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Sediment-hosted gold deposits in central Yukon have most of the diagnostic characteristics of Carlin-type gold deposits in Nevada. This study combines organic matter geothermometry with fluid inclusion microthermometry, clumped isotope data (Δ47) for late ore-stage hydrothermal calcite, and apatite fission-track analyses to constrain the thermal evolution of Carlin-type gold zones in central Yukon. The Tmax parameter derived from pyrolysis analyses indicates that organic matter is overmature and records regional temperatures of > 150 °C. Calcite and fluorite associated with the waning stage of mineralization at ca. 74 Ma have mean fluid inclusion homogenization temperatures of 123–173 °C, with an average salinity of 4.8 wt.% NaCl equiv. These temperatures overlap values of 91–162 °C determined from calcite clumped isotope measurements and are similar to data from Carlin-type deposits in Nevada. Fluid mixing is suggested by a variation of the isotopic composition of the fluid in equilibrium with calcite, with the higher temperature end-member having higher δ18OH2O values. In thermal models based on Tmax, fluid inclusion microthermometry, clumped isotope measurements, and apatite fission-track data, a higher temperature event at approximately 220 °C is consistent with pyrobitumen reflectance measurements. This event is either related to maximum tectonic burial prior to mineralization or to the flow of acidic hydrothermal fluids early in the main ore-stage. Each analytical technique used in this study is independent of the others and records part of the thermal and chemical evolution of the Yukon Carlin-type gold deposits and their host rocks.

Recent studies using the CO2 carbonate clumped isotope (13C-18O-16O, i.e., Δ47) paleothermometer and bulk isotopes (δ13C, δ18O) have brought new insights into the prevailing conditions during carbonate formation around marine methane seeps. These studies mostly revealed δ18O or paired δ18O and Δ47 disequilibria between precipitating minerals, water and DIC species. Here, we have sampled bivalves and cements from two modern, slow-release methane seeps located in the St. Lawrence Estuary. The bivalve shells have marine isotopic signals, whereas the cements show wide Δ47 (up to +0.05‰) and minor δ18O (+0.8‰) positive offsets relative to marine equilibrium, with a narrow δ13C range (−33.5 to −31.1‰). The observed isotopic trends show that, unlike in previous studies, the aragonite shells precipitated at full isotopic equilibrium, whilst the cements suggest differential disequilibrium precipitation. We propose that the suite of results were generated by distinct Δ47 and δ18O pathways, as supported by DIC-water isotopic exchange numerical experiments. The observed trends typify slow rates of methane oxidation and carbonate precipitation from residual gas with high-δ18O and low-Δ47 values after methane-derived CO2 diffusion. Overall, we suggest that the shells represent potential archives of seep conditions, and that the seep cements define a new Δ47 and δ18O domain widening the known spectrum of marine conditions producing natural carbonates. Our results, compiled with literature data, help refine the basis for interpreting carbonate precipitation mechanisms in ancient seeps or other geological settings.

Distinguishing between naphthenic acids (NAs) associated with oil sands process-affected water (OSPW) and those found naturally in groundwaters in contact with the bituminous McMurray Formation poses a considerable analytical challenge to environmental research in Canada's oil sands region. Previous work addressing this problem combined high-resolution Orbitrap mass spectrometry with carbon isotope values generated by online pyrolysis (δ

Anthropogenic activities such as industrialization, land use change and intensification of agriculture strongly contribute to changes in the concentrations of atmospheric trace gases. Carbon dioxide (CO2), oxidized N compounds(NOx), sulfur dioxide (SO2) and ozone(O3) have particularly significant impacts on plant physiology. CO2, the substrate for plant photosynthesis, is in the focus of interest as the ambiguous effect of its increasing concentration is controversially discussed. Is its increase beneficial for plants or are plants non-responsive? NOx, a product of combustion and lightning, can have either fertilizing or toxic effects depending on the concentration and form. This is also the case for reduced forms of nitrogen(NHy), which are mostly emitted from agricultural and industrial activities. In combination CO2and N compounds can have a fertilizing effect. SO2 and ground-level O3 are mostly phytotoxic, depending on their concentrations, daily and seasonal exposure dynamics, and tree health condition. Elevated concentrations of both substances arise from industrial combustion processes and car emissions. All of the above-mentioned gaseous compounds affect plant metabolism in their specific ways and to different degrees. This impacts the isotope fractionation leaving specific fingerprints in the C, O, (H) and N isotope ratios of organic matter. In this chapter we will show how the impact of increasing CO2 and air pollutants are reflected in the isotopic ratios of tree rings. Increasing CO2 shows a considerable variation in responses of δ13C and to a minor degree in δ18O. Ozone and SO2 exposure cause an overall increase of the δ13C values in tree rings and a slight decrease in δ18O, mimicking an increase in net photosynthesis (AN) and to a minor degree in stomatal conductance (gs). However, directly measured AN and gs values show the opposite, which does not always correspond with the isotope derived gas exchange data. NO2 concentration as it is found near highly frequented freeways or industrial plants causes an increase of δ13C while δ18O decreases. This indicates an increase in both AN and gs, which corresponds well with directly measured gas exchange data. Thus the air quality situation must be taken in consideration for the interpretation of isotope values in tree rings.

Nutritive, but detrimental if at high levels, several nitrogen (N) forms involved in air and soil biogeochemical reactions constitute the N load trees assimilate. Although a large body of literature describes series of tree-ring N isotopes (δ15N) as archival systems for environmental changes, several questions relative to the isotopic integrity and reproducibility of trends still linger in the dendroisotopist community. This chapter reviews the fundamentals of forest N cycling and examines trees as N receptors in their very position, at the interface between the atmosphere and pedosphere. The related scrutiny of intrinsic and extrinsic mechanisms regulating isotopic changes also underlines flaws and forces of tree-ring δ15N series as environmental indicators.

As anthropogenic nitrogen (N) emissions have been rising for decades, it is critical to develop natural archives that help understand how natural processes were modified in the past. Tree-ring δ

International audience; In northeastern Canada (Labrador), instrumental climatic data cover less than 70 years and long reconstructions from natural archives are non-existent. This study specifically aims at helping filling this gap of knowledge by testing the possibility of reconstructing the regional 1800–2009 discharge of the lower Churchill River from black spruce tree-ring δ13C and δ18O series. The results illustrate direct relationships of summer climatic variables/derived parameter (maximum temperature, total precipitation and vapor pressure deficit) with tree-ring isotope values. Importantly, they show an inverse correlation between combined tree-ring isotope series and regional river discharge due to common climate forcing. To a lesser extent, transpiration also affects the river discharge and tree-ring isotopic compositions. The reconstructed river discharge series agrees with an independent reconstruction based on the ANATEM method (1880–2009 period). The agreement between the two reconstructions validates the two approaches for reconstructing regional hydroclimatic conditions at high latitudes. Moreover, the reconstructions suggest that summer discharge has decreased over the past 200 years in eastern Labrador and more broadly at the Québec-Labrador peninsula scale. This trend correlates with the long-term summer Arctic Oscillation (AO) that influences summer regional climatic conditions. This research contributes with other studies to build up observations linking summer AO and eastern Canada climatic conditions, and calls for research on mechanisms explaining these relationships during summer.

Fugitive dust associated with surface mining activities is one of the principal vectors for transport of airborne contaminants in Canada’s Athabasca oil sands region (AOSR). Effective environmental management requires quantitative identification of the sources of this dust. Using natural abundance radiocarbon (Δ¹⁴C) and dual (δ¹³C, δ²H) compound-specific isotope analysis (CSIA), this study investigated the sources of dust and particulate-bound polycyclic aromatic compounds (PACs) deposited in AOSR lake snowpack. Lower Δ¹⁴C values, higher particulate and PAC loadings, and lower δ¹³C values for phenanthrene and C1-alkylated phenanthrenes/anthracenes (C1-Phen) at sites closer to the mining operations indicated unprocessed oil sand and/or petroleum coke (petcoke–a byproduct of bitumen upgrading) as major sources of anthropogenic fugitive dust. However, a Bayesian isotopic mixing model that incorporated both δ¹³C and δ²H could discriminate petcoke from oil sand, and determined that petcoke comprised between 44 and 95% (95% credibility intervals) of a C1-Phen isomer at lakes

The Hudson Bay sedimentary basin remained geologically overlooked until two decades ago. Recent efforts in understanding the paleogeothermal history of this basin has led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance as well as Rock-Eval analyses. While apatite fission tracks and organic maturity indicators tend to show relatively low maximum burial temperatures (60 to 80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells are reported across the Hudson Bay. Moreover, fluid inclusion microthermometry suggests homogenization temperatures for recrystallized syn-sedimentary marine calcite and late pore-filling burial calcite of 118 ± 25°C and 93 ± 10°C, respectively, in a carbonate mound sequence. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcite cements and diagenetically altered early marine phases. The integration of clumped isotopic data with other thermal indicators allows for reconstruction and refinement of the thermal-diagenetic history of these carbonates by confirming an episode of heating, likely of hydrothermal origin and prior to normal burial diagenesis, resetting both fluid inclusions and the clumped isotope indicators, without recrystallisation.

Climatic reconstructions based on tree-ring isotopic series convey substantial information about past conditions prevailing in forested regions of the globe. However, in some cases, the relations between isotopic and climatic records appear unstable over time, generating the “isotopic divergences”. Former reviews have thoroughly discussed the divergence concept for tree-ring physical properties but not for isotopes. Here we want to take stock of the isotopic divergence problem, express concerns and stimulate collaborative work for improving paleoclimatic reconstructions. There are five main causes for divergent parts in isotopic and climatic series: (1) artefacts due to sampling and data treatment, relevant for dealing with long series using sub-fossil stems; (2) stand dynamics, including juvenile effects mostly occurring in the early part of tree-ring series; (3) rise in atmospheric pCO2, which can directly influence the foliar behaviour; (4) change in climate, which may modify the isotope–climate causal links; and finally (5) atmospheric pollution, which may alter leaf and root functions. Future paleoclimate research would benefit from interdisciplinary efforts designed to develop further process-based models integrating multi-proxy inputs so as to help identify causes of isotopic divergences and circumvent some of them in inverse applications.

Although the environmental impacts of metal atmospheric emissions from point sources such as smelter have been extensively studied, very few studies have attempted to understand the influence of those emissions on nutrient cycles in the surrounding forests. This study investigates nutrient variations in space and time along with trace metals by statistical analysis of tree-ring series combined with the characterization of element concentrations in soil horizons. The research focuses on the Horne smelter (Rouyn Noranda, Quebec, Canada), because it released high atmospheric emissions of metals and gases between 1928 and 1990s. Tree-ring Sr/Mn ratios, and Mn and Sr z-score series reveal that surface soil pH recovered progressively within the 45 km footprint of the smelter since the end of acidic deposition in the late 1970s. The influence of acidic deposition on the current soil pH has become negligible. In other words, element bioavailability and root assimilation have changed through time due to soil acidification at proximal sites. The detrended tree-ring elemental series during the last century also suggest that summer temperatures partly control the elemental bioavailability to trees in soils. Moreover, tree-ring Zn and Mg series appear as key environmental indicators of metal deposition from the smelter. This research confirms previous findings indicating that elemental concentrations in black and white spruce trees may be used to evaluate the potential influence of smelter emissions on nutrient cycles. For a future informed and adaptive management of forests, understanding the potential modifications of nutrient regimes caused by anthropogenic contaminations is critical, especially in the context of global warming.

Studies in dendroisotope chemistry suggested that latewood cellulose contains better climatic records than whole-ring cellulose. However, this approach has never been tested on northeastern Canadian spruce trees. This study compares dendroisotopic series of cellulose from late and whole ring, and analyses their statistical relationships with hydro-climatic variables with the aim of selecting the best suited protocol for future hydro-climatic reconstruction in the downstream sector of Churchill River basin of Labrador, Canada. To this end, δ13C and δ18O series from latewood (LW) and whole ring (WR) α-cellulose of black spruce trees (Picea mariana [Mill.] B.S.P.) were produced for the 1940–2010 period. The results show strong correlations between LW and WR isotopic series suggesting that there are no important variation in the isotopic ratios during the growing year and that black spruce trees use photosynthates of the current growing season to form their earlywood. Moreover, LW and WR δ13C and δ18O show similar relationships with both maximum temperature (Tmax) and Churchill River discharge. Correlations are higher when combining δ13C and δ18O for LW and WR. Overall, those correlations support the indirect relationship between tree-ring isotopic series and river discharge, as they are integrators of several climatic variables and derived parameters (Tmax, relative humidity, evapotranspiration, etc.). The LW and WR isotopic series give similar statistical relationships with hydro-climatic variables, and the WR treatment is faster (separation easier compared to LW). Thus, for black spruce the use of combined isotopic series in WR can be favored over LW for hydro-climatic reconstruction in the study region.

There are clear motivations for better understanding the atmospheric processes that transform nitrogen (N) oxides (NOx) emitted from anthropogenic sources into nitrates (NO3-), two of them being that NO3- contributes to acidification and eutrophication of terrestrial and aquatic ecosystems, and particulate nitrate may play a role in climate dynamics. For these reasons, oxygen isotope delta values (δ18O, Δ17O) are frequently applied to infer the chemical pathways leading to the observed mass-independent isotopic anomalies from interaction with 17O-rich ozone (O3). Recent laboratory experiments suggest that the isotopic equilibrium between NO2 (the main precursor of NO3-) and O3 may take long enough under certain field conditions that nitrates may be formed near emission sources with lower isotopic values than those formed further downwind. Indeed, previously published field measurements of oxygen isotopes in NO3- in precipitation (wNO3-) and in particulate (pNO3-) samples suggest that abnormally low isotopic values might characterize polluted air masses. However, none of the air studies have deployed systems allowing collection of samples specific to anthropogenic sources in order to avoid shifts in isotopic signature due to changing wind directions, or separately characterized gaseous HNO3 with Δ17O values. Here we have used a wind-sector-based, multi-stage filter sampling system and precipitation collector to simultaneously sample HNO3 and pNO3-, and co-collect wNO3-. The nitrates are from various distances (125 km) downwind of different anthropogenic emitters, and consequently from varying time lapses after emission. The separate collection of nitrates shows that the HNO3 δ18O ranges are distinct from those of w- and pNO3-. Interestingly, the Δ17O differences between pNO3- and HNO3 shift from positive during cold sampling periods to negative during warm periods. The low pNO3-Δ17O values observed during warm periods may partly derive from the involvement of 17O-depleted peroxy radicals (RO2) oxidizing NO during that season. Another possibility is that nitrates derive from NOx that has not yet reached isotopic equilibrium with O3. However, these mechanisms, individually or together, cannot explain the observed pNO3 minus HNO3 isotopic changes. We propose differences in dry depositional rates, faster for HNO3, as a mechanism for the observed shifts. Larger proportions of pNO3- formed via the N2O5 pathway would explain the opposite fall–winter patterns. Our results show that the separate HNO3, wNO3- and pNO3- isotopic signals can be used to further our understanding of NOx oxidation and deposition. Future research should investigate all tropospheric nitrate species as well as NOx to refine our understanding of nitrate distribution worldwide and to develop effective emission reduction strategies.

Oil sands operations in Alberta, Canada generate large volumes (>840 × 106 m3) of oil sands process-affected water (OSPW) that contains contaminants that are toxic to aquatic life. OSPW is stored in open tailings ponds and leakage from the ponds presents a potential long-term environmental risk. However, the presence of naturally occurring saline water in the oil sands region in Alberta presents a challenge for delineating the impact of OSPW in cases where OSPW is leaked to the environment. Here, we characterize the inorganic chemistry and isotopic variations of boron (δ11B), lithium (δ7Li), and strontium ( e S r S W ) of OSPW from tailings ponds in order to evaluate the source of salinity in OSPW and the potential utilization of these isotope ratios as forensic tracers of OSPW migration in the environment. In addition to generating new data, we compiled published data to build a comprehensive dataset of the geochemical composition of different water sources in the oil sands region of Alberta. OSPW is brackish (TDS ∼ 1800 mgL−1), with elevated chloride (392 ± 184 mg L−1), boron (2.2 ± 0.4 mg L−1), and lithium (0.12 ± 0.11 mg L−1) concentrations relative to the Athabasca River that is used for bitumen extraction. OSPW is characterized by narrow ranges of δ11B (23.7 ± 1.8‰), δ7Li (16.3 ± 1.7‰), and 87Sr/86Sr ratios ( e S r S W =-3.9 ± 19.2). The geochemical and isotope ratios in OSPW reflect mixing of residual, saline formation water from Lower Cretaceous units with fresh surface water that has been modified by interactions with the solid oil sands. The elevated boron and lithium concentrations and δ11B, δ7Li and e S r S W variations we observed are distinct from the compositions of a shallow freshwater aquifer in the area (8.1 ± 5.0‰, 11.3 ± 0.9‰ and 9.7 ± 5.6, respectively) and the local rivers (15.6 ± 4.7‰, 15.1 ± 1.4‰ and 30.3 ± 16.0). However, groundwater and saline springs in the region presents a wider range of geochemical and isotopic values that are not always distinguishable from OSPW. The integration of boron, lithium, and strontium isotopes provides a potential monitoring tool for tracing OSPW release to local freshwater sources.

We report a historical record of atmospheric deposition in dated sediment cores from Hasse Lake, ideally located near both currently and previously operational coal-fired power plants in Central Alberta, Canada. Accumulation rates of spheroidal carbonaceous particles (SCPs), an unambiguous marker of high-temperature fossil-fuel combustion, in the early part of the sediment record (pre-1955) compared well with historical emissions from one of North America's earliest coal-fired power plants (Rossdale) located ∼43 km to the east in the city of Edmonton. Accumulation rates in the latter part of the record (post-1955) suggested inputs from the Wabamun region's plants situated ∼17-25 km to the west. Increasing accumulation rates of SCPs, polycyclic aromatic hydrocarbons (PAHs) and Hg coincided with the previously documented period of peak pollution in the Wabamun region during the late 1960s to early 1970s, although Hg deposition trends were also similar to those found in western North American lakes not directly affected by point sources. A noticeable reduction in contaminant inputs during the 1970s is attributed in part to technological improvements and stricter emission controls. The over one hundred-year historical record of coal-fired power plant emissions documented in Hasse Lake sediments has provided insight into the impact that both environmental regulations and changes in electricity output have had over time. This information is crucial to assessing the current and future role of coal in the world's energy supply.

Anthropogenic N emissions represent a potential threat for forest ecosystems, and environmental indicators that provide insight into the changing forest N cycle are needed. Tree ring N isotopic ratios (δ15N) appear as a contentious choice for this role as the exact mechanisms behind tree-ring δ15N changes seldom benefit from a scrutiny of the soil-to-tree N continuum. This study integrates the results from the analysis of soil chemistry, soil microbiome genomics, and δ15N values of soil N compounds, roots, ectomycorrhizal (EcM) fungi and recent tree rings of thirteen white spruce trees sampled in five stands, from two regions exposed to moderate anthropogenic N emissions (3.9 to 8.1 kg/ha/y) with distinctive δ15N signals. Our results reveal that airborne anthropogenic N with distinct δ15N signals may directly modify the NO3− δ15N values in surface soils, but not the ones of NH4+, the preferred N form of the studied trees. Hence, the tree-ring δ15N values reflect specific soil N conditions and assimilation modes by trees. Along with a wide tree-ring δ15N range, we report differences in: soil nutrient content and N transformation rates; δ15N values of NH4+, total dissolved N (TDN) and EcM mantle enveloping the root tips; and bacterial and fungal community structures. We combine EcM mantle and root δ15N values with fungal identification to infer that hydrophobic EcM fungi transfer N from the dissolved organic N (DON) pool to roots under acidic conditions, and hydrophilic EcM fungi transfer various N forms to roots, which also assimilate N directly under less acidic conditions. Despite the complexities of soil biogeochemical properties and processes identified in the studied sites, in the end, the tree-ring δ15N averages inversely correlate with soil pH and anthropogenic N inputs, confirming white spruce tree-ring δ15N values as a suitable indicator for environmental research on forest N cycling.

Nitrate transport in heterogeneous bedrock aquifers is influenced by mechanisms that operate at different spatial and temporal scales. To understand these mechanisms in a fractured sandstone aquifer with high porosity, a groundwater-flow and nitrate transport model—reproducing multiple hydraulic and chemical targets—was developed to explain the actual nitrate contamination observed in groundwater and surface water in a study area on Prince Edward Island, Canada. Simulations show that nitrate is leached to the aquifer year-round, with 61% coming from untransformed and transformed organic sources originating from fertilizers and manure. This nitrate reaches the more permeable shallow aquifer through fractures in weathered sandstone that represent only 1% of the total porosity (17%). Some of the nitrate reaches the underlying aquifer, which is less active in terms of groundwater flow, but most of it is drained to the main river. The river-water quality is controlled by the nitrate input from the shallow aquifer. Groundwater in the underlying aquifer, which has long residence times, is also largely influenced by the diffusion of nitrate in the porous sandstone matrix. Consequently, following a change of fertilizer application practices, water quality in domestic wells and the river would change rapidly due to the level of nitrate found in fractures, but a lag time of up to 20 years would be necessary to reach a steady level due to diffusion. This demonstrates the importance of understanding nitrate transport mechanisms when designing effective agricultural and water management plans to improve water quality.

The nitrogen isotope ratios (δ15N) of atmospheric N species are commonly suggested as indicators of N emission sources. Therefore, numerous research studies have developed analytical methodologies and characterized primary (gases) and secondary emission products (mostly precipitation and aerosols) from various emitters. These previous studies have generally collected either reduced or oxidized N forms, and sampled them separately prior to determining their δ15N values. Distinctive isotopic signals have been reported for emissions from various sources, and seasonality of the δ15N values has been frequently attributed to shifts in relative contributions from sources with different isotopic signals. However, theoretical concepts suggest that temperature effects on isotopic fractionation may also affect the δ15N values of atmospheric reaction products. Here we use a sector-based multi-stage filter system to simultaneously collect seven reduced and oxidized N species downwind from five different source types in Alberta, Canada. We report δ15N values obtained with a state-of-the-art gold-furnace pre-concentrator online with an isotope ratio mass spectrometer (IRMS) to provide representative results even for oxidized-N forms. We find that equilibrium isotope effects and their temperature dependence play significant roles in determining the δ15N values of the secondary emission products. In the end, seasonal δ15N changes here are mainly caused by temperature effects on fractionation, and the δ15N values of only two N species from one source type can be retained as potential fingerprints of emissions.

Little is known about how forests adjust their gas-exchange mode while atmospheric CO

Although requiring laborious analytical treatment, tree-ring series of nitrogen isotopes (δ15N) have gained popularity amongst researchers for their potential as environmental indicators as anthropogenic emissions increase globally with potential effects on forest N cycles. Previous studies suggested that tree-ring series correlate with climatic and air quality parameters. However, none discussed the level of replication required for expressing the population signals of specific species of trees. In this investigation, we studied 27 white spruce trees from two sites under distinct environmental conditions to evaluate the appropriate protocol for preparing consistent tree-ring δ15N series. The produced series indicate that high frequency (short-term, 15 years) δ15N trends show coherence between arithmetic means of individual series at replication levels as low as three trees, whereas middle-term pooled trends do not perform as coherently. The low frequency mean trends of individual series obtained for the two sites suggest that local biogeochemical soil conditions modified by anthropogenic emissions modulate the δ15N responses in trees. Hence, we propose that long-term tree-ring δ15N series constitute reliable environmental indicators.

Little is known about how forests adjust their gas-exchange mode while atmospheric CO2 rises globally and air quality changes regionally. The present study aims at addressing this research gap for boreal spruce trees growing in three different regions of Canada, submitted to distinct levels of atmospheric emissions, by examining the amount of carbon gained per unit of water lost in trees, i.e., the intrinsic water use efficiency (iWUE). Under pristine air quality conditions, middle-to long-term trends passed from no-reaction mode to passive strategies due to atmospheric CO2, and short-term iWUE variations mostly ensue from year-to-year climatic conditions. In contrast, in trees exposed to pollutants from a copper smelter and an oil-sands mining region, air quality deterioration generated swift, long-term iWUE rises immediately at the onset of operations. In this case, the very active foliar strategy sharply reduced the intra-foliar CO2 (Ci) pressure. Statistical modeling allowed identifying emissions as the main trigger for the iWUE swift shifts; subsequent combined effects of emissions and rising CO2 led to passive foliar modes in the recent decades, and short-term variations due to climatic conditions appeared all along the series. Overall, boreal trees under different regional conditions modified their foliar strategies mostly without changing their stem growth. These findings underline the potential of acidifying emissions for prompting major iWUE increases due to lowering the stomatal apertures in leaves, and the combined influence of rising CO2 in modulating other foliar responses. A fallout of this research is that degrading air quality may create true divergences in the relationship between tree-ring isotopes and climatic conditions, an impact to consider prior to using isotopic series for paleo-climatic modeling.

Potential seepage of naphthenic acids (NAs) from tailings ponds into surface water and groundwater is one of the main environmental concerns associated with the Canadian Athabasca oil sands mining operations. Here we report the application of

International audience; The Tambora eruption (1815 AD) was one of the major eruptions of the last two millennia and has noequivalents over the last two centuries. Here, we collected an extensive network of earlymeteorological time series, climate simulation data and numerous, well-replicated proxy records from Eastern Canada to analyze the strength and the persistence of the Tambora impact on the regional climate and forest processes. Our results show that the Tambora impacts on the terrestrial biosphere were stronger than previously thought, and not only affected tree growth and carbon uptake for a longer period than registered in the regional climate, but also determined forest demography and structure. Increased tree mortality, four times higher than the background level, indicates that the Tambora climatic impact propagated to influence the structure of the North American taiga for several decades.We also show that the Tambora signal is more persistent in observed data (temperature, river ice dynamics, forest growth, tree mortality) than in simulated ones (climate and forest-growth simulations), indicating that our understanding of the mechanisms amplifying volcanic perturbations on climates and ecosystems is still limited, notably in the North American taiga.

The continued growth of mining and upgrading activities in Canada's Athabasca oil sands (AOS) region has led to concerns about emissions of contaminants such as polycyclic aromatic hydrocarbons (PAHs). Whereas a recent increase in PAH emissions has been demonstrated within around 50 km of the main center of surface mining and upgrading operations, the exact nature of the predominant source(s) and the geographical extent of the deposition are still under debate. Here, we report a century-long source apportionment of PAHs using dual (δ(2)H, δ(13)C) compound-specific isotope analysis on phenanthrene deposited in a lake from the Athabasca sector of the Peace-Athabasca Delta situated ∼150 km downstream (north) of the main center of mining operations. The isotopic signatures in the core were compared to those of the main potential sources in this region (i.e., unprocessed AOS bitumen, upgrader residual coke, forest fires, coal, gasoline and diesel soot). A significant concurrent increase (∼55.0‰) in δ(2)H and decrease (∼1.5‰) in δ(13)C of phenanthrene over the last three decades pointed to an increasingly greater component of petcoke-derived PAHs. This study is the first to quantify long-range (i.e., >100 km) transport of a previously under-considered anthropogenic PAH source in the AOS region.

The downstream accumulation of polycyclic aromatic hydrocarbons (PAHs) in the Peace-Athabasca Delta (PAD), an ecologically important landscape, is a key issue of concern given the rapid development of the oil sands industry in Northern Alberta, Canada. In addition to PAHs derived from industrial activity (i.e., oil sands mining) within the Athabasca watershed, however, forest fires and erosion of fossil fuel deposits within both the Athabasca and Peace watersheds are two potentially important natural sources of PAHs delivered to the PAD. Consequently, evaluating the environmental impact of mining activities requires a quantitative understanding of natural, background PAHs. Here, we utilize molecular-level natural-abundance radiocarbon measurements on an amalgamated sediment record from a Peace River flood-susceptible oxbow lake in the northern Peace sector of the PAD to quantitatively discriminate sources of naturally occurring alkylated PAHs (fossil and modern biomass). A radiocarbon mass balance quantified a predominantly natural petrogenic source (93% petrogenic, 7% forest fire) for alkylated PAHs during the past ∼50 years. Additionally, a significant petrogenic component determined for retene, a compound usually considered a biomarker for softwood combustion, suggests that its use as a unique forest fire indicator may not be suitable in PAD sediments receiving Peace watershed-derived fluvial inputs.

Feeding the growing population of the world poses significant policy challenges for the sustainability of global ecosystems. A prime example is the degradation of water quality due to the growing imbalance in the terrestrial nitrogen (N) cycle linked to increasing production of reactive N (Nr). Environmental impacts such as groundwater quality degradation and eutrophication of coastal estuaries tend to be local in nature but may be closely connected to global economic factors. Environmental accounting of the N fluxes entering, leaving or remaining in Prince Edward Island (PEI), a small agricultural region, demonstrate the importance of a single industry (potato production) in controlling the local N cycle. The resulting burden of Nr has its most profound effect on groundwater, the sole source of drinking water and the primary pathway of N to the Province's economically and ecologically important estuaries. At the same time, agriculture is a vital part of the local economy, and regulators are faced with the challenge of meeting environmental goals and still maintaining an industry that is competitive and responsive to global market trends. New, innovative policy alternatives are needed to foster more effective implementation of sustainable agricultural practices. An approach that focuses on influencing consumer choices toward more environmentally responsible production practices at the point of origin may help remove some of the important, non-technical barriers to sustainable food production practices. In practice, a system that documents the environmental performance throughout the full supply chain from producer to retailer would have to be implemented.

Zinc isotopes (δ66Zn) are promising indicators for understanding biogeochemical processes and tracing sources in environmental geochemistry. This study, the first of its kind, proposes a treatment protocol for determining white spruce tree-ring Zn concentration and δ66Zn values. By pooling year-equivalent tree rings of four individual trees (total of 45 samples), the protocol produces reliable tree-ring Zn concentrationand δ66Zn values. In the end, comparing the pooled and mean values with the individual treesshows an excellent match. It suggests that the protocol has the potential to be applied in future environmental studies.

Climate reconstructions using stable isotopes (δ18O and δ13C values) in tree rings are based on relationships between present climatic conditions and isotopic series. This widely used approach relies on the assumption that correlations between stable isotopes and climatic conditions are steady over time. In this paper, we evaluate the strength of the correlations between δ18O and δ13C series with several climatic parameters on fourteen black spruce trees coming from three different sites, in northeastern Canada. We applied a 21-year moving window on the r Pearson calculated between stable isotopes and March–May and June–August precipitation, June–August and April–June maximal temperatures. Our results indicate that despite the large distance and differences in stand conditions between the sites, the three sites responded in the same way over time. We show that because the climatic ambiance has changed during the 1980–1990 period due to a positive North Atlantic Oscillation index the δ13C values are not controlled anymore by spring precipitation or summer maximal temperature in the following two decades. As opposed to δ13C series, the relationship between summer maximal temperature and δ18O values was stable over time, and decreased only in the last decade. All these results attest of a “divergence problem” in the last decades which is most pronounced for δ13C series. We conclude that the spruce δ18O series appears to be the most appropriate indicator for reconstructing June–August maximal temperature in the studied area despite the divergence issue, given that the calibration–validation tests and reconstruction can exclude the divergent last decade.

Direct monitoring of air quality does not cover more than the last three decades in most industrialized countries. For that reason studies using growth-ring carbon isotopes (δ 13 C) of several species of trees have recently investigated isotopic responses in the contexts of stationary and diffuse pollution in humid continental conditions. Here, the growth-ring δ 13 C series (1880–2009) of spruce trees living in sub-humid subarctic conditions were measured to assess if they represent indicators for air quality changes near oil sands (OS) developments initiated in northeastern Alberta in 1967. The measured δ 13 C pre-operation rings at two forest sites were analyzed along local climatic conditions to develop response-to-climate statistical models and predict the natural isotopic behaviour for the most recent part of the ring series. The measured trends and climate-modelled (natural) δ 13 C values strongly depart during the operation period, depicting anomalies which can be nicely reproduced by multiple regression models combining climate and a proxy for OS airborne emissions. This research allows envisioning the use of carbon dendroisotopic indicators to compensate for the lack of long-term air quality measurement, and monitor environmental conditions in the sub-humid terrestrial ecosystem exposed to emissions from oil sands operations which are predicted to increase in the future.

In the boreal zone of northeastern Canada, paleoclimatic reconstructions of millennial length are rare and long isotopic climatic records are unavailable. However, millennial tree-ring series could be constructed within the region by cross-dating sub-fossil stems preserved in the littoral part of lakes. Thus, there is a need to evaluate the potential of using stable isotopes of lakeshore black spruce trees (Picea mariana [Mill] B.S.P.) as proxies for climatic reconstruction. We collected four living riparian black spruce trees and we investigated the inter- and intra-tree correlations for four trees, at two different sampling heights (1 and 4 m), for their carbon (δ13C) and oxygen (δ18O) isotopes, as a test for potential long-term reconstruction. A significant correlation (Pearson coefficient) for the isotopic series was found for the two sampling heights (r = 0.92 for δ13C; 0.65 for δ18O), and between the four trees. We further assessed the climatic significance of the mean of the four trees. The strongest correlation of the δ13C series was with the mean of June to August vapor pressure deficit (VPD; r = 0.50), and the δ18O values with the June to August climatic index and June to July maximal temperature (r = − 0.61 and 0.55, respectively). This study suggests that δ18O series of riparian black spruce trees, and eventually their sub-fossil counterparts, can be used as proxies for reconstructing long climatic series in northeastern Canada.

Evaluating the impact that airborne contamination associated with Athabasca oil sands (AOS) mining operations has on the surrounding boreal forest ecosystem requires a rigorous approach to source discrimination. This study presents a century-long historical record of source apportionment of polycyclic aromatic hydrocarbons (PAHs) in dated sediments from two headwater lakes located approximately 40 and 55 km east from the main area of open pit mining activities. Concentrations of the 16 Environmental Protection Agency (EPA) priority PAHs in addition to retene, dibenzothiophene (DBT), and six alkylated groups were measured, and both PAH molecular diagnostic ratios and carbon isotopic signatures (δ(13)C) of individual PAHs were used to differentiate natural from anthropogenic inputs. Although concentrations of PAHs in these lakes were low and below the Canadian Council of Ministers of the Environment (CCME) guidelines, diagnostic ratios pointed to an increasingly larger input of petroleum-derived (i.e., petrogenic) PAHs over the past 30 years concomitant with δ(13)C values progressively shifting to the value of unprocessed AOS bitumen. This petrogenic source is attributed to the deposition of bitumen in dust particles associated with wind erosion from open pit mines.

The high levels of acid extractable organics (AEOs) containing naphthenic acids (NAs) found in oil sands process-affected waters (OSPW) are a growing concern in monitoring studies of aquatic ecosystems in the Athabasca oil sands region. The complexity of these compounds has substantially hindered their accurate analysis and quantification. Using a recently developed technique which determines the intramolecular carbon isotope signature of AEOs generated by online pyrolysis (δ(13)Cpyr), natural abundance radiocarbon, and high resolution Orbitrap mass spectrometry analyses, we evaluated the sources of AEOs along a groundwater flow path from a major oil sands tailings pond to the Athabasca River. OSPW was characterized by a δ(13)Cpyr value of approximately -21‰ and relatively high proportions of O₂ and O₂S species classes. In contrast, AEO samples located furthest down-gradient from the tailings pond and from the Athabasca River were characterized by a δ(13)Cpyr value of around -29‰, a greater proportion of highly oxygenated and N-containing compound classes, and a significant component of nonfossil and, hence, non-bitumen-derived carbon. The groundwater concentrations of mining-related AEOs determined using a two end-member isotopic mass balance were between 1.6 and 9.3 mg/L lower than total AEO concentrations, implying that a less discriminating approach to quantification would have overestimated subsurface levels of OSPW. This research highlights the need for accurate characterization of "naphthenic acids" in order to quantify potential seepage from tailings ponds.