Table 2-4. Benthic Fluxes Measures at the Jamestown 



North Study Site and Estimate Doubling Times 



for Cu, Ni, Mn and Fe in Narragansett Bay 



NOTES: 



(1 ) Based on twelve determinations. 



(2) Calculated excluding one anomalously high value believed to reflect 

 contamination. 



summertime, release of manganese from sediments is a major source of 

 manganese in Narragansett Bay, but release of nickel, copper and cadmium are 

 probably not significant. 



TRACE METAL BUDGETS IN NARRAGANSETT BAY: 

 Mn AND Cu AS EXAMPLES 



The preceeding discussion suggests that benthic fluxes will be a source of 

 Mn, but not Cu, to the waters of Narragansett Bay. The distribution of these 

 metals in the Bay provides a check on these conclusions, as will be seen from 

 the following discussion. 



Graham et al (6) did a mass balance for dissolved and particulate manganese 

 in Narragansett Bay in the Summer of 1973. Their results for the distribution 

 of dissolved manganese in the main part of the Bay are shown in Figure 2-5. It 

 is readily seen that dissolved manganese is not a single-valued function of 

 salinity: at a given salinity, surface waters have far lower manganese 

 concentrations than deep waters. The manganese concentration of surface 

 samples is far less than that expected from a simple conservative mixing model 

 in which the deep water concentration is approximately equal to the 

 conservative concentration. Graham et al (6) interpreted these results as 

 indicating that manganese is scavenged (presumably by oxidation and 

 precipitation) throughout the waters of the estuary, and bottom waters are 

 enriched relative to surface waters by the benthic flux of manganese. 



21 



