We have carried out a series of experiments aimed in large part at testing the 

 two hypotheses outHned above. We have proceeded by 1) determining the 

 concentrations of elements forming relatively soluble sulfides (Mn and Fe) and 

 elements forming relatively insoluble sulfides (Ni, Cu and Cd), along with 

 nutrients, pH, total CO2 (TCO^), SO^", and S~ in anoxic Narragansett Bay 

 sediments; 2) carrying out tracer experiments to determine the rate at which 

 organisms enhance the benthic flux of chemicals by pumping water across the 

 sediment-water interface, and using these results, along with diffusive flux 

 estimates, to predict total fluxes across the sediment-water interface; 

 3) measuring benthic fluxes directly via bell jar experiments, and using the 

 results both to check the prediction of the pore water data and flux model, and 

 to make direct determinations of metal benthic fluxes; and 4) working out the 

 mass balance of heavy metals in Narragansett Bay at one point in time, using 

 the Bay itself as a gigantic bell jar and thereby checking on the generality of 

 our benthic flux measurements. 



In this paper we summarize the results of this work. 



PORE WATER WORK 



Samples were collected in plexiglas box cores or PVC pipe. One centimeter 

 sediment slices were placed in polyethylene centrifuge bottles in a helium 

 atmosphere and centrifuged at in situ temperatures to separate pore waters. 

 Supernatant waters were filtered through acid-washed Nuclepore filters. The 

 concentration of TCO9 was determined by gas chromatography. Sulfate was 

 measured by BaSo^ coprecipitation using '-^-^Ba as a tracer. Sulfide and 

 ammonia were determined colorimetrically by the methods of Cline (3) and 

 Solorzano (10), respectively. Phosphate and silicate were determined by a 

 modified autoanalyzer procedure (1 1, 12). Dissolved manganese and iron were 

 determined by flameless atomic absorption spectrometry using either a 

 Perkin-Elmer 503 or 360 AAS with model 2100 graphite furnace deuterium arc 

 background corrector. Standards were prepared in Sargasso Sea water. Further 

 details of sample collection and the above analytical methods are given by 

 McCaffrey (8). 



Cd and Ni were determined by flameless atomic absorption after sample 

 concentration using a modification of the Co-APDC coprecipitation technique 

 of Boyle and Edmond (2). A 0.2 ml aliquot of a 4mM CoCU solution is added 

 to the pore water sample at pH 2, followed by addition of 0.4 ml of a 2% W/V 

 solution of APDC. The sample is shaken vigorously and allowed to sit for up to 

 30 minutes. It is then filtered through a 2.5 cm diameter, 0.4 jum micron 

 Nuclepore filter held by an acid-washed Millipore filter apparatus. The filter is 

 washed with several ml of deionized water, and placed in a polypropylene vial 

 containing 1 .0 ml of redistilled 3N HNO3. The precipitate is dissolved by 



10 



