Resource quantity controls biodiversity across scales, however the importance of resource quality to cross-scale patterns in species richness is seldom explored. We evaluated the relationship between stream basal resource quantity (measured as periphyton chlorophyll-a) and benthic invertebrate richness and compared this to the relationship of resource quality (measured as periphyton N:P) and richness at local and aggregate scales across 27 North American streams using data from the US National Ecological Observatory Network (NEON). At the local scale, richness peaked at intermediate levels of chlorophyll-a. In contrast, we found that richness had a slight negative linear relationship with increasing periphyton N:P. These local patterns suggest that resource quantity is more limiting for richness than quality at the low and high ends of the spectrum, whereas increasing resource quality gradually supported greater richness. At a larger aggregated scale, richness had a negative linear relationship with increasing chlorophyll-a and a steeper negative relationship with periphyton N:P. The negative, and unimodal relationship between chlorophyll-a and richness is consistent with patterns of eutrophication. Additionally, alternative environmental and biological factors that are associated with low diversity in high productivity environments (i.e. diminished nutritional quality, top-down forces, and disturbance) were poor predictors of invertebrate richness and resource quantity. These results suggest that excessive algal growth affects continental-scale patterns in invertebrate diversity. Collectively, we demonstrate that resource quantity and quality play important, yet differing roles in shaping biodiversity across spatial scales within stream ecosystems.