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pH

Diagram of pH. pH 1=battery acid, 2=lemon juice, 3-vinegar, 6.5=milk, 8.5=baking soda, sea water, 10.5=Milk of Magnesia, 12=ammonia, 13=lye. ph 3 to 4=Adult fish die. ph 4-5=Fish reproduction affected. pH 5-6.5=Normal range for precipitation. pH 6-8=Normal range of stream pH. pH 1-5=Acid rain.

What is pH?
The pH of a solution is a measure of its hydrogen ion (H-)activity. pH controls the degree of disassociation for many substances. Acidic conditions range from 0 to 6.9; alkaline conditions range from 7.1 to 14.0. The scale is logarithmic, so every one-unit change is actually a ten-fold change in acidity or alkalinity. The pH of surface waters is primarily affected by plant and algae growth during the summer. In the winter, pH is mainly affected by precipitation entering streams and rivers as rainfall runoff.   Rainwater typically has a low pH of around 5.6. Although organic acids of natural origins (i.e. tannic acids found in wetlands) are usually not a problem, mineral acid pollution is detrimental to fish. A pH range of 6.5 to 8.2 in most cases is suitable. pH values between 6.5 to 8.5 generally are recognized as best for the support of a diversified aquatic ecosystem.

 Examples of different pH levels:

Impact of pH on the environment:
Taking a single measurement of a water's properties is actually less important than looking at how the properties vary over time. If the pH of a stream remains constant over time, then factors in the environment around it might not be impacting it.  But if this same stream area changes over time, this is important information.  If  the pH of your creek begins to change, then you might suspect that something is going on somewhere that is affecting the water, and possibly, the water quality. So, often, the changes in water measurements are more important than the actual measured values.

The optimum pH for both freshwater fish and bottom dwelling invertebrates ranges anywhere from 6.0 to 9.0. Too low or high of a pH can cause any of the following:

  • deformed egg hatching
  • eggs turning pale or white
  • mosquito larvae were destroyed > 1.0 pH
  • death of trout  > 5.5

The pH of water affects the availability of certain minerals such as mercury, lead, iron and chromium and therefore can cause those minerals to be at toxic levels of solubility and be a contamination in aquatic life.

Optimal levels:
pH values between 7.0 and 8.0 are optimal for supporting a diverse aquatic ecosystem. A pH range between 6.5 and 8.5 is generally suitable. Acid conditions caused by acid rain is highly detrimental to aquatic macroinvertebrates and fish. If pH declines below 6.5 fewer salmon eggs hatch and aquatic insect levels drop. pH levels should not vary from natural conditions more than .2 due to human activities.

Testing for pH:
There are many ways to test a stream's pH.  Strips impregnated with a chemical indicator, probes attached to handheld computers, or more expensive diagnostic equipment can be used, but the most important factor is to do the test correctly, consistently, and to monitor a site over time.

 **Some above information courtesy of "Project Green"

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For information on the Washington Virtual Classroom or this website contact Sherry Schaaf at sschaaf@esd114.wednet.edu