Section 6D. Every individual who files a separate return and every husband and wife filing a return jointly may voluntarily contribute all or part of any refund to which they are entitled or may voluntarily add an amount onto any amount due to be credited to the Natural Heritage and Endangered Species Fund. At the beginning of each fiscal year, subject to appropriation, one dollar shall be credited from the General Fund to the Natural Heritage and Endangered Species Fund for each dollar contributed by the public in the prior fiscal year under the provisions of this section. The commissioner of the department of revenue shall certify to the state comptroller total revenues contributed to the Natural Heritage and Endangered Species Fund by individuals in the prior fiscal year.

A contribution made under this section may be made with respect to any taxable year at the time of filing the return of the tax imposed by this chapter for such taxable year; provided, however, that the commissioner shall prescribe the manner in which such contribution shall be made on the face of the return required by section five of chapter sixty-two C.

The commissioner shall annually report the total amount designated under this section to the state treasurer who shall credit such amount, plus accrued interest, to the Natural Heritage and Endangered Species Fund.