Heterogeneity and scaling of photosynthesis, respiration, and nitrogen uptake in three Atlantic Rainforest streams

Leaves, epilithon, macrophytes, and fine benthic organic material are central ecosystem compartments to food webs and mediate nutrient fluxes in streams. Most estimates of gross primary production (GPP) and ecosystem respiration (ER) are made at a reach scale, averaging across compartments. Thus, there is little information on how individual compartments contribute to and scale up to whole-stream estimates across watersheds. We compared estimates of GPP, ER, and nitrogen (N) uptake of individual ecosystem compartments (dm) and stream reaches (similar to 100 m) in three sizes of streams in a preserved Atlantic Rainforest watershed. The smallest stream had dense forest canopy cover, whereas the largest was more open. We measured substratum-specific rates of GPP and ER, as well as ammonium and nitrate N-15 uptake in recirculating chambers. We compared these decimeter-scale measurements to whole-stream estimates, using single-station dissolved oxygen (GPP and ER) and pulsed N uptake methods. Epilithon and macrophytes (when present) were the dominant GPP and N uptake compartments in open-canopy sites, and leaves contributed strongly to ER at all sites, even though they covered