What feeling is portrayed in the following lines?

I've known rivers.

Ancient, dusty rivers.

My soul has grown deep like rivers.

This is from "The Negro Speaks of Rivers."

A somber emotion, lost or sad.

It can be seen in the way that he continues to repeat the word rivers, yet each time adds more meaning behind the word. He's seen rivers, but not only plain rivers, the rivers have had an effect on him, and he feels similar to the ever flowing but never changing river.