When Glen Besa, the director of the Virginia chapter of the Sierra Club, got the news Wednesday that Del. Harvey Morgan (R-Gloucester) was retiring from the House of Delegates after 31 years, he sent a friend a note.

“Damn,” it read. “We’re losing all our friends.”

Morgan, chairman of the House’s Agriculture, Chesapeake and Natural Resources Committee, is the fourth legislator known for his interest in environmental causes to announce he will not run for reelection in November.

Morgan’s counterpart in the state Senate--Agriculture, Conservation and Natural Resources Committee chairwoman Sen. Patsy Ticer (D-Alexandria)--announced during the legislative session that she is retiring after 15 years in the senate.

So did Sen. Mary Margaret Whipple (D-Arlington), another stalwart of the environment.

As did Del. Albert Pollard (D-Northumberland), known as a particular defender of Chesapeake Bay clean-up.

Besa said the environmental community is very concerned about the near clean sweep of the lawmakers most concerned with environmental issues, especially the General Assembly prepares to take up proposal to lift Virginia’s moratorium on uranium mining in 2012.

“Those are real leaders, knowledgeable people with regards to the environment,” Besa said. ”Replacing four people, including a Republican — it’s a really a challenge.”

Besa said the retirements will push the Sierra Club to become more involved in this year’s elections, conducting more aggressive endorsement interviews and working more vigorously on behalf of those the group supports.

“As dismal as the loss of these legislators is, we’re not about to give up,” he said. “We’re going to be working even harder to make new friends and hold legislators accountable.”