This was the question I had- How is nutrient buil-up in the aquatic system affect the pH? What other factors in the aquatic system affect the pH?
Since this is not my area of expertise, I searched Google under the key words "aquatic system pH" to get these possible sources:
http://72.14.203.104/search?q=cache:F7hNCzsBe9EJ:www3.uakron.edu/education/OLN/lessons/smith/Aquatics.pdf+aquatic+system+pH&hl=en&gl=us&ct=clnk&cd=1&client=safari
http://water.usgs.gov/wid/FS_216-95/FS_216-95.html
http://72.14.253.104/search?q=cache:MOsmrVjivIQJ:envsci.rutgers.edu/~reinfelder/cpesnotes/carb.pdf+aquatic+system+pH&hl=en&gl=us&ct=clnk&cd=42&client=safari
I hope this helps. Thanks for asking.