Aruna S. Dixit

Diatom and chrysophyte functions and inferences of post-industrial acidification and recent recovery trends in Killarney lakes (Ontario, Canada)

The surface sediment diatom and chrysophyte assemblages from 33 Sudbury lakes were added to our published 72 lake data set to expand and refine the diatom and chrysophyte-based inference models that we had earlier developed for this region. Our calibration data set now includes 105 lakes, representing gradients for multiple environmental variables (e.g., lakewater pH, metals, and transparency). The revised models are based on the weighted averaging calibration and regression approach and include bootstrap error estimates. The pH model was the strongest (r2boot = 0.75, RMSEboot = 0.50). The chrysophyte-inferred pH model (r2boot = 0.79, RMSEboot = 0.48) that we developed was as robust as the diatom pH model. Diatom and chrysophyte inferred pH models were then applied to ‘top’ (surface sediments representing current conditions) and ‘bottom’ (generally from > 30 cm deep representing pre-industrial conditions) sediment diatom and chrysophyte assemblages of 19 Killarney area lakes near Sudbury. The top and bottom inferred pH results were compared to early-1970s measured pH data. These data suggest that, although many of the poorly buffered Killarney lakes had experienced acidification, marked pH recovery has occurred in many lakes within the last 25 years. Despite the stunning pH recovery, the present-day diatom and chrysophyte assemblages are significantly different from assemblages present during pre-industrial times. Our results suggest that biological recovery may require more time than chemical recovery. It is also likely that these lakes may never recover biologically because other anthropogenic stressors (e.g., climate warming and increased exposure to UV-B radiation) may now have greater influence on biological communities in Killarney/Sudbury area lakes than acidification.

Algal microfossils provide high temporal resolution of environmental trends

Sedimentary chrysophytes and diatoms from Baby Lake (Sudbury, Canada) were analyzed to assess lakewater trends associated with (i) the commencement of metal mining and smelting activity at the Coniston Smelter in 1913, and (ii) the closure of the smelter in 1972. We reconstructed several environmental variables (i.e. pH, total [Al], and [Ni]) by applying weighted-averaging regression and calibration models to our paleolimnological data. As a result of emissions from the Coniston Smelter, the lake started to acidify from a high pH of about 6.5 in 1940 to a low pH of 4.2 in 1975. During this period, inferred lakewater [Al] and [Ni] also increased dramatically. Following the closure of the smelter in 1972, inferred lakewater pH and metal concentrations recovered close to pre-industrial levels. The inferred pH recovery corresponds closely to the known lakewater pH recovery (a difference of about 0.4 and 0.6 of a pH unit was observed between measured pH, and chrysophyte and diatominferred pH, respectively). Our study demonstrates that algal microfossils can provide high resolution inferences of past environmental trends. This approach holds great potential for documenting a lakes response to decreased loadings of sulphate and metals, and in helping to establish and implement emission standards.

Paleolimnological assessment of damage to fish communities in three acidic, Canadian Shield lakes

Abstract Long-term fisheries data from small lakes are often sadly lacking. We employ three classes of sedimentary remains (mandibles of larval Chaoborus , diatom valves and chrysophyte scales) to verify that the fish communities of three small, acidic (pH 5.3–5.6) Canadian Shield lakes in south-central Ontario were richer 20–100 years ago at a time when the lakes were almost certainly less acidic. To do this, we first verify that Chaoborus americanus is never abundant in the presence of fish using data from a new survey of 50 lakes that corrects for methodological flaws of the past. We then examine changes with sediment depth in our three classes of indicators in Lakes Drummer, Little Eastern, and Shoelace. In all cases, appearrances of Chaoborus americanus and changes among algl remains in recent sediments suggest that fish were lost at a time when lake waters were acidifying, particulary because of pH depressions during spring melt. These results contribute to a growing body of literature indicating that the use of multiple sedimentary indicators can provide assessments of past limnological conditions that are of interest to both lake managers and aquatic ecologists. They also suggest that the fish communities of some small, currently acidic lakes in south-central Ontario were almost certainly richer in the past.

Setting Restoration Goals for an Acid and Metal-Contaminated Lake: A Paleolimnological Study of Daisy Lake (Sudbury, Canada)

ABSTRACT Many lakes in the Sudbury region of Ontario have been affected by acidic and metal inputs as a result of local smelting operations. Several initiatives are now underway to restore some of these systems. Long-term limnological data are rarely available, therefore lake managers must use proxy methods to set reasonable targets for lakes undergoing mitigation. Daisy Lake is presently an acidic (pH 4.7), metal-contaminated lake (Ni=370 μg L−1; Al=350 μg L−1), that has been selected for mitigation efforts. We used fossil pollen analysis to reconstruct past changes in terrestrial vegetation, and paleolimnological techniques (primarily diatoms and chrysophytes) to identify pre-disturbance conditions and to reconstruct past changes in water quality variables in Daisy Lake. Our data indicate that, if Daisy Lake and its watershed are limed to restore the lake to a state that approximates the pre-disturbance natural pH, the lake water pH has to be about 1.5 pH units higher than its present level.

The history and impact of air pollution at Čertovo Lake, southwestern Czech Republic

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the Šumava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from Čertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of 137Cs, 134Cs and 241Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the 210Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 μg g-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 μg cm-2 yr-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 μg cm-2 yr-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.

LAKE SEDIMENT CHRYSOPHYTE SCALES FROM THE NORTHEASTERN U.S.A. AND THEIR RELATIONSHIP TO ENVIRONMENTAL VARIABLES

Chrysophyte scale assemblages were analyzed in the surface sediments (0–1 cm) of 146 lakes sampled in the U.S. Environmental Protection Agency’s (EPA) Environmental Monitoring and Assessment Program–Surface Waters (EMAP‐SW) in the northeastern U.S.A. Chrysophyte data from the EMAP lakes were combined with a previous study of 71 Adirondack PIRLA (Paleoecological Investigation of Recent Lake Acidification) lakes and collectively analyzed to examine the indicator potential of scaled chrysophytes in the northeastern U.S.A. with respect to several environmental variables. Canonical correspondence analysis (CCA) was used to determine which environmental variables influenced the distributions of species. Forward selection and Monte Carlo permutation tests showed that 51% of the variance in the chrysophyte assemblages was related to pH. The other six significant variables (conductivity, chloride, total phosphorus [TP], elevation, lake depth, and watershed area) contributed an additional 31% of the total (82%) variance explained by the seven forward‐selected variables. Similar to previous studies, many taxa showed distinct distribution patterns with respect to pH. Partial and constrained CCAs indicated that, although all seven variables explained significant proportions of variation in the species data, a reliable inference model could be developed only for lake‐water pH. The strength of this model (R2= 0.78, RMSEboot= 0.47 of a pH unit) is comparable to a recently constructed diatom‐based model for the EMAP lakes. The use of both models in paleolimnological and biomonitoring studies would be advantageous because they would provide two independent lines of evidence of environmental change.

Paleolimnological investigation of three manipulated lakes from Sudbury, Canada

Stratigraphic changes in diatoms and chrysophytes from three manipulated Sudbury lakes were explored in an attempt to examine the influence of fertilization and/or neutralization on algal microfossil assemblages. Both diatom- and chrysophyte-inferred pH profiles indicate that the pH of Labelle Lake has remained fairly stable in the past. The study of Labelle and Middle lakes indicates that the addition of nutrients to acidic and non-acidic oligotrophic lakes did not directly influence diatom and chrysophyte species composition, perhaps because pH remained stable. The diatom and chrysophyte assemblages of Middle Lake only changed when the pH was raised. In Mountaintop Lake the recent shift in chrysophyte species composition and the resulting inferred pH decline is most likely related to a decline in mid-summer epilimnetic pH. Reliable paleolimnological inferences are difficult in lakes such as these because it is difficult to track limnological conditions in the absence of modern analogues.

Reading the Records Stored in the Lake Sediments: A Method of Examining the History and Extent of Industrial Damage to Lakes

In this chapter, the effects of air pollutants from the roasting beds and smelters on Sudbury area lakes are examined. A rather novel approach has been used to track the lake water quality changes that occurred in the past century. This approach uses the rapidly expanding science of paleolimnology, the study of the fossil record in the lake sediments. In the absence of long-term data, paleolimnological techniques using biological remains in lake sediment cores are being used extensively to provide quantitative assessments of past water quality in North America (Charles et al. 1990; Dixit et al. 1987, 1992c) and Europe (Battarbee et al. 1990).

Water Quality Changes from Human Activities in Three Northeastern USA Lakes

ABSTRACT Diatom and chrysophyte assemblages from sediment cores were analyzed to assess the long-term trends of lake water quality in French Pond (New Hampshire), Joes Pond (Vermont), and Kenoza Lake (Massachusetts) as part of the US EPAs EMAP-SW (Environmental Monitoring and Assessment Program-Surface Waters) program in the northeastern USA. Sediment characteristics and geochemical data were also examined to interpret past limnological and watershed changes. Geochemical data indicate that exports of ions from the watersheds have increased and the lakes have received higher trace metal inputs over the post-industrial period. Stratigraphic changes in common diatom and chrysophyte taxa indicate that, over the last century, distinct water quality changes have occurred. Using the diatom- and chrysophyte-based weighted averaging inference models developed for lakes in the northeast, past changes in assemblages were used to infer trends in lakewater total phosphorus (TP), pH, and CI. In French Pond, inferred TP, pH, and CI changes were small, whereas Joes Pond and Kenoza Lake have experienced major changes. The latter two lakes have become more eutrophic, and lakewater pH and CI have also increased from their background values. Inferred water quality changes are closely related to watershed disturbances and resulting eutrophication. Our study illustrates that the inference models developed in EMAP-SW can be successfully applied in establishing long-term water quality trends in lakes throughout the northeastern USA. These models and subsequent sediment core data will help lake managers to develop effective management plans and to establish suitable targets for the restoration of other lakes of concern.

Regional and historical distributions of lake-water pH within a 100-km radius of the Horne smelter in Rouyn-Noranda, Québec, Canada

The spatial distribution of lake-water pH near the Horne smelter in Rouyn-Noranda, Quebec, Canada, is affected not only by industrial sulphur dioxide emissions, but also by other anthropogenic and natural factors. Regional calcareous glaciolacustrine deposits from glacial lakes Barlow and Ojibway provide buffering capacity. Locally, some kettle lakes are buffered by silicate weathering. Small mines, tailings, and natural sources of acidity (e.g. peat basins, forested catchment areas with acidic soils) also contribute to lake acidification. Interpreting the modern regional distribution of lake-water pH, ranging from 3.7 to 9.3 in 99 lakes, is equivocal in this area where wind-transported emissions and buffering from calcareous glaciolacustrine deposits can yield similar spatial trends. However, in a parallel study, diatom assemblages have been used as bio-indicators of past lake-water pH since they respond to temporal shifts in environmental conditions, including lake-water acidity. The historical pH reconstructions for two lakes within a 100-km radius of Rouyn-Noranda suggest that they were naturally acidic before industrialization and have further acidified. Lac de la Pépinière was naturally acidic in the 1800s (pH 5.5) and reached a pH of 4.8 by 1998; its increased rate of acidification since 1927 corresponds to the beginning of mining and smelting operations.