By David Wartinbee, for the Redoubt Reporter
Ask any chemistry student and they will tell you the definition of pH is “the negative log of the hydrogen ion concentration.” Unfortunately, most folks don’t think in terms of hydrogen ion concentrations, let alone negative logs about anything.
It’s easy to say that if it’s that technical, I’ll let someone else worry about it. However, pH values are critical characteristics of streams, lakes, oceans and even the water in your bathtub. It even plays a critical role in how we preserve or store food and wash our hands.
What we really need to understand about pH is that we have a scale that goes from 1 to 14, and pH 7 is neutral. Anything above pH 7 is basic or alkaline, and anything below pH 7 is acidic. When the concentration of hydrogen ions is high, the water is acidic and the pH value is low. When the concentration of hydrogen ions is low, the solution is basic and the pH value is high. Pantry items like vinegar will have a pH in the range of 3. The bleach you clean with has a pH around 13.
Your shower water is closer to neutral with a pH range of 6 to 8. The bottled water you drink will be very close to pH 7. The stream where you go salmon or trout fishing is also going to be close to pH 7. The ocean where you go clam digging will be slightly basic at pH 8.
Perhaps you are seeing a trend. Water we use every day and the water where we catch our dinner will have values centered around pH 7. Most aquatic organisms, like invertebrates, fish and frogs, require near-neutral pH values in the water. There are only a handful of specialists that can survive in conditions that are strongly basic or acidic, and most of those are nonpathogenic bacteria or fungi.
Let’s think about clams, mussels and snails with calcium-rich shells. If they were in acidic water, like pH 5 to 6, their shells would simply dissolve away. Most aquatic insects will not survive when the water becomes acidic, and without insects in the water, there will be no trout, either. When I was a graduate student many years ago, I surveyed a pH 4, mine-acid drainage stream and never found a single aquatic insect or, as you can imagine, any fish.
With the exception of our somewhat acidic “brown water” streams and bogs, most of the lakes, ponds and streams in our area have pretty much neutral water. We can tell that by the presence of trout, lots of insects and snails. If it were not near neutral, those organisms simply wouldn’t be there. If most of our streams and lakes are close to neutral pH, what can upset this apple cart?
One easy way for water to become more acidic is to add extra carbon dioxide. If we take pure water and bubble carbon dioxide into it (like blowing bubbles with a straw) the water will become more acidic. That is exactly what soft-drink makers do with sugar water to make your favorite soda. When you leave an open, half-full soda bottle on the table over night, the carbon dioxide slowly bubbles out and is lost to the atmosphere. If you drink it in the morning, it tastes flat.
It was the acidic nature (pH 3 to 4) of your soft drink that gave you a tingle in the mouth yesterday. But with the loss of all that carbon dioxide overnight, it becomes much less acidic and loses its sparkle. If you start looking at labels, you will see that the soda makers also add some more stable acids to the solution to maintain the acidity when carbon dioxide bubbles away.
There are a number of very credible scientists who have warned that recent increases of carbon dioxide in the atmosphere are causing ocean waters to become more acidic. There are natural buffers in most water bodies that will help stabilize the pH even with an addition of extra carbon dioxide. However, the inherent buffering capacity is very limited and we are starting to strain the system. There are multiple reports of decreasing pH values being found in the oceans, and this is not a good sign for the organisms that live there.
The most common causes of major pH changes in freshwater systems are man-made. A variety of industrial activities involving the use of acidic compounds and indiscriminant discharge into a water body can have devastating effects.
Another common way of changing pH values in streams and lakes is by exposing certain compounds to the oxidizing effects of air. When sulfur-rich rocks are brought to the surface during mining activities, water and oxygen combine with those sulfur ions to form several different acids.
When sulfur-rich rocks were exposed during coal mining operations in Pennsylvania and West Virginia, the resulting acids sterilized huge numbers of trout streams. In case you are wondering, one of the reasons many folks are worried about the proposed Pebble Mine near Iliamna is that much of the rock found with the various ores is rich in sulfur.
While non-neutral pH values are usually bad for our streams and lakes, we often use acidic solutions to preserve various foods. Pickling recipes for vegetables or salmon call for the use of acidic vinegar or lemon juice because low pH solutions prevent the growth of most pathogenic bacteria. The dangerous bacterium Clostridium botulinum does not produce its nerve-deadening toxin (botox) when grown in pH 4 media.
In other processes, like making sauerkraut or yogurt, we encourage specific bacteria to grow and they release the acids for us during a process called fermentation. Soaps and bleaches are alkaline, and those high pH conditions also prevent the growth of many pathogen bacteria.
So, whether you can recite the definition of pH, it surely has played a role in something that you do. Perhaps you have used acids to preserve your foods, used alkaline soaps to clean your clothes or noticed water’s neutrality when there are fish in your streams.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.