The powers of the board of park commissioners shall be exercised by ordinance unless otherwise provided in this chapter. All ordinances shall be read twice, and at least eight days shall intervene between the readings. Ordinances shall be adopted by a yea and nay vote, shall be approved by the president, shall be published once in the official newspaper of the municipality, and shall go into effect within three days after the publication thereof. The enacting clause of all ordinances shall be: “Be it enacted by the board of park commissioners of the park district of the city of                     “.