Global Patterns of Metal and Other Element Enrichment in Bog and Fen Peatlands.

Peatlands are found on all continents, covering 3% of the global land area. However, the spatial extent and causes of metal enrichment in peatlands is understudied and no attempt has been made to evaluate global patterns of metal enrichment in bog and fen peatlands, despite that certain metals and rare earth elements (REE) arise from anthropogenic sources. We analyzed 368 peat cores sampled in 16 countries across five continents and measured metal and other element concentrations at three depths down to 70 cm as well as estimated cumulative atmospheric S deposition (1850-2009) for each site. Sites were assigned to one of three distinct broadly recognized peatland categories (bog, poor fen, and intermediate-to-moderately rich fen) that varied primarily along a pH gradient. Metal concentrations differed among peatland types, with intermediate-to-moderately rich fens demonstrating the highest concentrations of most metals. Median enrichment factors (EFs; a metric comparing natural and anthropogenic metal deposition) for individual metals were similar among bogs and fens (all groups), with metals likely to be influenced by anthropogenic sources (As, Cd, Co, Cu, Hg, Pb, and Sb) demonstrating median enrichment factors (EFs) > 1.5. Additionally, mean EFs were substantially higher than median values, and the positive correlation (< 0.40) with estimated cumulative atmospheric S deposition, confirmed some level of anthropogenic influence of all pollutant metals except for Hg that was unrelated to S deposition. Contrary to expectations, high EFs were not restricted to pollutant metals, with Mn, K and Rb all exhibiting elevated median EFs that were in the same range as pollutant metals likely due to peatland biogeochemical processes leading to enrichment of these nutrients in surface soil horizons. The global patterns of metal enrichment in bogs and fens identified in this study underscore the importance of these peatlands as environmental archives of metal deposition, but also illustrates that biogeochemical processes can enrich metals in surface peat and EFs alone do not necessarily indicate atmospheric contamination.

Recovery of Smelter-Impacted Peat and Sphagnum Moss: a Microbial Perspective.

Peatlands store approximately one-half of terrestrial soil carbon and one-tenth of non-glacial freshwater. Some of these important ecosystems are located near heavy metal emitting smelters. To improve the understanding of smelter impacts and potential recovery after initial pollution controls in the 1970s (roughly 50 years of potential recovery), we sampled peatlands along a distance gradient of 134 km from a smelter in Sudbury, Ontario, Canada, an area with over a century of nickel (Ni) and copper (Cu) mining activity. This work is aimed at evaluating potential shifts in bacterial and archaeal community structures in Sphagnum moss and its underlying peat within smelter-impacted poor fens. In peat, total Ni and Cu concentrations were higher (0.062-0.067 and 0.110-0.208 mg/g, respectively) at sites close to the smelter and exponentially dropped with distance from the smelter. This exponential decrease in Ni concentrations was also observed in Sphagnum. 16S rDNA amplicon sequencing showed that peat and Sphagnum moss host distinct microbiomes with peat accommodating a more diverse community structure. The microbiomes of Sphagnum were dominated by Proteobacteria (62.5%), followed by Acidobacteria (11.9%), with no observable trends with distance from the smelter. Dominance of Acidobacteria (32.4%) and Proteobacteria (29.6%) in peat was reported across all sites. No drift in taxonomy was seen across the distance gradient or from the reference sites, suggesting a potential microbiome recovery toward that of the reference peatlands microbiomes after decades of pollution controls. These results advance the understanding of peat and Sphagnum moss microbiomes, as well as depict the sensitivities and the resilience of peatland ecosystems.

Native plants facilitate vegetation succession on amended and unamended mine tailings.

Facilitating the establishment of native pioneer plant species on mine tailings with inherent metal and/or acid tolerance is important to speed up natural succession at minimal cost, especially in remote areas where phytoremediation can be labor intensive. We investigated vegetation community dynamics after ∼48 years of succession along two legacy Ni-Cu mine tailings and waste rock deposits in the Sudbury Basin, Ontario, Canada with and without various site amendments (i.e. liming and fertilization) and planting. Metal/acid tolerant pioneer plants (Betula papyrifera, Populus tremuloides, Pohlia nutans) appeared to facilitate the establishment of less tolerant species. Conifers and nitrogen-fixers less tolerant to site conditions were planted at the fully amended (limed, fertilized, planted) mine tailings site in the 1970s, but conifers were not propagating at the site or facilitating understory succession. The planted nitrogen-fixing leguminous species Lotus corniculatus was, however, associated with increased diversity. These findings have implications for long-term reclamation strategies in acidic mine waste deposits utilizing native species, as primary colonizing tree species are only recently emerging as candidates for phytoremediation. Novelty statement The potential for native species to act as facilitators for vegetation colonization has rarely been investigated on tailings, despite wide use in remediation of less toxic sites. This study provides a retrospective of over 40 years of plant growth following initial treatment of toxic tailings. We observed that regardless of tailings geochemical conditions, acid/metal tolerant pioneer plants were facilitating ecological succession on acidic Ni-Cu mine tailings sites.

Dry conditions disrupt terrestrial-aquatic linkages in northern catchments.

Aquatic ecosystems depend on terrestrial organic matter (tOM) to regulate many functions, such as food web production and water quality, but an increasing frequency and intensity of drought across northern ecosystems is threatening to disrupt this important connection. Dry conditions reduce tOM export and can also oxidize wetland soils and release stored contaminants into stream flow after rainfall. Here, we test whether these disruptions to terrestrial-aquatic linkages occur during mild summer drought and whether this affects biota across 43 littoral zone sites in 11 lakes. We use copper (Cu) and nickel (Ni) as representative contaminants, and measure abundances of Hyalella azteca, a widespread indicator of ecosystem condition and food web production. We found that tOM concentrations were reduced but correlations with organic soils (wetlands and riparian forests) persisted during mild drought and were sufficient to suppress labile Cu concentrations. Wetlands, however, also became a source of labile Ni to littoral zones, which was linked to reduced abundances of the amphipod H. azteca, on average by up to 70 times across the range of observed Ni concentrations. This reveals a duality in the functional linkage of organic soils to aquatic ecosystems whereby they can help buffer the effects of hydrologic disconnection between catchments and lakes but at the cost of biogeochemical changes that release stored contaminants. As evidence of the toxicity of trace contaminant concentrations and their global dispersion grows, sustaining links among forests, organic soils and aquatic ecosystems in a changing climate will become increasingly important.

Acid deposition in the Athabasca Oil Sands Region: a policy perspective.

Industrial emissions of sulphur (S) and nitrogen (N) to the atmosphere associated with the oil sands industry in north-eastern Alberta are of interest as they represent the largest localized source in Canada (with potential for future growth) and the region features acid-sensitive upland terrain. Existing emission management policy for the Regional Municipality of Wood Buffalo, where the industry is located, is based on a time-to-effect approach that relies on dynamic model simulations of temporal changes in chemistry and features highly protective chemical criteria. In practice, the policy is difficult to implement and it is unlikely that a scientifically defensible estimate of acidification risk can be put forward due to the limitations primarily associated with issues of scale, chemical endpoint designation (selection of chemical limit for ecosystem protection from acidification) and data availability. A more implementable approach would use a steady-state critical load (CL) assessment approach to identify at-risk areas. The CL assessment would consider areas of elevated acid deposition associated with oil sands emissions rather than targeted political jurisdictions. Dynamic models should only be (strategically) used where acidification risk is identified via CL analysis, in order to characterize the potential for acidification-induced changes that can be detrimental to sensitive biota within the lifespan of the industry.

Critical loads for alkalization in terrestrial ecosystems.

Critical loads are a risk assessment approach that has supported large decreases in atmospheric acidic deposition globally. In Canada, SOx emissions fell by approximately 70 % between 1990 and 2021, whereas total particulate matter (TPM) emissions increased by about 40 %, mostly after 2010. Base cations are a major component of TPM, and critical load models consider base cation deposition as beneficial to ecosystems insomuch as it reduces the risk of acidification. However, close to point sources, high levels of alkaline dust deposition have altered soil chemistry and caused an undesirable shift in ecosystem state; something that critical loads are designed to prevent. In this study, the simple mass balance model (SMB) was modified with the objective of preventing base cation accumulation in soil above an acceptable threshold. The concept was applied to a forested site close to large emission sources of sulphur, nitrogen, and base cations in the Oil Sands region of Alberta, Canada. At this site, base cation leaching measured at 25 cm was approximately three times higher than estimated background leaching and exceeded combined SO4 + NO3 leaching. The critical load for alkalization was exceeded under each scenario considered in this study, although the exceedance was marginal if all N in current deposition was assumed to leach from soil. While this framework can easily be applied to regional and national critical load efforts, the main uncertainties of the proposed approach include base cation deposition estimates, assumptions regarding the behavior of N in soil, the selection of an appropriate Alkle(crit) and the long-term immobilization of deposited base cations in soil.

Interactive effects of precipitation and above canopy nitrogen deposition on understorey vascular plants in a jack pine (Pinus banksiana) forest in northern Alberta, Canada.

Elevated nitrogen (N) deposition in the bituminous sands region of northern Alberta, Canada is localized but expected to increase over time. Here we seek to determine the effects of above canopy N deposition on understorey vascular plants in a jack pine (Pinus banksiana) stand in a five-year experimental study. Aqueous N (ammonium nitrate) was applied four times annually (May through October) via helicopter above the canopy between 2011 and 2015 across a narrow but environmentally relevant N deposition gradient (0, 5, 10, 15, 20 and 25 kg N ha-1 yr-1). Changes in vascular plant species richness, diversity and total vascular cover were best explained by throughfall water flux, but the positive responses to precipitation decreased with increasing N application. Arctostaphylos uva-ursi and Maianthemum canadense showed positive cover increases in wet years; however, the positive cover expansion at ≥5 kg N ha-1 yr-1 treatments was suppressed relative to controls. Total cover expansion was muted in low precipitation years in treatments ≥10 kg N ha-1 yr-1. In contrast, Vaccinium vitis-idaea cover changes ≥10 kg N ha-1 yr-1 were consistently negative. There were no differences in soil net N mineralization rates, plant foliar N or NO3- leaching among treatments. We conjecture the extensive moss/lichen layer of the forest floor that accumulates most of incoming N in throughfall allows them to outcompete vascular plants for water during higher precipitation years, effectively reducing vascular cover expansion relative to controls. This work suggests the response of vascular plants in xeric jack pine ecosystems may interact with climate and these interactions should be considered in risk assessment studies.

The impact of severe pollution from smelter emissions on carbon and metal accumulation in peatlands in Ontario, Canada.

Peatlands are unique habitats that function as a carbon (C) sink and an archive of atmospheric metal deposition. Sphagnum mosses are key components of peatlands but can be adversely impacted by air pollution potentially affecting rates of C and metal accumulation in peat. In this study we evaluate how the loss of Sphagnum in peatlands close to a copper (Cu) and nickel (Ni) smelter in Sudbury, Ontario affected C accumulation and metal profiles. The depth of accumulated peat formed during the 100+ year period of smelter activities also increased with distance from the smelter. Concurrently, peat bulk density decreased with distance from the smelter, which resulted in relatively similar average rates of apparent C accumulation (32-46 g/m2/yr). These rates are within the range of published values despite the historically high pollution loadings. Surface peat close to the smelters was greatly enriched in Cu and Ni, and Cu profiles in dated peat cores generally coincide with known pollution histories much better than Ni that increased well before the beginning of smelter activities likely a result of post-deposition mobility in peat cores.

Soil carbon pools and fluxes following the regreening of a mining and smelting degraded landscape.

Increasing forest cover by regreening mining and smelting degraded landscapes provides an opportunity for global carbon (C) sequestration, however, the reported effects of regreening on soil C processes are mixed. One of the world's largest regreening programs is in the City of Greater Sudbury, Canada and has been ongoing since 1978. Prior to regreening, soils in the City of Greater Sudbury area were highly eroded, acidic, rich in metals, and poor in nutrients. This study used a chronosequence approach to investigate how forest soil C pools and fluxes have changed with stand age in highly "eroded" sites with minimal soil cover (n = 6) and "stable" sites covered by soil (n = 6). Encouragingly, the relationship between stand age and soil C processes (litterfall, litter decomposition, soil respiration, fine root growth) at both stable and eroded sites were comparable to observations reported for jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Ait.) plantations that have not been subject to over a century of industrial impacts. There was a strong "home-field advantage" for local decomposers, where litter decomposition rates were higher using a site-specific pine litter compared with a common pine litter. Higher soil respiration at eroded sites was linked to higher soil temperature, likely because of a more open tree canopy. Forest floor C pools increased with stand age while mineral soil C and aggregate C concentrations decreased with stand age. This loss of soil C is small relative to the substantial increases in aboveground tree and forest floor C pools, leading to a sizeable increase in total ecosystem C pools following regreening.

How arsenic contamination influences downslope wetland plant and microbial community structure and function.

Mine tailings are prevalent worldwide and can adversely impact adjacent ecosystems, including wetlands. This study investigated the impact of gold (Au) mine tailings contamination on peatland soil and pore water geochemistry, vegetation and microbial communities, and microbial carbon (C) cycling. Maximum arsenic (As) concentrations in peat and pore water reached 20,137 mg kg-1 and 16,730 µg L-1, respectively, but decreased by two orders of magnitude along a 128 m gradient extending from the tailings into the wetland. Carbon and other macronutrient (N, P, K) concentrations in peat and pore water significantly increased with distance from contamination. Relative percent cover and species richness of vascular and non-vascular plants significantly increased with distance into the wetland, with higher non-vascular richness being found at intermediate distances before transitioning to a vascular plant dominated community. Bacterial and archaeal community composition exhibited a decreased proportion of members of the phylum Acidobacteria (notably of the order Acidobacteriales) and increased diversity and richness of methanogens across a larger range of orders farther from the tailings source, an indication of microbial C-cycling potential. Consistent with changes in microbial communities, in vitro microbial CH4 production potential significantly increased with distance from the contaminant source. This study demonstrates both the profound negative impact that metalliferous tailings contamination can have on above and belowground communities in peatlands, and the value of wetland preservation and restoration.

Liming legacy effects associated with the world's largest soil liming and regreening program in Sudbury, Ontario, Canada.

Limestone is a common amendment used to counteract soil acidity and metal pollution. Understanding the legacy effects of a one-time soil limestone application and subsequent afforestation is needed to evaluate the long-term success of remediation efforts. In this study, soil and tree chemistry were measured across 15 limed sites that were treated and planted 14 to 37 years ago in Sudbury, Ontario, along with two untreated sites. Soil pH and exchangeable base cation (calcium (Ca) and magnesium (Mg)) concentrations were generally elevated especially in surface organic [FH] horizons up to 37-years post limestone treatment. High site-to-site variation however, obscured clear patterns over time and base cation mass budgets were generally unable to account for the mass of added Ca and Mg. Metal partitioning (Kd) in soil was most influenced by soil pH rather than organic matter (OM) showing that metal availability increases as liming effects fade. This study shows that the legacy effects of soil liming can persist for several decades and are most apparent in the forest floor (FH), but legacy effects are quite modest, and it is likely that a considerable amount of limestone has been lost through erosion.

Variation in carbon and nitrogen concentrations among peatland categories at the global scale.

Peatlands account for 15 to 30% of the world's soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10-20 cm layer, were 440 ± 85.1 g kg-1 and 13.9 ± 7.4 g kg-1, with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446-532 g kg-1) and lowest in intermediate and extremely rich fens (375-414 g kg-1). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks.

Beyond the usual suspects: methanogenic communities in eastern North American peatlands are also influenced by nickel and copper concentrations.

Peatlands both accumulate carbon and release methane, but their broad range in environmental conditions means that the diversity of microorganisms responsible for carbon cycling is still uncertain. Here, we describe a community analysis of methanogenic archaea responsible for methane production in 17 peatlands from 36 to 53 N latitude across the eastern half of North America, including three metal-contaminated sites. Methanogenic community structure was analysed through Illumina amplicon sequencing of the mcrA gene. Whether metal-contaminated sites were included or not, metal concentrations in peat were a primary driver of methanogenic community composition, particularly nickel, a trace element required in the F430 cofactor in methyl-coenzyme M reductase that is also toxic at high concentrations. Copper was also a strong predictor, likely due to inhibition at toxic levels and/or to cooccurrence with nickel, since copper enzymes are not known to be present in anaerobic archaea. The methanogenic groups Methanocellales and Methanosarcinales were prevalent in peatlands with low nickel concentrations, while Methanomicrobiales and Methanomassiliicoccales were abundant in peatlands with higher nickel concentrations. Results suggest that peat-associated trace metals are predictors of methanogenic communities in peatlands.

Predicting acidification recovery at the Hubbard Brook Experimental Forest, New Hampshire: evaluation of four models.

The performance and prediction uncertainty (owing to parameter and structural uncertainties) of four dynamic watershed acidification models (MAGIC, PnET-BGC, SAFE, and VSD) were assessed by systematically applying them to data from the Hubbard Brook Experimental Forest (HBEF), New Hampshire, where long-term records of precipitation and stream chemistry were available. In order to facilitate systematic evaluation, Monte Carlo simulation was used to randomly generate common model input data sets (n = 10,000) from parameter distributions; input data were subsequently translated among models to retain consistency. The model simulations were objectively calibrated against observed data (streamwater: 1963-2004, soil: 1983). The ensemble of calibrated models was used to assess future response of soil and stream chemistry to reduced sulfur deposition at the HBEF. Although both hindcast (1850-1962) and forecast (2005-2100) predictions were qualitatively similar across the four models, the temporal pattern of key indicators of acidification recovery (stream acid neutralizing capacity and soil base saturation) differed substantially. The range in predictions resulted from differences in model structure and their associated posterior parameter distributions. These differences can be accommodated by employing multiple models (ensemble analysis) but have implications for individual model applications.

An assessment of the relationship between potential chemical indices of nitrogen saturation and nitrogen deposition in hardwood forests in southern Ontario.

Southern Ontario receives the highest levels of atmospheric nitrogen (N) deposition in Canada and there are concerns that forests in the region may be approaching a state of 'N saturation'. In order to evaluate whether potential chemical indices provide evidence of N saturation, 23 hardwood plots were sampled along a modeled N-deposition gradient ranging from 9.3 to 12.8 kg/ha/year. All plots were dominated by sugar maple (Acer saccharum Marsh.) and foliar N and foliar delta(15)N were positively correlated with modeled N deposition. However, forest floor N content and the C:N ratio were unrelated to N deposition, but were instead related to soil pH and annual temperature; lower C:N ratios and higher N content in the forest floor were found at the most acidic sites in the cooler, northern part of the study region despite lower N deposition. Likewise, delta(15)N values in surface mineral soil and the (15)N enrichment factor of foliage (delta(15)N foliage - delta(15)N soil) are correlated to soil pH and temperature and not N deposition. Further, potential N mineralization, ammonification, and nitrification in Ontario maple stands were highest in the northern part of the region with the lowest modeled N deposition. Nitrogen cycling in soil appears to be primarily influenced by the N status of the forest floor and other soil properties rather than N deposition, indicating that chemical indices in soil in these hardwood plots may not provide an early indicator of N saturation.

Edaphic factors influencing vegetation colonization and encroachment on arsenical gold mine tailings near Sudbury, Ontario.

Mine tailings are found worldwide and can have significant impacts on ecosystem and human health. In this study, natural vegetation patterns on arsenical (As) gold (Au) mine tailings located in Sudbury, Ontario were assessed using transects located at the edge of the tailings and on the tailings. Vegetation communities were significantly different between the edge and open tailings areas of the site. Arsenic concentrations in both areas were extremely variable (from 285-17,567 mg/kg) but were not significantly correlated with vegetation diversity at the site. Nutrients (carbon (C), phosphorus (P)) and organic matter concentrations were associated with higher diversity and with the presence of climax vegetation on the tailings, but there were no significant relationships between tailings chemistry and vegetation indices on the edge. Encroachment onto the tailings from the edge occurred in conventional succession patterns, with a clear gradient from grasses (Agrostis gigantea) to trees such as Picea glauca. On the tailings, a nucleation pattern was visible, distinct from conventional succession. Trees and shrubs such as Betula papyrifera and Diervilla lonicera were associated with higher diversity and higher nutrient concentrations in the underlying tailings, whereas grasses such as A. gigantea were not. We concluded that at all areas of the site, vegetation - particularly trees - was facilitating amelioration of the underlying tailings. Despite high concentrations of As, nutrients appeared to have a greater influence than metals on vegetation diversity.

Decreased atmospheric nitrogen deposition in eastern North America: Predicted responses of forest ecosystems.

Historical increases in emissions and atmospheric deposition of oxidized and reduced nitrogen (N) provided the impetus for extensive, global-scale research investigating the effects of excess N in terrestrial and aquatic ecosystems, with several regions within the Eastern Deciduous Forest of the United States found to be susceptible to negative effects of excess N. The Clean Air Act and associated rules have led to decreases in emissions and deposition of oxidized N, especially in eastern U.S., representing a research challenge and opportunity for ecosystem ecologists and biogeochemists. The purpose of this paper is to predict changes in the structure and function of North American forest ecosystems in a future of decreased N deposition. Hysteresis is a property of a system wherein output is not a strict function of corresponding input, incorporating lag, delay, or history dependence, particularly when the response to decreasing input is different from the response to increasing input. We suggest a conceptual hysteretic model predicting varying lag times in recovery of soil acidification, plant biodiversity, soil microbial communities, forest carbon (C) and N cycling, and surface water chemistry toward pre-N impact conditions. Nearly all of these can potentially respond strongly to reductions in N deposition. Most responses are expected to show some degree of hysteresis, with the greatest delays in response occurring in processes most tightly linked to "slow pools" of N in wood and soil organic matter. Because experimental studies of declines in N loads in forests of North America are lacking and because of the expected hysteresis, it is difficult to generalize from experimental results to patterns expected from declining N deposition. These will likely be long-term phenomena, difficult to distinguish from other, concurrent environmental changes, including elevated atmospheric CO2, climate change, reductions in acidity, invasions of new species, and long-term vegetation responses to past disturbance.

A synthesis of ecosystem management strategies for forests in the face of chronic nitrogen deposition.

Total nitrogen (N) deposition has declined in many parts of the U.S. and Europe since the 1990s. Even so, it appears that decreased N deposition alone may be insufficient to induce recovery from the impacts of decades of elevated deposition, suggesting that management interventions may be necessary to promote recovery. Here we review the effectiveness of four remediation approaches (prescribed burning, thinning, liming, carbon addition) on three indicators of recovery from N deposition (decreased soil N availability, increased soil alkalinity, increased plant diversity), focusing on literature from the U.S. We reviewed papers indexed in the Web of Science since 1996 using specific key words, extracted data on the responses to treatment along with ancillary data, and conducted a meta-analysis using a three-level variance model structure. We found 69 publications (and 2158 responses) that focused on one of these remediation treatments in the context of N deposition, but only 29 publications (and 408 responses) reported results appropriate for our meta-analysis. We found that carbon addition was the only treatment that decreased N availability (effect size: -1.80 to -1.84 across metrics), while liming, thinning, and prescribed burning all tended to increase N availability (effect sizes: +0.4 to +1.2). Only liming had a significant positive effect on soil alkalinity (+10.5%-82.2% across metrics). Only prescribed burning and thinning affected plant diversity, but with opposing and often statistically marginal effects across metrics (i.e., increased richness, decreased Shannon or Simpson diversity). Thus, it appears that no single treatment is effective in promoting recovery from N deposition, and combinations of treatments should be explored. These conclusions are based on the limited published data available, underscoring the need for more studies in forested areas and more consistent reporting suitable for meta-analyses across studies.

Correction: Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.

[This corrects the article DOI: 10.1371/journal.pone.0205296.].