Guy Moreau

The impact of brook trout (Salvelinus fontinalis) on an experimental stream benthic community: the role of spatial and size refugia

The importance of space and size refugia in allowing stream benthic insects to avoid predation by fish was tested by measuring the impact of brook trout on drifting, epibenthic and infaunal insects of different taxa and size-classes. Experiments were carried out in a replicated series of pebble-bottom, outdoor channels fed by a boreal forest stream in Quebec, Canada. Significant effects of fish on the size-structure of the insect populations were observed on at least one of the two sampling dates for epibenthic and drifting animals, but never for those in the infauna. The presence of fish significantly reduced the density of many epibenthic and drifting insects (maximum of 36% and 24% of the taxa, respectively), but this impact varied with time

Effects of experimental acidification on a lotic macroinvertebrate community

A three month experimental acidification was carried out on lotic bottom communities. Experiments were conducted under semi-natural conditions in plasticized wooden channels. Acidified communities (pH 4.0), with or without added aluminum, were compared with a reference community (pH 6.3–6.9). Added aluminum concentrations were respectively 0.2 and 0.4 mg 1−1 in experiments performed in 1982 and 1983. Water chemistry and taxonomic composition of the macroinvertebrate communities were monitored. Under acidified conditions, results were similar, with or without added aluminum. Mean abundances of all groups of organisms were lowered. Mayflies nearly completely disappeared from the acidified channels. The only organism not affected by the acidification was Microtendipes sp. Differences in the organism response were observed: Orthocladiinae (Rheocricotopus, Parametriocnemus, Corynoneura, Thienemanniella, Nanocladius, Cricotopus) and Ephemeroptera (Baetis, Habrophlebia, Habrophlebiodes, Paraleptophlebia, Ephemerella), especially early instars, were very sensitive to low pH, Chironomini and Tanypodinae were much less sensitive, while Tanytarsini were intermediate; Oligochaeta and Nematoda were difficult to classify, their response being different from one year to another. Organisms inhabiting the surface of artificial substrates disappeared very rapidly from the system, while those buried inside had a delayed reaction to acidification. Aluminum which was mainly in the monomeric form was not responsible for community modifications. Direct action of hydrogen ions through a physiological stress seems a more credible explanation. These results, induced by a continuous experimental acidification, suggest that if this small headwater stream undergoes acidification, the resulting invertebrate community will be very simplified, with only resistant species able to cope with the acid conditions.

Leaf decomposition in an experimentally acidified stream channel

Decomposition of Alnus rugosa and Myrica Gale leaves immersed in artificial stream channels fed by a small headwater creek was followed over a three month period. At the end of experiment, remaining weights of both leaf types confined in litter bags were significantly higher after immersion in experimentally acidified water (pH 4.0) than when immersed in control water (pH 6.2–7.0). For both types of leaves and for all sampling times, there was generally no difference in the C:N ratios between leaves in acidified and those in control water. In control water, oxygen uptake by microorganism on A. rugosa leaves was significantly higher after 46 days of immersion, whereas differences between treatments appeared only after 69 days for M. Gale leaves. Transfer of A. rugosa leaves from acid to control water led to a rapid increase in microbial activity; this increased activity was reflected in a fast weight loss of the leaves. For both leaf types, total numbers of macroinvertebrates were usually higher in litter bags immersed in control water. Macroinvertebrates colonizing the litter bags were mainly collector-gatherers: Chironomidae were numerically dominant in control leaf packs whereas Oligochaeta dominated in acid leaf packs. Macroinvertebrate biomass in M. Gale litter was higher in control than in acidified water, which contrasted with macroinvertebrate biomass in A. rugosa leaf packs which was not significantly different between treatments. Macroinvertebrate contribution to the breakdown of leaf litter was thus considered less important than the microbial contribution. This study demonstrated that decomposition of leaf litter in acidic headwater streams can be seriously reduced, mainly as a result of a lower microbial activity.

The effects of short-term and continuous experimental acidification on biomass and productivity of running water periphytic algae

The effect of short-term and continuous acidification on the primary production and biomass of periphyton was studied in seminatural conditions using an experimental device simulating streams ecosystems. After allowing periphytic algae to colonize unglazed ceramic tiles for 4 to 6 weeks under natural conditions, the pH of the water was lowered with sulfuric acid (H 2 SO 4 ) from 6.5 to 6.7 to 4 to 4.6 for short periods (12 to 72 h) or long periods (continuous acidification, 84 days). During short-term acidification, in all the experiments but one, there was a significant increase (up to 2.6 times as compared to the control) of the primary production and specific activity in the first 12 h, followed by a significant decrease and slow recovery from 48 h until the end of the experiment. If acidification is continuous, primary production and specific activity are significantly higher (between 10 to 15 times that of the control) in acidified channels, either with or without aluminum, by Day 33 and until the end. Biomass stayed constant or decreased in short-term acidification and increased (from 10 to 15 times) in continuous acidification.

Fish Responses to Acidity in Québec Lakes: A Review

To establish the impact of acidity on fish populations,studies were conducted in 37 Quebec lakes located in four regions; the reserve des Laurentides and Portneuf and the Charlevoix and Temiscamingue regions. Density (catch per unit effort) of brook chary (Salvelinus fontinalis) decreases with increasing acidity. Moreover, in the Charlevoix region, this species has disappeared from three acid lakes (4.6 ⩽pH⩽5.l) with low Ca levels. Unlike growth, condition demonstrates a close relationship to acidity in brook charr populations. The total Al concentration in gills decreases with increasing size and pH. Lake acidity and sensitivity to acidification introduces problems in gamefish management. A survey of 17 lakes of the Temiscamingue region reveals that species diversity and total fish biomass are much lower in acid lakes than non acid lakes. In addition, two acid lakes are devoid of fish. Cyprinidae and Johnny darters (Etheostoma nigrum) are abundant in lakes with a pH level of 5.9 to 7.0 but are absent in lakes with a pH lower than 5.2. The yellow perch (Perca flavescens) is the only fish that appears to be tolerant to a wide pH range. This species, however, is in poor condition in acid lakes as compared with non acid lakes.

Influence of acidification and aluminum on the density and biomass of lotic benthic invertebrates

Experiments were carried out in plasticized wooden channels fed by a small creek in the Reserve des Laurentides, 80 km north of Quebec city. Channels were naturally colonized by invertebrates for 65 d before treatment. Treated channels were acidified in August with dilute H2SO4 only, or with acid plus a solution of Al sulfate (final concentration of 0.19 mg L−1). The control channel received creek water only (pH 6.3 to 6.9). The addition of Al had no effect on invertebrate density and biomass. After 73 d of acidification, invertebrate densities were only one third the number found in the control channel. Invertebrate hiomass was not different within channels, although biomass was generally higher in the two acidified channels. Difference in densities between acidified and non-acidified channels was attributed to lack of colonization and not to an increase in drift. Microtendipes, a large and resistant larva of Chironomidae constituted a large fraction of the hiomass, largely outweighing numerous very small larvae. Effects on the density were attributed to the direct effect of low pH and not to indirect action through food limitations.

Colonisation par les micro-organismes, evolution chimique des feuilles de différentes espèces d'arbres (peuplier, aulne, myrique) dans des eaux oligotrophes du Bouclier canadien et incidence sur leur utilisation par les macro-invertébrés

Myrica gale, Alnus rugosa and Populus tremuloides leaves were incubated ‘in situ’ in the oligotrophic acid waters of the Canadian Shield (James Bay, Quebec) in order to follow microorganic decomposition, respiration and chemical transformations.Respiratory activities in decomposing speckled alder and trembling aspen leaves were more important than that in sweet gale. In spite of low nutrient concentrations in the water, nitrogen concentration increased in the three species while phosphorus levels increased only in the speckled alder during decomposition.

Relation entre habitat et peuplements de poissons: Essai de definition d'une methode numerique pour des rivieres nordiques

A study of fish communities was conducted in downstream sections of the Nottaway, Broadback and Rupert Rivers, northern Québec, in order to establish a relationship between communities and their habitat. The areas sampled are relatively homogenous and the number of species present is limited to 18, of which 11 are not abundant. Physical similarity between the 163 sampling stations is established using 5 characteristics observed in the field and is computed using a coefficient derived from the metric of Canberra. Six types of habitat are identified from the complete linkage clustering of the matrix of similarities between stations. Discriminant analysis of fish communities results in a prediction success of about 60% in classifying samples in their own habitat. This proposed numerical procedure may therefore be used as management tool.The community structure is interpreted in terms of the physical characteristics of the environment. Relative abundances of the 4 most discriminating species between habitats seem to be determined by water transparency, current speed and abundance of aquatic vegetation, these two last variables interacting in a complex fashion. Changes in community structure that arise because of predictable physical alterations to the environment may therefore be predicted only by relatively sophisticated numerical procedures, at least when the physical environment is relatively homogeneous and the species diversity low, as in northern rivers.

Reaction of lotic periphyton to experimental acidification

Two hypotheses that could explain increases in the biomass and production of lotic periphytic communities in acidified habitats were tested: 1) a greater bioavailability of P due to its greater release from sediments at low pH, and 2) utilization of S from the H2SO4 addition. The experiments were performed in semi-natural conditions by submitting the periphyton to either continuous or episodic acidification. The uptake of P and S by periphyton were determined at different times during the treatments. The increases in P and S uptake, in acidified habitats, are compatible with both hypotheses and could account for the increase in periphytic biomass and production.

Utilisation des feuilles de différentes espèces d'arbres (peuplier, aulne, myrique) par la faune benthique dans des eaux oligotrophes du Bouclier canadien

Sweet gale (Myrica gale), speckled alder (Alnus rugosa), and trembling aspen (Populus tremuloides) leaves were incubated in situ on artificial substrates in the oligotrophic acid waters of the Canadian Shield (James Bay, Quebec).Shredders preferentially chose leafy substrates when compared to leafless controls. The biomass and total number of the main colonizing invertebrates (Chironomidae, Ephemeroptera) were greater upon alder and aspen than upon sweet gale leaves, probably because of the latters resistance to decomposition. This resistance results in a greater period of nutriment availability allowing a continuum in the use of alimentary resources by macroinvertebrates.