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Over the past century, dissolved oxygen concentrations have decreased and metabolic CO2 has accumulated in the bottom waters of the Gulf of St. Lawrence (GSL) and Lower St. Lawrence Estuary (LSLE). Oxygen depletion has been attributed primarily to changes in ocean circulation in the northwest Atlantic Ocean, as well as an increase in the flux of organic matter at or near the seafloor and its accompanying biological oxygen demand. The accumulation of metabolic CO2 in these waters has led to their progressive acidification and a decrease in pH (0.3–0.4 pH unit) commensurate to the variation expected for global oceanic surface waters by the end of this century, albeit by a different mechanism (anthropogenic CO2 uptake from the atmosphere). The decrease in bottom-water pH of the GSL and LSLE is accompanied by a decrease in the carbonate ion concentration and the saturation state of the waters with respect to both calcite and aragonite (ΩC and ΩA). Although the Laurentian Trough sediments are mostly devoid of modern calcium carbonate fossils, detrital (Ordovician/Silurian) carbonates, eroded from Anticosti Island, accumulate on the seafloor. Evidence of carbonate mineral dissolution in the sediments of the Laurentian Trough is examined and supported by pore-water data and vertical variations of their inorganic carbon content. Historical, solid-phase profile data are used to estimate temporal variations of the sedimentary calcite dissolution rates and document the anthropogenic modification of the sediment record. [ABSTRACT FROM AUTHOR]

Habitat degradation associated with resource development is a major ecological concern, particularly in Canada's boreal zone where limited information on biodiversity is available. Habitat degradation can lead to reductions in biodiversity and ecosystem function, especially when drivers of variability and diversity patterns have not been identified for a region of interest. In this study, the distribution of diatom genera in the Peace-Athabasca Delta in northeastern Alberta was examined in relation to seasonal, geographic, and alkalinity gradients. Grab samples of six abiotic variables (total dissolved nitrogen, total dissolved phosphorus, dissolved iron, turbidity, pH, and specific conductance (SPC)) were taken from 12 remote wetlands over three sampling periods, and regressed against an ordination of diatom community composition to identify key environmental drivers of diatom community variation. Indirect gradient analysis identified two major gradients among sites. First, separation of sites among sampling periods showed successional seasonal changes in diatom community composition. Second, separation of sites from the Peace sub-delta and Birch sub-delta showed a gradient of geographic separation. Direct gradient analysis failed to explain the underlying drivers of these two gradients, but did show that alkalinity is a key driver of diatom community composition in the Embarras sub-delta, and that these sites could be particularly vulnerable to community changes associated with acidification. [ABSTRACT FROM AUTHOR]

In response to biotic and abiotic cues, the cladoceran genus Bosmina can undergo changes in body size and appendage length and shape over successive generations. To improve our understanding of the environmental controls on Bosmina size structure, we used paleolimnological techniques to examine Bosmina size responses to the extreme acidification and metal contamination, and then subsequent chemical recovery, of lakes in the vicinity of mining and smelting operations near Sudbury, Canada. During the acidification period, Bosmina antennule and carapace length significantly increased in three of the five study lakes, while mucro length significantly decreased in four of the five lakes. However, despite the recent return to pre-impact pH levels, the size structure of the present-day Bosmina community still differs from the pre-impact size distributions. We suggest that the continued dominance of the food webs by small invertebrate predators (e.g., cyclopoid copepods) is responsible for the persistent changes to Bosmina size structure. [ABSTRACT FROM AUTHOR]

We investigated mercury (Hg) concentrations in small fish (mainly yellow perch, Perca flavescens ; ∼60% of fish collected) and in blood of common loons ( Gavia immer ) that prey upon them during the breeding season on lakes in 4 large, widely separated study areas in Canada (>13 lakes per study area; total number of lakes = 93). Although surface sediments from lakes near a base metal smelter in Flin Flon, Manitoba had the highest Hg concentrations, perch and other small fish and blood of common loon chicks sampled from these same lakes had low Hg concentrations similar to those from uncontaminated reference lakes. Multiple regression modeling with AIC analysis indicated that lake pH was by far the most important single factor influencing perch Hg concentrations in lakes across the four study areas (R 2 = 0.29). The best model was a three-variable model (pH + alkalinity + sediment Se; Wi = 0.61, R 2 = 0.85). A single-variable model (fish Hg) best explained among-lake variability in loon chick blood Hg (Wi = 0.17; R 2 = 0.53). From a toxicological risk perspective, all lakes posing a potential Hg health risk for perch and possibly other small pelagic fish species (where mean fish muscle Hg concentrations exceeded 2.4 μg/g dry wt.), and for breeding common loons (where mean fish muscle Hg concentrations exceeded 0.8 μg/g dry wt., and loon chick blood Hg exceeded 1.4 μg/g dry wt.) had pH < 6.7 and were located in eastern Canada. [ABSTRACT FROM AUTHOR]

Multiple natural and anthropogenic stressors pose a serious threat to the health and diversity of biological communities. A growing body of research suggests that one consequence of these stressors has been a regional-scale loss of crayfish populations across south-central Ontario. The mechanisms contributing to the imperilment of crayfish probably include historical acidification and metal contamination, shoreline development and habitat loss, increased water temperature, declining [Ca] in lake water, and invasion by nonnative species (i.e., Smallmouth Bass and the rusty crayfish). Long-term monitoring data of crayfish populations in Algonquin Provincial Park (Ontario) have documented marked declines in Cambarus bartonii abundance despite the relatively isolated nature of the study lakes. Furthermore, monitoring data indicate that the onset of this decline may predate the monitoring record, thereby creating a need for the use of paleolimnological techniques to infer past conditions. We used a multiple proxy approach (i.e., diatoms and cladocerans) to reconstruct key environmental variables (e.g., pH) and long-term changes in lake chemistry (e.g., [Ca]) as they pertain to crayfish population loss. We found that interactions between pH and [Ca] have led to the decline in crayfish abundance and to the continued lack of recovery of these populations. Furthermore, lake-water [Ca] in all 4 Algonquin Park lakes are now <2.0 mg/L, the lowest hypothesized requirement for freshwater crayfish (2–10 mg/L), suggesting that short-term recovery of crayfish populations is unlikely, despite pH recovery. [ABSTRACT FROM AUTHOR]

Global climate change impacts marine ecosystems, directly and indirectly, especially in the Arctic and Antarctic. We show the first long-term (1920–2011) time-series of oceanographic change in Hudson Bay, an arctic marine ecosystem, based on coupled brachiopod-calcite stable and clumped isotope results. Long-term decrease in brachiopod δ 13 C parallels that of seawater-DIC in Hudson Bay, and after considering its seasonal sea ice coverage, it is similar to that of the 13 C-Suess effect observed in the North Atlantic and other regions. Acidification of Hudson Bay seawater leads warming by about 10–20 years, and with intensified warming from the 1970s to 2010s closely coupled to earlier sea-ice breakup. Post-industrial warming of Hudson Bay is initially slow, but in later years, faster and of greater magnitude than of the coeval global oceans. Our observations for the past 90 years suggest that climate-forced change contributed to an average increase of about 0.1 °C and 3.6 °C in sea-surface water temperature of Hudson Bay over the first 50 and subsequent 40 years, respectively. This 3.7 °C post-industrial warming of Hudson Bay seawater is about six times the 0.67 °C increase observed during the past 100 years in global ocean sea-surface temperature, which is about double the postulated increase of about 2 °C for polar regions. Our results are consistent with the general notion that polar marine environments, such as Hudson Bay, can serve as sensitive indicators of change in climate, and of change still to come for lower latitude ecosystems. [ABSTRACT FROM AUTHOR]

Wetlands are prevalent in the Sudbury, Ontario region and often operate at the interface between terrestrial and aquatic ecosystems, modifying water chemistry and potentially affecting the recovery of impacted lakes. The deposition of metals and sulphur in Sudbury in 2010-2012 was far below that reported in the 1970's, but still higher than background values. Wetlands in the area have accumulated large quantities of metals, and high concentrations of these metals in streams occurred primarily in response to SO4-related acidification events or associated with high dissolved organic carbon production in early summer. Concentrations of most metals in streams exceeded provincial guidelines and fluxes of some metals from catchments exceeded deposition inputs to lakes by as much as 12 times. The release of metals long after emissions reductions have been achieved must be considered in ecosystem recovery studies, particularly as dry conditions may become more prevalent in boreal regions affected by mining. [ABSTRACT FROM AUTHOR]

Abstract: Positive trends in dissolved organic carbon (DOC) concentration have been observed in surface waters throughout North America and northern Europe. Although adsorption in mineral soils is an important driver of DOC in upland streams, little is known about the potential for changes in DOC adsorption to contribute to these trends. We hypothesized that long-term declines in soil water Ca2+ levels, in response to declining acid deposition, might influence DOC adsorption and that this could contribute to long-term DOC trends in an upland forested catchment in south-central Ontario, Canada. Between 1987 and 2009, DOC concentrations increased significantly (p <0.05) in stream water and B horizon soil water (2 out of 3 sites). The null point DOC concentration (DOCnp), which is a measure of the soil water DOC concentration at equilibrium with the soil, ranged from 1.27 to 3.75mgL−1 in B horizon soils. This was similar to the mean DOC concentrations of B horizon soil water (2.04–6.30mgL−1) and stream water (2.20mgL−1), indicating that soil and stream water DOC concentrations are controlled by equilibrium processes at the soil–water interface. Adsorption experiments using variable Ca2+ concentrations demonstrated that as Ca2+ decreased the DOCnp increased (1.96 to 4.74mgL−1), which was consistent with the observed negative correlation between DOC and Ca2+ in B horizon soil water (p <0.05; r 2 =0.21). Additional adsorption experiments showed that Na+ had no effect on DOC adsorption (p >0.05), indicating that changes in DOC adsorption might be related to cation bridging. We conclude that declines in soil water Ca2+ concentration can contribute to increasing DOC trends in upland streams by reducing DOC adsorption in mineral soils. [Copyright &y& Elsevier]

Lakes around the metal smelters of Sudbury, Ontario, Canada offer a unique opportunity to study recovery processes in stressed aquatic ecosystems. Following major reductions in the atmospheric deposition of sulphur and metal particulates, chemical and biological recovery have been observed in many lakes; however, the magnitudes and trajectories of biological recovery are variable. Crustacean zooplankton communities have proven to be particularly valuable in tracking the biological recovery patterns in Sudbury lakes. In a survey of 87 lakes, zooplankton community structure revealed strong gradients related to acidification, metal contamination, trophic status and depth. The study lakes could be divided into four groups related to these gradients: acidified, recovered, urban and reference lakes. Community composition in recovered (to pH >6.0) lakes did not differ from reference lakes for copepods and cladocerans. In contrast, urban lakes subjected to the effects of watershed development as well as atmospheric metal contamination had either copepod or cladoceran communities that differed from reference conditions. Among the acidified lakes, most lakes with pH <5.5 contained species poor copepod communities; however, substantial community recovery was evident in lakes with pH >5.5. Our study illustrates the complexity of biological recovery processes in lakes subjected to multiple environmental stressors. Although substantial zooplankton community recovery clearly occurs as lakes recover from acidification, other stressors including metal contamination and eutrophication in urban environments may greatly affect recovery processes and outcomes. [ABSTRACT FROM PUBLISHER]

Thousands of lakes around Sudbury, in northeastern Ontario, Canada, were badly damaged by acid deposition and many were also metal-contaminated. Large reductions in atmospheric sulphur and metal emissions have led to widespread chemical improvements in these lakes, and recovery has been documented for various biota. These findings were very important in establishing the necessity and value of sulphur emission controls during the international debates about the effects of acid deposition and the need for cleaner air. Studies of northeastern Ontario lakes are continuing to advance our understanding of chemical and biological recovery processes; however, that knowledge is still incomplete. It has become apparent that the recovery of lakes from acidification is closely linked with the responses to, and interactions with, other large-scale environmental stressors like climate change and calcium declines. Developing a better understanding of lake recovery processes and their future outcomes within such a multiple stressor context will be difficult. It will demand the merging of various approaches, including monitoring, experimentation, paleolimnology, and modelling, and will require effective collaboration among different research and monitoring sites and various agencies and institutions engaged in environmental science. [ABSTRACT FROM AUTHOR]

Paleolimnological techniques are important for determining background ecological conditions and ecosystem responses to stressors when long-term data sets are absent. Research at the Dorset Environmental Sciences Centre (Ontario, Canada) has included paleolimnological studies to determine the effects of anthropogenic stressors on shield lakes, including eutrophication, acidic deposition, and climate change. Diatom-based total phosphorus (TP) inferences suggest that [TP] has declined in some lakes, despite increased inputs from anthropogenic sources. When coupled with siliceous algae-based pH inferences that suggest landscape-scale long-term acidification, these results indicate that the ecological effects of anthropogenic P inputs are being masked by the cumulative effects of multiple stressors. Detailed stratigraphic analyses of lakes that have experienced severe anthropogenic disturbances indicate that despite measured and inferred recovery in epilimnetic [TP] to predisturbance concentrations, pelagic communities have not recovered to predisturbance community composition; profundal communities and the variables associated with water quality (e.g., hypolimnetic oxygen) have also not recorded recovery. This suggests that (i) typical modeling approaches to quantify the effects of anthropogenic inputs on lake water [TP] should be used with caution and (ii) lake management approaches that follow the paradigm of “water quality recovery = biological recovery” may not be applicable to ecosystems being affected by multiple anthropogenic stressors. [ABSTRACT FROM AUTHOR]

We used multiple linear regression analyses to explore empirical relationships between dissolved organic carbon (DOC) concentrations, weather, and acidification in long-term data sets from 12 small Boreal Shield lakes in Ontario, Canada. In two lakes in which pH changes have been very large (4.5 to ~6.0), pH explained most of the temporal variation in DOC concentrations. In the remaining lakes, long-term average previous temperature (on the scale of a decade or more) was usually the best explanatory variable for DOC concentrations. Lake-specific multiple regression models constructed from long-term and short-term attributes of weather (long-term average previous temperature and precipitation, winter–spring precipitation, summer precipitation, summer sunshine) and pH explained between 41% and 96% of the temporal variation in DOC concentrations during the entire monitoring period for these lakes (n = 16–26 years). Multiple regression models considering only the period common to all lakes, 1987 to 2003 (n = 16–17 years), explained 35%–96% of the variation in DOC concentrations. The importance of long-term and short-term attributes of weather in explaining temporal variations in DOC concentrations suggests that changes in climate will have large effects on lake clarity; however, the interactions between weather-related effects may be very complex. [ABSTRACT FROM AUTHOR]

Rising dissolved organic carbon (DOC) concentrations observed at a number of sites in the northern hemisphere over recent decades are the subject of much debate, and recent reports suggest a link between DOC patterns in surface waters and changes in sulphate (SO4) related to droughts or deposition. In order to investigate the potential influence of changes in SO4 concentration on DOC patterns in south-central Ontario, we used long-term (1980–2001) stream monitoring data from a wetland-dominated catchment (Plastic Lake-1 subcatchment, PC1) that has been the focus of intensive investigations of both SO4 and DOC dynamics. Annual average volume-weighted DOC concentration increased significantly between 1980 and 2001, whereas SO4 concentration declined, but the decrease was not significant due to large increases in SO4 that occurred during drought years. There was no relationship between SO4 and DOC in annual data series; however, seasonal analyses indicated significant negative correlations between SO4 and DOC concentrations in spring (March–April–May), summer (June–July–August) and fall (September–October–November). In spring, DOC concentration was negatively correlated with flow whereas SO4 concentrations increased with flow, and their opposing relationships with discharge explain the negative correlation between SO4 and DOC in this season. In summer and fall, low SO4 concentrations occur during periods of low flow as a result of microbial SO4 reduction, whereas correspondingly high DOC concentrations in the summer and fall can be attributed to optimal conditions (i.e. stagnant flow, warm temperatures) for DOC production in the wetland. Increases in SO4 (and acidity) following droughts were not associated with declines in DOC; instead the primary impact of droughts on DOC was to limit DOC export due to diminished stream flow. Rather than an acidification effect, we suggest that negative relationships between SO4 and DOC were either directly (spring) or indirectly (summer/fall) caused by underlying relationships with hydrology. [ABSTRACT FROM AUTHOR]

A total of nine sediment cores were collected from the five deep basins of Kejimkujik Lake, located in southwestern Nova Scotia, Canada, in order to track changes related to surface-water acidification and to test reproducibility of results between sediment cores from different basins in a large lake. Present-day and pre-industrial (c. 1850) samples were analyzed from all cores and detailed diatom profiles were undertaken on three cores to determine the timing of acidification. All three detailed diatom profiles show declines in inferred pH starting in the early 1930–1940s. Since the 1940s, diatom-inferred lakewater pH has declined from a background pH of ∼5.8 (± 0.4) to a current diatom-inferred pH of ∼4.9 (± 0.1). This corresponds to the current (2001–2002) range of measured lakewater pH = 4.7–5.2 with a mean pH = 4.9. Species diversity of diatoms also declines markedly in all cores with the Hill’s N2 index decreasing from ∼5 to near 1. The pre-impact diatom assemblages were dominated by Aulacoseira spp. and have since changed to dominance by Asterionella ralfsii var. americana (>45 μm). All nine sediment cores showed similar changes in diatom assemblages, diatom-inferred pH, and timing of the onset of acidification. Thus, paleolimnological inferences from deepwater sediment cores were highly reproducible in this large, morphometrically complex lake system. [ABSTRACT FROM AUTHOR]

Increased sulphate (SO4) export from wetlands following summer droughts in central Ontario, Canada has been associated with the delayed chemical recovery of downstream surface waters following decreased sulphur (S) emissions. Prolonged summer droughts result in a decrease or cessation of stream flow, declines in wetland water table level and oxidation of reduced S compounds to SO4, which is subsequently flushed into drainage streams when stream flow resumes. Sulphate input-output budget calculations (1983–1995 and 1999–2001) at a conifer Sphagnum swamp in the Plastic Lake catchment, indicate that SO4 is retained in most years but is exported on a net basis following particularly severe summer droughts that result in the cessation of stream flow for more than 54 days (95% CI: 41–72 days). Hindcast calculations using long-term (1916–2000) stream discharge records from a nearby station indicate that while droughts occurred frequently in south-central Ontario over the past 85 years, sufficiently dry conditions to cause net SO4 export occurred in only18 of the past 85 years, and indicate a cumulative positive SO4 balance for the swamp (i.e. net SO4 retention). Furthermore, the S pool at the Plastic Lake swamp has been estimated to be ∼1500 kg S/ha in the upper 40 cm peat layer, which is large compared to the amount of net SO4 export that occurs even in years with particularly dry summers (e.g. −43 kg S/ha in 1987/88). Together, these data suggest that the wetland S pool at Plastic Lake has not been depleted by previous droughts and will continue to sustain episodic drought-related SO4 export for the foreseeable future. [ABSTRACT FROM AUTHOR]

Atlantic Canada receives the lowest acid deposition amounts in eastern North America, but has some of the most acidic surface waters on the continent, due to the low buffering provided by regional bedrock and wetlands that produce natural organic acids. Southwestern and eastern parts of Nova Scotia combine poor buffering, high organic acidity, and higher acid deposition, to produce extremely low surface water pH and acid neutralization capacity (ANC) values. Although sulfate deposition is decreasing, concurrent reductions in dissolved base cations, as well as the acid-base characteristics of natural organic acids, are not allowing the recovery of ANC or surface water pH. Spring-time acid pulses occur in Atlantic Canada, though these have been reduced in severity with decreases in winter acid deposition, while autumnal low pH pulses caused by organic acids are a regular occurence in Nova Scotia and must be separated from mineral acidity pulses. Geochemical modeling using both critical load and dynamic approaches, nevertheless predict improvements in the water chemistry of Nova Scotia lakes within the next 20 years. However, re-establishment of pre-acidification water chemistry in most of its lakes will require greater reductions in S emissions than are currently planned in Canada and the United States. [ABSTRACT FROM AUTHOR]

The response of twenty acid-sensitive headwater catchments in Nova Scotia to acidic deposition was investigated for the period 1850-2100 using a dynamic hydrochemical model (MAGIC: Model of Acidification of Groundwater in Catchments). To ensure robust model simulation, MAGIC was calibrated to the long-term chemical trend in annual lake observations (13-20 years). Model simulations indicated that the surface waters of all twenty catchments acidified to the 1970s but showed subsequent recovery (increases in acid neutralising capacity (ANC) and pH) as sulphate deposition decreased. However, under proposed future emissions reductions (approximately 50% of current deposition) simulated ANC and pH will not return to estimated pre-industrial levels by 2100. An ANC of 20µmolc L-1 and pH of 5.4 were defined as acceptable chemical thresholds (or critical chemical limits) for aquatic organisms in the current study. Under the proposed emissions reductions only one catchment is predicted to remain below the critical limit for ANC by 2100; three additional catchments are predicted to remain below the critical limit for pH. Dynamic models may be used to estimate target loads, i.e., the required deposition reductions to achieve recovery within a given time. Setting target loads at approximately 30% of current depositions would allow three of the four lakes to reach the chemical criteria by 2030. In contrast to the generally good prognosis for surface waters, soils lost an average of 32% of estimated initial base saturation and recovery is estimated to be very slow, averaging 23% lower than pre-acidification levels in 2100. [ABSTRACT FROM AUTHOR]

Two disturbed aquatic systems, Bowland Lake, a strongly acidic lake (pH = 4.9) in south-central Ontario, and the eutrophic Bay of Quinte at the northeastern end of Lake Ontario were selected as case histories for demonstration of an analytical protocol for defining and evaluating phytoplankton community rehabilitation targets. Bowland Lake was experimentally neutralized in 1983 to evaluate the efficacy of an application of a powdered limestone slurry for rehabilitating biological communities in the lake. The Bay of Quinte was identified by the International Joint Commission in 1985 as one of 42 'Areas of Concern' in American and Canadian waters of the Great Lakes for which a Remedial Action Plan is required to restore beneficial uses. Phosphorus loading controls were implemented in the Bay of Quinte drainage basin in late 1977 to early 1978. In both cases, pre- and post-treatment phytoplankton community structure data were used to assess the degree of phytoplankton community impairment and the response to remediation by comparing the phytoplankton communities to those from suitable reference locations. The rationale, development and application of model phytoplankton communities intended to serve as 'targets' for phytoplankton community rehabilitation are presented within a multivariate framework of community structure. It is recommended that these, or similar analytical protocols based on multivariate methods for defining community structure, be more widely applied when corrective actions are taken to rehabilitate aquatic systems. [ABSTRACT FROM AUTHOR]

Biological damage to sensitive aquatic ecosystems is among the most recognisable, deleterious effects of acidic deposition. We compiled a large spatial database of over 2000 waterbodies across southeastern Canada from various federal, provincial and academic sources. Data for zooplankton, fish, macroinvertebrate (benthos) and loon species richness and occurrence were used to construct statistical models for lakes with varying pH, dissolved organic carbon content and lake size. pH changes, as described and predicted using the Integrated Assessment Model (Lam et al., 1998; Jeffries et al., 2000), were based on the range of emission reductions set forth in the Canada/US Air Quality Agreement (AQA). The scenarios tested include 1983, 1990, 1994 and 2010 sulphate deposition levels. Biotic models were developed for five regions in southeastern Canada (Algoma, Muskoka, and Sudbury, Ontario, southcentral Québec, and Kejimkujik, Nova Scotia) using regression tree, multiple linear regression and logistic regression analyses to make predictions about recovery after emission reductions. The analyses produced different indicator species in different regions, although some species showed consistent trends across regions. Generally, the greatest predicted recovery occurred during the final phase of emission reductions between 1994 and 2010 across all taxonomic groups and regions. The Ontario regions, on average, were predicted to recover to a greater extent than either southcentral Québec or the Kejimkujik area of Nova Scotia. Our results reconfirm that pH 5.5–6.0 is an important threshold below which damage to aquatic biota will remain a major local and regional environmental problem. This damage to biodiversity across trophic levels will persist well into the future if no further reductions in sulphate deposition are implemented. [ABSTRACT FROM AUTHOR]

Between 1986 and 2001, thirty-nine lakes in southwestern New Brunswick in Atlantic Canada were surveyed for acid precipitation-related water quality changes. Most of the study lakes are located on granite bedrock and represent the most acid sensitive lakes in the province. Between 1987 and 1992, hydrogen ion deposition to the lake study area averaged 452 eq ha-1 yr-1, compared to 338 eq ha-1 yr-1 between 1993 and 2000, a 25% reduction. The lake chemistry data were evaluated by dividing the lakes into four clusters for each survey year based on their acid neutralizing capacity. Twenty percent of the lakes (cluster IV) had an average ANC of 40 μeq L-1 or greater and maintained an average pH of greater than 6 over the duration of the study period. A pH of 6 or greater is considered a healthy benchmark for maintaining biodiversity. The remaining 31 lakes (clusters I to III) had an average ANC of less than 40 μeq L-1 and maintained an average pH of less than 6. Other lake chemistry changes included a general decline in lake sulphate and colour over the duration of the survey period, followed by more recent improvements in calcium ion, pH and ANC, and notably higher but declining aluminum levels in lower ANC and pH lakes. Nitrate accounted for 37% of the acid deposition to the study area, however it was not detectable in the lakes. Although acid deposition has declined and these lakes are beginning to show signs of acid recovery, 80% of the study lakes remain acid sensitive having little buffering capacity with low calcium, pH and ANC. [ABSTRACT FROM AUTHOR]

Quantifying chemical variability in different lake types is important for the assessment of both chemical and biological responses to environmental change. For monitoring programs that emphasize a large number of lakes at the expense of frequent samples, high variability may influence how representative single samples are of the average conditions of individual lakes. Intensive temporal data from long-term research sites provide a unique opportunity to assess chemical variability in lakes with different characteristics. We compared the intra- and inter-annual variability of four acidification related variables (Gran alkalinity, pH, sulphate concentration, and total base cation concentration) in four lakes with different flushing rates and acid deposition histories. Variability was highest in lakes with high flushing rates and was not influenced by historic acid deposition in our study lakes. This has implications for the amount of effort required in monitoring programs. Lakes with high flushing rates will require more frequent sampling intervals than lakes with low flushing rates. Consideration of specific lake types should be included in the design of monitoring programs. [ABSTRACT FROM AUTHOR]

Presents a study that investigated recovery from acidification of lakes in Killarney Park, Ontario, Canada through the dynamic acidification model MAGIC. Effects of acidification in Killarney Provincial Park; Model calibration to match observed data; Assessment of recovery time for the different lakes.

Presents a study that investigated the recovery dynamics of fish populations in acid-stressed lakes near Sadbury and Killarney, Ontario, Canada. Rehabilitation experiments involving the stocking of 2 native sportfish, lake trout and smallmouth bass; Effect of the composition of fish communities in recovering lakes on lake trout reintroductions;

Presents findings in the effects of the recolonization of acid-damaged lakes in Killarney Park, Canada for 3 species of benthic invertebrates: 2 mayflies and an amphipod. Details of the synoptic survey of 119 Killarney Park lakes between 1995 and 1997; Dispersal of S. interpunctatum to all habitat patches within a lake; Time lag from estimated pH recovery to reestablishment and subsequent dispersal of mayflies.

Focuses on the results of a long-term reconstruction of the Daphnia community in Hannah Lake, Canada. Background on lake damage resulting from acidification; Overview of recovery work in the lake; Description of the zooplankter Daphnia; Screening of haplotypes by single-strand conformation polymorphism.

Presents a study that determined if zooplankton communities of lakes in Killarney Provincial Park, Ontario, Canada, recovered to a state typical of neutral lakes, once the pH rose above 6. Discussion on lakes damaged by acidification; Analysis of the changes in logged species abundances; Assessment on whether change in zooplankton communities represent recovery.

Presents results for phytoplankton communities response to acidification and recovery in Killarney lakes in Canada, sampled in 1998-2000. Analysis of community change; Species diversity and richness; Phytoplankton biomass and composition.Comparison with historical data from 8 of the Killarney lakes.

Presents a study that determined the influence of spatial and temporal scale of acidification on the resilience of epilithic assemblages during chemical recovery of Canadian boreal lakes. Effects of anthropogenic acidification of boreal lakes on several environmental variables; Indicators of recovery in acidifed lakes; Comparison of experimental and atmospheric acidification of lakes; Details of study lakes and sampling protocols.

Assesses the recovery of lakes in Southeastern Canada from the effects of acidic deposition. Trends near Smelter sources; Factors influencing chemical recovery; Predictions of biological recovery.

Increased pH in acid lakes changes the crustacean fauna from communities dominated by acid-tolerant species to communities dominated by more acid-sensitive species. Studies from Canada (Killarney) and southeastern Norway (Østfold county) have demonstrated that planktonic and littoral crustaceans can be used as indicators of such recoveries. In both places the cladocerans Alona rustica and Acantholeberis curvirostris were found in acidic lakes, whereas Alona costata and the copepod Eucyclops macrurus were found in near neutral lakes. The calanoids Diaptomus minutus in North America and Eudiaptomus gracilis in Europe, both dominate in acidic water, and may ecologically be equivalent species. Sometimes the same species occur at different pH in the two continents. Bosmina longirostris and Alonella excisa may serve as examples, but a pertinent question is whether or not they are really the same species. [ABSTRACT FROM AUTHOR]

The sublittoral chironomid fauna of 22 lakes in Killarney Park, Ontario, Canada were examined for their response to different levels of acidification. Included in the analysis were naturally acidic lakes, lakes acidified by atmospheric deposition but now recovering, and unacidified circumneutral lakes. pH in the study lakes ranged from 4.6 to 7.7. No correlation was found between species richness and pH, nor between abundance and pH. Acid neutralizing capacity (ANC), the temperature at the sampling depth, pH, and dissolved organic carbon were the variables contributing significantly in a canonical correspondence analysis of the abundance data. ANC was the most important variable in describing the chironomid community, accounting for about 9% of the variance in the species data. This study is the first step in an effort to model the changes in the chironomid community of recovering acidified lakes and the results suggest that ANC may be an important predictor variable. [ABSTRACT FROM AUTHOR]

The article focuses on a study on the influence of drought-induced acidification on the recovery of plankton in Swan Lake in Canada. Topics discussed include recovery of aquatic ecosystems from acidification in response to reductions in atmospheric emissions of sulfur dioxide in North America and Western Europe, biotic recovery and decreased water quality due to drought-induced acidification events, and response of the crustacean zooplankton to re-acidification.

To date, estimates of freshwater critical loads have been based on a single sample site within a given area, in the UK the `most sensitive' surface water in each 10 km grid square. The critical loads obtained are thus highly dependent on the sites chosen, and at a relatively coarse spatial resolution. To produce a higher resolution critical load assessment, the PEARLS (Prediction of Acidification and Recovery on a Landscape Scale) procedure has been used to estimate critical loads across a large (248 km2), partially acid-sensitive catchment in Southwest England. PEARLS utilises available soils and land-use databases, and sampled stream chemistry data, to derive characteristic runoff compositions for a set of landscape types. Mixing equations are then used to calculate runoff chemistry, and subsequently critical loads, throughout the stream network. Results show major spatial variability, with critical loads lowest in streams draining peat-moorland headwaters, and generally increasing downstream as agricultural land contributes an increasing proportion of runoff. The 5th percentile freshwater critical load for the catchment is estimated at 0.29 keq H+ ha-1 yr-1, and critical loads are exceeded for around 40% of total stream length. The PEARLS methodology provides a novel opportunity to assess the spatial variability in freshwater critical loads, and to provide estimates of exceedance at whole catchment scale. It has potential application in the assessment of surface water sensitivity to acidification across wider areas in the UK and elsewhere. [ABSTRACT FROM AUTHOR]

Summary1. The littoral microcrustacean community (Cladocera and Copepoda) was examined from 1989 to 1991 in a lake experimentally acidified to pH 4.5, and from 1992 to 1997 during the early stages of pH recovery. 2. Cladoceran abundance declined significantly from 1989 to 1991 (pH 4.5), but species richness did not change. Acantholeberis curvirostris, Simocephalus serrulatus, Latona spp. (Latona setifera, L. parviremis), and all species of chydorid Cladocera declined markedly in abundance while at pH 4.5. The abundance of cyclopoid copepods was low and Ceriodaphnia and calanoid copepods were absent. 3. Recovery of the community was subsequently monitored as pH was incrementally changed to a target pH 5.1 in 1992 and 1993, and to 5.8 in 1994–97. Species richness remained unchanged. Chydorid cladocerans remained at low abundance in 1992, and only Chydorus cf. brevilabris increased substantially from 1993 to 1996. Non-chydorid Cladocera increased in abundance in 1992, declined again in 1993, then gradually increased (mainly due to Ophryoxus gracilis) in 1994–96. All species declined in 1997 as minnows recolonized the lake. The calanoid copepod Leptodiaptomus minutus was present in low numbers in 1997. 4. The microcrustacean community in the littoral zone of Lake 302S has not yet shown consistent signs of recovery from acidification. [ABSTRACT FROM AUTHOR]

• Long-term rotations with/without nitrogen (N) and phosphorus (P) fertilization. • Multiple techniques: P-NMR, P K-edge XANES, P fractionation, phosphatase assays. • Soil pH and organic carbon were significant predictors of soil P forms. • Long-term fertilization altered P forms by changing soil chemistry. • Rotation phase altered total and organic P concentrations regardless of fertilization. Efficient phosphorus (P) management is important for crop production and environmental sustainability of cropping systems. The effects of the agricultural management practices of crop rotation and fertilization on soil P forms and cycling were investigated in plots in Swift Current, SK, Canada, under three crop rotation phases [fallow (F), wheat after fallow (WF), and wheat after wheat (WW)], with four nitrogen (N) and/or P fertilizer treatments (+N+P, -N+P, +N-P, and -N-P), using techniques including sequential fractionation, 31P nuclear magnetic resonance (P-NMR), and P K-edge X-ray absorption near-edge (P-XANES). Soil total P (TP) and organic P (P o) concentrations were significantly reduced in F and WW phases compared to WF regardless of fertilization practice. Compared to WW, WF had the highest grain yield and nutrient uptake. Fertilization with N and P significantly influenced soil total carbon (C), total N, TP, and Mehlich 3-P concentrations and acid phosphatase activities, as well as the concentration of some P pools by sequential fractionation and stable P determined by P-XANES. Stopping P fertilization significantly increased the proportions, but not concentrations, of soil P o determined by P-NMR compared to plots still receiving P fertilizers, while the concentration of total diesters increased in plots fertilized with N. Redundancy analysis showed that soil pH and organic C were the significant predictors of P forms in these soils, suggesting that long-term N and P fertilization altered soil P forms by changing soil chemical properties. [ABSTRACT FROM AUTHOR]

Explores the applications of the Menge-Sutherland (MS) model to acid-stressed lake communities in Sudbury, Ontario. Increase in species richness with pH; Variability of the importance of competition in food web structure at low pH; Effects of acidification; Zooplankton communities.

• Tree planting on degraded land has been identified as an effective carbon capture strategy. • Unclear how associated restoration treatment influence carbon sequestration. • Tree carbon pool increased with greater restoration effort. • Existing site characteristics influence carbon sequestration potential. • Land managers must balance restoration cost with carbon sequestration. Landscape carbon storage is a key component of climate change mitigation. Tree planting on degraded land has been identified as an effective carbon capture strategy, but it is unclear how various associated restoration treatments influence carbon sequestration. In this study, we measured carbon pools in jack pine (Pinus banksiana Lamb.) stands subject to different restoration treatments within severely damaged upland areas in the metal mining region of Sudbury, Ontario, Canada. Treatments included: i) soil amendment (liming, fertilizing and grass/legume seeding) followed by jack pine planting, ii) jack pine planting alone, iii) soil amendment only, and iv) untreated plots with some natural regeneration as a result of improving air quality in the region. Twenty-four years after the initial treatments, we measured the carbon storage in coarse and fine woody debris, herbs, shrubs, forest floor (LFH), mineral soil, and trees. The carbon pool in planted trees was 1.5 times higher in plots when soil amendments were applied. This increase in the tree carbon pool was the result of greater carbon sequestration per individual jack pine tree rather than changes in tree density or arrival of new species. Similarly, naturally regenerated white birch (Betula papyrifera Marshall) in the amended plots stored 1.7 times more carbon than white birch in the untreated plots. Tree planting proved essential on this landscape with natural tree regeneration rates very low even 50 years after local pollution was massively reduced. However, tree planting surprisingly did not significantly affect total carbon storage in these exposed upland sites. Total ecosystem carbon varied from 21.4 Mg ha−1 to 124.5 Mg ha−1 across all plots (mean of 67.6 ± 4.8 Mg ha−1) but no statistically significant differences were observed among the treatments. Soil organic carbon (SOC) proved to be the largest carbon pool across plots and stored on average 66% of total ecosystem carbon. However, at this early stage the restoration treatments had no influence on SOC pools on this highly degraded landscape, which still appears to be severely affected by ongoing erosion of surface soil and metal contamination. The restoration treatment also did not significantly affect the understory or downed woody debris carbon pools. This study demonstrates that the current restoration treatments used in Sudbury do influence the amount of carbon sequestrated mainly through tree restoration on this industrially degraded landscape, but long-term storage potential is still limited by poor soil conditions. [ABSTRACT FROM AUTHOR]

The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite üpwelling onto Large portions of the continental shelf, reaching depths of -.40 to 120 meters along most transect tines and all the way to the surface on one transect off northern California. Although seasonal upwetting of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area. [ABSTRACT FROM AUTHOR]

Presents observations of rainfall and lake chemistry at Swan Lake, Canada. Climate change and acidification; Exposure of lakewater to atmospheric littoral sediments containing reduced sulphur dioxide; Implications of a decrease in dissolved organic carbon concentration to ultraviolet radiation.

1. Lake 302S in the Experimental Lakes Area of Canada was acidified from pH 6.7 (1981) to 5.1 (1986). The pH was further reduced to 4.5 in 1987 and held at that level until 1991. From 1992 to 1995, the pH was allowed to increase to a target value of 5.8. 2. The response of the phytoplankton community to decreasing pH from 6.0 to 5.1 was similar to that observed in another experimentally acidified lake (223) and in other atmospherically acidified lakes. Acidification affected species diversity of both the phytoplankton and epilithon. Phytoplankton diversity was positively correlated with pH. Epilithic algal diversity was more variable and did not correlate with pH. 3. Phytoplankton biomass was enhanced by acidification as the assemblage shifted from a dominance of chrysophytes to large dinoflagellates (Gymnodinium sp. and Peridinium inconspicuum). Epilithon biomass was unaffected, but dominance shifted from filamentous cyanophytes (Lyngbya) to acidophilic diatoms (Tabellaria quadriseptata and Anomoeonis brachysira). 4. The only taxon to be similarly affected in both the phytoplankton and epilithon was the cyanobacteria, being significantly reduced below pH 5.1. During early recovery (pH 5.5–5.8), cyanobacteria increased and species present prior to acidification recolonized both habitats. 5. In the early stages of recovery, planktonic and benthic assemblages remained more similar to acidified than natural assemblages, but more profound change began at pH > 5.5. [ABSTRACT FROM AUTHOR]

The impact of simulated acid rain on soil leachate and xylem chemistry in a young Jack pine (Pinus banksiana Lamb.) stand in the boreal forest of northern Ontario was evaluated. Permanent plots (5 x 2 m) were established in 1981 which were sprayed twice monthly with simulated acid rain, adjusted to pH 5.6, 4.0, 3.5, 3.0 or 2.5 with a 2:1 molar ratio of sulphuric (H2SO4) to nitric acid (HNO3) in addition to ambient rainfall. Sprays were applied between Juneand September for 5 yr. Unsprayed plots were also monitored. The pH of soil leachate collected between 1981-1985 was reduced significantly by the acid sprays and concentrations of sulphate (SO42-), nitrate (NO3-), calcium (Ca), magnesium (Mg), aluminium (Al), manganese (Mn), and zinc (Zn) increased in the A, B and C horizons. The soil recovered rapidly from the spraytreatments, although residual effects were found in soil leachate samples collected during 1986-1987, particularly in the C horizon. Trees receiving spray acidified to pH 2.5 had higher concentrations of Ca, Mn, Cd and Rb in tree-rings formed between 1981-1985 compared to trees receiving spray acidified to pH 4.0 or to trees receiving ambientrainfall alone. Some of the changes in soil chemistry resulting fromthe application of acidic sprays are reflected in the chemistry of Jack pine tree rings and these chemical signals in tree rings may be used as indicators of soil acidification. [ABSTRACT FROM AUTHOR]