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.     

Tracking Recovery Patterns in Acidified Lakes: A Paleolimnological Perspective

Long-term data are often lacking to effectively assess patterns of lake acidification and recovery. Fortunately, paleolimnological techniques can be used to infer past changes in lakewater acidity and related variables by means of biological indicators, such as diatom valves and chrysophyte scales, preserved in ²¹⁰Pb-dated sediment cores. We summarize paleolimnological data that we have gathered from 36 Sudbury (Ontario) and 20 Adirondack Park (New York) lakes to estimate the magnitude of lake acidification and any subsequent recovery in these lake systems. In both regions, many lakes were shown to have acidified considerably, some over two pH units, since the 1850s. Although some recovery was noted in both lake regions, Sudbury lakes generally showed larger increases in inferred lakewater pH with recent declines in sulfur emissions. Possible explanations of these differences include the greater decrease in sulfate deposition in the Sudbury area, as well as generally longer residence times of lakes in Sudbury, perhaps allowing for more in-lake alkalinity generation. In addition, Sudbury lakes generally had higher pre-industrial pH levels, suggesting that lakes with higher natural buffering capacities are more likely to recover more quickly with declines in deposition, even if they had been acidified to a great extent.     

Correlation of surface sediment diatoms with the present lake water pH in 28 Algoma lakes,Ontario, Canada

The surface sediment diatom analysis of 28 Algoma lakes (pH 4.40–8.13) indicates that even though each lake has a widely different aquatic environment and characteristic diatom assemblage, a definite relationship exists between the lake water pH and their diatom assemblages. In the acidic lakes acidobiontic and acidophilous diatom species predominate whereas in circumneutral and alkaline lakes circumneutral and alkaliphilous diatoms were most common. Cluster analysis of the pH indicator diatom assemblages grouped the study lakes into three distinct cluster groups. These groups also closely corresponded to lake water pH. On the basis of published ecological information as well as their presence in our study lakes, the pH indicator status of a number of diatom taxa have been discussed. A detailed listing of the diatom taxa identified and their pH indicator status is provided in order to facilitate their use in future diatom-inferred pH studies.     

Acid Sensitivity of Lakes in Nova Scotia,Canada: Assessment of Lakes at Risk

The sensitivity of surface waters to acidic deposition is governed by the interaction of catchment geology, soils, topography, land use, climate and atmospheric deposition. Accordingly at the landscape scale, catchment attributes may be used to predict lake chemistry (for example, acid neutralising capacity (ANC), pH, calcium (Ca²⁺) and dissolved organic carbon (DOC)). Empirical (multiple linear regression) models based on average measured chemistry (2000–2006) for 204 lakes in Nova Scotia (NS) Canada, and their catchment attributes, were used to predict chemistry for all lakes in NS (n = 6104). Damage to aquatic biota, such as loss of species and/or reduced biodiversity has been widely evaluated using critical chemical thresholds commonly based on pH, ANC and Ca²⁺. The proportion of sensitive lakes in NS (that is, the stock at risk) was estimated as lakes with ANC less than 20 μeq l⁻¹, pH below 6, and Ca²⁺ less than 75 μeq l⁻¹ (13, 73 and 74%, respectively). Many lakes in NS are characterized by high DOC (>7 mg l⁻¹); in these lakes organic acids contribute to total acidity, making anthropogenic influences difficult to discern. To account for the potential contribution of organic acidity, all lakes with pH below 6 (and DOC < 7 mg l⁻¹) and lakes below a threshold for ANC adjusted for organic acids were quantified; 63% of the lakes fell below either of these thresholds. Despite substantial reductions in sulphur emissions in North America since the 1980s, many lakes in NS remain at risk to acidic deposition.     

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.     

Paleolimnological assessment of limnological change in 10 lakes from northwest Saskatchewan downwind of the Athabasca oils sands based on analysis of siliceous algae and trace metals in sediment cores

The extraction of bitumen from the Athabasca oil sands is rapidly expanding, and emission of sulphur and nitrogen oxides has substantially increased. To determine whether lakes downwind of this development in northwest Saskatchewan have been detrimentally impacted since development of the oil sands, a paleolimnological assessment of ten lakes was carried out. Analysis of diatom valves and inferences of diatom-inferred pH indicated that emissions have not resulted in widespread chronic acidification of acid-sensitive lakes ~80–250 km east and northeast of the oil sands development around Fort McMurray and Fort Mackay. However, one of the closest sites to the development indicated a slight decline in diatom-inferred pH, but the two next closest sites, both of which had higher alkalinity, did not show any evidence of acidification. There were also no consistent trends in the concentration or flux of total or individual priority pollutants including lead, mercury, copper, zinc and vanadium. The sedimentation rates in most lakes increased since the mid-1900s, along with increased flux of both diatoms and scaled chrysophytes. Subtle changes in the species assemblages of diatoms and increased flux of diatoms and chrysophyte scales are consistent with recent climate change in this region.     

Changes in diatom-inferred pH and add neutralizing capacity in a dilute, high elevation, Sierra Nevada lake since A.D. 1825

SUMMARY. 1. We developed equations which describe relationships between the relative abundance of diatom assemblages in the surface sediments of twenty-seven Sierra Nevada lakes and the present pH and acid neutralizing capacity in these lakes.
2. These equations were employed to reconstruct pH and acid neutralizing capacity at twenty-four depth intervals in a 20 cm long sediment core from Emerald Lake, a dilute, high elevation lake, located in Sequoia National Park, California, U.S.A.
3. The diatom-inferred pH and acid neutralizing capacity values indicated that neither pH nor acid neutralizing capacity exhibited significant trends since about A.D. 1825. We conclude from our diatom analysis that Emerald Lake has not been affected by acidic deposition.     

Paleolimnological evidence for recent acidification of Big Moose Lake,Adirondack Mountains,N.Y. (USA)

Big Moose L. has become significantly more acidic since the 1950s, based on paleolimnological analyses of sediment cores. Reconstruction of past lakewater pH using diatom assemblage data indicates that from prior to 1800 to ca. 1950, lakewater pH was about 5.8. After the mid-1950s, the inferred pH decreased steadily and relatively quickly to about 4.6. Alkalinity reconstructions indicate a decrease of about 30 eq · l^-1 during the same period. There was a major shift in diatom assemblage composition, including a nearly total loss of euplanktonic taxa. Chrysophyte scale assemblages and chironomid (midge larvae remains also changed in a pattern indicating decreasing lakewater pH starting in the 1950s. Accumulation rates of total Ca, exchangeable and oxide Al, and other metals suggest recent lake-watershed acidification. Cores were dated using²¹⁰Pb, pollen, and charcoal. Indicators of watershed change (deposition rates of Ti, Si, Al) do not suggest any major erosional events resulting from fires or logging. Accumulation rates of materials associated with combustion of fossil fuels (polycyclic aromatic hydrocarbons, coal and oil soot particles, some trace metals, and sulfur) are low until the late 1800s-early 1900s and increase relatively rapidly until the 1920s–1930s. Peak rates occurred between the late 1940s and about 1970, when rates declined.The recent decrease in pH of Big Moose L. cannot be accounted for by natural acidification or processes associated with watershed disturbance. The magnitude, rate and timing of the recent pH and alkalinity decreases, and their relationship to indicators of coal and oil combustion, indicate that the most reasonable explanation for the recent acidification is increased atmospheric deposition of strong acids derived from combustion of fossil fuels.     

Morphological variation in populations of the diatom Asterionella ralfsii W. Smith from Nova Scotia,Canada

Preliminary investigations of the diatom genus Asterionella ralfsii W. Smith from Kejimkujik National Park, Nova Scotia indicate that its morphology differs from other reported forms. Mean cell length increased between the spring and the fall. Bimodal distribution of length classes occurred in several lakes and was not related to measured environmental variables. The need for further work on this species in this and other geographical areas is considered.     

Eutrophication of moderately deep Dutch lakes during the past century: flaws in the expectations of water management?

We studied the trophic development of the past 30–100 years in eight moderately deep Dutch lakes based on their sedimentary fossil diatom assemblages. The dominant diatoms indicating meso- to eutrophic conditions were Aulacoseira subarctica, Cyclotella ocellata, C. cyclopuncta, C. meneghiniana, Puncticulata bodanica, Aulacoseira granulata, Cyclostephanos dubius, C. invisitatus, Stephanodiscus hantzschii, S. medius, and S. parvus. Ordination of diatom data separated the lakes into four groups according to their total phosphorus concentrations (TP), water supply, water management, and origin. The first group consists of dike-breach lakes, which were in stable eutrophic to hypertrophic conditions throughout the past century with diatom-inferred TP (DI-TP) concentrations of between 70 and 300 μg l⁻¹. The main factors influencing these dike-breach lakes are river management, ground water supply of riverine origin, and local land use. The second group are artificial lakes of fluctuating oligo- to mesotrophic conditions and DI-TP concentrations of 10–30 μg l⁻¹. Only one of the artificial lakes showed a DI-TP increase due to changes in catchment agricultural practice. A third group includes an artificial moat and an inland dike-breach lake with DI-TP concentrations of 50–100 μg l⁻¹. The fourth group contains an individual dike-breach lake with stable mesotrophic conditions of 50 μg l⁻¹ throughout the past century. Rather than showing a regional pattern, the studied lakes behave very individualistically with regard to their trophic history, reflecting changes in the local hydrology and in their nutrient sources.     

A multi-proxy paleolimnological reconstruction of trophic state reference conditions for stratified carbonate-rich lakes in northern Germany

This study aims to identify reference conditions (nutrient status and diatom assemblages) as required by the European Water Framework Directive (WFD) for stratified, carbonate-rich lowland lakes with a large watershed area (watershed area to lake volume ratio (WV) > 1.5 km² 10⁻⁶ m⁻³) and a retention time (RT) from 0.1 to 10 years (Central Baltic Lake-Type 1, German Lake-Type 10) in European ecoregion 14. Diatoms, pollen and geochemistry were analysed from sediment cores of six lakes from northern Germany representing different subtypes of Lake-Type 10 (varying WV and RT) and covering the past 290–1,750 years. Historic total phosphorus levels were inferred using diatom-based transfer functions selected from a merged European data set and from optimised data sets identified with the moving-window approach. Pollen and geochemical proxies were used to identify occurrence and intensity of anthropogenic catchment usage. Lake trophic state reference conditions and associated diatom assemblages were identified for three of the six study lakes. In contrast, according to fossil pollen assemblages, two lakes were already strongly impacted by intensive catchment usage when the oldest investigated sediments were laid down. Thus, reference conditions of these already eutrophic lakes could not be identified. Similarly, the lowermost samples of a core from the sixth lake showed signs of impact, and it remains unclear whether the identified dystrophic conditions occurred naturally or if they were due to the drainage of wetlands in Medieval times. Lakes with a relatively small WV (1.5–5.0 km² 10⁻⁶ m⁻³) and RT > 1 year were naturally oligotrophic to low mesotrophic and a typical, representative diatom assemblage was identified. In contrast, typical reference conditions or diatom assemblages for lakes with higher WV (5–18.6 km² 10⁻⁶ m⁻³) and RT < 1 year could not be identified as chemical precipitation and upstream lakes (nutrient sinks or sources) additionally influenced natural nutrient levels. Therefore, the reference situation of both trophic state and diatom assemblages in a lake may be strongly influenced by other modifying, limnological processes in addition to WV and RT. Overall, this study helps to implement the WFD by identifying reference conditions and by discussing the level of differentiation of lake types required to set reference conditions. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Sedimentary diatom assemblages and their utility in computing diatom-inferred pH in Sudbury Ontario lakes

Surface sediment diatoms from 30 Sudbury lakes were analyzed to establish a relationship between diatoms and limnological characteristics of these lakes. Factor analysis of various chemical and physical variables suggested that most of the variance was associated with the pH, pH-metal, and conductivity factors. Factor analysis of common diatom taxa indicated that the distribution of most of these diatoms is closely related to lake water pH and/or pH related factors. Regression analysis of various pH indicator assemblages with measured lake water pH also demonstrated significant relationships. Among the transfer functions employed to compute diatom-inferred pH, multiple regressions using pH indicator assemblages proved to be the best. Using this method an accuracy of about 0.3 pH unit can be achieved, even for lakes which have received large trace metal inputs concurrent with increase in acidity. The presence of planktonic diatoms in acidic lakes suggests that the widely accepted hypothesis that planktonic diatoms are greatly reduced in waters at pH below 5.6 is not always true.     

Diatoms,lake acidification and the Surface Water Acidification Programme (SWAP): a review

The Surface Water Acidification Programme (SWAP) was set up as collaborative research project involving scientists from Norway, Sweden and the UK. Its aim was to evaluate the factors responsible for fish decline in acid streams and lakes. A substantial sub-project was concerned with the palaeolimnological evidence for acidification and its causes. The central technique used was diatom analysis. In order to harmonise methodology between the seven diatomists from four laboratories in three countries a programme of taxonomic quality control was organised, involving slide exchanges, ‘blind’ counting, and regular workshops. In addition a calibration data-set of surface sediment diatoms and water chemistry from 170 lakes was constructed and archived on DISCO, the UCL diatom database. This data-set was used to generate diatom-chemistry transfer functions for pH, DOC and total Al using a weighted averaging technique. Application of the pH transfer function to sediment cores from a range of lakes demonstrated a dose-response relationship between lake sensitivity to acidification (as represented by mean Ca²⁺ values) and acid deposition (g S m ^-2 yr ^-1), indicating the overwhelming importance of acid deposition as the cause of lake acidification.     

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.     

Bioaccumulation of mercury in yellow perch (Perca flavescens) and common loons (Gavia immer) in relation to lake chemistry in Atlantic Canada

Mercury biomagnifies in aquatic foodwebs in freshwater lakes, and common loons (Gavia immer) breeding in eastern Canada can be exposed to reproductively toxic concentrations of mercury in their fish prey. We assessed the bioaccumulation and biomagnification of mercury in juvenile and adult common loons, and their preferred prey: yellow perch (Perca flavescens) in Kejimkujik National Park (KNP), Nova Scotia by measuring mercury levels and stable isotope ratios in tissues. Total mercury levels and stable-carbon (δ¹³C) and nitrogen isotope ratios (δ¹⁵N) were determined in composite whole-fish samples from lakes in KNP and blood samples from juvenile and adult loons captured on lakes in KNP and southern New Brunswick. Geometric mean mercury concentrations were 0.15 and 0.38 μg/g (wet wt.) in small (9-cm fork length) and large (17-cm fork length) yellow perch, and were 0.43 and 2.7 μg/g (wet wt.) in blood of juvenile and adult common loons, respectively. Mercury concentrations in perch and loons were positively associated with body mass and δ¹⁵N values. Juvenile loons and large yellow perch had similar mercury levels and δ¹⁵N values, indicating similar trophic status despite their 22-fold difference in body mass. Mercury concentrations were higher in yellow perch and common loons in acidic lakes. Our findings highlight the importance of both chemical and ecological factors in understanding mercury biomagnification in lakes and associated risks to fish-eating wildlife. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Effects of benthic filamentous algae on the sediment–water interface in an acidic mining lake

Natural alkalinity generation by microbial sulphate reduction in acidic lakes is usually inhibited by the low pH and a low primary production which results in a lack of suitable organic carbon sources. In some acidic mining lakes mass developments of filamentous benthic algae occur. The effects of this periphyton layer on the biogeochemistry of the sediment–water interface were investigated by in situ microsensor measurements and laboratory incubations in Mining Lake Grünewalder Lauch (Germany). Microsensor measurements showed that the oxic–anoxic boundary was located in the periphyton layer and was moving up and down depending on light triggered photosynthesis. The sediment itself was permanently anoxic. The diurnal redox shift and the maintenance of neutral conditions in the periphyton layer lead to an effective precipitation of iron and phosphorus. Under the periphyton layer very high sulphate reduction rates up to 265 nmol cm⁻³ d⁻¹ were measured in the sediment. These are the highest rates reported for mining lakes so far. The microbial activity was high enough to keep the pH in the surface sediment neutral and contributed to natural alkalinity production. Handling editor: L. Naselli-Flores     

Lake diatom response to recent Arctic warming in Finnish Lapland

High-resolution palaeolimnological data from a number of remote and nonpolluted lakes in Finnish Lapland reveal a distinct change in diatom assemblages. This parallels the post-19th century Arctic warming detected by examination of long-term instrumental series, historical records of ice cover and tree-ring measurements. The change was predominantly from benthos to plankton and affected the overall diatom species richness. A particularly strong relationship was found between spring temperatures and compositional structure of diatoms. The change is irrespective of the lake type and catchment characteristics, and is reflected by several other biological indicators, such as chrysophytes and zooplankton, suggesting that entire lake ecosystems have been affected. No corresponding change in the diatom-inferred lake-water pH was observed; hence, atmospheric fallout of acid substances cannot have been the driving force for the observed biological change. The mechanism behind the diatom response is unclear, but it may be related to decreased ice-cover duration, prolonged growing season and increased thermal stability. We postulate that 19th century Arctic warming, rather than acidic or other anthropogenic deposition, is responsible for the recent ecological changes in these high latitude lakes.