were detected for 6 of the 7 taxa investigated, but represented only 3% of total variance in predicted DM. Similarly, preservation methods and measured body dimension each accounted for a small (0–3%) fraction of total variance. Variation among investigators (12–50%) and continents (1–17%) were more important and might have reflected methodological or regional and latitudinal differences. Increasingly precise taxonomical levels explained progressively lower proportions of the total variance, a result indicating that family or a more precise taxonomic level provided a robust estimate of most invertebrate DM even if the equations were derived from other sites. However, overall variability induced by L–DM relationships was smaller than variability in total invertebrate density among replicate samples (coefficient of variation [CV]  =  19–97%), a result indicating that more effort should be devoted to improving the accuracy of invertebrate density estimates than to developing site-specific L–DM relationships to assess benthic biomass in freshwater.

A Short-Term Study of Vertical and Horizontal Distribution of Zooplankton During Thermal Stratification in Lake Kinneret, Israel

This study documents for the first time both vertical and horizontal distribution patterns of the zooplankton community in Lake Kinneret during the period of thermal stratification. The zooplankton distribution patterns were explored in relation to abiotic (temperature, oxygen) and biotic (picocyanobacteria, ciliates, flagellates, phytoplankton, fish) environmental gradients. Sampling was carried out on 6–7 July 1992 at five stations and six depths from nearshore to offshore. Zooplankton abundance and biomass varied from 5 to 267 ind. l−1(mean: 95 ind. l−1), and from 0.1 to 65 d.w. mg m−3(mean: 24 d.w. mg m−3). Zooplankton taxonomic groups (Rotifera, Cladocera, Cyclopoida, Calanoida) and size classes (micro-, meso- and macrozooplankton) showed peaks of maximal density and biomass in the epilimnetic and metalimnetic strata (5 and 14 m). Depth, accounting for 31–39% of total spatial variation, reflected the vertical distribution of zooplankton in relation to temperature and oxygen declines, and the higher concentration of food resources (protists and phytoplankton) in the epilimnion and metalimnion. Onshore–offshore distance, accounting for 17–22% of the total spatial variance, reflected different distribution patterns shown among zooplankton groups and size classes. The macrozooplankton (Copepoda, Cladocera) was more abundant offshore, whereas microzooplankton (Rotifera and nauplii) predominated nearshore. These horizontal distribution patterns were related to small increases in temperature and phytoplankton biomass, and higher concentrations of fish in the littoral zone. Although limited to a short temporal scale, our study indicated that zooplankton spatial distribution in Lake Kinneret during the period of thermal stratification was related to physicochemical, food and predation factors, manifested differently along the vertical and nearshore–offshore gradients.

Drug abuse as a risk factor of multiple sclerosis: case-control analysis and a study of heterogeneity.

The etiology of multiple sclerosis (MS) remains unknown despite considerable research involving a number of disciplines for many decades. Cluster analysis was used to disentangle the possible heterogeneity of MS, based on clinical characteristics of 108 subjects. Further on, a case-control study was conducted within each subgroup found with the cluster analysis, to test with more validity environmental risk factors, such as alcohol, tobacco, medication and drug abuse. The controls with a rheumatoid arthritis condition were matched to the cases on age, gender and same postdiagnostic period and were recruited from the same hospital. Three main groups of MS subjects were obtained from the cluster analysis, distinguished by the gender, the presence or not of family history and the degree of severity of their physical disability. The results showed that drug abuse was the only risk factor with a statistically significant odds ratio for overall and for the unique female group without familial history of MS.

Bioassessment of Benthic Macroinvertebrates in Wetland Habitats of Lake Saint-Pierre (St. Lawrence River)

We evaluated the potential of vegetation and sediment habitats in wetlands of the St. Lawrence River for developing a macroinvertebrate bioassessment program with reference conditions. During September 2004, we collected macroinvertebrates in emergent vegetation and sediment in both fluvial sites (reference) and tributary-plume sites (impacted) in waters of the north and south shores of Lake Saint-Pierre (St. Lawrence River). In each habitat, we compared taxa richness, abundance, and community structure of macroinvertebrates between reference and impacted sites, and used multivariate models to relate macroinvertebrate community to environmental conditions. Each habitat was suitable for discriminating reference fluvial sites from impacted tributary-plume sites based on macroinvertebrate communities. In emergent vegetation, macroinvertebrates were dominated by epibenthic fauna such as crustaceans (Gammaridae, Asellidae) and molluscs (Valvatidae) at fluvial sites, and insect larvae (Chironomidae, Caenidae) at tributary-plume sites. In sediment, macroinvertebrates comprised a greater proportion of endobenthic fauna such as Oligochaeta and Sphaeridae. Crustaceans and molluscs were still dominant at fluvial sites and Oligocheata and Chironomidae at tributary-plume sites. No strong difference was depicted in macroinvertebrate composition between north and south shore water masses. Environmental variables explained a higher proportion of variance in macroinvertebrate community composition in emergent vegetation than in sediment (68% versus 44%). Macroinvertebrate composition in sediment was more related to metal contamination, whereas macroinvertebrate composition in emergent vegetation was related primarily to vegetation type and water quality. Relevance of the study for bioassessment of macroinvertebrates in the St. Lawrence River using the reference condition approach is discussed.

The response of invertebrates in moss and in gravel to water level fluctuations in a Québec stream

To assess the response of stream communities to water level fluctuations, we measured the biomass and taxonomic composition of invertebrates colonizing substrata at varying depths, and thus more or less frequently exposed as flow declined. We compared the response of invertebrate communities in the moss Fontinalis dalecarlica and in gravel throughout the growing season in a small Quebec stream. Depth explained a large proportion of the variation in invertebrate biomass in moss for all dates (from 50-80%). Invertebrate biomass was lower on shallow mosses frequently exposed than on deeper ones, which remained submerged. In contrast, depth was never significantly related to invertebrate biomass in gravel. A significant fraction of the variation in invertebrate taxonomic composition was explained by substratum type (moss versus gravel) and exposure (estimated through depth) for all sampling dates (Canonical Correspondence Analysis). In particular, grazers were more common and abundant in moss than in gravel, suggesting a stronger reliance on periphyton on the part of moss-dwelling communities, and consequently greater vulnerability to periphyton reduction upon exposure. Invertebrates inhabiting gravel appear less affected by reductions in water level as they can burrow in the substratum at low flow. Gravel habitats tend to be lower on the streambed than moss, and consequently emerge less often. In view of forecasts of increased variability in stream water levels arising from climate changes, our study stresses the need to consider the differential vulnerability of communities on different substrata to hydrological disturbances.

Planktonic Community Dynamics over Time in a Large Reservoir and their Influence on Carbon Budgets

The aim of this chapter was to determine the influence of zooplankton organisms on carbon cycling within reservoirs and lakes from Northern Quebec. The first part of the paper presents results from LG-2 reservoir where zooplankton dynamics were followed from 1 year prior to impoundment to 6 years after flooding. In terms of community structure, flooding was associated with an increase in zooplankton biomass with the strongest effects observed for cladocerans and rotifers. This increase was related to changes in the physical characteristics of the sampled sites (water residence time, temperature and turbidity), chemical characteristics of the water (total phosphorus) and the abundance of resources (Chl. a).