Blood isn't the only natural system that uses acid/base buffers. Limestone is made of calcium carbonate. How would you expect the pH of a lake with limestone bedrock to compare to other lakes after several years of acid rain?
Since the lime stone acts as a filter I believe the pH would be around 4 to 9 it wouldn’t be too acidic because of the lime stone and it wouldn’t be too alkaline because there’s no chemicals in it
