I'm perplexed. I too regularly read scientific papers on natural ecology, and in my opinion sulfate reduction occurs wherever sulfates are present. In the oceans, it ubiquitous. It occurs in ponds regularly.sulphidogenesis is rather rare in nature.
Yes, in peat bogs it may be insignificant if the water is very sparsely mineralized, and therefore sulfates are present in meager quantity. Methanogenesis occurs in such places instead.
I hate to disagree with you, @Simon Cole , really. Oxygen penetrates as deep as biological oxygen demand allows. Other factors like coarseness of the sediment or water flow above the sediment are secondary factors.I am less open minded to the possibility that it could form in aquariums because I tend to think that substrates are likely to be permeable to dissolved oxygen and that the chemical conditions for microbial sulphidogenesis are unfavourable and would probably take a very long time to develop.
In commercial substrates containing lots of easily degradable organic matter BOD is very high, oxygen cannot penetrate very deep and anaerobic activity is huge. Sulfate reduction (to sulfide) occurs.
When hydrogen sulfide moves upward it gets oxidized either biotically (faster) or abiotically before it reaches the water column. That's the normal state of affairs. But if the BOD is too high, the boundary between oxic and suboxic zone is above the sediment and the disaster happens - hydrogen sulfide leaks into water column. Obviously, this is what happened to thread starter.
In our tanks, sulfate reduction is often relegated to very deep zones not because of deep oxygen penetration but because nitrates are abundant, nitrate reduction zone (denitrification) is huge and only below this zone sulfate reduction may occur.