Low pH Lakes Research Articles

Increasing diversity and biotic homogenization of lake plankton during recovery from acidification

Determining biodiversity responses to environmental change, such as acidification, is critical for ecosystem projections under future global change scenarios. Here, we analyzed three plankton communities of phytoplankton, crustaceans and rotifers in 28 lakes in the Adirondack Park, USA, during 1994–2012, and examined the spatiotemporal trends in their alpha and beta diversity during recovery from acidification. For all plankton assemblages, Shannon diversity increased towards recent years and high lake pH, and there was an increasing community dissimilarity with pH changes. The spatial mean Bray-Curtis dissimilarities across all lakes decreased over time for phytoplankton and rotifers leading to an increase in spatial homogenization. Such a homogenization cooccurred however with the overall increasing diversity in this region, which contrasts with the previous classic view that homogenization is mainly driven by loss of species and results in biodiversity loss. We further observed lower temporal mean beta diversity in low-pH lakes for crustaceans and rotifers, but not for phytoplankton. Generally, spatial and temporal mean beta diversity of the three taxonomic groups were primarily driven by lake-water ion variables, and rotifers were also constrained by nutrients and climate. Collectively, our results show how and why plankton community compositions vary over space along with acidification recovery, and further highlight the importance of spatiotemporal studies combined with long-term monitoring programs in assessing biodiversity change during the recovery of disturbed ecosystems.

Carbon dissolution effects on pH changes of RAMP lakes in northeastern Alberta, Canada

Study regionThis study focuses on boreal lakes in the Athabasca Oil Sands Region (AOSR), Alberta, Canada between latitude 55.68°N and 59.72°N and longitude 110.02°W and 115.46°W. Study focusThis study focuses on interpretation of hydrochemistry from 50 lakes thought to be acid sensitive, and so monitored by the Regional Aquatic Monitoring Program (RAMP) over the last two decades. This study uses basic statistics, principal component analysis, lithological evidence, CO2 saturation estimates, mineral equilibria and δ13CDIC measurements to describe and assess controls on pH and to investigate causal factors of observed pH increase in the lakes. New hydrological insights for the regionOur assessment provides evidence of two main geochemical processes that control pH increase, namely carbonate dissolution and organic matter uptake, the latter a particularly important component of alkalinity in low pH lakes. Lakes in all subregions show strong evidence of dissolution of marine carbonates of undetermined source, and lake water appears to be trending from CO2 super-saturation towards atmospheric CO2 equilibrium. This supports the hypothesis of carbonate input due to permafrost thaw via surface or groundwater pathways, but also reveals likely influence from CO2 dissolution mechanisms related to climatic influence on ice cover duration.

Global changes may be promoting a rise in select cyanobacteria in nutrient-poor northern lakes.

The interacting effects of global changes-including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes-are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient-poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient-poor Swedish lakes over 16years (1998-2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon-specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.

Influence of in ovo mercury exposure, lake acidity, and other factors on common loon egg and chick quality in Wisconsin.

A field study was conducted in Wisconsin (USA) to characterize in ovo mercury (Hg) exposure in common loons (Gavia immer). Total Hg mass fractions ranged from 0.17 µg/g to 1.23 µg/g wet weight in eggs collected from nests on lakes representing a wide range of pH (5.0-8.1) and were modeled as a function of maternal loon Hg exposure and egg laying order. Blood total Hg mass fractions in a sample of loon chicks ranged from 0.84 µg/g to 3.86 µg/g wet weight at hatch. Factors other than mercury exposure that may have persistent consequences on development of chicks from eggs collected on low-pH lakes (i.e., egg selenium, calcium, and fatty acid mass fractions) do not seem to be contributing to reported differences in loon chick quality as a function of lake pH. However, it was observed that adult male loons holding territories on neutral-pH lakes were larger on average than those occupying territories on low-pH lakes. Differences in adult body size of common loons holding territories on neutral-versus low-pH lakes may have genetic implications for differences in lake-source-related quality (i.e., size) in chicks. The tendency for high in ovo Hg exposure and smaller adult male size to co-occur in low-pH lakes complicates the interpretation of the relative contributions of each to resulting chick quality.

Mercury and other element exposure in tree swallows nesting at low pH and neutral pH lakes in northern Wisconsin USA

The primary objective of this study was to determine whether tree swallows (Tachycineta bicolor) demonstrate similar responses to lake pH and mercury (Hg) contamination in northern Wisconsin as do common loons (Gavia immer). Similar to common loons, Hg concentrations in the blood of tree swallow nestlings were higher, Hg concentrations in eggs tended to be higher, and egg size tended to be smaller at low (<6.2) pH lakes. In contrast to common loons, tree swallow nestling production was not lower at low pH lakes. Based on modeling associations, Hg concentrations in tree swallow eggs and nestling blood can be used to predict Hg concentrations in common loons without the invasive or destructive sampling of loons. Mean concentrations of cadmium, manganese, and mercury in nestling livers were higher at low pH lakes than neutral pH lakes. Concentrations of cadmium, chromium, mercury, selenium, and zinc were not at toxic levels.

Effects of methylmercury exposure on the behavior of captive-reared common loon (Gavia immer) chicks

Behavioral effects resulting from exposure to dietary methylmercury (MeHg) have been reported in studies of several wildlife species. However, quantifying the impact of contaminant exposure on wild populations is complicated by the confounding effects of other environmental stressors. We controlled confounding stressors in a laboratory study to quantify the level of dietary MeHg exposure associated with negative effects on the fitness of captive-reared common loon (Gavia immer) chicks. We evaluated the effect of MeHg on loon chick behavior by employing several assays, including measures of righting reflexes, responsiveness to taped parental calls, reaction to frightening stimuli, and estimates of time activity budgets. Evidence suggested that as chicks aged, those exposed to nominal dietary dose levels of 0.4 and 1.2 microg Hg/g wet-weight in food (average estimated delivered dietary level of 0.55 and 1.94 microg Hg/g, respectively) were less likely (p < 0.01) to right themselves after being positioned on their backs during outdoor trials (> or =37 days old) compared to chicks on the control diet. We detected differences (p < 0.05) in several response variables with respect to source of eggs. Chicks from nests on low-pH lakes tended to spend more time on resting platforms, spent less time in the shade, were more likely to walk across a platform upon release and do it quicker, were less responsive to a frightening stimulus, and exhibited less intense response to parental wail calls than did chicks from neutral pH-lakes. Rapid MeHg excretion during feather growth likely provides loon chicks protection from MeHg toxicity and may explain the lack of behavioral differences with dietary intake. Lake source effects suggest that in ovo exposure to MeHg or other factors related to lake pH have consequences on chick behavior.

Mercury biomagnification in the food webs of acidic lakes in Kejimkujik National Park and National Historic Site, Nova Scotia

Mercury (Hg) concentrations in fish from acidic lakes (pH &lt; 6.0) are typically elevated above those from near-neutral systems. It is unknown whether high biomagnification rates through the supporting food web can explain elevated Hg concentrations in top predators from low pH lakes. To investigate this, we collected yellow perch ( Perca flavescens ), brown bullhead ( Ameiurus nebulosus ), banded killifish ( Fundulus diaphanous ), golden shiner ( Notemigonus crysoleucas ), and littoral and pelagic invertebrates from four acidic lakes in Kejimkujik National Park and Historic Site (KNPNHS), Nova Scotia, Canada, and analyzed them for total Hg and methyl Hg (MeHg), and δ13C and δ15N to determine sources of energy and trophic position, respectively. Mercury biomagnification rates (slopes of log Hg versus δ15N) varied significantly among the four lakes but did not explain the among-lake differences in perch Hg; these slopes were also within the range published for near-neutral systems. Rather, Hg concentrations in yellow perch (i.e., predatory fish) in KNPNHS were higher in lakes with higher MeHg in lower-trophic-level organisms and suggest that processes influencing Hg uptake at the base of the food web are more important than rates of food web biomagnification for understanding the variation in concentrations of this contaminant among top predators.

Effects of methylmercury exposure on the immune function of juvenile common loons (Gavia immer)

We conducted a dose-response laboratory study to quantify the level of exposure to dietary Hg, delivered as methylmercury chloride (CH3HgCl), that is associated with suppressed immune function in captive-reared common loon (Gavia immer) chicks. We used the phytohemagglutinin (PHA) skin test to assess T-lymphocyte function and the sheep red blood cell (SRBC) hemagglutination test to measure antibody-mediated immunity. The PHA stimulation index among chicks receiving dietary Hg treatment did not differ significantly from those of chicks on the control diet (p = 0.15). Total antibody (immunoglobulin [Ig] M [primary antibody] + IgG [secondary response]) production to the SRBC antigen in chicks treated with dietary methylmercury (MeHg), however, was suppressed (p = 0.04) relative to chicks on control diets. Analysis indicated suppression of total Ig production (p = 0.025 with comparisonwise alpha level = 0.017) between control and 0.4 microg Hg/g wet food intake treatment groups. Furthermore, the control group exhibited a higher degree of variability in antibody response compared to the Hg groups, suggesting that in addition to reducing the mean response, Hg treatment reduced the normal variation attributable to other biological factors. We observed bursal lymphoid depletion in chicks receiving the 1.2 microg Hg/g treatment (p = 0.017) and a marginally significant effect (p = 0.025) in chicks receiving the 0.4 microg Hg/g diet. These findings suggest that common loon chick immune systems may be compromised at an ecologically relevant dietary exposure concentration (0.4 microg Hg/g wet wt food intake). We also found that chicks hatched from eggs collected from low-pH lakes exhibited higher levels of lymphoid depletion in bursa tissue relative to chicks hatched from eggs collected from neutral-pH lakes.

Effects of methyl mercury exposure on the growth of juvenile common loons.

We conducted a dose-response laboratory study to quantify the level of mercury exposure associated with negative effects on the development of common loon chicks reared in captivity from hatch to 105 days. A dose regimen was implemented that provided exposure levels that bracketed relevant exposure levels of methyl mercury found in loon chicks across North America. We observed no overt signs of mercury toxicosis and detected no significant effect of dietary mercury exposure on growth or food consumption. However, asymptotic mass was lower in chicks that hatched from eggs collected from nests on low pH lakes relative to eggs from neutral pH lakes. Rapid excretion of methyl mercury during feather growth likely provides loon chicks protection from methyl mercury toxicity and may explain the lack of convincing toxicological findings in this study. Lake-source effects suggest that in ovo exposure to methyl mercury or other factors related to lake pH have consequences on chick development.

Lake water geochemistry on the western Kola Peninsula, north-west Russia

Water samples were taken from 120 lakes spread over the western half of the Kola Peninsula, NW Russia. The samples were analysed for 37 elements, pH and electrical conductivity. Lake water chemistry appears in most cases to be dominated by a Ca/Na–HCO 3 signature, characteristic of natural carbonate/silicate weathering. Input of elements from marine derived salts and from the Ni industry (roasting plant at Zapoljarnij, smelter at Nikel and smelter/refinery at Monchegorsk) emissions are restricted to limited regions. Considering that 3 of the world's largest point source emitters of SO 2 are located within the area, the median lake water pH is surprisingly close to neutral (6.6, range 4.2–7.4). Indeed some of the apparently SO 4 contaminated lakes nearest to the smelters yield the highest pH values. Changes in climate and vegetation from north to south within the survey area probably have an influence on element concentrations and pH as observed in the lake waters. Proton displacement by sea salt cation input provides an explanation of low pH lakes in coastal areas.

Assessing water quality changes in the lakes of the northeastern United States using sediment diatoms

Diatom assemblages were selected as indicators of lake condition and to assess historical lake water quality changes in 257 lakes in the northeastern United States. The "top" (surface sediments, present-day) and "bottom" (generally from &gt;30 cm deep, representing historical conditions) samples from sediment cores collected from lakes and reservoirs were analyzed for diatom assemblages. The distribution of diatom species was closely related to several environmental variables, primarily lake water pH, total phosphorus, and chloride. Using weighted-averaging calibration and regression approaches, we constructed predictive models to infer these variables from the diatom assemblages. The diatom-based inference models were then used to assess the current status of lake water quality and to assess historical changes in lake water conditions in natural lakes over the past 150 years. Changes were also assessed in reservoirs. Population estimates of historical changes in limnological variables were made for all lakes of the northeast United States and also for lakes in the Adirondacks, New England Uplands, and Coastal Lowlands/Plateau ecoregions. The extent of cultural impact has been quite variable among the ecoregions, with marked water quality deterioration occurring in hundreds of lakes. Chloride and phosphorus levels have increased, especially in lakes that currently have high concentrations. Low-pH lakes have become more common in all three ecoregions. The maximum abundance of low-pH lakes was recorded in the Adirondacks, an area receiving the highest acidic precipitation in the northeast. In the Coastal Lowlands/Plateau, there has been a clear increase in eutrophic lakes, as inferred by total phosphorus. This was accompanied by a marked increase in the number of lakes with high chloride levels.

Seasonal patterns of mercury species in water and plankton from softwater lakes in Northeastern Minnesota

Twelve softwater lakes in NE Minnesota were sampled in spring, summer, and fall of 1992 and 1993 for labile (unextracted) methyl-Hg, total (extracted) methyl-Hg, and total Hg in lake water and net plankton (≥300 µm). The lakes are small (5.6–56 ha), low productivity, headwater drainage or seepage lakes. They are acid-sensitive (ANC ≤200 µeq/L) but not low pH lakes (average pH 6.6). The lakes ranged in color from 8.5 to 70 PCU. Statistical analysis of the water chemistry variables and mercury species support the conclusion that these were a homogeneous set of lakes; therefore, seasonality of mercury forms was analyzed on combined (mean) data from the 12 lakes. Methyl-Hg in water declined throughout the growing season. HgT also declined sharply from spring to summer but increased again in the fall. In contrast to the methyl-Hg and Hg in water, concentrations in plankton were at the lowest levels in spring and rose to higher levels in summer. The mass of mercury in plankton increased from spring to fall, as did the methyl-Hg fraction, which increased from 20% of HgT in spring to 52% in autumn. Bioaccumulation factors (BAF) for methyl-Hg in net plankton increased over the growing season. Overall, log BAF for HgT in net plankton (wet wt.) was 4.45. Log BAF for methyl-Hg in plankton was 4.90 to 5.43 depending on the analytical form of methyl-Hg in water (labile or total). Seasonal patterns of methyl-Hg and HgT did not covary in water, but did covary in plankton. These results support the conclusion that measurement of Hg in water is not adequate in itself to determine the amount of bioavailable Hg (i.e., methyl-Hg) in a lake. Labile (unextracted) methyl-Hg could be a useful measurement of bioavailable Hg. Labile methyl-Hg exhibits the same seasonal patterns as total methyl-Hg, but does not require the extraction steps necessary for measuring total methyl-Hg.

GEOGRAPHIC TREND IN MERCURY MEASURED IN COMMON LOON FEATHERS AND BLOOD

The common loon (Gavia immer) is a high-trophic-level, long-lived, obligate piscivore at risk from elevated levels of Hg through biomagnification and bioaccumulation. From 1991 to 1996 feather (n = 455) and blood (n = 381) samples from adult loons were collected between June and September in five regions of North America: Alaska, northwestern United States, Upper Great Lakes, New England, and the Canadian Maritimes. Concentrations of Hg in adults ranged from 2.8 to 36.7 μg/g (fresh weight) in feathers and from 0.12 to 7.80 μg/g (wet weight) in whole blood. Blood Hg concentrations in 3 to 6-week-old juveniles ranged from 0.03 to 0.78 μg/g (wet weight) (n = 183). To better interpret exposure data, relationships between blood and feather Hg concentrations were examined among age and sex classes. Blood and feather Hg concentrations from the same individuals were significantly correlated and varied geographically (r2 ranged from 0.03 to 0.48). Blood and feather Hg correlated strongest in areas with the highest blood Hg levels, indicating a possible carryover of breeding season Hg that is depurated during winter remigial molt. Mean blood and feather Hg concentrations in males were significantly higher than concentrations in females for each region. The mean blood Hg concentration in adults was 10 times higher than that in juveniles, and feather Hg concentrations significantly increased over 1 to 4-year periods in recaptured individuals. Geographic stratification indicates a significant increasing regional trend in adult and juvenile blood Hg concentrations from west to east. This gradient resembles U.S. Environmental Protection Agency-modeled predictions of total anthropogenic Hg deposition across the United States. This gradient is clearest across regions. Within-region blood Hg concentrations in adults and juveniles across nine sites of one region, the Upper Great Lakes, were less influenced by variations in geographic Hg deposition than by hydrology and lake chemistry. Loons breeding on low-pH lakes in the Upper Great Lakes and in all lake types of northeastern North America are most at risk from Hg.

Common loons (Gavia immer) nesting on low ph lakes in northern Wisconsin have elevated blood mercury content

Common loons (Gavia immer) nesting on low ph lakes in northern Wisconsin have elevated blood mercury content

Elevated Levels of Arginine Vasotocin in the Brain of Brook Trout (Salvelinus fontinalis) from Acid Lakes: A Field Test of a Potential Biomarker for Acid Stress

The levels of arginine vasotocin (AVT), an osmoregulatory peptide, were determined by radioimmunoassay in brain tissue of brook trout (Salvelinus fontinalis) of a wide size range (50–380 mm) from softwater Laurentian lakes ranging in pH from 5.0 to 6.9 at different seasons. Multivariate models (ANCOVA) were developed to quantify the relationship between AVT, pH, body size, and season. Brain AVT levels increased with body size, and the allometric slope was highest in the low-pH lakes (pH 5.0-5.5). Although brook trout &gt; 150 mm had higher brain AVT levels at low pH, no significant differences were detected for brook trout &lt; 150 mm. We hypothesize that the sensitivity of brook trout at the parr stage to acid stress may be linked to their inability to mobilize a hormonal response involving AVT. The seasonal variation in brain AVT levels was similar in all the lakes studied, summer levels being the highest. Although this field study revealed that AVT levels depend also on factors other than acid stress (body size and season), our ANCOVA models allow adjustment for the effects of these covariables. Analyses of this type can be used to field test and calibrate biomarkers for use in ecotoxicology.

Relative Survival of Hatchery-Reared Lake Trout, Brook Trout, and F1Splake Stocked in Low-pH Lakes

A matched-planting experiment was conducted to determine the most suitable salmonid genotype for stocking in former lake trout lakes that currently are too acidic to support lake trout reproduction. Hatchery-reared lake trout Salvelinus namaycush, brook trout Salvelinus fontinalis, and F1 splake S. namaycush × S. fontinalis were planted in May 1989 at age 18–19 months in four lakes with pH values of 4.9–5.4. Relative survival of the three genotypes was assessed during a 4-d holding period immediately after stocking and by gillnetting during the summer of 1990. During the 4-d holding period, survival of lake trout (23%) was significantly lower than that of brook trout (98%) and splake (92%). Gillnetting recovery rates were 0–0.9% for lake trout, 0–1.8% for brook trout, and 1.1–15.0% for splake. The results of this study suggest that splake are the most suitable of these three salmonid taxa for stocking on a put–grow–take basis in lakes of pH 4.9–5.4

Influence of Dissolved Organic Carbon, pH, and Microbial Respiration Rates on Mercury Methylation and Demethylation in Lake Water

Effects of changes in DOC concentrations, pH, and microbial respiration rates on specific rates of mercury methylation and demethylation in lake water were studied using radioisotopic techniques. Increased concentrations of DOC resulted in decreased specific rates of net methylation, possibly as a result of complexation of inorganic mercury with DOC. A reduction in pH from 7.0 to 5.0 had the greatest effect, causing large to moderate increases in net methylation rate at both low and high DOC concentrations (500–2600 μM). Rates of respiration (indicative of general rates of microbial activity), which were insensitive to pH change over the range tested (5.0–7.0), had the smallest effect on net methyl mercury production rates. We propose the following explanations for three situations in which high mercury concentrations are commonly found in fish. (1) in acidified dilute clear-water lakes, high fish mercury concentrations may be a result of enhanced in-lake methylation; (2) in brown-water circumneutral lakes, where in-lake methylation is inhibited by high DOC concentrations, terrestrial inputs of methyl mercury may be most important; and (3) in brown-water, low-pH lakes, both in-lake and terrestrial sources of methyl mercury may contribute to elevated mercury concentrations in fish.

Effect of pH on the bioaccumulation of low level, dissolved methylmercury by rainbow trout (Oncorhynchus mykiss)

An inverse relationship has been observed between pH and McHg concentration in freshwater fish. Many hypotheses exist regarding the mechanisms which lead to elevated levels of organic Hg in fish from low pH lakes. To determine if pH has a direct effect on the rate of McHg bioaccumulation in fish, rainbow trout fingerlings (Oncorhynchus mykiss) were exposed to a low concentration of aqueous methylmercuric chloride (1.38 ± 0.49 ng·L−1) at four pH-levels (8.2, 7.0, 6.3, 5.8) for eight weeks. McHg and total Hg were specifically determined on whole fish homogenates and water samples. The pH was found to have a significant: inverse effect on the rate of McHg bioaccumulation in the fish only in the lowest exposure level. Fish held at pH 5.8 had an uptake rate of 1.11 ± 0.07 ng·g−1·d−1, while those at pH ≥ 6.3 had a MeHg tissue uptake rate of ≤ 0.64 ± 0.07 ng·g−1·d−1. Total body burden of MeHg in the fish held at pH 5.8 also showed an elevated level of MeHg when compared with fish held at higher pH-levels, but the difference was less dramatic. These results suggest that a portion of the Hg burden in fish from low pH systems may be due to the direct effects of low pH on bioaccumulation, but that a threshold may exist above which pH does not play a significant role.

Metal concentrations in crayfish tissues in relation to lake pH and metal concentrations in water and sediments

Cambarus bartoni from two acid lakes, Cambarus robustus from one acid lake, and Orconectes virilis from one acid and two circumneutral lakes were analyzed for the following concentrations: Mn, Fe, Al, Zn, Cu, and Cd in gill; Mn, Fe, Al, Zn, and Cu in muscle; and Mn, Al, Fe, Zn, Cu, Ca, Mg, Ba, and S in carapace tissue. Analysis of covariance and canonical variates analysis were used to illustrate differences in the six crayfish populations, based on the elemental content of the three tissues. Gill Cd was significantly greater in all four crayfish populations from the acid lakes, as compared to crayfish from circumneutral lakes. Subsequent canonical variates analysis separated crayfish from acid lakes from those sampled from two circumneutral lakes, based on gill Cd concentrations and to a lesser extent on gill Mn concentrations. Carapace elemental composition was also significantly different among the six crayfish populations, with the canonical variates analysis separating crayfish of acid-lake origin from those captured in circumneutral lakes, based on differences in Mg and Mn content of the carapace; carapaces of crayfish from acid lakes had more Mn and less Mg relative to crayfish carapaces from circumneutral lakes. The elemental composition of crayfish muscle was the least variable and the least indicative of differences in elemental content among the six populations. Conditions of low pH may be preventing the normal mineralization of crayfish carapaces, as evidenced by crayfish from acid lakes having carapaces with lower Mg concentrations relative to crayfish from circumneutral lakes. More importantly, however, increases in gill Cd in crayfish from low-pH lakes appear to be a pH-related effect rather than being attributable to differences in Cd accumulation among species or to abiotic factors such as concentrations of Cd in the sediments, dissolved organic carbon, or water-borne Ca concentrations. As crayfish are an important food resource for many fish and semiaquatic animals, they could be a key vector in the trophic transfer of Cd from the aquatic to the terrestrial environment.

Survival of Introduced Smallmouth Bass in Low-pH Lakes

We measured survival of caged overwintering young-of-the-year and introduced, free-swimming adult smallmouth bass Micropterus dolomieui in five Ontario lakes that varied in pH from 4.9 to 5.9 (winter values). No hatchery-reared young survived in lakes that ranged in pH from 4.9 to 5.9 and in total aluminum from 55 to 215 μg/L. The only lake in which young survived the winter (2–100% survival) had a pH of 5.9 and a total Al of 34 μg/L. Survival of overwintering young in the laboratory was high (92–100%) at all pH levels tested (4.9–6.0). Differences in metal (AI, Cu, Zn, Ni, Mn) concentrations may account for survival differences between the field and laboratory and between lakes with similar pH. Adult smallmouth bass were transferred to four of the same lakes (19–24 fish/lake) used for the experiment on young fish. Population size estimates for the introduced adults were obtained from snorkeling surveys conducted during three spawning seasons (1987–1989). Estimated population size, expressed as a percentage of the number stocked, was highest (41–55%) in the lake with pH 5.9, low (4–12%) in the lake with pH 5.4, and zero in two lakes with pH 4.9–5.2.