The transport, transformation, and trophic transfer of bioactive metals in an urban impacted buoyant river plume.

摘要

At the mouth of the Hudson River estuary, one of the most urbanized and pollution impacted estuaries in North America, estuarine water forms a buoyant plume which transports nutrients and contaminants into the Mid-Atlantic Bight. As part of the LaGrangian Transport and Transformation Experiment (LaTTE), the transport, transformation, and zooplankton bioaccumulation of contaminant and terrestrial metals (Ag, Al, Cd, Cu, Fe, Hg, Mn, Pb, Zn) in the plume were examined in May 2004, April 2005, and May 2006. In order to determine the low level concentrations of dissolved metals in plume waters, an improved method for determining metals in seawater by online column preconcentration, isotope dilution HR-ICP-MS was developed. Within the plume, metal concentrations generally decreased as plume waters were diluted with low metal shelf water. Within the plume, particle sinking was an important loss mechanism for metals. The formation of a narrow coastal current resulted in rapid down shelf (southward) transport of plume constituents, while the formation of a large recirculating eddy delayed down shelf transport, resulted in increased particle sinking, and may result in cross shelf (eastward) transport if shifting winds advect plume waters offshore. Results suggest that while plume particulate matter was composed of a mixture of biogenic and terrigenous material, metals were primarily (54-100%) associated with terrigenous particles. Hg in the plume was largely associated with particulate matter (median 61%) and dissolved Hg had similar concentrations as those in North Atlantic surface waters. Water-particle distribution coefficients (KD) for Hg were relatively constant in 2004 and 2005, but decreased within the plume within the phytoplankton bloom at mid salinity in 2006, suggesting that plume phytoplankton may release Hg binding ligands in response to metal stress. With the exception of Cd, metals in plume copepods were elevated relative to oceanic copepods. Modeling results show that trophic transfer was an important bioaccumulation pathway for Cd, Cu, and Zn, while the importance of this pathway for Ag was less clear. Comparison with toxicity data suggests that plume zooplankton may experience sub-lethal toxic effects from Ag and Zn, however future work will be required to confirm or refute this hypothesis.