[Loler]

Hello all,

I read a document in which the authors stated "Sulfate and sulfide both exist within a system just in varying proportions, and speciation is dependent on Eh/pH. If one side of the equation changes, the other will transform to balance it out".

The system they are referring to is an engineered wetland, with low amounts of labile carbon but was amended with gypsum and therefore has high sulfate concentrations.

The authors have stated that in deeper zones of the wetland (5-10m below ground surface), where it is fully saturated, and where oxygen penetration is minimal, aqueous sulfide would be the main form of sulfate that exists. However, they have provided no evidence, and the carbon that exists in that zone is highly recalcitrant (meaning it is not readily degradable by sulfate reducing bacteria). So how can they say that the main form of sulfur is sulfide in this zone if the sulfate reduction process is not occurring, or very limited, due to low amounts of labile carbon?

Isn't it common for sulfate to be main form of S even in anaerobic zones? The sulfate reduction process sure is usually carbon limited in high sulfate systems (e.g. marine sediments and even salt lakes). As far as I know, the Eh/pH tell you about the stability of the species.

[Corribus]

I have just learned that aqueous sulfide doesn't even exist. So there's that.

(By the way, this might be one of the most awesome paper titles I've ever seen. In the future I will strive to include a "WARNING: KEEP OUT" sign in all of my table of contents graphics.)

[Loler]

I have just learned that aqueous sulfide doesn't even exist. So there's that.

(By the way, this might be one of the most awesome paper titles I've ever seen. In the future I will strive to include a "WARNING: KEEP OUT" sign in all of my table of contents graphics.)

Interesting article! Yes, but surely H₂S and HS^- should still be in aqueous form given that pH is usually found around that range in environments. For instance, in the case of the wetland I mentioned above it is around netural. So the species should be bisulfide (HS-). Given such, does my reasoning in the post above make sense? In regards to the authors' claims about assuming the existence of bisulfide based on Eh/pH?

[Corribus]

Oh heck, it looks like I pasted the link wrong. 

Here is the abstract and TOC. Here is the full text.