The board shall establish in each of the trust funds an account to which are credited the proceeds from the sale of any public lands, except sales under s. 24.09 (1) (bg), on or after May 3, 2006, that are required by law to be deposited in the funds. Moneys credited to the accounts in the funds may only be used to invest in land under s. 24.61 (2) (a) and for the payment of expenses necessarily related to investing in land under s. 24.61 (2) (a).