Canadian Shield Lakes Research Articles

Host length, age, diet, parasites and stable isotopes as predictors of yellow perch (Perca flavescensMitchill), trophic status in nutrient poor Canadian Shield lakes

We used data from parasites and stable isotopes of yellow perch, Perca flavescens, to determine trophic status in four small Canadian Shield lakes as parasites allow the identification of both prey and non-prey dietary components in the host's community. Stable C isotope ratios for all perch ranged from ∼ −34 to −19‰ while stable N isotope ratios ranged from ∼4.5 to 12.5‰. These ranges are larger than those observed in many other fish species. Perch age was the most significant predictor of stable C isotope ratio and perch parasite fauna was the most significant predictor of stable N ratios. In particular, parasite fauna indicative of zooplanktivorous or piscivorous perch were most accurate for predicting fish trophic position and thus stable isotope ratio. Fish length and age showed fewer significant relationships with isotope ratios than parasite infracommunity or diet and suggests that trophic category for perch cannot always be predicted based on size.

Comparison of nets and pump sampling gears to assess zooplankton vertical distribution in stratified lakes

The efficiency of a cantilevered bridle net was tested in comparison with a Wisconsin net and a pumping system to sample zooplankton organisms in three water layers (epi-, meta- and hypolimnion) of three Canadian Shield lakes. Variations among samplers were compared to variations due to within-lake vertical distribution of zooplankters and among lake variations. For each lake and water layer, we also assessed the efficiency of the three methods according to the catches of zooplanktonic taxa. The highest percentages of variation were generally due to lake or water-layer effects; interaction between sampling gears and water layers was above 50% for most taxa, except cladoceran. Sampling methods explained more variation than the lake effect for some zooplankton taxa, indicating that using different sampling devices could potentially alter the among-lake variation interpretation of zooplankton abundance. The pumping system captured higher densities of animals per taxa than the cantilever and the Wisconsin nets. The cantilever net generally captured mobile taxa more efficiently (Polyarthra vulgaris, copepods, Daphnia sp., Diaphanosoma brachyurum and chaoborids) than the Wisconsin net and the pumping system, but its efficiency varied among water layers.

Modeling diagenesis of lead in sediments of a Canadian Shield lake

Triplicate porewater lead concentration profiles were determined on six occasions in a Canadian Shield lake. Total Pb concentrations were also measured in a dated core obtained at the same site. This information, as well as an extensive dataset comprising ancillary geochemical measurements on porewaters and sediment and the population densities of benthic animals, is used in a one-dimensional transport-reaction diagenetic model to investigate the transport and mobilization of Pb in these sediments. Application of the model consistently indicates the presence of a zone of Pb production to the porewaters that lies above a zone of Pb consumption. The profiles of various porewater constituents and thermodynamic calculations indicate that Pb is mobilized in the zone of production by the reductive dissolution of iron oxyhydroxides, whereas it is removed in the zone of consumption by precipitation as a solid sulfide. Rate constants are estimated for reductive iron dissolution (k d Fe(III) = 2.0 ± 0.5 × 10 −1 cm 3 mol −1 s −1), Pb adsorption on iron oxyhydroxides (k ads Pb = 98 ± 55 cm 3 mol −1 s −1), and Pb precipitation (k ppt Pb = 8 × 10 −20 mol cm −3 s −1 to 16 ± 13 × 10 −22 mol cm −3 s −1, depending on the solubility product assumed for the precipitation of PbS). According to model calculations, diagenetic processes, such as remobilization, molecular diffusion, bioturbation, and bioirrigation have a negligible influence on the solid phase Pb profile. In agreement with this finding, the present-day fluxes of dissolved Pb by diffusion (J D Pb = −6.5 × 10 −11 mol cm −2 yr −1), bioturbation (J B Pb = −1.1 × 10 −13 mol cm −2 yr −1), and bioirrigation (J I Pb = −1.5 × 10 −11 mol cm −2 yr −1) are small compared to the flux of Pb deposited with settling particles (J S Pb = 5.3 × 10 −9 mol cm −2 yr −1).

Sensitivity of northern redbelly dace, Phoxinus eos, to chemical alarm cues

The northern redbelly dace, Phoxinus eos (Cope, 1862), is subject to predation by brook trout, Salvelinus fontinalis (Mitchill, 1814), in Canadian Shield lakes, particularly when individuals migrate to the pelagic zone at sunset to feed on zooplankton and fish shoals break up into single individuals. The objectives of the present study were to (i) determine whether northern redbelly dace react to skin extracts from conspecifics and thus potentially use chemical alarms to detect predators in nature, (ii) characterize the fright reaction in northern redbelly dace under different concentrations of alarm substance, and (iii) estimate the active space of the alarm substance in this species. Northern redbelly dace responded to skin extracts of conspecifics with a series of antipredator behaviours. The dace moved closer to the substrate and away from the area where the alarm substance was injected, increased both the cohesion and polarization of their schools, and performed more dashing and freezing behaviours. The observed responses were closely correlated with the concentration of the skin extract solution, suggesting that individuals could use this sensitivity to different concentrations of alarm substance to estimate the risk of predation in nature. The dilution experiment allowed us to estimate that 1 cm2 of northern redbelly dace skin contains enough alarm substance to generate a response of individuals in 110 558 L of water, which corresponds to a cube with sides of approximately 4.8 m. Indirect evidence suggests that the northern redbelly dace could use chemical alarm cues to assess the risk of predation by brook trout in nature.

Thermal Characteristics and Energy Balance of Various-Size Canadian Shield Lakes in the Mackenzie River Basin

This study addresses the thermal and energy budget characteristics of four different-size Canadian Shield lakes in the Mackenzie River basin during the ice-free season of 2000. The objectives are to characterize and compare the surface temperature and thermal structures, and to quantify the magnitudes and flux rates of the energy balance components of each lake. This study highlights the variability in thermal and energy balance characteristics arising from differences in mean lake depth and surface area. The lakes exhibit similar temporal patterns for air temperature, net radiation, wind speed, and wind direction. Net radiation and wind speed are highest over the largest lake, Great Slave Lake, due to colder surface temperatures and lengthy across-lake wind fetch, respectively. During the warming phase of the summer, surface temperature is inversely related to mean depth; however, during the cooling phase this relationship reverses. The shallowest of the four lakes remains isothermal during the entire ice-free period, while the three larger and deeper lakes are all dimictic. A lag in the onset of thermal stratification in the dimictic lakes is positively correlated with mean depth and surface area. Large evaporative water losses correspond to periods of low net radiation and cold dry air over Great Slave Lake. However, over the smaller, shallower lakes periods of high evaporation occur on days with high net radiation and warm, dry air. The capacity of larger lakes to store more heat results in longer ice-free periods and higher evaporation. Maximum heat content increases and occurs later for lakes of greater depth. Maximum evaporative rates occur later and cumulative evaporation is highest for lakes of greater depth and area. The ratios of total open water evaporation for the four lakes in order of size (smallest 5 1.0) are 1.0 : 1.2 : 1.3 : 1.4. Evaporation magnitudes are discussed in the context of other temperate and high-latitude lake studies.

The differing crustacean zooplankton communities of Canadian Shield lakes with and without the nonindigenous zooplanktivore Bythotrephes longimanus

The nonindigenous predatory cladoceran Bythotrephes longimanus is spreading rapidly among Canadian Shield lakes, but only one case study of its impacts exists. In Harp Lake, the abundances of several cladoceran and one cyclopoid species fell after the invasion, and far fewer species benefited. To determine if Harp Lake provides typical results, we compared the summer crustacean zooplankton communities of 17 invaded and 13 noninvaded (reference) lakes in Ontario. The communities of the two lake groups differed. Average species richness was 30% higher in the reference (15.3 species) vs. the invaded lakes (11.8 species). Total zooplankton biomass was significantly lower in the invaded lakes, mainly because of lower abundances of all common epilimnetic cladoceran species. As these results were quite similar to those of Harp Lake, it is apparent that current summer zooplankton communities of Canadian Shield lakes with Bythotrephes differ substantially from noninvaded lakes.

Predicting the location of optimal habitat boundaries for lake trout (Salvelinus namaycush) in Canadian Shield lakes

The optimal habitat boundary for lake trout (Salvelinus namaycush Walbaum) has been defined as that portion of the lake having both more than 6 mg·L–1 oxygen and temperature less than 10 °C. Here we use an existing hypolimnetic oxygen model to define the lower boundary of the optimal habitat by identifying the depth at which 6 mg·L–1 oxygen occurs at the end-of-summer stratification period. Then we develop a new model to predict the 10 °C depth or upper habitat boundary for the same date. These two boundaries can be used in conjunction with measured individual strata volumes to calculate the optimal habitat volume. Parameters needed for the models include lake morphometry, total phosphorus (TP) concentration, and Secchi depth or dissolved organic carbon (DOC) concentration. Thus, the optimal habitat model can be used to predict the effects on optimal habitat volumes of changes in trophic status (increases or decreases in TP), or changes in light transmission (caused by changes in DOC or its surrogate in these lakes, i.e., Secchi depth) that result from changes in climate, land use, acid–base status, or incident ultraviolet radiation levels.

Energy Budget Processes of a Small Northern Lake

Abstract There is a paucity of information on the energy budget of Canada's northern lakes. This research determines processes controlling the magnitude of energy fluxes between a small Canadian Shield lake and the atmosphere. Meteorological instruments were deployed on a floating platform in the middle of a 5-ha lake during the 1999 and 2000 open-water seasons. High attenuation of incoming radiation at shallow depths and the sheltered location of the lake allows a strong thermocline to develop during the summer months, which prevents deeper water from exchanging energy with the atmosphere. Only after the lake becomes isothermal in late August do deeper waters interact with the atmosphere. When the lake is warming, evaporation is controlled by net radiation, but when the lake is cooling, turbulent energy fluxes are mainly influenced by the vapor pressure deficit. An empirically derived logarithmic relationship was identified between the Bowen ratio and the vapor pressure deficit. The Canadian Global Energ...

Littoral Microcrustacean (Cladocera and Copepoda) Indicators of Acidification in Canadian Shield Lakes

Littoral Microcrustacean (Cladocera and Copepoda) Indicators of Acidification in Canadian Shield Lakes

Littoral microcrustacean (Cladocera and Copepoda) indicators of acidification in Canadian Shield lakes.

We identify littoral microcrustacean indicators of acidification in 2 surveys of Canadian Shield lakes conducted 10 years apart. We found a total of 90 cladoceran and copepod species with richness increasing severalfold from acidic to nonacidic lakes. The fauna of the nonacidic lakes differed between the surveys. The 1987 survey employed activity traps, and caught more littoral taxa than the more recent, net-haul-based survey. Similar faunas were identified in the acidified lakes in both surveys, and several good indicator species were identified. For example, Acanthocycops vernalis was restricted to lakes with pH < 6. Sinobosmina sp. was very common but only in lakes with pH > 4.8. Tropocyclops extensus, Mesocyclops edax, and Sida crystallina were commonly found but only at pH > 5, and Chydorus faviformis only at pH > 5.9. These indicators showed promise in gauging the early stages of recovery from acidification in 3 lakes that were included in both surveys.

Stable Pb isotopes and PAHs as indicators of lead contamination sources in a lake of the Rouyn-Noranda area

We determined the depth distribution of total Pb and its stable isotope composition ( 206 Pb/ 207 Pb, 206 Pb/ 208 Pb, 206 Pb/ 204 Pb) in a dated sediment core collected at the deepest site, in the hypolimnion of a headwater Canadian Shield lake, located 25 km downstream from a metal smelter in operation since 1927. The isotopic ratios reveal the occurrence of one natural and two anthropogenic types of Pb over the last century. One of the anthropogenic Pb, predominant in the sediments accumulated in the early 20 th century, likely derives from coal combustion ( 206 Pb/ 207 Pb≃1.185). The second anthropogenic Pb has a signature similar to that of the ore processed during several decades at the smelter ( 206 Pb/ 207 Pb≃1.000); its contribution to the total Pb concentration sharply increased from 1927 to 1975 and then decreased steadily to the sediment surface.

Littoral Microcrustacean (Cladocera and Copepoda) Indicators of Acidification in Canadian Shield Lakes

Littoral Microcrustacean (Cladocera and Copepoda) Indicators of Acidification in Canadian Shield Lakes

Evidence of phosphorus-limited individual and population growth of Daphnia in a Canadian Shield lake

We performed bag experiments in a Canadian Shield lake with generally high seston (suspended food particles mainly composed of algae) carbon (C):phosphorus (P) ratios, and investigated the responses of individual and population growth of herbivorous Daphnia dentifera on their abundance with (+P) and without (−P) a phosphorus enrichment to lake water. In both treatments, increased abundance of D. dentifera reduced seston C concentration and was accompanied by decreases in population and individual growth rates. However, P-enrichment increased seston P concentration and then reduced seston C:P ratio from 400–700 to ca 100 (by atoms). As a result, both individual and population growth rates were significantly higher in the +P treatment at all animal abundances even though seston C concentrations were similar between the treatments. The magnitude of the growth enhancement by the P-enrichment was independent of animal abundance. Stepwise regression analyses revealed that 71 and 90% of the variance in the population and individual growth rates, respectively, were explained by seston C and P concentrations, and that the contribution of the seston P concentration was roughly the same as that of seston C. Such joint effects of seston C and P indicate that food quality (P content) as well as food quantity (C concentration) can influence Daphnia not only at the level of individual growth but also at the level of population dynamics in P-limited lakes. Our results thus strongly corroborate the hypothesis that the population development of a key herbivore Daphnia in P-limited Canadian Shield lakes is inhibited by the direct effects of P-limited food on individual growth, which weaken the strength of trophic cascading interactions starting from piscivorous fish through planktivorous fish and zooplankton to algae.

The importance of the sediment pathway in the radionuclide dose received by aquatic non-human biota: Reconstruction and mapping of spatiotemporal partitioning in Perch lake sediments over a 40-year period

There is a growing interest in assessing risk to non-human biota following exposure to radionuclides . However, before dose to aquatic biota can be determined, it is critical to have a solid understanding of radionuclide concentrations in key environmental phases due to their importance in determining external and internal dose. Further understanding of a system can be reached by monitoring temporal changes in radionuclide levels in these phases, especially if assessing the success of remediation activities. The current study has focused on estimating inputs of 90 Sr, 137 Cs and 60 Co to the sediments of a small, Canadian Shield lake located downstream of two Waste Management Areas at AECL's, Chalk River Laboratories site over a 40-year period. Overall, it was found that 137 Cs and 60 Co inputs have declined in the lake over the last 40 years, which resulted in a net depletion of these radionuclides from the sediments over time. Strontium-90 inputs have remained fairly constant over this time period with 90 Sr retention in lake sediments of approximately 15%. It is expected that benthic biota will receive approximately a 2- to 6-fold higher radionuclide dose than pelagic organisms, on average, particularly when feeding in the depositional zone of the lake.

Accumulation of damaged bacteria and viruses in lake water exposed to solar radiation

Ambient ultraviolet radiation (UVR) is known to have direct negative effects on aquatic bacteria at the molecular level, damaging DNA, and at the level of community metabolism, but little is known about the effects of UVR at the cellular level. In order to study the direct and indirect effects of UVR on bacterioplankton, we developed a staining protocol based on the exclusion nucleic acid stain TOPRO-1 that allows the detection of cells with damaged membranes. We used this protocol to assess the effect of UVR in water samples collected from Lac Cromwell, a small dystrophic Canadian Shield lake. Samples were incubated 5 d in situ in a series of dialysis bag experiments under natural solar radiation. Samples with and without grazers were suspended in the lake's epilimnion and received graded amounts of ambient UVR. Abundances of bacteria, viruses and heterotrophic nanoflagellate grazers, and the number of TOPRO+ cells were monitored. In samples exposed to full solar radiation, a marked increase in the number of bacteria that took up the exclusion nucleic acid stain TOPRO, an indicator of cellular damage, was observed. The rate of accumulation of damaged bacteria reached a maximum of 13.5% d -1 and was a direct function of the UVR intensity in solar radiation. There was also an increase in the mean total viral abundance in bags exposed at the surface. We hypothesize that this increase in viral number was due to the induction by UVR of the lytic cycle in lysogenic bacteria. In the presence of grazers, however, the virus-to-bacteria ratio was lower and the bacterial mortality attributable to viral lysis was reduced by half, from 10.7 to 4.6 % d -1 . These observations strongly suggest that grazers and viruses are competing for the same bacteria and that grazers may play an important role in regulating the proportion of bacterial mortality caused by viruses. Our results show that high intensities of ambient UVR, particularly in the surface waters of lakes with shallow epilimnia or those that undergo periods of microstratification, may be an important factor influencing bacterial mortality, either directly or indirectly via the induction of lysogenic bacteria.

Parasite effects on the survival, growth, and reproductive potential of yellow perch (Perca flavescens Mitchill) in Canadian Shield lakes

Three parasites of yellow perch, Perca flavescens, in four Canadian Shield lakes were studied for their effects on perch growth and mortality. Glugea sp. xenomas in cells of the intestinal wall and in visceral fat and Apophallus brevis metacercariae infecting the musculature reduced the growth of perch, causing mortality in younger and smaller fish. High numbers of Raphidascaris acus encysted in the liver of yellow perch correlated significantly with a reduction in visceral-fat mass in age 1+ females and age 0+ and 1+ males. A significant correlation in these subsamples indicates that host sex, size, trophic status, and relative mass of the liver are linked to R. acus density. Our data suggest that interactions among parasitic infections and age, size, and sex of the fish host can affect growth and survival of the host, especially during periods of low energy inputs and reproductive stress.

Diatom-inferred dissolved organic carbon reconstructions provide assessments of past UV-B penetration in Canadian Shield lakes

Paleolimnological approaches have provided strong inference models for lake-water acidity and metal concentrations in Sudbury-area lakes, but calibration data have not yet been explored for inferring lake-water dissolved organic carbon (DOC). A review of available limnological data provided DOC values for 80 of our 105 calibration lakes, allowing us to examine the relative importance of DOC in determining the distribution of diatom assemblages in Canadian Shield lakes, such as those in the Sudbury region. Canonical correspondence analysis (CCA) indicated that lake-water DOC explained a significant proportion of variation in the diatom data. Our weighted-averaging DOC model showed a strong relationship (r2 = 0.63) between measured and inferred DOC. Using this model, we reconstructed historical DOC concentrations in three Sudbury-area lakes, and then estimated temporal changes in UV-B penetration. These reconstructions showed that lake water DOC concentrations and underwater UV-B penetration have changed markedly in two of the three lakes modeled. The close correspondence between inferred and measured DOC for the 1980s in all three lakes provides further evidence that we have accurately inferred DOC concentrations. Quantitative DOC reconstructions in Sudbury-area lakes offer an excellent technique for assessing past changes in DOC concentrations and UV-B penetration in Canadian Shield lakes.

Diatom-inferred dissolved organic carbon reconstructions provide assessments of past UV-B penetration in Canadian Shield lakes

Diatom-inferred dissolved organic carbon reconstructions provide assessments of past UV-B penetration in Canadian Shield lakes

Parasite effects on the survival, growth, and reproductive potential of yellow perch (&lt;i&gt;Perca flavescens&lt;/i&gt; Mitchill) in Canadian Shield lakes

Parasite effects on the survival, growth, and reproductive potential of yellow perch (&lt;i&gt;Perca flavescens&lt;/i&gt; Mitchill) in Canadian Shield lakes

Responses of a lake outlet community to light and nutrient manipulation: effects on periphyton and invertebrate biomass and composition

1. Experimental channels were installed at the outlet of a small Canadian Shield lake to study the role of light and nutrients on the regulation of periphyton and invertebrate biomass and taxonomic composition. Light (93% reduction) and nutrients (four‐fold increase of ambient total phosphorus (TP) concentration) were manipulated in a factorial design experiment. 2. Periphyton chlorophyll a (Chl a), measured four times during the 12‐week experiment, increased due to higher irradiance but was unaffected by phosphorus enrichment. Over the experiment, periphyton biomass was, on average, three times higher in open than in shaded channels. 3. Algal taxonomic and growth form composition were affected by light and phosphorus enrichment. The proportion of cyanophytes was significantly higher in unenriched, shaded channels (45%) compared to the three other treatments. Single cells and colonial forms were dominant in shaded channels, whereas filamentous and chain‐forming algae were prevalent in open channels. 4. Total invertebrate biomass remained unchanged over time and among treatments. At the beginning of the experiment, all the channels were dominated by Chironomidae and filter feeders (Simuliidae and Hydropsychidae). After 55 days, filter feeders became clearly dominant (60%) in all treatments except in the enriched, open channels where there was a significant shift in the functional group composition toward grazers (snails and oligochaetes). Among filter feeders, Simuliidae increased in shaded channels.