Beginning January 1, 1998, the sheriff of the city of St. Louis shall receive for his or her services the sum of sixty-six thousand dollars per annum, and beginning January 1, 1999, the sheriff of the City of St. Louis shall receive for the sheriff’s services the sum of seventy-two thousand six hundred dollars per annum. Beginning January 1, 2000, the compensation of the sheriff of the city of St. Louis may be annually increased by an amount equal to the annual salary adjustment for employees of the City of St. Louis as approved by the board of aldermen of such city. Said sum and the compensation of his or her deputies and assistants shall be paid out of the treasury of the City of St. Louis in equal semimonthly installments. For additional duties hereunder imposed, the sheriff shall mail all petit jury summons.