Dissolved mercury concentrations and reactivity in mangrove waters from the Itacurussa Experimental Forest, Sepetiba Bay, SE Brazil

Mangrove waters from the Itacurussa Experimental Forest (IEF), SE Brazilare enriched in reactive-Hg (15 ± 2.0 pM) and total-Hg (28 ±2.5 pM) relative to open bay waters (4.5 ± 3.0 pM and 19 ±8.5 pM, for reactive-Hg and total-Hg respectively). Mercury concentrationsand reactivity varied according to tidal flux in mangrove creek waters.Reactive-Hg concentrations were higher in ebb tide waters ranging from 4.5to 8.5 pM, than in flood water (< 1.0 to 3.5 pM), whereas total-Hgconcentrations were higher in flood waters, from 40 to 360 pM, than inebb water (30 to 250 pM). Low-Hg, open bay waters are enriched in Hgwhen flowing over mud flats prior to entering the IEF, where it mixes withpore waters containing extremely high Hg concentrations (up to 2,500pM). Similar distributions of Hg and DOC in pore waters, suggests thatDOC may facilitate Hg migration through the sedimentary column, asshown for other estuarine areas. Mud flat pore waters are the more likelysource of total Hg to mangrove waters, but not for reactive Hg. Theseresults suggest that mangroves act as a sink to total Hg, as has been shownfor other trace metals at the IEF and other mangrove forests. On the otherhand mangroves act as a source of reactive Hg to adjacent coastal waters.The mechanisms involved in this processes have not been studied in thispaper. However, the similar distribution of DOC and Hg among thedifferent water masses of the IEF, suggest that the dynamics of Hg-DOCcomplexes may play a dominant role.