I was reading old stream, new stream; the study you are involved with at the Boardman River. There are some considerations you may be missing. There are several ways to study epiphytes and microorganisms. This is a link to USGS, but, there is also studies of such dimension with Virginia Tech. Link: http://water.usgs.gov/nrp/proj.bib/sav/Epi/epi.htm

Spot sampling doesn't reveal an entire years dynamic. That aside, the study river experienced traumatic change. There was a tidal wave that swept through that area and changed the entire dynamic. There was not a gentle change that allowed the microscopic and macro flora and fauna to survive. That needs to accompany your study otherwise it is going to be misinterpreted.