My pH values are jumping around unpredictably!

Look at the pH! Is this possible?

This graph is a good example of curious pH readings in a data set. Here the pH values seem to be bouncing back and forth over a range of almost 3 pH units. What do you think might be going on in this case? Keep in mind that pH's are usually fairly steady measurements unless there is a major disturbance to a stream, or lake such as periodic waste discharge, a very large rainfall, a large algae bloom,or a change in flow rate due to upstream snowmelt. A good example of a periodic change in water flow might also be the discharge from a reservoir upstream. This would significantly affect pH values measured downstream. This set of temperature data shows nice, predictable seasonal trends.

Is this right? Should my pHs be this jumpy?

Here we see another GLOBE hydrology site where the pH values seem to be a little unpredictable. They jump over a pH range of 7.4 to 9.6. Does this seem reasonable to you? Are there major disturbances going on, or do these data merely reflect part of the learning process?

So enough talk, whats going on? Possible reasons for jumpy pH values:

• This could be real! If we believe that the jumpy data being measured is actually a real pattern, then we need to look for reasons. For example, if your school was located on a tidal river, then pH values might change dramatically with the inflows and outflows of seawater.
• Maybe the school group hasn't been being as careful as they could have. The readings might be caused by inconsistently following the protocols.