Mathematics – Logic
Scientific paper
Jun 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000gecoa..64.1843s&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 64, Issue 11, p. 1843-1857.
Mathematics
Logic
2
Scientific paper
The distributions and seasonal variability of total dissolved Cu (TDCu) and Cu-complexing ligands in sediment pore waters have been investigated at two contrasting sites in the Chesapeake Bay. Two ligand classes, which differ on the basis of the conditional stability constants (K′cond) of their Cu complexes, were detected at all depths at both sites. At the sulfidic, muddy, mid-Bay Sta. M, concentrations and values of log K′cond ranged from 390 12,500 nM and ≥7.2 >8.9, respectively, for the stronger ligand class (L1S) and 75 6,420 nM and 6.2 7.9 for the weaker ligand class (L2S). At the bioturbated, sandy Sta. S in the lower Bay, respective concentrations and values of log K′cond ranged from 135 807 nM and ≥7.6 ≥10.2 for L1S and 40 1,410 nM and 6.6 9.2 for L2S. For comparison, one pore water profile from a slope station off of the Chesapeake Bay also showed the presence of two ligand classes, with respective concentrations and values of log K′cond of 140 270 nM and 8 >11 for L1S and 30 180 nM and 7 10 for L2S. These ligands are in large excess relative to ambient TDCu concentrations (<0.1 24.3 nM), thereby maintaining very low inorganic Cu concentrations (typically <0.1 to <100 pM) and a high degree of organic complexation (87.2 >99.9%) of Cu in Bay and slope sediment pore waters. Thus, virtually all TDCu fluxing from these sediments is complexed during sediment-water exchange. A relatively small fraction of the TDCu is exchanged as inorganic species, which are widely regarded as the most bioavailable form of Cu. Higher ligand concentrations at Sta. M suggest that sulfide or organic ligands containing reduced S contribute to the pool of complexing ligands; however, the exact nature and sources of the ligands in Bay pore waters are not known. The progressive increase in conditional stability constants of the CuL2S complexes from the mid-Bay to the slope sediments may reflect differences in biological or chemical processes at each site, as well as differences in the type of Cu-complexing organic matter. Total ligand concentrations (L1S + L2S) are 15 to >100 times higher in the upper intervals of the pore waters relative to ligand concentrations in the bottom waters of the Chesapeake Bay (30 60 nM), consistent with previous observations of fluxes of these ligands from the sediments to overlying waters. These results suggest that sediments are potentially significant sources of Cu-complexing ligands to the overlying waters of the Chesapeake Bay, and perhaps, other shallow water estuarine and coastal environments. Copper-complexing ligands released from sediment pore waters may play an important role in influencing Cu speciation in overlying waters.
Burdige David J.
Donat John R.
Skrabal Stephen A.
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