Coarse detritus in the form of leaves and wood, as well as fine benthic organic matter, provides the majority of energy for food webs in headwater streams.  Nutrient mobilization occurring due to land use change likely affects these resources.  We predicted that nutrient enrichment would have differential effects on fine (< 1 mm) and coarse (> 1 mm) organic matter fractions, due to four factors: 1) substrate carbon to nutrient ratios, 2) differential colonization by fungi vs. bacteria, 3) the differential response of fungi vs. bacteria to nutrient enrichment and 4) the nutrient content of fungi and bacteria.  We quantified microbial biomass and changes in nutrient content of fine and coarse particulate organic matter in two southern Appalachian headwater streams: one reference and one that had been receiving long-term nutrient enrichment for 5 years.  Our results show greater changes in coarse vs. fine material in the enriched stream because of the importance of fungi which dominate coarse fractions in these headwater streams and responded most positively to increased nutrients. Changes in nutrient content of basal resources are consistent with other parts of our larger study that suggest these differential effects may track through the food web, potentially altering trophic pathways.