Recovery of previously acidified lakes near Coniston,Canada following reductions in atmospheric sulphur and metal emissions

The purpose of the present study was to assess the rate of recovery of acidified lakes located near the town of Coniston following an abrupt reduction in atmospheric SO₂ and metal emissions at the Coniston smelter which closed in 1972. The water chemistry of several lakes was studied over a period of 16 yr (1968–1984). In one extremely acidic lake close to the smelter, the pH increased from 4.05 in 1972 to 5.8 in 1984. Conductivity, as well as concentrations of SO₄, Cu, Ni, Co, Mn, and Zn decreased by 60% to 90% in the lake water during the same period. In another initially less acidic lake nearby, the increase in pH was less dramatic, while the decrease in conductivity, SO₄, and some metals was similar to that of the more acidic lake. Local SO₄ deposition decreased approximately 75 % while Cu and Ni deposition decreased by 90% following closure of the Coniston smelter. These results indicate that even severely acidified lakes can improve within a few years following a substantial reduction in atmospheric S emissions; and that in some regions recovery can occur due to reductions in SO₂ emissions even in the absence of concurrent NO_x control.     

Environmental factors influencing the rate of spread of the grassDeschampsia cespitosa invading areas around the sudbury nickel-copper smelters

A study has been made of the soil chemistry and atmospheric quality at 9 Sudbury area sites where populations ofDeschampsia cespitosa have invaded the contaminated industrial barrens near the smelters since 1972. The rate of increase in cover within marked quadrats was greater at sites near the discused Coniston smelter than at sites near the two active smelters. Air quality monitoring, using bulk collectors and sulphation plates, indicated substantial drops in phytotoxic air pollutants during the 1978–79 smelter shutdowns. Surface loadings of various metals were evident in soil at sites near the active smelters, whereas this was no longer true at sites near the Coniston smelter disused since 1972. However, water extractable levels of Ni and Cu at these sites remained as high as those found near the active smelters which also have high extractable soil Al. Both comparative studies and multiple regression analysis indicate that the rate of increase in cover ofD. cespitosa in the populations studied correlate best with particulate deposition of Cu and Ni followed by sulphation rate and then by soil extractable Al. These findings are discussed in relation to tolerances of local populations, as well as to the potential effects of airborne particulates on growth.     

Trends in small lake water chemistry near Sudbury,Canada, 1983–1991

While many studies have documented improvements in chemical conditions of large lakes near Sudbury, Canada in response to reduced smelter emissions, few have examined changes in water chemistry of small lakes. We studied trends in water chemistry of 97 small (<10 ha), shallow (<15 m) lakes northeast of Sudbury that are important habitat for breeding waterfowl. Currently, many small lakes near Sudbury are acidified, with little acid-neutralizing capacity and with relatively high concentrations of Al, Mn, and Ni. We also present evidence of short-term improvements in pH and SO₄ levels, but demonstrate that, over a nine year period, there has been no consistent, long-term trend of chemical recovery. Chemical conditions in these lakes varied considerably between 1983 and 1991, and responded quickly to changes in precipitation levels. However, the present condition of most lakes suggests that further reductions in emissions will be required to improve these habitats for breeding waterfowl.     

recent lake acidification and recovery trends in southern quebec,canada

A total of 51 lakes in southern Quebec, Canada, were sampled between 1985 and 1993 to study changes in water chemistry following reductions in SO₂ emissions (main precursor of acid precipitation). Time series analysis of precipitation chemistry revealed significant reductions in concentrations and deposition of SO₄ ^2- from 1981 to 1992 in southern Quebec as well as reductions in concentrations and deposition of base cations (Ca²⁺, Mg²⁺), NO₃ ^- and H⁺ in the western section of the study area. Reductions in atmospheric inputs of SO₄ ^2- have resulted in decreased lakewater SO₄ ^2- concentrations in the majority of the lakes in our study, although only a small fraction (9 of 37 lakes used in the temporal analysis) have improved significantly in terms of acidity status (pH, acid neutralizing capacity – ANC). The main response of the lakes to decreased SO₄ ^2- is a decrease in base cations (Ca²⁺+Mg²⁺), which was observed in 17 of 37 lakes. Seventeen lakes also showed significant increases in dissolved organic carbon (DOC) over the period of study. The resulting increases in organic acidity as well as the decrease in base cations could both play a role in delaying the recovery of our lakes.     

Water quality changes in sudbury area lakes: A comparison of synoptic surveys in 1974–1976 and 1981–1983

A survey was carried out during the summers of 1981–1983 to re-sample 209 Sudbury, Ontario area lakes originally sampled in 1974–1976. Between the study periods, SO₂ emissions from the Sudbury metal smelters were reduced by ～ 50%. Observed water quality changes included increases in pH and decreases in SO₄ ^?, Ni, and Cu concentrations. The degree of observed changes showed a general relationship to distance from the Sudbury smelters, indicating that reduced contaminant deposition from Sudbury sources was responsible for the observed improvements. Although changes in water quality have occurred in many Sudbury area lakes over the course of this study, many lakes remain acidic and metal-contaminated.     

Changes in the chemistry of lakes near Subury,Ontario following reductions of SO2 emissions

Emissions of SO₂ in the Sudbury area declined from an estimated average of 1.41 × 106 tonne yr^?1 in 1973–78 to 0.68 × 10⁶ tonne yr^?1 in 1979–85. As a result, SO₄ concentrations of lakes in the area have decreased, and the pH of each of the acidic lakes that was studied has increased. Aluminum, Cu, Ni and Zn concentrations have also decreased; however, the latter three metals have probably declined because of reductions in emissions of metals from the smelters rather than because of the pH changes in the lakes.     

The effect of nickel and copper deposition from a mining and smelting complex on coniferous regeneration in the boreal forest of northern Manitoba

Airborne pollutants in the form of SO₂ and heavy metals have been dispersed over the boreal forest in the Thompson area of northern Manitoba since 1961. Metal deposition has been found in soils and plant material to a distance of 35 km from the Inco nickel smelter. Studies were initiated in 1979 to determine effects of Ni and Cu on coniferous regeneration of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill) BSP.).Studies included metal accumulation in cones, effects on seed quality, seed germination and seedling response in metal contaminated soils. Nickel and Cu accumulation in cones of both species declined rapidly with distance from the smelter. Seed quality and germination potential was not related to metals in cones or air pollutant influence in general. Nickel and Cu accumulation in surface organic soils was inversely related to distance from the smelter. A significant inverse correlation was determined between seedling growth and Cu/Ni concentrations in surface organic soils. Metal accumulation in soils within 5 km of the nickel smelter inhibited root growth of conifer seedlings.     

Sudbury Sediments Revisited: Evaluating Limnological Recovery in a Multiple-Stressor Environment

Paleolimnological techniques were utilized to determine whether diatom and scaled chrysophyte assemblages in Daisy, Swan, and Tilton lakes (Sudbury, Ontario) have recovered toward their preimpact conditions as a result of reduced inputs of anthropogenic pollutants (SO ₄ ^2? and metals) or whether other environmental stressors have affected recovery trajectories. In addition, geochemical analysis was used to track trends in sedimentary nickel and copper concentrations through time. Preindustrial algal assemblages were primarily dominated by circumneutral to alkaline and pH-indifferent taxa. However, with the onset of open-pit roasting and smelting operations, there was a stratigraphic shift toward acid-tolerant species. With wide-scale smelter emission reductions commencing in the 1970s, scaled chrysophyte assemblages in Swan and Daisy lakes have started to show signs of biological recovery in ～1984 and ～1991, respectively. Although the scaled chrysophyte assemblage in Tilton Lake has not recovered toward the predisturbance assemblage, the decline in acidophilic taxa and increase in circumneutral taxa in recently deposited lake sediments indicate that the community is responding to increased lake water pH. Conversely, diatom assemblages within each of the study lakes have not begun to recover, despite well-documented chemical recovery. It is suspected that biological recovery in Sudbury area lakes may be impeded by other environmental stressors such as climate warming. Copper and nickel concentrations in lake sediments increased with the onset of mining activities and subsequently declined with emission controls. However, metal concentrations in lake sediments remain elevated compared to preindustrial concentrations. Together, biological and geochemical evidence demonstrates the clear environmental benefits associated with smelter emission controls.     

Patterns of water chemistry among twenty-seven oligotrophic lakes in Kejimkujik National Park,Nova Scotia

A cluster analysis was used to apportion 27 oligotrophic lakes in southwestern Nova Scotia into five multivariate groups on the basis of patterns of covariation of 11 chemical variables (Cl, SO₄, Gran alkalinity, organic anions, Ca, Mg, K, Na, H⁺, and color). These groups are described in terms of the average values of the chemical variables. The relationships among the groups were investigated by an ordination by detrended correspondence analysis. The first, and by far the strongest axis of the ordination separated lakes with relatively large concentrations of alkalinity, from strongly colored lakes with large concentrations of H⁺ and organic anions. Axis 2 separated acidic lakes, from lakes with large concentrations of Ca and alkalinity.     

The use of calibrated lakes and watersheds for estimating atmospheric deposition near a large point source

We have measured the input and output rates of substances to and from both lakes and watersheds in the Sudbury and Muskoka-Haliburton areas of Ontario. At the former location, we have conducted mass balance studies on 5 lakes and their watersheds for 2½ yrs. At the latter site, we have measured mass balances for 6 lakes and about 30 individual watersheds for the past 5 yrs. Substances studied included SO₄ ^2?, NO₃ ^?, NH₄ ⁺, H⁺, major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and HCO₃ ^?. During the course of the investigation at Sudbury we have made several observations that indicate that the inputs of some substances, specifically SO₄ ^2? or SO₄ ^2?-precursors and strong acids, to lakes and watersheds are underestimated when measured as bulk deposition (i.e. by collection in a continuously open container): (a) The output of SO₄ ^2? from the calibrated watersheds was substantially greater than the input measured as bulk deposition. (b) The SO₄ ^2? concentrations of the lakes could not be explained on the basis of the measured inputs. An additional input directly to the lake surface was needed to obtain a mass balance. (c) The net input of acids measured as bulk deposition to the watersheds was much less than the acid consumed, which was estimated by the net output of Ca²⁺, Mg²⁺, Na⁺, K⁺, Al³⁺, and the net retention of NO₃ ^?. (d) The major cation content of the study lakes could be explained on the basis of weathering reactions in the lakes' watersheds only if the input of strong acid had been underestimated. When these observations were quantified, they indicated a major portion of the total input of SO₄ ^2?-precursors and of strong acid was not included in our bulk deposition measurements. Deposition of SO₂ is the most likely explanation for these observations.     

comparison of sulphur and heavy metal contents and their regional distribution in humus and moss samples from the vicinity of Nikel and Zapoljarnij,Kola Peninsula,Russia

Terrestrial moss and humus (the O-horizon) are often used separately for determining and monitoring airborne heavy metal pollution. Here, we directly compare the results of analyses of moss and humus samples taken at a density of one site per 300 km² in a 12 000 km² area (45 samples) around the nickel smelter in Nikel, the nickel ore roasting plant in Zapoljarnij, both in Russia, and the iron ore mine and mill near Kirkenes in Norway. The samples were air dried, digested in conc. HNO₃ and analysed for more than 30 elements by ICP-MS and ICP-AES at the laboratory of the Geological Survey of Finland (GTK). For most elements, observed levels and variations are considerably greater in soil than in moss. The main contaminants, Ni and Cu, reach equally high median levels in the moss and soil, but maximum values are far higher in soil. Both media show comparable regional distribution patterns for the heavy metals, but not for sulphur. Cu and Ni can be used to delineate the limits of contamination in the survey area. Both media show the same picture, with a generally very steep gradient from east to west and background levels being reached 30–50 km from the nickel smelter. When moss is used, Cu/Ni, Cu/S and Ni/S ratios can be used to separate input from the smelting and roasting proccesses in Russia. Both media are well suited to use separately to detect airborne pollution in this heavily contaminated area. The moss data are generally easier to interpret, but moss is not available at the most polluted sites. Levels for many elements other than Cu and Ni are close to the detection levels in moss samples, but not in humus samples. Information gathered from both media thus complement each other in a regional multi-element survey.     

Seasonal and long-term temporal patterns in the chemistry of Adirondack lakes

There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO₄ ^2?. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca²⁺, Mg²⁺, K⁺, Na⁺; C_B) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO₃ ^?, while lakes in the central and eastern Adirondacks had lower NO₃ ^? concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 Μeq L^?1 during base flow periods may experience decreases in ANC to near or below 0 Μeq L^?1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO₄ ^2?, consistent with decreases in SO₂ emissions and SO₄ ^2? in precipitation in the eastern U.S. Reductions in SO₄ ^2? have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO₃ ^? that occurred in most of the ALTM drainage lakes.     

Multi-criteria Analysis of Air Pollution with SO2 and PM10 in Urban Area Around the Copper Smelter in Bor, Serbia

This work presents the results of 4 years long monitoring of concentrations of SO₂ gas and PM₁₀ in the urban area around the copper smelter in Bor. The contents of heavy metals Pb, Cd, Cu, Ni, and As in PM₁₀ were determined and obtained values were compared to the limit values provided in EU Directives. Manifold excess concentrations of all the components in the atmosphere of the urban area of the townsite Bor were registered. Through application of a multi-criteria analysis by using PROMETHEE/GAIA method, the zones were ranked according to the level of pollution.     

Climate confounds detection of chemical trends related to acid deposition in upper Midwest lakes in the USA

Between 1983–94, as acid deposition rates declined, SO₄ ^2? concentrations decreased in 18 of 28 lakes monitored by the upper Midwest LTM program. The expected recovery of ANC and pH was less common, however. Differences in climate may account for divergent trend patterns across the region. Only in Minnesota, where climatic shifts were less pronounced, did we observe a general pattern of increasing lake ANC and pH accompanying declines in SO₄ ^2?. In contrast, the widespread negative trends in lake SO₄ ^2? in the upper Michigan lakes were generally not associated with recovery of ANC and pH, but with decreases in Ca+Mg. These cation decreases may be linked to decreased groundwater inputs during the drier climatic conditions characterizing the study period and decreases in Ca+Mg in atmospheric deposition. In many of the Wisconsin lakes, an overall decline in SO₄ ^2? was precluded by SO₄ ^2? increases during a 4-year drought midway through the study period. During the drought, declining lake water level and volume caused evaporative concentration of solutes, and may have decreased the areal extent of sulfate reduction. Despite controls on sulfur emissions across the region, recovery of pH and ANC has been hindered by climatic shifts and concurrent decreases in atmospheric deposition of cations.     

Trends and patterns in lake acidification in the State of Vermont: Evidence from the Long-Term Monitoring Project

Twenty-four low acid neutralizing capacity (ANC) lakes in Vermont have been monitored since 1980 to characterize their chemical variability, and to determine if they exhibit temporal trends in acid/base chemistry. Many of the lakes exhibit significant decreasing trends in SO₄ ^2? and base cation (C_B) concentrations, but few exhibit significant changes in pH or ANC. An examination of all trend results (significant and insignificant) suggests a tendency for ANC and pH values in these lakes to be increasing, but either the changes are too small, or the number of observations too small, for these trends to be significant. Data from these lakes suggest that the primary responses of surface waters in this region to declining rates of SO₄ ^2? deposition are decreases in SO₄ ^2? concentrations and rates of cation leaching from watershed soils. Decreasing rates of c_b deposition may combine with lower rates of cation leaching to produce declines in c_B that are very similar to measured declines in SO₄ ^2? concentration. Vermont lakes exhibit their lowest ANC values in spring, attributable, for the most part, to dilution of c_B concentrations during spring snow melt. Concentrations of SO₄ ^2? are also more dilute in the spring, but c_B decreases are greater, and the net effect is a lowering of ANC. One quarter of the Vermont lakes monitored exhibit strong seasonality in NO₃ ^? concentrations, with peak concentrations near 70 Μeq L^?1. In these lakes, spring increases in NO₃ ^? concentrations are more important than C_B dilution in producing minimal spring ANC values.     

Long-term trends in the chemistry of precipitation and lake water in the Adirondack Region of New York,USA

Long-term changes in the chemistry of precipitation (1978–94) and 16 lakes (1982–94) were investigated in the Adirondack region of New York, USA. Time-series analysis showed that concentrations of SO₄ ^2–, NO₃ ^–, NH₄ ⁺ and basic cations have decreased in precipitation, resulting in increases in pH. A relatively uniform rate of decline in SO₄ ^2– concentrations in lakes across the region (1.81±0.35 eq L^–1 yr^–1) suggests that this change was due to decreases in atmospheric deposition. The decrease in lake SO₄ ^2– was considerably less than the rate of decline anticipated from atmospheric deposition. This discrepancy may be due to release of previously deposited SO₄ ^2– from soil, thereby delaying the recovery of lake water acidity. Despite the marked declines in concentrations of SO₄ ^2– in Adirondack lakes, there has been no systematic increase in pH and ANC. The decline in SO₄ ^2– has corresponded with a near stoichiometric decrease in concentrations of basic cations in low ANC lakes. A pattern of increasing NO₃ ^– concentrations that was evident in lakes across the region during the 1980's has been followed by a period of lower concentrations. Currently there are no significant trends in NO₃ ^– concentrations in Adirondack lakes.     

Trends in the Chemistry of Acidified Bohemian Lakes from 1984 to 1995: I. Major Solutes

Temporal changes in major solute concentrations in six Czech Republic lakes were monitored during the period 1984–1995. Four chronically-acidic lakes had decreasing concentrations of strong-acid anions (C_SA = SO₄ ^2- + NO^{3 -} + Cl^-), at rates of 3.0 to 9.0 μeq L^-1 yr^-1. Decreases in SO₄ ^2-, NO₃ ^-, and Cl^- (at rates up to 5.1 μeq L^-1 yr^-1, 3.2 μeq L^-1 yr^-1, and 0.6 μeq L^-1 yr^-1, respectively) occurred. The response to the decrease in deposition of S was rapid and annual decline of SO₄ ^2- in lake water was directly proportional to SO₄ ^2- concentrations in the acidified lakes. Changes in NO₃ ^- concentrations were modified by biological consumption within the lakes. The decline in C^SA was accompanied in the four most acidic lakes by decreases in Al_T, increases in pH at rates of 0.011 to 0.016 pH yr^{- 1}, and decreases of Ca²⁺ and Mg²⁺ (but not Na⁺) in three lakes. The acid neutralizing capacity (ANC) increased significantly in all six lakes. Increases in base cation concentrations (CB = Ca²⁺ + Na⁺ + Mg²⁺ + K⁺) were the principal contributing factor to ANC increases in the two lakes with positive ANC, whereas decrease in C_SA was the major factor in ANC increases in the four chronically-acidic lakes. The continued chemical recovery of these lakes depends on the uncertain trends in N deposition, the cycling of N in the lakes and their catchments, and the magnitude of the future decrease in S deposition.     

Spatiotemporal dynamics of the pollution of Al–Fe-humus podzols in the impact zone of a nonferrous metallurgical plant

The dependence of the level of contamination of the upper horizon of Al–Fe-humus podzols (Podzols Rustic) with heavy metals (Ni, Cu) on the distance from the Severonickel smelter (Monchegorsk, Murmansk oblast) was studied on a number of test plots in the medium-aged pine stands. It was found that metal concentrations in the soils could be reasonably approximated by the negative exponential function. In the buffer zone of the smelter, the concentrations of Ni and Cu exceed background values by 8–17 times; in the impact zone, by 50–100 times. The study of the dynamics of acid-soluble forms of Ni and Cu in the organic horizons of podzols on the key plots showed that the boundaries of polluted territory shift towards background regions despite the recent five–eightfold decrease in the emissions. The concentrations of heavy metals in the litter horizons continued to increase in the buffer zone. In the impact zone, their contamination remained at the very high level. Firm bounding of heavy metals in the organic horizon coupled with their continuing aerial input did not allow the beginning of the soil self-purification process, which might last for decades and centuries. Raster electron microscope and X-ray spectral microanalysis showed that particles (>85%) of the ashed matter of organic horizons from the background region, the buffer zone, and the impact zone is mainly represented by various soil-forming minerals and iron oxides (in particular, magnetite). In the samples from the impact zone, about 5% of the mineral particles had the surface morphology and chemical composition typical of dust particles emitted into the air by metal smelters. Most probably, these spherical particles represented magnetite Fe₃O₄ enriched in heavy metals (Cu, Ni).     

Recent Temporal Patterns in the Chemistry of Small,Acid-sensitive Lakes in Central Ontario,Canada

We monitored the chemistry of 603 small water bodies in three acid-sensitive regions of central Ontario, Canada (Algoma n=235, Muskoka n=216, Sudbury n=152) between 1988^-1996 to determine whether they have responded to recent SO2 emission reductions, and whether any chemical changes were related to lake characteristics. During the study, 27-56% of lakes declined in SO₄ ^2- concentrations, 41-57% declined in base cation concentrations, but only 26-28% increased in pH or ANC (acidity status). Increases in pH were greatest in lakes with low ANC, but had weak relationships to lake color or volume. No consistent trends were observed for DOC, NO₃ ^- or TP concentrations. Clearly, the long-term biological recovery of these sensitive aquatic ecosystems will depend on interactions among several environmental stressors, including acidification.     

Fluoro‐mobilization of metals in a Slovak forest soil affected by the emissions of an aluminum smelter

Depositions originating from a central Slovak Al smelter may increase metal solubility in adjacent soils because they contain F (mainly HF). The reason for fluoro‐mobilization of metals may be the formation of soluble fluoro‐metal complexes or the mobilization of organic matter and subsequent formation of organo‐metal complexes. The objectives of our work were (1) to assess the extent of metal mobilization by fluoride in a Slovak Lithic Eutrochrept affected by the emissions of an Al smelter and (2) to model the dissolved metal species with the help of a chemical equilibrium model (MINEQL+). The O (Moder), A, and B horizons were equilibrated with solutions at F concentrations of 0, 0.9, 2.7, and 9.0 mmol l^—1. In the extracts, the concentrations of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Zn, dissolved organic carbon (DOC), free and complexed F, and the pH and electrical conductivity (EC) were determined. The heavy metal concentrations in the O horizon (Cd: 0.99, Cr: 18.0, Cu: 44, Ni: 26, Pb: 110, and Zn: 84 mg kg^—1) were 2.5 to 9 times larger than those in the A and B horizons. The concentrations of H₂O‐soluble F decreased from the O (261 mg kg^—1) to the A (103 mg kg^—1) and B horizon (92 mg kg^—1). In batch experiments increasing addition of F increased the equilibrium concentrations of Al, Cr, Cu, Fe, Ni, Pb, and DOC in all samples, of Cd in the A, and of K in the B horizon. At the same time the concentrations of complexed F and pH increased whereas EC decreased. Chemical equilibrium modelling indicated that the mobilizing effect of F resulted from the formation of fluoro‐Al complexes and organo‐complexes of all other metals.