Ex officio members shall serve for the term of their elective office. Of the six (6) appointed citizen members, two (2) shall serve for a period of one year, two (2) for a period of two (2) years, two (2) for a period of three (3) years, etc. Thereafter, such appointed citizen members shall serve for a period of three (3) years. Vacancies shall be filled by appointments for unexpired terms only. (1997 Code)