The goal of this study was to determine if natural fires and logging have a significant impact on abundance, growth, and size structure of fish populations in 38 lakes of the Laurentian Shield (Quebec, Canada). The watersheds of nine of these lakes underwent logging and nine underwent natural fires, while the 20 remaining lakes were used as references. No significant differences were found among the three lake groups in the catch per unit of effort of the most abundant species: white sucker (Catostomus commersoni), northern pike (Esox lucius), yellow perch (Perca flavescens), lake whitefish (Coregonus clupeaformis), fallfish (Semotilus corporalis), brook trout (Salvelinus fontinalis), walleye (Stizostedion vitreum), and burbot (Lota lota). No significant difference was found among control, burned, and logged lakes in the back-calculated length of yellow perch, for which age determinations were made. However, we found that the proportions of small yellow perch and white sucker were significantly lower in p...

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Impact of logging and natural fires on fish communities of Laurentian Shield lakes

The effects of forest clearcut and regrowth on a small (8.1 ha) stained lake were studied using a 200-year record of fossil carotenoids and chlorophylls. Comparison of high-resolution cores recovered from exposed, sheltered, and reference lake basins showed that annual laminations of sediments ceased concomitant with logging (ca. 1870-1890), indicating a fundamental change in the lake mixing regime. Biological responses to forest harvest included elimination of deepwater populations of anaerobic photosynthetic bacteria and reduced abundance of metalimnetic chrysophytes. Photosynthetic bacteria remained absent for over 100 years, while sediment laminae and chrysophytes have only returned since around 1970. In contrast, populations of epilimnetic phytoplankton (cyanobacteria, chlorophytes, cryptophytes) were unaffected by the clearcut. Analysis of sediment profiles did not reveal evidence of eutrophication or of increased flux of organic matter following watershed disturbance. Instead, fossil records were m...

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Century-long effects of forest harvest on the physical structure and autotrophic community of a small temperate lake

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10-min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired-catchment analysis revealed that partial-retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post-harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post-harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre-harvest regression models for shallow groundwater were not suitable for applying the paired-catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre-harvest year. Copyright © 2012 John Wiley & Sons, Ltd.

Stream and bed temperature variability in a coastal headwater catchment: influences of surface‐subsurface interactions and partial‐retention forest harvesting

Logging and wildfires are important perturbation factors of the Canadian Boreal forest, but their effects on aquatic communities remain largely unknown. Here, we assess the ecological effects of logging and wildfires on aquatic communities, based on changes in crustacean zooplankton size spectra among logged, burnt and unperturbed lakes of the Canadian Precambrian Boreal Shield. A laboratory version of the Optical Particle Counter (OPC-1L) was used to establish the crustacean size spectra of zooplankton samples collected in 38 lakes characterized by different catchment conditions: logged in 1995 (nine 'logged' lakes); burnt in 1995 (nine 'burnt' lakes); left unperturbed over the past 70 years (20 reference lakes). Size spectra are characterized by crustacean biovolume in 22 size classes, from 200-300 μm equivalent spherical diameter (ESD) to 2300-2400 μm ESD. Size spectra in logged and burnt lakes were on average shifted towards larger size classes relative to reference lakes, although the reference and burnt groups of lakes were the only pair statistically different from one another (at a = 5%). As a result, biovolume of crustacean organisms >1100 μm ESD in burnt lakes was on average higher by 366 and 388%, respectively, 1 and 2 years following catchment perturbations relative to reference lakes. Among a set of 15 water quality variables and 14 fish species density variables, potassium concentration and white sucker density were the most important environmental correlates of crustacean size structure.

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Influence of catchment deforestationby logging and natural forest fires on crustacean community size structure in lakes of the Eastern Boreal Canadian forest

Perturbations on ecosystems can have profound immediate effects and can, accordingly, greatly alter the natural community. Land-use such as forestry activities in the Canadian Boreal region have increased in the last decades, raising concerns about their potential impact on aquatic ecosystems. The objective of this study was to evaluate the impact of forest harvesting on trophic structure in eastern Canadian Boreal Shield lakes. We measured carbon and nitrogen stable isotopes values for aquatic primary producers, terrestrial detritus, benthic macroinvertebrates, zooplankton and brook trout (Salvelinus fontinalis) over a three-year period in eight eastern Boreal Shield lakes. Four lakes were studied before, one and two years after forest harvesting (perturbed lakes) and compared with four undisturbed reference lakes (unperturbed lakes) sampled at the same time. Stable isotope mixing models showed leaf-litter to be the main food source for benthic primary consumers in both perturbed and unperturbed lakes, suggesting no logging impact on allochthonous subsidies to the littoral food web. Brook trout derived their food mainly from benthic predatory macroinvertebrates in unperturbed lakes. However, in perturbed lakes one year after harvesting, zooplankton appeared to be the main contributor to brook trout diet. This change in brook trout diet was mitigated two years after harvesting. Size-related diet shift were also observed for brook trout, indicating a diet shift related to size. Our study suggests that carbon from terrestrial habitat may be a significant contribution to the food web of oligotrophic Canadian Boreal Shield lakes. Forest harvesting did not have an impact on the diet of benthic primary consumers. On the other hand, brook trout diet composition was affected by logging with greater zooplankton contribution in perturbed lakes, possibly induced by darker-colored environment in these lakes one year after logging.

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Impact of Forest Harvesting on Trophic Structure of Eastern Canadian Boreal Shield Lakes: Insights from Stable Isotope Analyses

Brook trout, Salvelinus fontinalis (Mitchill), angling data, collected between 1971 and 1991, were analysed before, during, and after logging operations for 20 lakes located within 200 m of a clear-cutting area and 16 reference lakes undisturbed by logging. The mean weight of catches by anglers remained unchanged over the three periods, while catches per unit of effort (CPUE) and biomass per unit of effort (BPUE) decreased, respectively, by 18% and 22% after clear-cutting. These changes reflected a significant modification in population dynamics probably caused by logging operations. Results indicated that the negative impacts on aquatic fauna were felt more strongly on water bodies located in watersheds where deforestation was more severe; CPUE was inversely correlated with a cumulative cutting index (CI) developed from physiographic parameters. An increasing interannual trend of the spring-flood discharge in the order of 8% was noted. It was hypothesized that this increase might damage spawning and nursery habitats, hence affecting recruitment and offering a possible part of the explanation for the variations in fishing success. The cause-to-effect links and the mechanisms associated with changes affecting fish populations following deforestation remain to be clarified.

Effects of forestry clear‐cutting on numbers and sizes of brook trout, Salvelinus fontinalis (Mitchill), in lakes of the Mastigouche Wildlife Reserve, Québec, Canada

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Effects of forestry clear‐cutting on numbers and sizes of brook trout, Salvelinus fontinalis (Mitchill), in lakes of the Mastigouche Wildlife Reserve, Québec, Canada