Diatom associations collected from polyurethance foam (PF) substrates were surveyed through time along a nutrient enrichment gradient in Smith Mountain Lake, Virginia. A qualitative model is proposed which emphasizes the adaptive characteristics, or life-form strategies, of the most abundant diatoms in an association and relates them to generalized environmental conditions. The model provides a framework for readily describing complex habitat variations within the lake and supplies a means of interpreting successional changes occurring on the substrates.