Tom,

Maybe this can help you in terms of biostatistical analysis. - Biostatistical Analysis (International Edition) – NHBS

Jerrold H Zar, 756 pages, b/w illustrations, tables

Regards,

Mersi mult

i believe a group in up state New York performed an experiment on the finger lakes where they purposefully acidified the lakes to see what happens. 

As far a pH goes, the pH of surface fresh water will be well below 7.0. The pH of salt water is usually above 7.0. I believe that it is around 7.5. 

Generally, a short term drop or raise in pH is not that bad. When the pH is continuous, that is bad. (acid mine drainage.) The type and quality of the water way is important too. 

This does not directly speak to your question, but you may want to look at research focused on the pH of the Southern Ocean where about 40% of atmospheric carbon is believed to be absorbed.  

I don't agree with your information that with a change like 7 +- 1.5 pH, almost everything dies! Some life forms are definitely sensitive to such pH change but if you consider rain events (heavy down pouring or continuous rain)or areas suffering from acid rain or the aquatic systems (lakes rivers, oceans) suffering from acidification under the current regime of high carbon dioxide concentration) all biota never gets wiped out! It's not 1 & 0. Hence we study different magnitudes and degrees of impact on different life forms belonging to different hierachical level of complexity.  Please have concrete background information and a solid hypothesis before you start with the problem.

7+- 1.5 may be there is change in biodiversity but no to death.

but it may be different from each organism to another, but I belive for juveniles or larvea this could some mortality,

but for 7+-0.5 I think it is the same.

but the question how could you design this pH system in the environment?

how could you control it ?

I think it is not possible

regards