Determination of Process Rates

The gross SRR as measured by SO/ technique comes closest to the overall sulfate reduction that takes place in the sediment. The 

In the following, we will use data of Jorgensen et al. (2004) from the Black Sea as an example to illustrate the differences between the two approaches. Fig. 8.18 shows results from the deep sulfidic part of the Black Sea where macrofauna are unable to live and where bioirrigation is therefore absent (although current-induced advective pore water transport may take place near the sediment surface). Sulfate reduction rates were measured experimentally by the radiotracer method down to 20 cm depth in the sediment (Fig. 8.18 A). 

A multi-G model of Westrich and Berner (1984) was applied to fit a smooth curve to these rate data. The model assumes that the sediment organic matter that feeds sulfate reduction consists of three pools, each of which is degraded exponentially over depth and time, but each having its own pool size and exponential decay constant. Fig. 8.18 B and C show that this model fits well with both the measured sulfate reduction rates in the upper sediment layer and the sulfate curve in the deeper sediment down to 330 cm depth. 

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