WASHINGTON (Jan. 9, 11:25 a.m. ET) — Lisa Jackson, the head of the U.S. Environmental Protection Agency, who had become a frequent target of Republican and various industry attacks, is stepping down this month.

Jackson will end her four-year term as the nation’s top environmental officer sometime around President Barack Obama’s second inauguration. In a short statement announcing her departure, Jackson thanked Obama for nominating her and having the confidence in her to do the job.

“I will leave EPA confident the ship is sailing in the right direction, and ready in my own life for new challenges, time with my family and new opportunities to make a difference,” she wrote in the statement.

Obama said Jackson had an unwavering commitment to the health of American families and children.

“Under her leadership, the EPA has taken sensible and important steps to protect the air we breathe and the water we drink, including implementing the first national standard for harmful mercury pollution, taking important action to combat climate change under the Clean Air Act, and playing a key role in establishing historic fuel economy standards that will save the average American family thousands of dollars at the pump, while also slashing carbon pollution,” Obama said in a statement.

He called her an important part of his team.

Jackson, 50, spent a total of 20 years with the EPA, 16 of them early in her career. She also worked for the New Jersey Department of Environmental Protection for six years.

The move was not a complete surprise as cabinet members and top political appointees often do not serve more than one presidential term. Carol Browner served all eight years of Bill Clinton’s presidency, the longest tenure of an EPA administrator. No other EPA administrator has served more than four years. Both George W. Bush and Ronald Reagan had three EPA administrators during their eight years in office.

Reaction to Jackson’s departure was deeply partisan, with those on the left side of the aisle praising her and those on the right calling for a more moderate choice in a successor.

“Secretary Jackson played the environmental ‘bad cop’ to President Obama’s more moderate ‘good cop,’ but the result of their tag-team effort has been a huge expansion of the EPA’s power,” said S.T. Karnick, director of research at the Hartland Institute, a libertarian think tank, in a statement.

He said appointing another EPA head like Jackson could drive the economy downward with more regulations that threaten jobs.

David Foster, executive director of the BlueGreen Alliance, said Jackson was a tireless advocate for a better, cleaner environment, praising some of her various initiatives, including instituting greenhouse gas emission regulations.

“Her steadfast leadership elevated vitally important issues like climate change by issuing the proposed Carbon Pollution Standard, limiting the amount of greenhouse gas emissions from future power plants,” he said. “She was key in negotiating the highest vehicle fuel economy standards in a generation.”

Michael Brune, executive director of the Sierra Club, said Jackson was a strong advocate for clean air, clean water, a stable climate and public health, all the face of detractors.

“With her leadership, our country has made a big down payment on its goals to reduce carbon pollution,” he said in a statement. “Millions of Americans will breathe easier and have access to safe, clean water.”

One of Jackson’s earliest issues was coal ash, as a massive coal ash spill in Tennessee occurred just months before she took office. EPA has been slow to address the issue, delaying various rulemaking on the issue, including deeming coal ash as a hazardous substance if it is not being reused.

That proposal had coal ash recyclers worried, saying the designation of coal ash being a Subtitle C substance would give it a stigma, making a secondary market for the material tough.

Republican lawmakers introduced legislation to force EPA to regulate the substance under Subtitle D and environmental groups have sued EPA for delaying final ruling on the issue. Ultimately, the issue will likely be decided in 2013, after Jackson’s replacement is named.

“I hope this resignation indicates that the administration is going to moderate its position regarding the use of coal, but only time will tell,” said U.S. Rep. Morgan Griffith, R-Va., said in a statement.