Chattahoochee Riverkeeper has worked the past 1½ years on a “seamless transition” in top leadership, as one of Georgia’s most recognizable faces in environmental advocacy heads into retirement. The big change takes effect today as Sally Bethea, the environmental watchdog group’s founding riverkeeper and executive director, hands over reins to a couple of longtime, loyal employees. Jason Ulseth, technical programs director, becomes riverkeeper, and Juliet Cohen, who had served as general counsel, will serve as executive director.