3.2 Bioaccumulation of MeHg in streams
Larvae of the families Aeshnidae and Corduliidae were the most widely distributed dragonflies collected at GRPO, inhabiting all four stream sites and accounting for 64% of the 201 larvae sampled and analyzed (Table 4). Larvae from three other dragonfly families, including 22 cordulegastrids, 1 gomphid, and 50 libellulids, were found at one or two of the four sites. Mean concentrations of MeHg in larval dragonflies from the four stream sites ranged from 118 to 190 ng/g dry weight in aeshnids and from 136 to 185 ng/g in corduliids. Methylmercury accounted for more than 90% of the total Hg in dragonfly larvae for most taxa and stream sites. For example, mean %MeHg in larvae from the four stream sites ranged from 91% to 97% in corduliids and from 81% to 94% in aeshnids.