René Canuel

Production of the greenhouse gases CH4 and CO2 by hydroelectric reservoirs of the boreal region

The emission fluxes and the distribution of dissolved methane (CH4) and carbon dioxide (CO2) were determined for 11 sampling stations in two hydroelectric reservoirs (flooded since 1978 and 1993) located in the James Bay territory of northern Quebec. The measured benthic fluxes for the two greenhouse gases were found to be either higher or similar to those determined at the water-air interface during the ice-free sampling periods. For the 2 year duration of the study, emission fluxes of CH4 to the atmosphere generally varied between 5 and 10 mg m−2 d−1, while those for CO2 ranged from 500 to 1100 mg m−2 d−1. Furthermore, through the use of static chambers at the water-air interface, we determined that the emission fluxes for the gases are controlled by molecular diffusion. Our calculated fluxes have been separated into two groups: (1) regular emission fluxes and (2) above-average emission fluxes. The first type comprises the majority of fluxes measured during the sampling periods (i.e., 88% for CH4 and 87% for CO2). The second group reflects unusual sampling conditions (e.g., strong winds, water column depths of less than 1 m, or flooded peatland mats floating at the surface). Although data for this group are limited, our preliminary results suggest that they may be an important component in an atmospheric emissions budget for large reservoirs. Concentration profiles for CH4 and CO2 dissolved in the water column clearly show that oxidation and/or horizontal advection of these gases are controlling factors in their subsequent release to the atmosphere. Most of the CH4 is oxidized within the first 25 cm above the flooded soil-water interface. Consequently, neither benthic emissions of CH4 and CO2 nor the type of flooded soil appear to control atmospheric emissions of these gases from hydroelectric reservoirs.

Greenhouse gas emissions from reservoirs of the western United States

= 0.81; p < 0.0001). All other correlations between GHG diffusivefluxes and independent variables tested were weak and/or not significant. Finally,while attempting to resolve the spatial variability in diffusive fluxes, we were able tocluster reservoirs neither according to geological nor ecological criteria.

New Evidence on Variations of Human Body Burden of Methylmercury from Fish Consumption

Epidemiologic studies commonly use mercury (Hg) level in hair as a valid proxy to estimate human exposure to methylmercury (MeHg) through fish consumption. This study presents the results yielded by a complete data set on fish consumption habits, Hg levels in edible fish resources, and corresponding Hg accumulation in hair, gathered in three distinct communities of eastern Canada. For one of these communities, the average hair Hg concentration was 14 times less than the expected value based on calculated daily oral exposure and current knowledge of MeHg metabolism. This finding could be explained by differences in specific genetic characteristics and/or interactive effects of other dietary components.

Sources and early diagenesis of lignin and bulk organic matter in the sediments of the Lower St. Lawrence Estuary and the Saguenay Fjord

Elemental and molecular organic matter concentrations were analyzed in sediments from the Lower St. Lawrence Estuary and the Saguenay Fjord in order to evaluate the historic evolution of pulp and paper mills solid-waste inputs in the system in the last decades and the relative reactivities of lignin and bulk organic materials in coastal sediments. A qualitative estimation of vascular plant sources to the Saguenay Fjord shows that the sedimentary terrigenous plant material is comprised predominantly of gymnosperm woods. In the deeper sediment horizons of the upper Saguenay basin, low intensive lignin parameters (C/V and S/V) and high percentages of lignin to total sedimentary organic carbon ( > 20%) all indicate elevated concentrations of woody gymnosperm tissues unprecedented in coastal sediments and directly related to the intense activity of the regions pulp and paper industries. The increased control on solid organic wastes from industrial effluents into the Saguenay river in the late 1980s to early 1990s is clearly apparent from increasing intensive parameter values and decreasing lignin fractions to the total sedimentary organic carbon (= 6-8%) in the upper basin surface sediments. Elemental and molecular analyses of fjord sediments, all indicate that most of the solid-phase discharge of lignified material by the pulp and paper industry is deposited rapidly close to the mouth of the river without reaching the downstream basins. In the St. Lawrence Estuary, intensive lignin parameters indicate that gymnosperm tissues are a major component of the sedimentary vascular plant material but with a significant fraction composed of angiosperm and nonwoody tissues. These latter types of organic tissues are particularly important components of terrigenous material in sediments deposited prior to the 1910-1920s. Acid/aldehyde ratios in most cores studied do not indicate clear-cut oxidative degradation of lignin material prior to its introduction in the aquatic system. The only exceptions are the two estuarine cores, where slightly elevated acid/aldehyde ratios relative to the range for fresh vascular plant tissues, might indicate mild aerobic fungal degradation of the sedimentary lignin material. Organic carbon, total nitrogen, organic phosphorus and lignin derived phenols all exhibited decreasing concentrations with core depth in the sediments of the Lower St. Lawrence Estuary. First-order degradation rate constants for all four chemical categories ranged between 0.02-0.05 yr -1 . The order of apparent reactivity among the different organic compounds is TN ≥ C org > P org > lignin at the head of the Laurentian channel and lignin TN = C org > P org further downstream. The surprising diagenetic selectivity observed at the upstream station is probably due to a higher flux of fresh, labile organic matter that reaches the sediment-water interface and degrades preferentially to more refractory materials such as lignin. Further downstream, little diagenetic selectivity was observed below the sediment-water interface indicating an overall refractory nature of the sedimentary organic matter. Finally, the differences in reactivity observed between C org and P org at both stations contradict earlier assumptions that no fractionation occurs between organic carbon and phosphorus during anaerobic degradation.

Comparison of greenhouse gas emissions from an old tropical reservoir with those from other reservoirs worldwide

Flooding of forest soils, following the creation of reservoirs, worldwide is a significant anthropic source of GHG emissions. In fact, since 1993, i t has been observed that the impoundment of large forest areas in the boreal region leads to an increase in CO, and CH4 evasion to the atmosphere (Ruoo et al. 1993, DucHEMIN et al. 1995, 1998, VAisANEN et al. 1996). Up to now there have been only a few data sets available to describe anthropic greenhouse gas (GHG) emissions from tropical reservoirs (GALY-LACAUX et al. 1997, KELLER & STALLARD 1994). However, these measurements tend to demonstrate that tropical reservoirs are also important sources ofGHG. Furthermore, FEARNSIDE (1995) concluded, from extrapolations based on these results, that tropical reservoirs could emit larger quantities of GHG than boreal reservoirs. The purpose of this paper is to present a first data set of GHG evasion measurements, from a 21-year-old tropical reservoir in the Brazilian Amazon, and to compare it with data sets published for other reservoirs of the tropical and boreal region. According to the geochemical dynamics of tropical environments, i t is expected that the GHG emissions from the tropical reservoir would be greater than those from boreal and temperate ones.

An Ecosystem Approach to Describe the Mercury Issue in Canada: From Mercury Sources to Human Health

It has been decades now since the international scientific community initially raised the issue of mercury (Hg) contamination in the global environment. The presence of Hg in ecosystems is ubiquitous, even in the absence of local/regional contamination point sources. Almost all fish consumers (occasional or frequent) are exposed to this contaminant. Governments of the industrialized countries have invested considerable financial and human resources, in order to better understand the biogeochemical behavior and cycling of Hg and its impacts on the health of populations. Indeed, our knowledge of the sources and fate of this pollutant has greatly evolved since these early reports. Numerous protocols, technical documents, epidemiological and clinical studies, detailing precise aspects of the Hg cycle have been published. However, given the complexity of environmental processes leading to the accumulation of Hg in fish tissue, and the relative importance of fish as a protein source among communities, most available literature fails to fully evaluate the level of risk to health (and/or the health benefits related to fish consumption) encountered by fish consumers in their daily lives. This paper summarizes the learning acquired through a wide-scale integrated study of the mercury (Hg) pathways in lake environments of three distinct regions located in Eastern Canada : Lake St. Pierre (LSP), Labrador (Lab), and Abitibi (Ab). This research was accomplished by a multidisciplinary team of researchers assembled under the auspice of the Collaborative Mercury Research Network (COMERN), a major Canadian initiative supported by numerous universities and government agencies throughout the country. The prime focus of the study was to link human exposure to Hg with particular local/regional environmental and socioeconomic characteristics and settings. Two conditions must co-occur to define a situation where higher Hg exposure can be identified for populations/sub-populations/ groups : Frequent fish consumption;Mercury levels of concern in the edible fish resource.

Human exposure to mercury as a consequence of landscape management and socio-economical behaviors: Three case studies in Canada

We have launched in 2001 the NSERC-supported pan-Canadian Collaborative Mercury Research Network. This COMERN project addresses the urgent need for the development of a framework enabling researchers, political stakeholders, and communities concerned by the mercury question to evolve towards an interdisciplinary association capable of synergistically combining our knowledge on Hg into an original synthesis. We are presently working at developing a simple index representative of the specific vulnerability of an ecosystem to Hg bioaccumulation and subsequent transfer to humans. This index includes two concepts: (1) the sensitivity to bioaccumulation, induced and influenced by factors such as the Hg loading, the different transport and methylation processes, and human activities and (2) the adaptability of the ecosystem, an evaluation of its resilience, or its capacity to recover and/or to cope with the contamination, taking into account the social and political resources within the communities impacted. We started to apply this approach to four distinct case studies representative of the large spectrums of both Hg contamination and Hg exposure through fish consumption in Canada, i.e. sports fishers of lakes of the boreal forest, commercial fishers of the industrialized region of the St Lawrence River, first nation communities in Labrador and seafood consumers of the Bay of Fundy.