Fjords, sulfate reduction

It is appropriate to discuss sulfate reduction in ponds, lakes and fjords together because each exhibits similar variations of either a seasonal or epi-... 

An example of sulfate reduction in a shallow fjord estuary is the upper basin of the Pettaquamscutt River (Rhode Island, U.S.A.) studied by Orr and Gaines (1973). It is normally well-stratified water but, every few years, there is overturn which mixes near-surface oxygenated water with the bottom water containing biogenic sulfide. In a time span of just over one month after an overturn in November 1971, 80% of the sulfide was oxidised. After stratification was re-established, the sulfide remained below 4 m depth and accumulated at a calculated rate of 48 g S m" y. ... 

Sulfate reduction rates in the deep basin sediments of the Saguenay Fjord are relatively low in comparison to other coastal environments (32 nmol cm-2 d-1 integrated over the top 30 cm), and the pore water is only weakly depleted in sulfate. Sulfate reduction is more intense, however, in the rapidly accumulating... 

Diagenesis and elemental cycling in oxic or suboxic sediments in Saguenay Fjord is to some extent governed by different processes than in fully anoxic systems, where organic matter oxidation and sulfate reduction have been taking place without interruption for a considerable length of time. This has led to a situation where sulfide is present in the water column. 

Anoxic water samples, because they contain little in the way of particles, are far easier than aquifer materials to develop radioassays for the measurement of arsenate reduction. Arsenic speciation quantitatively changes from arsenate to arsenite with vertical transition from the surface oxic waters to the anoxic bottom depths of stratified lakes and fjords (55,56). This also occurs in Mono Lake, California (57), a transiently meromictic, alkaline (pH = 9.8), and hypersaline (salinity = 70-90 g/L) soda lake located in eastern California (Fig. 11). The combined effects of hydrothermal sources coupled with evaporative concentration have resulted in exceptionally high ( 200 fiM) dissolved arsenate concentrations in its surface waters. Haloalkaliphilic arsenate-respiring bacteria have been isolated from the lake sediments (26), and sulfate reduction, achieved with... 

The conditions required for pyrite formation (reduction of sulfate and availability of reactive iron phases) exist in the Saguenay Fjord. Indeed, the high... 

---