It seems nothing is safe from the tidal waves set off by the shifting of the tectonic plates that supported the national economy. The effects are now said to have washed away a promising and relatively new member of the Pittsburgh school board.

Heather Arnet, who has represented District 2 since being elected to replace then school board member and now city Councilman Patrick Dowd in 2007, announced her resignation last week. She is the executive director of the Women and Girls Foundation of Southwest Pennsylvania and in her letter of resignation she wrote that the recession "has had a devastating impact on the local nonprofit community and the constituents we serve."

In stepping down to concentrate on her professional job, an odd development to be sure, Ms. Arnet poses a double regret. In the first place, it is deeply disappointing she cannot finish her term, although some will be glad she is going. Former supporters were not pleased when she voted to close the Pittsburgh Schenley High School building a year ago and fault her for failing to ask tough questions about Superintendent Mark Roosevelt's academic-improvement efforts.

Of course a school board member can't please everyone, but the final regret here is about unrealized potential. When we endorsed her in the primary election two years ago, we observed that this young woman originally from Miami who is a 1997 graduate of Carnegie Mellon University "is the perfect example of the sort of bright, young professional that Pittsburgh is always seeking to attract." In short, Ms. Arnet might have gone on to greater things in elective office and those hopes are now set back.

The choice for a replacement falls to Mayor Luke Ravenstahl, and he has already said something encouraging concerning his criteria: "Ms. Arnet was devoted to student achievement and a champion of education, the Pittsburgh Promise and the city of Pittsburgh. Her replacement must possess these same values."

Indeed, values -- and we would say solid credentials such as personal achievement and a good education -- should be decisive. Mr. Ravenstahl should not seek to placate those who want someone who will take a harder line with Mr. Roosevelt. That would be unfair to those who think the superintendent is doing a good job. The voters will have their say in less than two years and at that time the issues will be foremost.

For the moment, the mayor should pick the best candidate on merit alone and let the chips fall where they may as regards Mr. Roosevelt, who is likely to have majority support whoever is selected. Pick well, Mr. Mayor, and thank you, Ms. Arnet.