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
Email: streamdoctor@aol.com
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 streamdoctor@aol.com.
Originally published October 24th, 2004 on Fly Anglers Online by Robert Younghanz.