Abstract
Mercury (Hg) biomagnification through estuarine food webs remains a significant health concern for exposure both to humans and to fish-eating wildlife. To improve our understanding of how variation in trophic structure among communities influence Hg biomagnification, we conducted a study from 2011-2015 in the Caloosahatchee Estuary. Over 613 samples of biota from 78 species of fishes and macroinvertebrates, along with seston and sediments were collected from the upper, middle and lower estuary for Hg and stable nitrogen and carbon isotope analyses over the four-year study. Trophic magnification slopes (i.e., from the regression of log Hg concentration versus δ15N), an indicator of biomagnification efficiency, were 0.196 ±0.03 (±95%CI) and 0.207 ±0.15 in the lower and mid estuary, respectively. Although the food web in the lower reach of this highly-altered urban estuary had a shallower slope, biomagnified Hg was relatively high in top predator fishes; twelve species had average Hg that exceeded U.S. EPA’s water quality criterion to protect human health. The relationship between log Hg and δ15N was weaker in the mid-estuary food web and broke down completely for the upper-estuary food web due to altered nitrogen isotope signatures from anthropogenic nitrogen inputs and from fish movement in and out of river backwaters.