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Terrestrial ecosystems in the humid tropics play a potentially important but presently ambiguous role in the global carbon cycle. Whereas global estimates of atmospheric CO2 exchange indicate that the tropics are near equilibrium or are a source with respect to carbon, ground-based estimates indicate that the amount of carbon that is being absorbed by(More)
Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and(More)
Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High(More)
Results from two regional surveys and multi-lake seasonal studies were used to investigate the variability of phytoplankton photosynthesis and planktonic community respiration in central Amazon floodplain lakes. Hypothesized effects of optical and chemical variables on planktonic photosynthesis and respiration were examined statistically. Changes in(More)
A case of an adult with chronic active hepatitis associated with giant multinucleated liver cells is presented. The giant liver cells in this case are widespread and the picture resembles neonatal hepatitis. The morphology, pathogenesis, and epidemiology of giant hepatocytes found in human neonates and adults and in experimental animals is discussed.(More)
Taurocholate concentrations in fetal and neonatal rats were determined by radioimmunoassay. Total body taurocholate pool size varied from 0.0049 +/- 0.0008 to 203 +/- 8 nmol/g body weight from day 5 of gestation to 5 d after birth. A 50-fold increase in taurocholate pool size was observed between days 15 and 19 of gestation. The distribution of taurocholate(More)
[1] Large Amazonian rivers are known to emit substantial amounts of CO 2 to the atmosphere, while the magnitude of CO 2 degassing from small streams remains a major unknown in regional carbon budgets. We found that 77% of carbon transported by water from the landscape was as terrestrially-respired CO 2 dissolved within soils, over 90% of which evaded to the(More)
BACKGROUND The Amazon River runs nearly 6500 km across the South American continent before emptying into the western tropical North Atlantic Ocean. In terms of both volume and watershed area, it is the world's largest riverine system, affecting elemental cycling on a global scale. RESULTS A quantitative inventory of genes and transcripts benchmarked with(More)
Methane (CH4 ) fluxes from world rivers are still poorly constrained, with measurements restricted mainly to temperate climates. Additional river flux measurements, including spatio-temporal studies, are important to refine extrapolations. Here we assess the spatio-temporal variability of CH4 fluxes from the Amazon and its main tributaries, the Negro,(More)