Abstract. Most lakes worldwide are supersaturated with carbon dioxide (CO2) and consequently act as atmospheric net sources. Since CO2 is a major greenhouse gas (GHG), the accurate estimation of CO2 exchanges at air/water interfaces of aquatic ecosystems is vital in quantifying the carbon budget of aquatic ecosystems overall. To date, lacustrine CO2 emissions are poorly understood, and lake carbon source proportions remain controversial, largely due to a lack of integration between aquatic and terrestrial ecosystems. In this paper a new process-based model (TRIPLEX-Aquatic) is introduced incorporating both terrestrial inputs and aquatic biogeochemical processes to estimate diffusive emissions of CO2 from lake systems. The model was built from a two-dimensional hydrological and water quality model coupled with a new lacustrine CO2 diffusive flux model. For calibration and validation purposes, two years of data collected in the field from two small boreal oligotrophic lakes located in Quebec (Canada) were used to parameterize and test the model by comparing simulations with observations for both hydrodynamic and carbon process accuracy. Model simulations were accordant with field measurements in both calibration and verification. Consequently, the TRIPLEX-Aquatic model was used to estimate the annual mean CO2 diffusive flux and predict terrestrial dissolved organic carbon (DOC) impacts on the CO2 budget for both lakes. Results show a significant fraction of the CO2 diffusive flux (~30–45%) from lakes was primarily attributable to the input and mineralization of terrestrial DOC, which indicated terrestrial organic matter was the key player in the diffusive flux of CO2 from oligotropical lake systems in Quebec, Canada.

Most natural freshwater lakes are net greenhouse gas (GHG) emitters. Compared to natural systems, human perturbations such as watershed wood harvesting and long‐term reservoir impoundment lead to profound alterations of biogeochemical processes involved in the aquatic cycle of carbon (C). We exploited these anthropogenic alterations to describe the C dynamics in five lakes and two reservoirs from the boreal forest through the analysis of dissolved carbon dioxide (CO2), methane (CH4), oxygen (O2), and organic carbon (DOC), as well as total nitrogen and phosphorus. Dissolved and particulate organic matter, forest soil/litter and leachates, as well as dissolved inorganic carbon were analyzed for elemental and stable isotopic compositions (atomic C:N ratios, δ13Corg, δ13Cinorg and δ15Ntot). We found links between the export of terrestrial organic matter (OM) to these systems and the dissolved CO2 and O2 concentrations in the water column, as well as CO2 fluxes to the atmosphere. All systems were GHG emitters, with greater emissions measured for systems with larger inputs of terrestrial OM. The differences in CO2 concentrations and fluxes appear controlled by bacterial activity in the water column and the sediment. Although we clearly observed differences in the aquatic C cycle between natural and perturbed systems, more work on a larger number of water bodies and encompassing all four seasons should be undertaken to better understand the controls, rates, and spatial as well as temporal variability of GHG emissions, and to make quantitatively meaningful comparisons of GHG emissions (and other key variables) from natural and perturbed systems.

Seasonal snow is an active media and an important climate factor that governs nutrient transfer in Arctic ecosystems. Since the snow stores and transforms nutrients and contaminants, it is of crucial importance to gain a better understanding of the dynamics of contaminant cycling within the snowpack and its subsequent release to catchments via meltwater. Over the course of a two-month field study in the spring of 2008, we collected snow and meltwater samples from a seasonal snowpack in Ny-Ålesund, Norway (78°56′N, 11°52′E), which were analyzed for major inorganic ions and some organic acids, as well as total, dissolved, bioavailable mercury (THg, DHg, BioHg, respectively) and monomethylmercury (MMHg) species. We observe a seasonal gradient for ion concentrations, with surface samples becoming less concentrated as the season progressed. A significant negative correlation between BioHg and MMHg was observed in the snowpack. MMHg was positively and significantly correlated to methanesulfonate concentrations. Based on these results, we propose a new model for aerobic methylation of mercury involving species in the dimethylsulfoniopropionate cycle.

A mechanistic semi-empirical carbon cycle model of the La Grande reservoir complex in northern Quebec, Canada was conceived in order to investigate the climate impact of such a large alteration of the continental water cycle. The model includes inputs from the drainage basin, organic matter release from flooded soils, CO2 emissions across the water–atmosphere interface and sedimentation. Most input data stems from previous research by our group on those ecosystems. The model includes the seven reservoirs of the La Grande complex and was run for periods of 50 and 100 years. Terrigeneous dissolved, particulate and suspended soil carbon fluxes and concentrations were computed. Over 100 years, 31.3×1012gC are released from flooded soils, equivalent to 28–29% of inputs from the drainage basin. 40–74% of dissolved organic carbon is mineralized. CO2 fluxes over 100 years are 50.5–79.8×1012gC, 46.4–67.9×1012gC more than in the absence of reservoirs. The increase in mineralization of organic matter and in CO2 emissions is a result of the increase in cumulated water residence time due to the creation of the reservoirs. Changes in other carbon sinks and sources likely offset a part of this additional carbon flux to the atmosphere. In the first years following flooding of the reservoir, organic carbon release from flooded soils exceeds CO2 emissions, implying the downstream export of large quantities of eroded soil organic carbon. After this initial period, CO2 emissions are fuelled by organic carbon originating from the drainage basin.

The dry ice sowing experiment (DISE) consisted in adding dry ice to a lake and monitoring the subsequent evasion of carbon dioxide (CO2). DISE allowed us to evaluate two approaches commonly used for measuring aquatic CO2 diffusive fluxes: the boundary layer equation (BLE) from Cole and Caraco (1998) and a particular model of static chamber (SC). CO2 evasion measurements with both approaches were compared to CO2 mass budgets as a relative reference to define their recovery coefficients (p). p for the BLE and the SC over the whole measurement period were 101 +/- 14% and 115 +/- 56%, respectively. Results from discrete sampling intervals revealed that the BLE generally provided estimations in good agreement (80-130%) with the mass budgets during both daytime and nighttime. Variations in p for the BLE were related to wind speed and, consequently, piston velocity (k600). The SC overestimated CO2 evasion during daytime (149 +/- 39%), and underestimated it during nighttime (57 +/- 18%). Variations in p for the SC were related to k600, stemming mainly from the alteration of the air/ water temperature gradient.

In order to evaluate the role of photochemistry in the carbon dioxide (CO2) generation from a 10-year-old boreal reservoir, the photomineralization of dissolved organic matter (DOM) was assessed and compared to a boreal river as well as to boreal and temperate lakes during July and August, 2003. Sterile water samples were irradiated by sunlight over the whole photoperiod and subsequently analyzed for CO2. Mean energy-normalized apparent photochemical yield of CO2 (an index of DOM photoreactivity normalized for the energy absorbed by samples) was significantly higher in the reservoir (27.7 ± 13.0 mg CO2·m−3·kJ−1) and the boreal river (35.8 ± 2.3 mg CO2·m−3·kJ−1) than in the boreal lakes (15.5 ± 5.1 mg CO2·m−3·kJ−1). The DOM photoreactivity of the temperate lakes (20.9 ± 8.1 mg CO2·m−3·kJ−1) was not statistically different from any type of boreal water bodies. There was no significant difference in either the integrated photoproduction of CO2 (273–433 mg CO2·m−2·d−1) or the potential photochemical contribution to CO2 diffusive fluxes (56–92%) among these water bodies. DOM photoreactivity was significantly affected by the cumulative hydrological residence time (CHRT) when considering the whole data set. However, when considering only the boreal water bodies, iron (Fe) and manganese (Mn) also intervened. The fact that DOM photoreactivity was related to CHRT as well as to Fe and Mn concentrations, which are respectively permanent and long-lasting features of the reservoir, suggests that the photoproduction of CO2 is not likely to decrease over time. This process may therefore play a substantial role in the long-term CO2 emissions from boreal reservoirs during the summer, its potential contribution to CO2 diffusive fluxes being estimated at 56 ± 29 %.

AbstractMost studies dealing with greenhouse gas (GHG) emissions from large boreal reservoirs were conducted during the ice‐free period. In this paper, the potential methane (CH4) and carbon dioxide emissions are estimated for two hydroelectric reservoirs, as well as for a small experimental reservoir from boreal latitudes (northern Quebec, Canada) at the ice break‐up event through diffusion (diffusive fluxes) and release of bubbles (bubbling fluxes). The results of this preliminary study suggest that the winter diffusive fluxes at the air–water interface of the sampled reservoirs represent < 7% of their cumulative carbon emissions during the ice‐free period. Furthermore, the release upon ice‐break of CH4 bubbles accumulated under the ice cover during the winter could represent 2% of the summer carbon emissions from hydroelectric reservoirs in northern Quebec. The results presented herein suggest that the GHG emissions upon ice break‐up from the boreal reservoirs investigated are a small, but non‐negligible, component of their annual GHG emissions.

AbstractThe ever‐increasing demand for energy over the recent development of societies has spurred the construction of hydroelectric facilities. Since dams were first used to generate hydropower around 1890, their construction rate increased tremendously to peak during the 1950s and the 1980s. Today, about 25% of the 33,105 large dams (≥15 m height) listed by the International Commission on Large Dams (ICOLD) are used for hydropower generationand currently provide 19% of the world's electricity supply. Although over 150 countries operate hydroelectric plants, Brazil, China, Canada, Russia, and the United States produce more than 50% of the world's hydropower. According to data from 1996, hydroelectric reservoirs worldwide cover an estimated 600,000 km2.

Six reservoirs located in the Western United States (F. D. Roosevelt, Dworshak, Wallula, Shasta, Oroville, and New Melones) were sampled in order to estimate their greenhouse gas (GHG) emissions. Two types of fluxes were assessed: (1) diffusive fluxes of methane (CH4) and carbon dioxide (CO2) at the air/water interface and (2) degassing fluxes of CH4 and CO2 from water passing through the turbine spillways. Diffusive flux measurements indicated that the surface of the reservoirs were a source of CH4 during the sampling period (from +3.2 to +9.5 mg CH4 m−2 d−1). Oroville (+1026 mg CO2 m−2 d−1) and Shasta (+1247 mg CO2 m−2 d−1) surfaces were also sources of CO2. In contrast, the surface of all the other reservoirs constituted sinks for CO2 (from −349 to −1195 mg CO2 m−2 d−1). Degassing fluxes ranged from +0.003 to +0.815 t CH4 d−1, and from +16 to +324 t CO2 d−1. Daily GHG budgets ranged from +0.146 to +2.228 t CH4 d−1, and from −15 to +224 t CO2 d−1. Degassing fluxes represented an important term of these budgets. A significant correlation was observed between the magnitude of CO2 diffusive fluxes and the water pH (R2 = 0.81; p < 0.0001). All other correlations between GHG diffusive fluxes and independent variables tested were weak and/or not significant. Finally, while attempting to resolve the spatial variability in diffusive fluxes, we were able to cluster reservoirs neither according to geological nor ecological criteria.

Trace levels of three organophosphate insecticides (OPI) were detected in eight fish species from the region of Santarém, State of Pará, Brazil. Individual concentrations of OPI in fish ranged from less than the detection limit to 2,1 ppb. Mean concentrations of chlorpyrifos, malathion, and methyl-parathion were 0,3 ± 0,3, 0,1 ± 0,1, and 0,3 ± 0,3 ppb, respectively. Pellona flavipinnis, the largest and fattest piscivorous species analyzed, was the most contaminated. Since an inhabitant of this Amazonian region consumes 220 g of fish per day on average, ingested doses of chlorpyrifos, malathion, and methyl-parathion may reach up to 308, 220, and 462 ng·d-1, respectively. Compared to acceptable daily intakes (ADI), quantities of OPI absorbed via fish consumption on a daily basis are far below deleterious levels. We estimated that even considering the highest OPI contents detected, the average daily fish consumption of anadult of 60 kg would have to increase by ca. 1 950, 5 450, and 2 600 times to reach ADI of chlorpyrifos, malathion, and methyl-parathion, respectively. Neither fish diet nor fish lipid content enabled us to completely explain the interspecific differences observed.

Le 2 octobre dernier, Hydro-Quebec rendait public son projet de construction d’une centrale au gaz naturel a cycle combine de 800 megawatts a Melocheville. Le debut des travaux est prevu pour 2003 alors que la mise en operation de la centrale se fera en 2006. D’emblee, la decision d'Hydro-Quebec, une societe dont l’expertise est essentiellement hydroelectrique, peut surprendre. Elle suggere par ailleurs de questionner les impacts environnementaux d’un tel projet, particulierement devant la ne...

Many potentially harmful pesticides for both human health and the environment are used in Brazilian Amazon. However, no scientific datum on pesticide usage is presently available for this region. Consequently, it is difficult to assess which substances arc used and in which quantities. As an important premise for future work on pesticide contamination in the county of Santarém (State of Pará, Brazil), a survey was conducted in order to qualify and quantify the use of some pesticides in this region. This investigation was made between January and March 1997 and August and October 1998 and revealed use of several organophosphates, synthetic pyrethroids and carbamates insecticides. Furthermore, many herbicides and fungicides were listed. These pesticides are used for agriculture, domestic, and sanitary programs. This paper also provides a first estimation of quantities of some insecticides commonly used in agriculture (chlorpyrifos, malathion, metamidophos and methyl-parathion). The annual consumption for these four compounds is estimated at ca. 1 910 kg. Organophosphate insecticide consumption in the county of Santarém seems to be lower than the Brazilian average in terms of «per capita» and «per agricultural area» consumptions. Nevertheless, this county uses toxic substances on sensitive environments such as floodplains (várzeas), making relevant a thorough study on the potential contamination of this environment and its biota.

Depuis la fin des annees 50, l'Amazonie bresilienne est devenue l'une des regions du monde les plus touchees par la confrontation entre la conservation de l'environnement et developpement regional. Avec son territoire de 5 217 423 km2 et ses nombreuses ressources naturelles, elle semblait, aux yeux de bien des dirigeants bresiliens, pouvoir contribuer activement au redressement de l'economie nationale. Ainsi, au fil du temps, divers acteurs ont mis en chantier l'Amazonie et l'on modele par le...