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.     

Diatom and Chrysophyte Algal Response to Long-Term PCB Contamination from a Point-Source in Northern Labrador,Canada

The long-term response of diatom and chrysophyte communities to local PCB contamination was examined in an impacted and referencelake in northern Labrador. Beginning in the late 1950s, lake Saglek-2 (SK-2) received direct inputs of the contaminant in runoff, leaving a record of rising PCB concentrations in lake sediments. An examination of sediment samples spanning the past～ 150 yr revealed chrysophyte and diatom assemblages characteristic of clear, slightly acidic, oligotrophic lakes, butsurprisingly little change in either community was observed through time. The lack of response may be explained by severalfactors. For example, elevated PCB concentrations in lake sediments may not reflect bioavailable concentrations in lakewater. Therefore, realized concentrations may be too low to exhibit detrimental effects in phytoplankton communities. Our findings do, however, have important implications for studies ofclimate change in circumpolar regions. First, we provide additional evidence that climatic change has been minimal in northern Labrador, in contrast to changes observed in other Arctic and sub-Arctic regions. Second, our findings support thenotion that recent, marked changes in species composition observed in other Arctic lakes are the result of recent climatechange and not caused by the contamination of lakes from the long-range transport of pollutants.     

Diatom Inferred Acidity History Of 32 Lakes On The Kola Peninsula,Russia

The Kola Peninsula is characterised by vast environmental contrasts. Large areas are almost in pristine condition. However, mining and associated industrial activity generate one of the largest sources of heavy metal and sulphur emissions in the world and create `technogenic wastelands' around smelters. Due to the lack of monitoring data, insufficient knowledge is available regarding the acidification history of lakes on the peninsula. In this study, palaeolimnological techniques were used to reveal the pre-industrial pH status of 32 small lakes in order to evaluate the role of human impacts on freshwater ecosystems. Diatom-inferred pH reconstructions demonstrated that for 22 (68.75%) of the lakes, the pH was below 6.5 and in eight (25%) below 6.0 during the pre-industrial period; signs of recent acidification could be detected only in seven lakes of which five are located relatively close to current pollution sources. Furthermore, no substantial changes between the pre-industrial and modern species richness and composition were observed, indicating relatively stable environmental conditions. Most of the lakes seem to have undergone long-term acidification and are mainly affected by natural acidifying factors (e.g., vegetation, bedrock, climate, sea salt). The effect of anthropogenic emissions seems to be surprisingly geographically restricted and controlled mainly by the surrounding topography and prevailing winds. However, although many lakes seem to be in relatively pristine condition, only a significant reduction in heavy metal and sulphur emissions will prevent the lakes from acidifying in the future.     

Cladoceran Response to Calcium Decline and the Subsequent Inadvertent Liming of a Softwater Canadian Lake

Lake water calcium (Ca) decline has recently been recognized as a stressor impacting softwater lake districts that have experienced long-term patterns of acid deposition and/or timber harvesting. Declining aqueous Ca levels may impact the survival of aquatic biota, particularly Ca-rich cladoceran taxa such as daphniids. Daphnia pulex are sensitive to laboratory Ca levels below 1.5?mg?l^?1; however, responses of cladoceran communities to Ca decline in natural environments require further study. Dickie Lake (Ontario, Canada) is the site of an inadvertent natural experiment, providing insight into the effects of changing aqueous Ca availability upon cladoceran communities, as the lake has a history of acidification, followed by recent (1990s) Ca additions to the watershed via applications of calcium-rich road dust suppressants. Paleolimnological analyses were used to examine changes in cladoceran community structure (with a focus upon Ca-rich daphniids) from pre-industrial times to present day. Three distinct temporal stages were apparent in Dickie Lake??s daphniid community: 1870?C1950, 1950?C1990, and 1990?Cpresent. The daphniid community of the pre-industrial assemblages was dominated by members of the Daphnia longispina species complex, but shifted in the late 1950s to more acid- and Ca-insensitive members of the D. pulex species complex. During the most recent stage, coincident with dust suppressant applications, both daphniid complexes are well represented. Observed transitions between daphniid species complexes provide further evidence of the influence of Ca availability upon cladoceran community structure, indicating the potential importance of the controlled addition of Ca to freshwater systems (i.e., liming) as a mitigation/recovery strategy as Ca declines continue.     

Diatom-based pH reconstruction studies of acid lakes in Europe and North America: A synthesis

The analysis of diatom assemblages in lake sediments is being increasingly used to reconstruct past trends in the pH of acid lakes. This paper briefly reviews the data that are now available for Europe and North America and concludes that the evidence is consistent with the acid deposition hypothesis for recent lake acidification.     

Critical Nitrogen Deposition Loads in High-elevation Lakes of the Western US Inferred from Paleolimnological Records

Critical loads of nitrogen (N) from atmospheric deposition were determined for alpine lake ecosystems in the western US using fossil diatom assemblages in lake sediment cores. Changes in diatom species over the last century were indicative of N enrichment in two areas, the eastern Sierra Nevada, starting between 1960 and 1965, and the Greater Yellowstone Ecosystem, starting in 1980. In contrast, no changes in diatom community structure were apparent in lakes of Glacier National Park. To determine critical N loads that elicited these community changes, we modeled wet nitrogen deposition rates for the period in which diatom shifts first occurred in each area using deposition data spanning from 1980 to 2007. We determined a critical load of 1.4 kg N ha^?1 year^?1 wet N deposition to elicit key nutrient enrichment effects on diatom communities in both the eastern Sierra Nevada and the Greater Yellowstone Ecosystem.     

Tracking the Limnoecological History of Lake Hiidenvesi (Southern Finland) Using the Paleolimnological Approach

We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940s, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at ~?1960–1980 CE being finally replaced by eutrophic taxa from the 1990s onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970s onward. A chironomid-based reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950s, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid- and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970s/1980s. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.     

Longitudinal patterns in bird reporting rates in a threatened ecosystem: Is change regionally consistent?

Work in many parts of the world has discussed the decline of biodiversity in regions dominated by agriculture. We report the results of a major study documenting the longitudinal profiles of birds between 1998 and 2009 within 66 patches of temperate woodland in a heavily cleared and grazed agricultural region of south-eastern Australia. Many researchers have forecast the loss of bird biota from this region and others that also were formerly dominated by temperate woodland.We had sufficient high quality data to analyse the longitudinal profiles of reporting rates for 76 of the 116 individual bird species recorded in our 12-year study. Unexpectedly, only four of the 76 species analysed (5.6%) exhibited a significant negative linear decrease in reporting rate. More surprisingly, 32 (42.1%) exhibited a significant positive linear increase in reporting rate, including several taxa of conservation concern. These increases occurred despite a series of below-average rainfall years. Reporting rates were too low to formally model long-term trends in some other bird species widely considered to be of conservation concern such as the Diamond Firetail (Stagonopleura guttata) and Speckled Warbler (Chthonicola sagittata).Many authors have used functional (and other) groups to forecast bird species likely to be lost from Australia’s temperate woodlands. However, we found no clear links between life history attributes and long-term trend patterns of species.Our findings contrast with recent findings from other temperate woodland-dominated regions in eastern Australia where losses in bird populations have been documented. However, they parallel other investigations such as in central New South Wales. These similarities among, and differences between, studies suggest regional differences in temporal patterns in bird population dynamics. Many of the observed changes in reporting rates were positive and they provide hope that forecast future losses of a large proportion of existing temperate woodland bird assemblages in south-eastern Australia may not be realised uniformly in all regions.     

Dependence of bryophyte species on young, mature and old growth wet eucalypt forest

Maintenance of old growth forest has been argued to be important for the future of many bryophyte species, but there has been no empirical test of this proposition. Bryophytes constitute much of the plant biodiversity in Tasmanian tall open-forests dominated by Eucalyptus regnans and Eucalyptus obliqua. These forests have a low level of protection in their old growth stage. We ask whether if there is a concentration of bryophyte species in particular forest age classes and assess its significance for biological conservation. The bryophyte species at 99 forest sites were recorded and related to young, mature and old growth age classes using ANOVA. Only two bryophyte taxa were confined, with statistical confidence, to one of these classes. Succession in bryophyte assemblages takes the relay floristics form, with a few highly frequent species in the young forest, most of which do not persist in later stages, a large number of species establishing in middle-aged forests, some dying out with their short-lived hosts by the time of the old growth forest stage, and liverworts becoming more prominent with age. Species concentrated in the old growth phase of these eucalypt forests have all been recorded from secure reserves in this and other vegetation types. If present patterns of land use continue, and no extensive wild fires occur in the reserved old growth forest, almost all bryophyte species of E. regnans and E. obliqua mixed forest are likely to survive. This may not be the case in other regions of the world, where reservation may be poorer than in Tasmania.     

Acidification of Nova Scotia lakes I: Response of diatom assemblages in the Halifax area

A comparison is made of diatom remains in surficial lake sediments collected in 1971 and 1980. Changes of similar magnitude towards more acid tolerant assemblages are observed in four lakes studied in detail despite widely differing aquatic environments. No attempt is made to reconstruct past chemistry, the significant point being that at the most fundamental level, local lacustrine biological systems are being stressed to the point of alteration. The pattern of that alteration with emphasis on ‘simplification’ is discussed with the suggestion that rates of acidification may be as important as net changes.     

Stimulation of Phototrophic Pelagic and Benthic Metabolism Close to Sediments in Acidic Mining Lakes

Young, very acidic mining lakes have ecological potentials that are quite different from those of natural lakes: Whereas their primary production and hence their algal biomass is mostly limited by carbon and phosphate, their species composition is largely controlled by the extreme chemical composition of their water (low pH, high metal and sulfate concentrations). As a consequence, their phytoplankton biomass corresponds to the oligo- to mesotrophic level and the dominant taxa of plankton belong to Chrysophyceae, Chlorophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae whereas the benthic communities are dominated by euglenoids and diatoms. In some lakes, all these taxa are found permanently or sporadically in considerably high quantities either in their hypolimnion or at the sediment surface, indicating a remarkable ecological potential for primary production of these environments. We therefore hypothesize that input of inorganic carbon and phosphorus by groundwater or the replenishment of these nutrients by microbial processes at the sediment/water interface are the main stimulants of primary production in mining lakes.     

Surface-water Acidification and Reproducibility of Sediment Cores from Kejimkujik Lake, Nova Scotia, Canada

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.     

Relationship Between Landscape Characteristics,History, and Lakewater Acidification in the Adirondack Mountains,New York

Interactions between acidic deposition and watershed characteristics were evaluated for a group of lakes in the Adirondack Mountains, New York. Landscape characteristics were compiled and examined relative to paleolimnological inferences of historical acidification. Results of estimates of acidification using the Model of Acidification of Groundwater in Catchments (MAGIC) and paleolimnological analysis were compared to physical, biological, and landscape change data, including such factors as watershed disturbance, logging, fire, and windthrow, to evaluate if inclusion of additional processes could improve model estimates. Results of bivariate and multivariate analysis confirmed that lakes that have experienced historical acidification tend to be those that receive relatively high amounts of precipitation and have short hydraulic residence times. These variables explained 58% of the diatom-inferred acidification. A combined model of long-term precipitation amount, hydraulic residence time, and recent blowdown accounted for 71% of the historic acidification in the Adirondacks. Lakes that have increased in pH since pre-industrial times tend to be those subject to substantial human disturbance and those that burned during major fires recorded after 1900. The magnitude of the discrepancy between MAGIC model and diatom-inferred hindcasts of acidification was not significantly correlated with any of the landscape change variables, suggesting that additional modifications to the MAGIC model to take into account landscape change are not likely to appreciably improve model performance.     

Accumulation of cadmium and other metals in organs of plants growing around metal smelters in Japan

Abstract

It is well known that some plants can adapt to a high concentration of metals that would be lethal to other plant species and also accumulate toxic metals in their body up to a very high level (Peterson 1983). Athyrium yokoscense communities are often observed on highly polluted soils with heavy metals originating from mining or smelting facilities. A. yokoscense and some species of plants which can grow vigorously on highly polluted soils have attracted the attention of miners and investigators as indicator plants for mining areas (Honjo 1990; Nishizono et al. 1987).     

Complexity in the Biological Recovery of Tatra Mountain Lakes from Acidification

Alpine lakes of the Tatra Mountains were severely affected by acidification, with minimum recorded values of pH ～4.5 in the mid-1980s. Since the 1990s, a dramatic decrease in the deposition of acidifying compounds has led to a considerable reversal in lake water chemistry (to pH～5 in the most severely affected lakes). We studied changes of planktonic crustaceans and chironomid occurrence during the acidification period and the following period of recovery from acidification in three categories of 50 Tatra Mountain lakes (non-acidified, acidified and strongly acidified, according to their status at the beginning of the 1980s). In acidified and strongly acidified lakes, the planktonic crustaceans completely disappeared already by about 1976 except for a few individuals of ubiquitous species in littoral zone due to acidification-induced oligotrophication. In strongly acidified lakes, the original planktonic crustaceans disappeared and littoral species became more abundant already before 1976 due to acidification-induced eutrophication and aluminium toxicity. These processes were quickly reversed following the increase in lake water pH. Extinct species started to return to several acidified and strongly acidified lakes already in the beginning of 1990s. The process of recovery was delayed in many other lakes of the same categories, however, or it did not even start before 2008 despite the improved water chemistry and feeding resources (concentration of chlorophyll-a). Compared to planktonic crustaceans, the reaction of chironomids to acidification and recent recovery has been less pronounced. An analysis of sediment records showed that fluctuations in relative abundance of the dominant chironomid taxa and a decrease of their density occurred. In spite of the fact that chironomid fauna exhibited clear signs of recovery in the last two decades, the recovered assemblage does not exactly reflect the pre-acidification status in the lake. The occurrence and higher proportion of more thermophilous chironomid species in some alpine lakes of all categories could be correlated with increasing air temperature. The considerable effect of climatic factors may thus prevent the full re-establishment of the original status even when the acidification stress completely ceases. The delayed return of planktonic crustaceans to some recovered lakes could be a consequence of the short water residence time of these lakes. In addition, a shortening of the water residence time in recent decades, probably related to recent climate change, in interaction with the ecology of planktonic crustaceans, may possibly be causing further delays in their return.     

Conserving organisms over large regions requires multi-taxa indicators: One taxon’s diversity-vacant area is another taxon’s diversity zone

There is an increasing use of indicator taxa to predict spatial patterns in other taxa, yet it is unclear how well species from one taxonomic group may serve as indicators of species richness in other groups with different ecological needs. We analysed spatial patterns of diversity in several arthropod taxa from the Turkish fauna (Scorpiones, Chilopoda, Coleoptera Cicindelidae, Hydrophilidae (gen. Laccobius), Nitidulidae, Tenebrionidae Pimeliini, Chrysomelidae Cryptocephalinae, and Lepidoptera Hesperioidea and Papilionoidea) to test whether there are multi-group hotspots or whether different groups have different areas of maximum diversification. We used three metrics of diversity: species richness, residuals from the species–area relationship, and species/area ratios. In each group, the three metrics were significantly positively correlated. However, the hotspots identified using one metric show small agreement with those identified by other metrics. Although patterns of cross-taxon diversity were significantly and positively correlated for all metrics, hotspots of different groups show little overlap. Moreover, proportions of non-target species captured by hotspots of a target taxon were usually moderate. On the other hand, we found that hotspots of certain groups tend to be concentrated in particular regions, and some groups were good surrogates for others. The Mediterranean and Central and Eastern Anatolian ecogeographic regions included hotspots of species richness for most taxa. Using the species/area ratios, all groups had at least one hotspot in the Marmara and Eastern Black Sea regions, and most groups also in the Mediterranean and Eastern Anatolian regions. Hotspots identified using the residuals from the species–area relationship are concentrated mostly in the Eastern and Central Anatolian regions. These results are explained with reference to the historical biogeography of the study area, the ecological needs of the different taxa and compared with the distribution of National Parks. For an effective conservation approach, we advocate the use of subsets of species as surrogates for all species, provided that selected subsets are representative of animals with different ecological needs and biogeographical histories.     

Effects of introduced fish on macroinvertebrate communities in historically fishless headwater and kettle lakes

Widespread fish introductions have led to a worldwide decline in the number of fishless lakes and their associated communities. Studies assessing effects of fish stocking on native communities in historically fishless lakes have been limited to high-elevation headwater lakes stocked with non-native trout. Little is known about the effect of fish stocking in historically fishless and hydrologically isolated lowland kettle lakes. We compared the effects of introduced fish on macroinvertebrate communities in kettle lakes stocked with centrarchids, salmonids, and cyprinids, and headwater lakes stocked with brook trout (Salvelinus fontinalis) in Maine, USA. Fish had significant effects on macroinvertebrate community structure in both lake types, with reduced species richness and abundances of taxa characteristic of fishless lakes. The effects of introduced fish were more pronounced in headwater lakes despite a less diverse fish assemblage than in kettle lakes. We attribute this to abundant submerged vegetation providing refuge from fish predation and reduced stocking frequency in kettle lakes. We assessed effects of stocking duration on macroinvertebrates in a subset of headwater lakes with known dates of trout introduction. Species richness and abundance of most taxa declined within 3 years following trout introduction; however, richness and abundance were least in lakes with long stocking histories (?40 years). Macroinvertebrates previously identified as fishless bioindicators were absent from all stocked lakes, indicating that trout rapidly eliminate these sensitive taxa. Conservation of this historically undervalued ecosystem requires protecting remaining fishless lakes and recovering those that have been stocked.     

Sulphate in Sudbury, Ontario, Canada, Lakes: Recent Trends and Status

Sulphur emissions from the Sudbury, Ontario, metal smelting industry have affected thousands of lakes in Ontario, Canada. Reductions in these emissions during the 1970's resulted in reduced lakewater SO₄ concentrations and other water quality changes in the 1970's and 1980's. Further declines in lakewater SO₄ concentrations have accompanied additional recent S emission reductions achieved by 1994. Recent (1997) SO₄ concentrations are still related to distance from the Sudbury smelters. A strong inverse relationship with distance is evident to about 45 km, and is most pronounced in lakes within about 20 km. In lakes beyond 45 km, dissolved organic carbon (DOC), which was correlated with hydrological response time and total phosphorus concentrations, was the best correlate with recent SO₄ concentrations, indicating that some slowly-flushing, oligotrophic lakes still exhibit a "Sudbury" effect. Most lakes beyond 45 km, however, showed SO₄ declines and recent SO₄ concentrations comparable to lakes around Dorset, ～200 km from Sudbury, suggesting that these lakes are now most affected by the long-range atmospheric transport of S.     

Diatoms as indicators of the rate of lake acidification

Autecological studies of diatoms as pH indicators have opened the way to estimating a lake's past pH on the basis of its diatom species composition and relative abundance. Estimating the rate of lake acidification from its sediment subfossil diatoms is possible when these subfossils can be identified and accurately enumerated in the surface sediments of 20 to 30 lakes. Once this is done the diatoms down the length of the sediment core of one or more of these lakes can be enumerated and the pH inferred at each depth. This technique holds considerable promise in assessing the temporal impact of acid precipitation for acid-sensitive lakes. When loga values were regressed against observed pH for 28 lakes located north of Lake Superior, a significant (P < 0.01) correlation (r = 0.89) resulted. Downcore diatom stratigraphy for one of these lakes indicated that its pH had dropped from 6.2 to 5.2 over the last 20 yr while a second lake had dropped from a pH of 7.1 to 5.2 over the last 30 yr.     

Collembola diversity in the critically endangered Cape Flats Sand Fynbos and adjacent pine plantations

The replacement of indigenous vegetation by commercial alien plantations can strongly affect invertebrate species richness and composition. This has been demonstrated for some invertebrate taxa in the Fynbos vegetation of the Western Cape, but the response of litter-dwelling Collembola has not been documented. Here we compared the richness and abundance of litter-dwelling Collembola assemblages in Pinus radiata plantations and in adjacent rehabilitated Cape Flats Sand Fynbos (CFSF) in the Tokai Forest Reserve, Western Cape, South Africa. A total of 48 Collembola morphospecies was identified, of which 14 species were recorded exclusively from the pine plantations, and six exclusively from the CFSF. Abundance and morphospecies richness was higher in the pine plantations than in the CFSF, with 34 morphospecies found in the CFSF, and 42 morphospecies in the pine plantations. Fourteen species were likely invasive taxa, of which eight were found in CFSF, and 13 in the pine plantations. Multivariate analyses indicated significant differences in the assemblages of the two habitat types based on abundance, but using presence–absence data only, no difference was found. Significant relationships were found between springtail richness and abundance and site humidity, which differed between the CFSF (drier) and pine plantation (moister), likely accounting for the differences in richness and abundance among habitat types.