Export and bioaccumulation of methylmercury in streams draining distinct soils in the Central Brazilian Amazon, 2012-2013

•Soil type influence the export of methylmercury to the river•Streams draining distinct soils had different accumulation in their food chain•Greater export and concentration of methylmercury in stream during the rainy season•Allochthonous insectivores showed no variation in mercury between streams Upland forest streams of the Central Amazon are unique aquatic systems.These small streams have short, unpredictable and multimodal flood-pulses that are influenced by local rainfall. The biogeochemical cycles in these systems are almost unknown. This study investigated the role of soil type on the export and bioaccumulation of methylmercury (MeHg) in upland forest streams of the Central Amazon during a complete annual cycle. Limnological measurements and water samples for MeHg analyses were collected monthly from October 2012 to October 2013 in two headwater streams drained by different soil types, spodzol (Campina Stream) and oxisol (Barro Branco Stream), in natural forest reserves. Shrimp and fish were collected for total mercury (THg) in April 2013 in both streams. MeHg in water varied from 0.04 to 0.50 ng/L in the Campina Stream and between