Particle-Water Interactions of Ni and Zn in Coastal Waters

Abstract

Samples of suspended particulate matter (SPM) and sediment were collected from the Humber coastal zone during six seasonal and inter-annual surveys (November 1993 - July 1995) on board RRS Challenger as part of the NERC Land Ocean Interaction Study (LOIS) initiative. Concentrations of Ni, Zn, Fe and Mn, extracted using a 1M HCl digest, were determined by atomic absorption spectrometry techniques. Particulate Ni and Zn both exhibited a pronounced seasonal distribution in the Humber coastal zone. Significant metal-salinity relationships were obtained for both metals indicating the Humber Estuary to be a significant source of Nip and Znp to the region. Metal distributions in the coastal zone were influenced by residual flow and tidal range at the mouth of the estuary, as well as wind speed and direction. Estimated fluxes of dissolved and particulate Ni and Zn from the Humber mouth to the North Sea indicated significant seasonal variation for both metals (17-290 kg dayˉ¹ Ni; 34-1737 kg dayˉ¹ Zn) and identified transport in the particulate phase dominant in autumn/winter (61-82 % Ni; 68-92 % Zn) but less significant in spring/summer (2-41 % Ni; 15-72 % Zn). Comparison to estuarine inputs suggested retainment of Ni and Zn within the Estuary. In the Humber mouth and throughout the Plume Nip and Znp concentrations significantly correlated to Fep suggesting uptake onto Fe-oxyhydroxide phases was important. Trace metal settling velocities indicated a significant seasonal variation in the settling of Ni (<1-163 µm sˉ¹) and Zn (2-218 µm sˉ¹) with these metals generally settling slower than the average SPM in winter but at the same rate in spring. Particle-solute interactions of Ni and Zn, investigated using the radioisotopes ⁶³Ni and ⁶⁵zn, indicated significant variation in metal partitioning (Kd) for the SPM end-members of the Humber coastal zone with Ni Kd's varying from 6.7 x 10² for Holderness Cliff material, to 13.0 x 10² for estuarine SPM and up to a maximum of 22 x 10² during spring/summer phytoplankton blooms. These results provide the basis of a consistent seasonal data base of trace metal distributions within the Humber coastal Zone which will substantially contribute to the development and parameterization of a fine sediment transport model for trace metal contaminants in coastal zones.