Effective at the expiration of the present term of office of the municipal board of commissioners, the salary of the mayor or chair of the board of commissioners shall be thirty-two thousand one hundred dollars ($32,100) per annum and the salary of each associate commissioner shall be twenty-eight thousand eight hundred ninety dollars ($28,890) per annum. Beginning in 1983 and ending in 1985, there shall be a seven percent annual increase in salary for such commissioners. This salary shall be in lieu of all salaries, expense allowances, emoluments, or other types of compensation heretofore granted; provided, however, that in addition to the salary provided by this section such members shall be entitled to reimbursement for actual expense incurred by them in performance of their official duties. The salaries herein provided shall be paid out of the city treasury in equal weekly installments at the end of each week.