[spirochete]

Why does the addition of the conjugate base of a strong acid, such as SO₄^2-, increase the acididity of a solution?  If there are no protons there how can it make things more acidic?

This question has its roots in biochemistry/microbial ecology but technically it's most related to inorganic chemistry.  For example, microbes which reduce sulfate to sulfite and/or sulfide are important in bioremediation of acid mine drainage sites.  Although sulfide is a fairly strong acid it's also volatile and thus dissipates from the environment easily.  Sulfide oxidizers worsen the situation for obvious reasons.

[Yggdrasil]

SO₄^2- is the conjugate base of a weak acid (HSO₄^- and thus acts as a weak base).  HSO₄^- itself is a conjugate base of a strong acid, but is acidic because it can form SO₄^2-.

I think the answer may have more to do with the biochemistry.  Is it possible that the oxidation/reduction of these sulfur oxyanions consumes/releases H⁺?

[spirochete]

Now that you mention it that sounds more correct.  Thanks for the idea.