Two poetic devices (literary devices are called poetic devices when applied to poetry) that are related to sound, sound devices, that are immediately apparent in this iambic tetrameter (da DA / da DA / da DA / da DA) lyric (poetic persona speaks of his/herself) are alliteration and a couplet rhyme scheme.
Alliteration is when the first consonate of proximal words (next to or nearby each other) are the same, as in "A tunnel of green gloom" and "The poppy and the pansy."
A couplet rhyme scheme is when two adjacent lines have end rhymes or near-rhymes, for example like in these two adjacent lines with near-rhyme:
The stream mysterious glides beneath,
Green as a dream and deep as death.