Hydropower or non-market values of nature : a contingent valuation study of Jägala Waterfalls, EstoniaEhrlich, Üllas; Reimann, MartRecent Researches in Energy, Environment, Devices, Systems, Communications and Computers : International Conference on Energy, Environment, Devices, Systems, Communications, Computers (EEDSCC'11) : Venice, Italy, March 8-10, 20112011 / p. 232-237 : ill