Mercury concentrations in macrophytes, periphyton, and detritus in the Everglades, Florida, USA, with special attention to Utricularia species

Elevated mercury (Hg) levels in biota is one issue facing the Everglades ecosystem in south Florida, USA. Methylmercury (MeHg) is a concern in the environment because it bioaccumulates through the food web and can harm fauna and humans if ingested through contaminated food sources (e.g., fish). Total mercury (THg) and MeHg concentrations were measured in several common macrophyte species, periphyton, and detritus in the Everglades to investigate Hg concentrations spatially and among different ecosystem components. At each site, two species from the carnivorous genus Utricularia, U. purpurea and U. foliosa, which are widespread and abundant in Everglades sloughs, had much higher average tissue MeHg concentrations (2.4–81 ng/g dry weight [dw]) than all other sampled macrophytes (<1.5–7.5 ng/g dw), periphyton (0.4–6.2 ng/g dw), and detritus (<1.5–5.7 ng/g dw). The Utricularia species were likewise enriched with THg (14.6–115 ng/g dw) compared to the other macrophytes (2.6–27 ng/g dw), although slough detritus had the highest THg at most sites (24–182 ng/g dw). The Utricularia species generally had a higher average percent of THg as MeHg (8.2–75%) compared to the other macrophytes, periphyton, and detritus (0–32%). MeHg concentrations in Utricularia species were quite variable among sites with a spatial distribution that generally reflected historical Hg concentration patterns known in mosquitofish (Gambusia holbrooki). Utricularia species merit further investigation to understand how they accumulate relatively high MeHg concentrations and how they might influence Hg accumulation up the food web.