| Summary: | Very little is known on the ecosystem impacts of emissions from geothermal power plants. The emissions, comprising mainly of non- condensable gases (NCGs) i.e. carbon dioxide, hydrogen sulphide, methane and trace elements such as arsenic, boron, antimony and mercury, have the potential to deposit and accumulate in ecosystems. At elevated levels, some NCGs can cause ecosystem stress, especially H 2 S and the trace elements. The aim of this thesis is to assess the effects of these elements on terrestrial ecosystems around two geothermal areas in contrasting biomes i.e. Kenya and Iceland. Dominant plant species around each geothermal study area, Tarchonanthus camphoratus shrub in Kenya and Racomitrium lanuginosum moss in Iceland, were used as bio-indicators and concentrations of sulphur, arsenic, boron, antimony and mercury were mapped in their tissues and soils at increasing distances from the power plants along the prevailing wind direction in field surveys. Patterns of plant growth and health along the same distances and wind direction gradients were also studied to assess any potential effects related to the power plants. Controlled experiments were thereafter carried out on the same plant species to assess in detail the effects of the most abundant phytotoxic NCG, i.e. H 2 S gas, on plant growth and health. Results of the field surveys and experiments indicated that the main geothermally emitted component, H 2 S gas, deposits and accumulates in plants and soils. The measured trace element concentrations in plants and soils (from the field surveys): arsenic, boron, antimony and mercury, did not show strong patterns attributable to the geothermal power plant emissions. Further, results of the surveys in relation to geothermal power plant emissions showed weak indications of effects on Tarchonanthus camphoratus shrub growth and health around the Olkaria geothermal power plants in Kenya, while in Iceland, the growth of Racomitrium lanuginosum moss was reduced around the Hengill geothermal power plants. ...
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