Metal analysis of submerged aquatic vegetation in the lower St. Johns River, Florida

The St. Johns River, Florida's longest river, is threatened by a variety of factors, including anthropogenic disturbances and global climate changes. Metal pollution in the Lower St. Johns River (LSJR) in Northeast Florida has been well documented. Submerged aquatic vegetation (SAV) are ecologically important plant species, known to accumulate metals and other pollutants from their surrounding environments, and have been declining in the LSJR in recent years. In this study, eight SAV taxa (Vallisneria americana, Ruppia maritima, Chara sp., Najas guadalupensis, Eleocharis sp., Hydrilla verticillata, Zannichellia palustris, and Sagittaria subulata) were collected along the LSJR from Central Florida northward to Jacksonville and the Atlantic Ocean. More than 200 SAV samples were identified, digested, and measured for a suite of metals. Mean (± standard deviation) metal concentrations in µg/g dry mass in all taxa sampled were 1.76 (± 2.75) cadmium, 35.8 (± 52.24) copper, 4.16 (± 5.74) lead, 119 (± 229) nickel, 0.98 (± 1.40) silver, and 203 (± 376) zinc. SAV metal concentrations varied across species and collection sites. In general, Z. palustris and Eleocharis sp. had the highest metal concentrations. Furthermore, a comparison of SAV metal concentrations to sediment quality guidelines for the LSJR indicated that toxicity may occur to biota exposed to these SAV. This study provides new data about SAV health in the LSJR and may help in the development of new management strategies.