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Emission of hydrogen from deep and shallow freshwater environments.

Emission von Wasserstoff aus tiefen und flachen Süßwasserökosystemen
: Schütz, H.; Conrad, R.; Goodwin, S.; Seiler, W.

Biogeochemistry (1988), Nr.5, S.295-311
ISSN: 0168-2563
Fraunhofer IFU; 2002 in Helmholtz-Gesellschaft integriert
ebullition; Gasblase; lake sediment; lake water; paddy field; Pflanzentransport; plant mediated gas flux; Reisfeld; Seesediment; Seewasser

In-situ partial pressures of hydrogen in anoxic profundal lake sediments reached values of up to 5 Pa which were more than 5 orders of magnitude lower than the partial pressures of methane. Analysis of gas bubbles collected from anoxic submerged paddy soil showed H2 partial pressures in the range of +- 1.3 Pa being ca. 4 orders of magnitude lower than the CH4 partial pressures. H2 emission rates, on the other hand, were less than 3 orders of magnitude lower than the CH4 emission rates indicating that H2 and CH4 were oxidized to a different extent in the rhizosphere of the soil before they reached the atmosphere, or that H2 was produced by plants. More than 70% of the emitted H2 reached the atmosphere via plant-mediated flux. The rest was emitted via ebullition from the anoxic soil and, in addition, was produced in the paddy water. A significant amount of H2 was indeed found to be produced in the water under conditions where thalic algae and submerged parts of the rice plants produced o xygen by photosynthesis. Very little H2 was emitted via molecular diffusion through the paddy water; in addition, this amount was less than expected from the degree of supersaturation and the diffusional emission rate of CH4 indicating a relatively high rate of H2 consumption in the surface film of the paddy water. The total H2 source strength of rice padies and other freshwater environments was estimated to be less than 1 Tg yr E-1, being negligible in the atmospheric budget of H2. (IFU)