The commissioner shall have authority to enter into agreements with landowners for the conservation of wetlands. These agreements shall be entered into for a period of five or ten years, with provision for renewal for additional five-year or ten-year periods. The commissioner shall re-examine the payment rates at the beginning of the fifth year of any ten-year initial or renewal period and before the beginning of any renewal period and, providing that funds are available, make needed adjustments in rates for any initial or renewal period.