The city council shall have the power to establish such commissions as shall be necessary for the effective accomplishment of municipal business; provided, however, that a councilman shall be a member of each commission. Appointment of city commissioners shall be for a term not to exceed four years. No person shall be reappointed as a member of a city commission who has served continuously for six years, until at least one year shall have elapsed after the expiration of the sixth year of such service.