Research on how N is retained and removed from stream networks has focused on microbial metabolic pathways, such as denitrification. An alternative pathway for N to escape streams is in the form of emerging aquatic insects, and unlike denitrification, previous studies suggest that this pathway may be stimulated by increased availability of P. We tested the hypothesis that the flux of N exported from streams through insect emergence increases relative to flux through denitrification with increasing levels of stream P. We measured emergence and denitrification rates at 7 lowland stream sites in Costa Rica that differ in dissolved P levels and substrate characteristics. Emergence N flux ranged from 2.0 to 16.3% of measured denitrification rates and was not related to any measured physical or chemical variables. Sediment redox conditions were the best predictor of denitrification rates. Our emergence results suggest that most invertebrate biomass production in these streams is consumed by in-stream predators, keeping this N in the stream ecosystem. Nevertheless, our findings indicate that in streams with low denitrification rates, emergence should be considered as an additional pathway of N removal from stream ecosystems.
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