Jean-François Hélie

Seasonal changes in the sources and fluxes of dissolved inorganic carbon through the St. Lawrence River—isotopic and chemical constraint

The St. Lawrence River ranks 16 th in the world rivers for its freshwater discharge into the ocean, but its particulate fluxes are relatively low due the upstream presence of the Great Lakes system. Using notably 13 C measurements in total dissolved inorganic carbon (DIC) at several stations along stream, earlier studies provided information on dissolved inorganic carbon (DIC) fluxes through the St. Lawrence, with some constraints on spatial trends with respect to the in situ DIC metabolism. Here, we further document annual DIC-fluxes and seasonal changes in DIC supplies and DIC-metabolism, downstream. Chemical and isotopic measurements were performed in 1998, on a biweekly basis, at four different sites. These sites represent respectively the Great Lakes outflow into the St. Lawrence system, supplies from two tributaries (one with a silicate-rich Precambrian bedrock, the other with a carbonate-rich Paleozoic bedrock), and the St. Lawrence outflow into the maritime estuarine system. The 1998 survey yielded a total annual DIC flux of � 6 � 10 12 to 7 � 10 12 g of carbon at the Quebec City outlet, about 40% higher than estimates from earlier studies. This represents about 1.5% of the world river DIC supplies to the ocean. Very strong seasonal variations are observed between the summer low water levels, when water supplies from the Great Lakes into the riverine system may represent up to 80% of the total outflow of the St. Lawrence River, and the spring snowmelt period, when tributaries may provide up to 80% of this outflow. d 13 C-DIC values respond to this seasonal cycle, with near isotopic-equilibrium values with atmospheric CO2 during summer, and strongly depleted values in other seasons, notably during the spring high outflow period. This seasonal isotopic cycle is more pronounced at the Quebec City outlet, where the influence of 13 C-depleted DIC supplies from tributaries is stronger than upstream. The low d 13 C-DIC values observed from fall to spring, may be due to a combination of the following factors: (i) enhanced supplies of 13 C-depeleted DIC from soils and ground waters from watersheds, (ii) higher oxidation rates of dissolved or particulate 13 C-depleted organic carbon, and (iii) a reduced incidence of the in situ photosynthetic activity. The outflow and isotopic seasonal cycles result notably in a strong negative correlation between d 13 C-DIC values and discharge rates. Estimates of DIC supplies from tributaries vs. those from the Great Lakes were calculated using either chemical or isotopic approaches. DIC supplies from tributaries vary between � 5% and 60% of total DIC. Examination of pCO2 data indicates a negligible seasonal variability at the Great Lakes outlet, with a mean annual value near equilibrium with atmospheric CO2 .I n contrast, strong seasonal changes are observed downstream, at Quebec City, with minimum pCO2 values in summer and a mean

Methane Baseline Concentrations and Sources in Shallow Aquifers from the Shale Gas-Prone Region of the St. Lawrence Lowlands (Quebec, Canada)

Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconventional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ(13)C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n = 81), municipal (n = 34), and observation (n = 15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of <0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ(1)(3)C signature of 19 samples was > -50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration, and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.

Sphagnum δ13C values as indicators of palaeohydrological changes in a peat bog

Late-Holocene peat stratigraphy of a Canadian boreal peat bog was examined to evaluate the potential of Sphagnum δ13C values as surface moisture proxy indicators. Isotopic measurements were compared to testate amoebae-inferred water-table depth reconstructions, plant macrofossil assemblages and past decomposition levels inferred by colorimetric humification. AMS radiocarbon dates were coupled with 210Pb dates to establish peat chronology. Although the mechanisms underlying carbon fractionation processes in peatlands are not well understood, we demonstrate that Sphagnum δ 13C values have potential for palaeohydrological reconstructions, since variations presented by the isotopic values can generally be correlated with the other proxy records, especially during drier episodes.

Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, l-Valines, Polyethylenes, and Oils

An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ(2)H(VSMOW-SLAP) values from -210.8 to +397.0 mUr or ‰, for δ(13)C(VPDB-LSVEC) from -40.81 to +0.49 mUr and for δ(15)N(Air) from -5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C16 n-alkanes, n-C20-fatty acid methyl esters (FAMEs), glycines, and l-valines, together with polyethylene powder and string, one n-C17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a (2)H-enriched vacuum oil. A total of 11 laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic normalization against international primary measurement standards. The use of reference waters in silver tubes allowed direct normalization of δ(2)H values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Because of exchangeable hydrogen, amino acid RMs currently are recommended only for carbon- and nitrogen-isotope measurements. Some amino acids contain (13)C and carbon-bound organic (2)H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.

Strontium isotope characterization of wines from Quebec, Canada.

The (87)Sr/(86)Sr isotope ratios were measured on grape, wine and soil samples collected in 13 commercial vineyards located in three major wine producing areas of Quebec (Canada). The soils yield Sr isotope ratios that are intimately related to the local geology and unambiguously discriminate the different producing areas. A strong relationship exists between the (87)Sr/(86)Sr isotope ratios of the wine and the grapes. This suggests that the vinification process does not alter the overall Sr budget. Although the Sr isotope ratios of the grapes do not show a strong correlation with the bulk Sr isotope composition of the soil, they do correlate strongly with the Sr isotope composition contained in the labile fraction of the soil. This indicates that the labile fraction of the soil represents the Sr reservoir available to the plant during its growth. This study demonstrates that the Sr isotope approach can be used as a viable tool in forensic science for investigating the provenance of commercial wines.

222Rn activity in groundwater of the St. Lawrence Lowlands, Quebec, eastern Canada: relation with local geology and health hazard

One hundred ninety-eight groundwater wells were sampled to measure the (222)Rn activity in the region between Montreal and Quebec City, eastern Canada. The aim of this study was to relate the spatial distribution of (222)Rn activity to the geology and the hydrogeology of the study area and to estimate the potential health risks associated with (222)Rn in the most populated area of the Province of Quebec. Most of the groundwater samples show low (222)Rn activities with a median value of 8.6 Bq/L. Ninety percent of samples show (222)Rn activity lower than 100 Bq/L, the exposure limit in groundwater recommended by the World Health Organization. A few higher (222)Rn activities (up to 310 Bq/L) have been measured in wells from the Appalachian Mountains and from the magmatic intrusion of Mont-Saint-Hilaire, known for its high level of indoor radon. The spatial distribution of (222)Rn activity seems to be related mainly to lithology differences between U-richer metasediments of the Appalachian Mountains and magmatic intrusions and the carbonaceous silty shales of the St. Lawrence Platform. Radon is slightly enriched in sodium-chlorine waters that evolved at contact with clay-rich formations. (226)Ra, the parent element of (222)Rn could be easily adsorbed on clays, creating a favorable environment for the production and release of (222)Rn into groundwater. The contribution of groundwater radon to indoor radon or by ingestion is minimal except for specific areas near Mont-Saint-Hilaire or in the Appalachian Mountains where this contribution could reach 45% of the total radioactive annual dose.

Field Metabolic Rate Is Dependent on Time-Activity Budget in Ring-Billed Gulls (Larus delawarensis) Breeding in an Anthropogenic Environment

Environmental and behavioral factors have long been assumed to affect variation in avian field metabolic rate (FMR). However, due to the difficulties in measuring continuous behavior of birds over prolonged periods of time, complete time-activity budgets have rarely been examined in relation to FMR. Our objective was to determine the effect of activity (measured by detailed time-activity budgets) and a series of extrinsic and intrinsic factors on FMR of the omnivorous ring-billed gull (Larus delawarensis). The experiment was conducted during the incubation period when both members of the pair alternate between attending the nest-site and leaving the colony to forage in aquatic and anthropogenic environments (city, agricultural). FMR was determined using the doubly labeled water method. Time-activity budgets were extrapolated from spatio-temporal data (2-5 days) obtained from bird-borne GPS data loggers. Gulls had low FMRs compared to those predicted by allometric equations based on recorded FMRs from several seabird species. Gulls proportioned their time mainly to nest-site attendance (71% of total tracking time), which reduced FMR/g body mass, and was the best variable explaining energy expenditure. The next best variable was the duration of foraging trips, which increased FMR/g; FMR/g was also elevated by the proportion of time spent foraging or flying (17% and 8% of tracking time respectively). Most environmental variables measured did not impact FMR/g, however, the percent of time birds were subjected to temperatures below their lower critical temperature increased FMR. Time-activity budgets varied between the sexes, and with temperature and capture date suggesting that these variables indirectly affected FMR/g. The gulls foraged preferentially in anthropogenic-related habitats, which may have contributed to their low FMR/g due to the high availability of protein- and lipid-rich foods. This study demonstrates that activities were the best predictors of FMR/g in ring-billed gulls, thus providing strong support for this long-standing theory in bioenergetics.

Processes governing the stable isotope composition of water in the St. Lawrence river system, Canada†

ABSTRACT Linkages between δ18O–δ2H and hydrological processes have been investigated from isotopic time series recorded in the St. Lawrence River basin. Three stations were monitored from 1997 to 2008. They include the Ottawa River, the St. Lawrence River main channel at Montreal and the fluvial estuary. All sites depict seasonal isotopic cycles characterized by heavy isotope depletions during the snowmelt period and heavy isotope enrichments throughout the ice-free period. The data define δ2H–δ18O regression lines falling below the meteoric water line. In the Ottawa River, calculations suggest that approximately 8 % of the total inflow to the basin is lost through evaporation. In the St. Lawrence River main channel, seasonal isotopic fluctuations most likely reflect hydrological processes occurring within the Great Lakes and mixing with tributaries located downstream. In the St. Lawrence River fluvial estuary, isotopic data allow partitioning streamflow components and suggest that the recorded seasonal variations mainly respond to mixing processes.

Diffusive CO2 Flux at the Air-Water Interface of the Robert-Bourassa Hydroelectric Reservoir in Northern Québec : Isotopic Approach (13C)

Hydroelectric reservoirs and lakes in boreal Quebec produce greenhouse gases (GHG) mainly in the form of CO2. No method exists, however, which can directly measure the flux of CO2 across the air-water interface and the methods that are currently used are only representative of a small surface area and a specific time period. The objective of the current study is to improve and validate an isotopic approach to estimate the annual CO2 flux across the air-water interface. The model requires the calibration of isotopic fluxes into and out of the interface. When applied to the Robert- Bourassa hydroelectric reservoir in boreal Quebec, this model estimated an average CO2 diffusive flux across the air-water interface of 225±51 mg CO2·m−2·d−1 in the summer of 2000 and of 446±93 mg CO2·m−2·d−1 in the summer of 2001. These average fluxes are representative of the whole icefree period.

Dietary habits in New France during the 17th and 18th centuries: An isotopic perspective

OBJECTIVE Little attention has been given, so far, to the early colonial diet in New France from an isotopic perspective. Historical records that compare France to New France suggest a shift toward a more diverse diet, including a higher protein intake due to an improvement in living conditions in the New World, despite the retention of ancestral dietary habits. This hypothesis will be explored here. MATERIALS AND METHODS Stable carbon (organic and mineral) and nitrogen isotopes were measured on 43 individuals from Notre Dame cemetery (first Catholic parish church cemetery in Montreal, 1683-1803) as well as 13 French compatriots from La Rochelle, France (Protestant Hospital Cemetery, 1765-1792). Intragroup variation (age at death, sex, and/or burial location) was investigated and compared to compiled data from various northeastern North American sites (N = 99). RESULTS The Notre Dame sample means are as follows: -19.6‰ versus VPDB for δ13 Ccollagen , -12.22‰ versus VPDB for δ13 Ccarbonate , and 11.5‰ versus AIR for δ15 N. They are significantly lower than both La Rochelle (-18.4‰, -11.67‰, and 12.7‰, respectively, p ≤ .005) and the northeastern North American groups used for this comparison (p = .000). DISCUSSION The isotopic values obtained from Notre Dame cemetery suggest that the diet was mainly based on C3 resources with limited C4 resources. Although different from all comparable contemporary sites, colonial Montreals diet remains most similar to La Rochelle, France. This study agrees with historians who have suggested that French dietary traditions seem to have been retained among the early colonial inhabitants of Montreal.