The impact of geothermal power plants on forest vegetation. A case study at Travale (Tuscany, Central Italy)

A survey of the crown status of Turkey oak (Quercus cerris L.) trees in the boron-rich area at Travale (Southern Tuscany, Italy) was carried out in order to evaluate the impact of geothermal power plants. Crown thinness was assessed and morphological and chemical tests were carried out on leaf samples. Leaf area and dry weight were determined as morphological parameters; while the chemical measurements performed included nitrogen and potassium (among the nutrients), and sulphur, boron, arsenic and mercury (among the elements of geothermal origin). Acute damage was found only in the area immediately adjacent to the outlets and is the result of the action of boron; crown thinness, on the other hand, is affected by the nature of the geological substrate. High quantities of sulphur were found in leaves throughout the survey area, due both to the availability of this element in the geopedological substrate and to the atmospheric input of geothermal H2S. The leaf content of this element correlates negatively with the distance from the power plants. Boron and arsenic are the other geothermal origin elements most commonly found in plant matrices. The presence of these two elements is associated with leaf area reduction and/or an increase of specific dry weight. The most significant impact on the environment appears to be exerted by the southernmost power plant, where there is an unfavourable ratio between quantity of emissions and height of the chimneys.