Your use of first person present tense is pretty good! I like it. It's nt awkward or stilted at all.
If there was anything I found wrong, I think maybe you might show instead of tell a little bit more. Like this passage:
I feel a new fervour seize my body, counteracting the numb front. I know now that I can’t die before reaching my home. Where there once dwelt doubt, I feel determination that I will make it to the river alive. Nathan’s writing has, if not stirred any emotion, given me the strength to go on.
Instead of the last two sentences, you could change it to SHOW that she/he is determined. Make her physically act (eg getting up, picking up her pace, etc.) rather than using monologue to convey it. One sentence, or maybe just half a sentence, would be enough to "tell" her/his determination, simply as a confirmation of what's being shown.
Overall, it's great! It sets a very nice atmosphere and the imagery is subtly worked into the paragraphs so as not to slow down the pacing. The sensory details are vivid but not dry or slow. Keep writing!
If there was anything I found wrong, I think maybe you might show instead of tell a little bit more. Like this passage:
Instead of the last two sentences, you could change it to SHOW that she/he is determined. Make her physically act (eg getting up, picking up her pace, etc.) rather than using monologue to convey it. One sentence, or maybe just half a sentence, would be enough to "tell" her/his determination, simply as a confirmation of what's being shown.
Overall, it's great! It sets a very nice atmosphere and the imagery is subtly worked into the paragraphs so as not to slow down the pacing. The sensory details are vivid but not dry or slow. Keep writing!