Dr. Bjarni Gautason : The isotopic composition of moss... (6-10-2016)

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Dr. Bjarni Gautason (Iceland Geosurvey)

The isotopic composition of moss from lava fields surrounding geothermal power plants in SW Iceland - Implications for moss deterioration

Jeudi 6 octobre 2016 à 13h30/ Thursday, October 6, 2016, 1:30pm

Local PK-7605, 201 ave. Président-Kennedy, UQAM

Résumé / Abstract:

The environmental impact of utilizing geothermal energy for power production in conventional power-plants includes disposal of spent fluids and release non-condensable gases (NCG’s). Reinjection of spent fluid has the combined benefit of maintaining fluid mass within the geothermal system and reducing the environmental impact of power-production. Re-injection of at least part of the spent fluid is now commonplace. In Iceland, experimental re-injection of NCG’s (e.g. CO2 and H2S) shows promise, but has still not become part of routine operation of geothermal power plants.  It has been suggested that the deterioration of moss in the lava fields surrounding the geothermal power-plants is the result of increased emissions of H2S. In an effort to understand better the potential environmental impact of NCG’s such as H2S we collected samples of woolly fringe moss (Rhacomitrium lanuginosum) from the lava-fields around the geothermal powerplants at Hellisheiði and Nesjavellir, in SW-Iceland. These samples, collected at the end of the growing season in 2014, have been analyzed for the abundance and isotopic composition of S, N and C. In addition, we have obtained isotopic data on moss samples collected in 2008, for a study on trace-element abundance in moss, from the same areas. A clear signal of hydrothermal/magmatic sulfur is detected in the moss samples closest to the power plants. Furthermore, the data forms a mixing array between hydrothermal/magmatic and marine derived sulfur. Sulfur isotopes are useful for tracking hydrothermal input in the moss samples. They may provide a means to study the rate of decay of the hydrothermal/magmatic signal in moss that will presumably accompany successful reduction in emissions concomitant with re-injection of NCG’s.