Nearly two years ago, Mark Tercek left his job as a managing director at Goldman Sachs to attend to an ecosystem devoted to another kind of green: the Nature Conservancy. TNC, which watches over 119 million acres of land in more than 30 countries, has a significantly different culture from the one he’d dominated on Wall Street. While conducting his first organization-wide online meeting in 2008, Tercek swigged from a Poland Spring water bottle. The next day, he was greeted by half a dozen welcome gifts from colleagues in the form of reusable water containers. “Not so good to be the brand-new head of the biggest conservation organization and drinking out of a plastic water bottle,” he says.