(1) The trustees of a public library district may establish a library depreciation reserve fund for the replacement and acquisition of property, capital improvements, and equipment necessary to maintain and improve district library services.
(2) Money for the library depreciation reserve fund is those funds that have been allocated for district library services in any year but which have not been expended by the end of the year. The money includes but is not limited to county appropriations, federal reserve sharing funds, and public and private grants.
(3) The money held in the library depreciation reserve fund may be invested as provided by law. All interest earned on the fund must be credited to the library depreciation reserve fund.