Environmental Protection Agency administrator Lisa Jackson announced her resignation yesterday. Although many expected her to stay on in a second Obama term — like Clinton EPA head Carol Browner who stuck it out for two full terms — Jackson declared it was time to seek new opportunities. So who comes next and what will this mean for environmental regulation? Jackson was an aggressive EPA head, who pushed stringent regulatory initiatives wherever possible. Some of her efforts, like more stringent air quality standards, were too much for the administration to support (at least so long as it faced reelection). Others, such as new rules governing coal-ash and further rounds of greenhouse gas regulations, are still waiting in the wings. Like other administration officials, some of her rules benefited preferred industries, so it’s no wonder the renewable-fuel lobby praised her tenure. This isn’t the last we’ve heard of Jackson, to be sure. An EPA Inspector General investigation of her use of outside e-mail addresses to evade disclosure continues, and EPA’s new regulations will bear her fingerprints for years to come.