Trace metal geochemistry in sediments from the Miramichi estuary, New Brunswick

Abstract

Organic matter, mineralogy, and texturally-related qualities combine to control the total concentration and reactivity of trace metals in the sediments of the Miramichi estuary. Concentrations of lignin-rich organic matter, up to 10% of the total sediment weight in the central estuary, correlate with analytical results for trace elements which show that more than 40% of the total Mn, Zn, and Cu is held in the oxidizable and organically-bound form. Mineralogical influences are most obvious in the river portion of the system where total Mn concentrations average 695 μg/g, Zn averages 282 μg/g, Cu averages 32 μg/g, and Pb averages 200 μg/g in the less than 63 μm size fraction of the sediments. In the marginal marine Miramichi Bay, total concentrations of these four trace elements in the fine sediment fraction are diminished by 9–57%, with respect to the equivalent size fraction of the river sediments.The concentration of all trace elements in the coarse fraction (> 63 μm) is considerably less as compared with the fine fraction. In these sediments mineralogical associations are more pro nounced. Very high organic carbon content (up to 23%) is associated with sediments in which more than 25% of the Mn, Zn, and Cu is organically bound. Weak acid leachable Ca in the coarse sediments of the bay is 21 times higher as compared with the equivalent river sediment fraction and this CaCO3 indication is associated with a twofold increase in total Cu and Pb.When compared with sediments from other areas of eastern Canada, the Miramichi sediments have at least twice as much weak acid leachable Zn, and this higher level of reactive metal is associated with high organic carbon content in the top 15 cm of cored sediments. Suggested sources for this recent addition of metal in association with organic matter are the mining activities as well as urban and industrial effluents.