Relationship between oxygen consumption and sediment‐water fluxes of heavy metals in coastal marine sediments

Abstract

AbstractThe relationship between benthic oxygen demand and the sediment–water flux of six heavy metals (cobolt [Co], nickel [Ni], copper [Cu], zinc [Zn], cadmium [Cd], and lead [Pb]) was examined at two locations: New Bedford Harbor and Buzzards Bay, Massachusetts, USA. Dissolved metal fluxes were measured in laboratory microcosms incubated in the dark at in situ temperatures, and microcosms were collected over different seasons to examine temporal and spatial variability in the fluxes. The net flux of all metals was generally out of the sediments. However, at low rates of benthic oxygen demand, net flux of Pb and Co was into the sediments. When data from the two sites are combined, regression of metal fluxes (normalized to sediment metal content) against benthic oxygen demand was significant for all metals (r2 = 0.58‐0.85), with all slopes significantly different from zero. The flux values (normalized to sediment metal content) ranged from ‐1.4 (mmole/m2/d)/(mole/mole C)sediment for Zn during winter to 42 (mmole/m2/d)/(mole/mole C)sediment for Cd during summer months. The magnitude of the fluxes generally showed the following relationship: Cd < Zn < Co, Ni, Cu < Pb, indicating higher relative mobility for Cd and lower mobility for Pb. The estimated annual fluxes of metals to New Bedford Harbor and Buzzards Bay amount to ˜0.06% (Pb) to 25% (Cd) of the inventory of metals in the top 2 cm of sediments and can equal the inventory of metals in the water column on a time scale as short as 7 d for Zn.