Joseph W. "Chip" Marshall, president and chief executive officer of the Philadelphia-based Temple University Health System, has announced he is stepping down after seven years in the job. The Temple system has 7,500 employees and annual revenue of about $1 billion. It includes Temple University, Jeanes and Northeastern hospitals and Temple's Episcopal Campus. It operates in a particularly challenging financial arena, because a high percentage of its patients are covered by Medicaid. Temple representatives said patient volume this year was lower than predicted, a problem the system was addressing by recruiting more physicians.