Long-term trends in limnological characteristics in the Aurora trout lakes, Sudbury, Canada

Paleolimnological techniques were employed to document the limnological histories of the aurora trout lakes, located in the Sudbury region of Ontario. Two of these lakes are of special interest to fisheries managers, as they represent the only known native habitats of a rare strain of brook trout: the aurora trout. These lakes were limed as part of restoration efforts. Stratigraphic changes in diatom and chrysophyte assemblages from dated lake sediment cores indicate that all the lakes have been impacted by anthropogenic acidification, although the timing and the magnitude of acidification were different amongst the lakes. For example, Whirligig Lake was likely the most naturally acidic lake in the past, but it had further acidified since about 1960. This lake was limed in 1989 and then again in 1993. In Whitepine Lake, acidification started 1940; however, in the most recent sediments (1992), some recovery in lakewater acidity has occurred. In Little Whitepine Lake (a reference lake), acidification started earlier (1920) and the lakewater pH continued to decline until about 1990. This lake was limed in 1989. The chrysophyte paleoindicators suggest a recent recovery in this lake. The successful re-introduction of aurora trout in Whirligig and Whitepine lakes is undoubtedly related to the improved water quality through liming but, based on our paleolimnological indicators, the lakes' limnological characteristics (e.g. pH and metal concentrations) are still different from those present before atmospheric deposition of strong acids from the Sudbury smelters.     

Aquatic Ecosystem Responses to Rapid Recovery from Extreme Acidification and Metal Contamination in Lakes Near Wawa, Ontario

In the region northeast of Wawa, Ontario (Canada), many circumneutral lakes downwind of a nearby iron-sintering plant were strongly acidified (pH 3–4) in response to the emissions of large amounts of sulfur dioxide from 1939–1998. Following closure of the plant in 1998, lakewater pH has returned to circumneutral conditions due to the high buffering capacity of the local geological substrate. Prior paleolimnological analyses of dated sediment cores have detected some biological recovery among algal communities (diatoms and chrysophytes), although they have not returned to their pre-impact assemblages. Here we take a broader ecosystem approach, and build upon the algal analyses by examining cladoceran sedimentary assemblages, and spectrally-inferred chlorophyll a and dissolved organic carbon (DOC) from the same dated sediment cores. Similar to the algal communities, recent cladoceran sedimentary assemblages from three impacted lakes remain in an altered state relative to the pre-impact period (for example, increased relative abundances of Chydorus brevilabris and reduced cladoceran density in sediments). However, trends in the spectrally-inferred chlorophyll a and DOC were mixed, with long-term decreases in the study lake closest to the plant and long-term increases within the other lakes. Collectively, the multi-proxy paleolimnological analyses of these markedly acidified lakes demonstrate the delayed biological recovery from acidification (and differences in timing) across multiple trophic levels, despite the near-elimination of acid deposition almost a decade previously, which led to a striking recovery in lakewater pH and increased food availability.     

Elevated metal concentrations inhibit biological recovery of Cladocera in previously acidified boreal lakes

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Long-term lake acidification trends in high- and low-sulphate deposition regions from Nova Scotia,Canada

Diatom-based paleolimnological techniques were used to study 14 lakes from two regions of Nova Scotia which represent regions of high and low sulphate deposition. Using decadal scale intervals, changes in diatom assemblages and diatom-inferred pH were tracked in relation to deposition of anthropogenic-sourced strong acids. Eight study lakes were located in Kejimkujik National Park in the southwestern part of the province, which receives an annual sulphate deposition (2000–2002) of ~10.5 kg ha⁻¹ yr⁻¹. These lakes showed significant changes in diatom assemblages with overall diatom-inferred acidification of ~0.5 pH units starting between 1925 and 1940, with the timing of acidification related to pre-industrial (or pre−1850) lakewater pH. Six study lakes were located in Cape Breton Highlands National Park, in northern Nova Scotia, a region of lower sulphate deposition. These lakes did not show any consistent trends in diatom assemblages or inferred pH values consistent with recent acidic deposition, but rather variations that may be related to climatic influences. Nova Scotia lakes that have been most impacted by acidic deposition had the lowest pre-industrial lakewater pH values and were in an area of relatively high sulphate deposition. Handling editor: K. Martens     

DISTRIBUTION OF THE GENUS CYCLOTELLA IN RELATION TO pH IN PRECAMBRIAN SHIELD LAKES: IMPLICATIONS FOR DIATOM-INFERRED pH1

Recent research on relationships between diatoms and pH suggests that the genus Cyclotella exhibits a strong relationship with lake acidity, being almost totally absent below pH 5.5. This decline has been used as an indicator of lake acidification in paleolimnological studies. In this study C. stelligera V.H. and C. kützingiana Thwaites were abundant in Precambrian Shield lakes with pH as low as 4.5. Cyclotella comta (Ehr.) Kütz. was found in lakes of pH < 5.5, but maximum abundance was observed in lakes of pH > 5.5. Cyclotella michiganiana Skv. was found in lakes of pH < 6.0. These results indicate that the use of C. stelligera, C. kützingiana, and possibly C. comta, in paleolimnological investigations of lake acidification, should be approached with caution. These taxa may exhibit a decline in abundance with decreasing lakewater pH, but this is partially a morphometric effect not necessarily related to anthropogenic acidification.     

Glasgow Lake: an early-warning sentinel of lake acidification in Cape Breton Highlands National Park (Nova Scotia,Canada)

In contrast to other lakes studied in Cape Breton Highlands National Park (Nova Scotia, Canada), our paleolimnological results indicated that Glasgow Lake has been impacted by acidic deposition starting in the early 1900s. Based on analysis of diatom assemblages, the lake experienced a decrease in diatom-inferred lakewater pH from a pre-industrial pH of ~5.8 to a current pH of 5.3 (2000–2002 measured mean pH = 5.0) as well as a decrease in diatom-inferred Gran-alkalinity. In this study, diatom-based paleolimnological techniques were used in conjunction with a dynamic biogeochemical model (MAGIC) to assess both the timing and extent of the acidification trend, as well as determine a probable explanation as to why this lake, and none of the other 15 Cape Breton Highlands lakes studied for paleolimnology thus far, acidified under a peak non-marine sulphate deposition load of 43.6 mmol_c m⁻² year⁻¹ in the mid-1970s. Steady-state models estimate that Glasgow Lake had the lowest buffering capacity of six study lakes and estimated critical sulphate loading of <1 mmol_c m⁻² year⁻¹. MAGIC also estimated a loss of charge balance alkalinity from a pre-1850 value of 38 μmol_c l⁻¹ to a low of 12 μmol_c l⁻¹. While no evidence of biological recovery has been recorded, MAGIC estimates an increase in charge balance alkalinity to 27 μmol_c l⁻¹ in 2002 in response to decreased SO₂ emissions. Of the five other lakes that were modelled, all showed trends towards more acidic states and subsequent increases in charge balance alkalinity; however, the empirical paleo-diatom approach applied to these lakes showed no evidence of acidification. Thus, Glasgow Lake has the lowest buffering capacity among the Cape Breton Highland study lakes and serves as a sentinel of potential acidification trends and recovery in this region. Handling editor: J. Saros     

Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data. 2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake). 3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake. 4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity. 5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.     

Reconstruction of pH by chrysophycean scales in some lakes of the Southern Alps

Chrysophycean scales were examined in surface sediments collected from 22 high mountain lakes on the southern slope of the Central Alps, some in Italy and some in Switzerland. The study area receives slightly acidic precipitation and summer lake pH ranges between 5.2 and 8.0. In each lake chrysophycean scale assemblage was dominated by one or two species and its composition was related to lakewater pH. Five short cores were examined in low-alkalinity lakes and evidence of recent lake acidification was found.     

Acid rain recovery may help to mitigate the impacts of climate change on thermally sensitive fish in lakes across eastern North America

From the 1970s to 1990s, more stringent air quality regulations were implemented across North America and Europe to reduce chemical emissions that contribute to acid rain. Surface water pH slowly increased during the following decades, but biological recovery lagged behind chemical recovery. Fortunately, this situation is changing. In the past few years, northeastern US fish populations have begun to recover in lakes that were historically incapable of sustaining wild fish due to acidic conditions. As lake ecosystems across the eastern United States recover from acid deposition, the stress to the most susceptible populations of native coldwater fish appears to be shifting from acidification effects to thermal impacts associated with changing climate. Extreme summer temperature events – which are expected to occur with increasing frequency in the coming century – can stress and ultimately kill native coldwater fish in lakes where thermal stratification is absent or highly limited. Based on data from northeastern North America, we argue that recovery from acid deposition has the potential to improve the resilience of coldwater fish populations in some lakes to impacts of climate change. This will occur as the amount of dissolved organic carbon (DOC) in the water increases with increasing lake pH. Increased DOC will reduce water clarity and lead to shallower and more persistent lake thermoclines that can provide larger areas of coldwater thermal refuge habitat. Recovery from acidification will not eliminate the threat of climate change to coldwater fish, but secondary effects of acid recovery may improve the resistance of coldwater fish populations in lakes to the effects of elevated summer temperatures in historically acidified ecosystems. This analysis highlights the importance of considering the legacy of past ecosystem impacts and how recovery or persistence of those effects may interact with climate change impacts on biota in the coming decades.     

The effect of anthropogenic acidification on the hydrofauna of the lakes of the West Tatra Mountains (Slovakia)

Fourteen West Tatra lakes were studied, of which one could be considered to be recently anthropogenically acidified and eight others classified as acidification-endangered. In the anthropogenically acidified lake, the zooplankton assemblage has been substantially altered (three mountain-lake crustacean species have been eliminated). Several littoral macrobenthic species sensitive to acidification have either been eliminated from the acidified and acidification-endangered lakes or occur only sporadically. The effect of acidification has so far not been observed on the benthic fauna of the lakes medial which is probably due to the higher pH below the surface of sediment. In comparison with the High Tatra, acid depositions have had a less pronounced effect on the lakes of the West Tatra.     

Perch,Perca fluviatilis L., in Small Lakes: Relations between Population Characteristics and Lake Acidity

Perch population characteristics of small lakes were examined with a special reference to lakes which have acidified recently due to atmospheric deposition of air pollutants. The population density and biomass of perch were higher in an acid (pH 4.5) clear water lake with low aluminium concentration than in recently acidified (pH 4.3–4.7) clear water lakes with higher aluminium levels. The structure of perch population in an acid (pH 4.4) humic lake was similar to recently acidified clear water lakes. The population density and the biomass of perch were significantly higher in 6 lakes with pH>5.0 than in 6 lakes of pH<5.0 whereas the mean age and length at a given age were higher in the more acid lakes.     

Comparative responses of phytoplankton during chemical recovery in atmospherically and experimentally acidified lakes1

Twenty lakes recovering from a century of atmospheric acid deposition over Northeastern Ontario were resurveyed for phytoplankton following a 20‐year period and were compared with a 23‐year study of an experimentally acidified lake, L302S (Experimental Lakes Area, ON, Canada). Phytoplankton species significantly tracked abiotic changes during both acidification and chemical recovery in all lakes based on concordance testing. However, ordination analyses showed that many phytoplankton communities had not returned to their preacidification state. Significant explanatory variables of taxonomic responses were pH, dissolved organic carbon (DOC), and inorganic nutrients (N, P), based on canonical correspondence analysis (CCA). Increases in DOC and pH influenced a significant taxonomic shift from acid‐tolerant dinoflagellates to a diverse assemblage of cyanobacteria, chlorophytes, and diatoms. Declining nitrogen levels defined a secondary environmental gradient, which was characterized by a decrease in filamentous green algal abundance. L302S remained remote in ordination space from the more chronically and heavily polluted lakes in Northeastern Ontario, indicating that experimental acidification provided a conservative estimate of the true damage to atmospherically polluted lakes. However, L302S did increasingly resemble lakes in Northeastern Ontario, suggesting that experimental acidification simulated the impacts of moderate levels of atmospheric pollution. Our findings demonstrate the importance of ecological history in understanding the responses by boreal lake ecosystems to environmental change.     

The PIRLA project: Paleoecological investigations of recent lake acidification

The PIRLA project is a broadly interdisciplinary paleolimnological investigation of five to fifteen comparable watershed/lake systems from each of four low-alkalinity regions in North America that are currently receiving acid deposition. The areas are the Adirondack Mountains (N.Y.), northern New England, northern Great Lakes states, and northern Florida. The primary objective of the study is to provide a detailed reconstruction of the recent acidification histories of a representative suite of lakes from each of the regions. The study will increase our understanding of the timing, rates, and magnitude of acidification (and other chemical changes), and the regional and inter-regional patterns of lake acidification.     

Classification of the Tatra Mountain lakes (Slovakia) using chironomids (Diptera,Chironomidae)

Chironomid assemblages in thirty-three mountain lakes situated above tree line in the Slovakian part of the Tatra Mountains were studied during 2000–2002. Chironomid species/taxa, collected as pupal exuviae, were correlated with physical, chemical, and lake morphometry variables of 22 lakes. Two-way indicator species analysis (TWINSPAN) was used to classify the lakes into four distinct groups: higher situated alpine lakes, lower situated alpine lakes, subalpine lakes and acidified lakes. Presence/absence of eight taxa was identified as indicative for this classification. In discriminant function analysis, pH, dissolved organic carbon, altitude and lake area were the most significant variables reflecting differences among groups of lakes. This model of four variables allowed 77% success in the prediction of group membership. A multiple regression model with lake area, concentration of magnesium and total phosphorus accounted for 37% of the variance in taxa richness. Lakes with greater area contained more chironomid taxa than smaller ones. Lakes with higher alkalinity and higher trophic status tend to support more taxa. Canonical correspondence analysis (CCA) indicated that most variation in the composition of chironomid assemblages was related to pH and to altitude. The results can be used as reference data for long-term monitoring of the Tatra lakes, especially in connection with a recovery from acidification and global climatic change.     

Fossil diatom inferred reconstruction of the pH history of two acidic,clear water lakes from insular Newfoundland,Canada

Palaeoecological research has been used to evaluate the impact of acidic deposition on lakes in insular Newfoundland. Terrestrial organic deposits in the region have considerable influence on freshwaters and have placed constrains on interpretation of the degree of anthropogenic acidification. In this paper, a region-specific calibration equation unique to clear water lakes (colour values 15) is developed from diatom assemblages in surface sediments from 22 lakes. The inferred pH history of two acidic, clear water lakes is then developed with a view to eliminating the influence of organic acidity from the interpretation of historical acid-base chemistry. The pH histories of the two lakes suggest modest declines (0.3 to 0.4 unit) in the most recent strata (i.e. since the 1930's). Both lakes demonstrate an increase in inferred pH in the surface horizon, which is consistent with declines in acidic deposition in the region since the mid 1970's. The magnitude and timing of the pH trends in these two lakes is common to those previously developed from more highly coloured lakes. The similar magnitude and onset of pH declines in lakes with varying amounts of organic influence provides no palaeolimnological evidence to suggest a contribution to, or modification of, lake acidification by organic acids.     

Responses of insects,especially Chironomidae (Diptera), and mites to 130 years of acidification in a Scottish lake

About 130 years of anthropogenic acidification of Round Loch of Glenhead, SW Scotland, has resulted in successively decreased stability, diversity, productivity and survival rate of the non-biting midge (Diptera: Chironomidae) fauna. Similar trends have also been observed among mayflies, caddis-flies and water mites. The first effects of anthropogenic acidification on the insect and mite fauna, as evidenced by palaeolimnological analyses of²¹⁰Pb-dated sediment cores, occurred as early as around 1850, i.e. earlier than in any other lake hitherto studied. The drop in the lake's pH was first indicated by decreased stability and changes in species composition of chironomids and mayflies in the littoral zone. Major changes in the profundal chironomid fauna did not take place until about 1950, when mean lake pH dropped below 5.0. At the same time, the littoral insect fauna became even more unstable and the first significant elimination of species occurred. Comparison with insect fauna of other lakes suggests that a pH of less than 5 might be critical for the ecological conditions in many acidified lakes. None of the twelve most common chironomid species present prior to the acidification of the lake had disappeared after 120–130 years of considerable acidification, and they are all common in oligotrophic lakes with a pH of 6.5–7.0. This is in contrast to the effects of heavy acidification on other aquatic animal groups. Chironomids are probably more sensitive to lake trophic status than lake acidity.     

Effects of emission reductions from the Sudbury smelters on the recovery of acid- and metal-damaged lakes

Aquatic ecosystems in a 17,000 km² area around Sudbury, Ontario, Canada, have been affected by the atmospheric deposition of pollutants from nearly a century of operations at the Sudbury area metal smelters. Effects were most severe in the lakes closest to the smelters which historically received very high deposition of both acid and metal particulates. After smelter emissions were greatly reduced in the 1970‘s, evidence began to emerge of improvements in lake water quality, and some recovery of biological communities, and the emphasis of Sudbury area monitoring programs changed from the assessment of damage to the tracking of recovery patterns. Further reductions in smelter emissions during the1990‘s have been accompanied by continuing improvements in aquatic habitat quality, but the evaluation of lake responses to emission controls is complicated by the interaction of lake acidity and metal concentrations with other factors. Weather-related variations in storage and release of sulphur from lake catchments appear to greatly influence chemical recovery. Despite the general water quality improvements observed to date, some lakes are still highly acidic and elevated levels of copper and nickel persist in the water and sediments of many lakes. Severely damaged biological communities have been slow to recover, probably reflecting a combination of continuing habitat quality limitations and restricted opportunities for dispersal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water chemistry of high elevation Colorado wilderness lakes

High elevation alpine and subalpine Rocky Mountain lakes in Colorado and southeastern Wyoming were examined to determine regional variability in water chemistry and their sensitivity to atmospheric deposition. Acid neutralizing capacity, pH, conductivity and concentrations of major anions and cations were compared. Regional differences in water chemistry are evident. The south-eastern most lakes have significantly higher pH, conductivity, ANC, and sums of acid and base concentrations than lakes in the other regions of the state. In contrast the north-western most lakes are significantly more dilute than those from other regions. Despite these two regional differences, most regions are similar in having a wide range of variability in potential sensitivity of their lakes to acidification and nitrogen export. Many wilderness areas in western and eastern regions contains lakes that are extremely sensitive and other lakes not susceptible to deposition. Overall, 70% of the Colorado lakes are sensitive to acidification and 15% are extremely sensitive to acidification. All of the regions had lakes that are classified as susceptible or sensitive to acidification, with 12 of the 17 areas having all of their sampled lakes susceptible or sensitive. Generally NO concentration in surface waters decreased from mid-season to late season; yet a large number of the lakes export NO late in the season, suggesting nitrogen saturation. The results confirm the sensitivity of high elevation wilderness aquatic ecosystems in all regions of Colorado to acidification and nitrogen deposition.     

Fish predation,lake acidity and the composition of aquatic insect assemblages

Aquatic insect assemblages were sampled in 2 sets of 18 small lakes in 2 regions of northeastern Ontario. Both sets included lakes with and without fish. In the set near Sudbury, fishless lakes were acidic. Using a standardized sweep net procedure, fishless lakes in both areas were found to have a greater abundance and richness of insects than lakes with fish. Irrespective of pH, fishless lakes supported a similar aquatic insect assemblage which was characterized by an abundance of nekton, especially Notonectidae, Corixidae, Graphoderus liberus (Dytiscidae) and Chaoborus americanus (Chaoboridae). Those taxa were typically absent from lakes with fish, which often had a marked abundance of Gerridae. It is concluded that fish predation is the most immediate factor structuring such aquatic insect assemblages, and is responsible for their change coincident with lake acidification.     

Cladocera and Anostraca from the Interior Plateau of British Columbia,Canada, as paleolimnological indicators of salinity and lake level

Cladoceran and anostracan species assemblages were identified from the surface sediments of 33 closed–basin lakes from the southern Interior Plateau of B.C. in order to explore their effectiveness as quantitative indicators of lakewater salinity and ionic composition. These lakes were chosen to maximize the range of lakewater salinity concentrations (freshwater through hypersaline) as well as brine composition (sulphate and carbonate dominated systems). The distribution of the anostracans and cladocerans were strongly correlated with lakewater salinity, ionic composition and lake depth. Based on these strong relationships significant predictive models were developed, using weighted-averaging techniques, to infer lakewater salinity based on the species composition of anostracans and cladocerans in surface sediments. Furthermore, models were developed to infer lake depth that are superior to previously used techniques based on the ratio of planktonic/littoral Cladocera. Given that the species composition of anostracans and cladocerans can be used to infer changes in salinity and lake level, and that their remains can be identified from sedimentary profiles, there is considerable potential in using their assemblages as paleolimnological indicators of past climatic conditions. This revised version was published online in July 2006 with corrections to the Cover Date.