A revolving fund in the custody of the state treasurer, to be known as the natural resources equipment fund, is hereby created to be expended by the department without appropriation solely for the purchase of equipment, machinery, and supplies for the use of the department and for the payment of the costs of repair and maintenance of such equipment, machinery, and supplies. During the 2007-2009 fiscal biennium the legislature may transfer such amounts as represent the excess balance of the fund to the state general fund.