The Stream Doctor

October 24th, 2004

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. Hi, I am a college student and have to type a lab report. One of the aspects we are looking at is the pH of a stream and the effects different forest types have on it. Our findings indicated that the more conifers you had around the stream the more acidic or lower your pH was. Assuming this is true how come? The further we got from the conifer stand the pH gradually started to climb. Any reason why?

A. Although it is fairly typical that leachates from coniferous trees, and the soil below them, are acidic, it is less easy to translate this to stream water chemistry because many factors interact to produce the pH you find in a stream. Coniferous leachates are high in organic acids such as fulvic and hummic acid; these would tend to contribute an excess load of hydrogen ions into the ground water and thence into the stream - thus lowering the pH. However, geological processes play an important role in stream ph also. If your stream is high in a watershed, groundwater has had less time to interact with geological materials and is usually more acidic. Certain rocks leach unique chemicals that interact to produce the water chemistry you find. Specific tree species also have unique chemical interactions. White pine, for instance, leaches high amounts of nitrate to the soil below the trees, and this could influence acidity.

On a practical note. I tried growing some vegetables in a small garden in my back yard; part of the plot was under a pine tree. The vegetables grew just fine - but those under the pine tree were practically inedible, and I'm sure it was from the leachate under the pine tree because those vegetables outside of the "drip zone" were fine.

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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