Geothermics 61 (2016) 149–159 Contents lists available at ScienceDirect Geothermics jo ur nal home p ag e: www .elsevier.com/locate/geothermics Concentrations of sulphur and trace elements in semi-arid soils and plants in relation to geothermal power plants at Olkaria, Kenya Thecla M. Mutia a,b,c,∗ , Thráinn Fridriksson d , Ingibjörg S. Jónsdóttir a,e a Faculty of Life and Environmental Sciences, University of Iceland, Sturlugotu 7, 101 Reykjavik, Iceland b United Nations University, Geothermal Training Programme, Orkustofnun, Grensasvegur 9, 108 Reykjavik, Iceland c Geothermal Development Company Limited, P.O Box 17700, 20100 Nakuru, Kenya d ISOR, Iceland Geosurvey, Grensasvegur 9, 108 Reykjavik, Iceland e Department of Arctic Biology, University Centre in Svalbard, UNIS, 9171 Longyearbyen, Norway a r t i c l e i n f o Article history: Received 14 September 2015 Received in revised form 20 January 2016 Accepted 21 January 2016 Available online 17 February 2016 Keywords: Tarchonanthus camphoratus Leaf damage Plant growth trait a b s t r a c t Exploitation of geothermal energy is considered to have minimal ecological impacts. However, this assumption has not been widely studied. We tested the hypothesis that emitted elements from geother- mal power plants would be enriched in both plant tissue and soil close to the power plants with consequences for plant health. The concentrations of sulphur, arsenic, boron, antimony and mercury in the soil and leaves of the dominating shrub, Tarchonanthus camphoratus, were assayed and associated foliar injury and growth traits assessed at variable distances and directions from two geothermal power plants in Kenya, Olkaria I (operated since 1981) and Olkaria II (since 2003). Sulphur concentration in the leaves was elevated close to the power plants and decreased with increasing distance, implying atmo- spheric input of sulphur to the ecosystem from the power plants. Similar trends were not detected in soil and with the other elements. Our study design did not support the observed higher degree of leaf injury close to the power plants. Similarly, any association of growth traits with distance or location was not detected. The results were compared with data from a reference site well out of the range of element deposition from the power plants. Overall, the levels of sulphur, arsenic, boron and antimony in leaves of T. camphoratus and sulphur, and boron concentration in soil around the Olkaria I and Olkaria II geother- mal power plants were higher than at the reference site. Furthermore, the number of healthy leaves per shrub and stem circumference were lower around the power plants than the reference site, while leaf damage and other plant growth traits did not differ. In spite of relatively weak indication of the harmful effects of the geothermal power plants on the dominating shrub species, follow-up experimental studies and studies on more sensitive ecosystem components are recommended to advise existing mitigation measures against chronic exposure from the emitted gases and associated impacts. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Geothermal energy is listed among those world’s renewable energy sources considered to have minimal ecological impacts with a great potential for the future (Bayer et al., 2013; Wong and Tan, 2014). However, a range of non-condensable gases (NCGs) and trace elements typically ranging from less than 0.2% to over 25% weight of steam (Rodríguez, 2014) are emitted from the power plants dur- ing the energy conversion process. Some of these components have been reported to deposit in the surrounding ecosystems (Bargagli ∗ Corresponding author at: Geothermal Development Company Limited, P.O Box 17700, 20100 Nakuru, Kenya. E-mail address: teclamutts@gmail.com (T.M. Mutia). et al., 1997; Bacci et al., 2000; Paoli and Loppi, 2008), but the consequences are still poorly known. Potentially, they can cause toxicological stress on human beings, plants, and other ecosys- tem components (Bayer et al., 2013). With increasing utilization of this energy source there is an urgent need for detailed studies on ecological responses to geothermal power plant emissions. Commonly, the NCG fraction comprises 73–98% w/w carbon dioxide (CO 2 ), 1–24% w/w hydrogen sulfide (H 2 S), 0.02–0.65% w/w methane (CH 4 ), 0.1–8% w/w hydrogen (H 2 ), 0.3–16% w/w nitrogen (N 2 ), 0.1–3% argon (Ar), and traces ( <0.001% w/w) of radon, boron, mercury, arsenic, antimony, and ammonia in gaseous and dissolved form (Baldi, 1988; Bargagli et al., 1997; Loppi et al., 1998; Gunerhan, 1999; Loppi, 2001; Bussotti et al., 2003; Rodríguez, 2014). Of these gases, H 2 S poses a major concern due to its odour and potential tox- icity even at low concentration. The trace elements are also widely http://dx.doi.org/10.1016/j.geothermics.2016.01.017 0375-6505/© 2016 Elsevier Ltd. All rights reserved.