Mapping the global flux of biomass and contaminants from rivers by emerging aquatic insects
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Abstract: Freshwater aquatic insects transport essential nutrients to terrestrial food webs when they emerge as adults. Contamination of freshwater ecosystems alters this transport by reducing emergence and/or causing the contaminants themselves to be transported. The mechanisms of contaminant and nutrient transport are relatively well-studied in freshwater ecosystems from individual lab and field experiments. However, the cumulative global transport of nutrients and contaminants from freshwater ecosystems is unknown. We addressed this gap by harmonizing >300 records of freshwater insect production and >800 records studies of nutrient and contaminant tissue concentrations in adult aquatic insects. Using Bayesian modeling, coupled with machine-learning to predict aqueous contaminant concentrations in rivers, we preliminarily estimate that earth’s rivers export >2 teragrams of insect emergence dry mass per year. This amount is derived from an average areal flux of ~1.8 mgDM/m2/y, an amount that varied with mean annual precipitation. Combining these flux estimates with modeled tissue concentrations will provide additional estimates of the global flux of nutrients (N, P, C, PUFA), trace metals, mercury, herbicides, fertilizers, pesticides, and pharmaceuticals. Our work helps to place into context the important role of emerging aquatic insects in transporting aquatic-derived elements and molecules to terrestrial food webs.