Fig. 2. MeHg bioaccumulation in seston size fractions in response to experimental treatments.

(A) Conceptual illustration of carbon incorporation and transfer between trophic levels for an autotrophic (NP_low and NP_high)–based and heterotrophic (TM)–based pelagic food web, illustrating an increased number of trophic levels as a potential cause of enhanced MeHg bioaccumulation in a heterotrophic food web. DIC, dissolved inorganic carbon. (B and C) Average MeHg concentration (pmol g⁻¹ d.w.) in seston size fractions (50 to 100, 100 to 300, and >300 μm; n = 3 for each fraction) and average for all size fractions (n = 9) collected at the end of the experiment (day 57) from the different mesocosm treatments (n = 3 per treatment), that is, low nutrient input (NP_low, blue bars), high nutrient input (NP_high, green bars), and terrestrial NOM input (TM, red bars). Error bars are given as SE. (B) Bioaccumulation of MeHg originating from the Hg^II tracer added into the water (²⁰⁴Hg^II_wt) and (C) bioaccumulation of MeHg originating from the MeHg tracer added to the water column (Me¹⁹⁹Hg_wt).