Nicolas Soumis

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.

Presence of organophosphate insecticides in fish of the Amazon River

Trace levels of three organophosphate insecticides (OPI) were detected in eight fish species from the region of Santarem, State of Para, 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.

Assessing carbon dynamics in natural and perturbed boreal aquatic systems

Most natural freshwater lakes are net greenhouse gases (GHG) emitters. Compared to 25 natural systems, human perturbations such as watershed wood harvesting and long term reservoir 26 impoundment lead to profound alterations of biogeochemical processes involved in the aquatic 27 cycle of carbon (C). We exploited these anthropogenic alterations to describe the C dynamics in 28 five lakes and two reservoirs from the boreal forest through the analysis of dissolved carbon 29 dioxide (CO2), methane (CH4), oxygen (O2), and organic carbon (DOC), as well as total nitrogen 30 (TN) and phosphorus (TP). Dissolved and particulate organic matter, forest soil/litter and 31 leachates, as well as dissolved inorganic carbon (DIC) were analyzed for elemental and stable 32 isotopic compositions (atomic C:N ratios, δ13Corg, δ13Cinorg and δ15Ntot). We found links between 33 the export of terrestrial OM to these systems and the dissolved CO2 and O2 concentrations in the 34 water column, as well as CO2 fluxes to the atmosphere. All systems were GHG emitters, with 35 greater emissions measured for systems with larger inputs of terrestrial OM. The differences in 36 CO2 concentrations and fluxes appear controlled by bacterial activity in the water column and the 37 sediment. Although we clearly observed differences in the aquatic C cycle between natural and 38 perturbed systems, more work on a larger number of water bodies, and encompassing all four 39 seasons should be undertaken to better understand the controls, rates, as well as spatial and 40 temporal variability of GHG emissions, and to make quantitatively meaningful comparisons of 41 GHG emissions (and other key variables) from natural and perturbed systems.

Characterization of pesticide consumption in the county of Santarém, Pará, Brazil

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 Santarem (State of Para, 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 Santarem 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 (varzeas), making relevant a thorough study on the potential contamination of this environment and its biota.