Re: Calcium in water - more than you want to know...

Actually, a good bit of the eastern US, west of the mountain chain where
Neil lives, is underlain by limestone, which is calcium carbonate rock.
Parts of Missouri, Tennessee, Arkansas, Kentucky, Oklahoma, and farther
south were under a shallow inland sea at one time, which led to deep
deposits of carbonate. Surface waters in this region tend to be pretty
much saturated with calcium carbonate.

In addition to the calcium carbonate being left behind as the water
evaporates in caves, water moving thru saturated soil above limestone
rock becomes 'super saturated' with calcium carbonate due to the
presence of increasing concentrations of carbonic acid.  As rain water
moves thru the soil, more carbon dioxide dissolves in the water, which
forms carbonic acid.

Once the water moves back out into the air (springs, cave drip, etc),
the reaction goes the other way, carbon dioxide is re-released to the
atmosphere, the water becomes less acid, and calcium carbonate
precipitates out.

So part of the formations in limestone caves results from evaporation,
but part comes from precipitation once the percolating water reaches the
air.

If you live near a spring fed stream in limestone country, you can see
this happening after one of our long rainy spells following a dry
spell.  Here, it takes a day or so for the water to move all the way
from the surface of the hills above my house, down through the soil, and
out in the spring fed stream.  The water is clear until the fresh batch
of dissolved carbonate is flushed out, then it takes on a translucent
bluish color for about a day, then is back to normal.   The
concentration of <dissolved> calcium stays constant except at the point
where water comes out of the ground.

Oak Ridge National Lab, where I worked for 30 years, has an intensively
studied watershed and stream system on limestone geology, & I got to
hear seminars about the work going on there.  Hope I didn't botch the
details too badly - not my area of expertise, for sure!

From additional research done by folks I used to work with, I learned
that there are other, acid-forming, non-calcium, rock formations in the
mountains, both here and near where Neil lives.  In the Cumberland
Plateau, slightly west of where I live, there are sulfur bearing rocks
that are not a problem unless they are exposed to the atmosphere.  Strip
mining for coal exposed a lot of these rocks which resulted in major
acidification of streams.

In the Great Smoky Mountains between here and Neil's house, other
sulfide bearing rock formations were exposed during road construction &
had a similar effect.  In this region, I think sulfur tends to be the
metal of greatest concern, tho in other regions, there are other
problems.

More about acid rain, rocks, and stream water acidification from
http://pubs.usgs.gov/of/of95-810/export/saa-acid-abstract.asc

<Acid deposition sensitivity map of the Southern Appalachian Assessment
Area: Virginia, North Carolina, South Carolina, Tennessee, Georgia, and
Alabama>

<Rocks composed of mostly calcium- or calcium-magnesium carbonate
(limestones, dolomites, marbles, and calcareous rocks) are rated as
having low susceptibilities [to acid rain], as are most mafic rocks
(gabbros, mafic paragneisses and schists, amphibolites), predominantly
mafic volcanic rocks, diabase, and ultramafic rocks and mafic-ultramafic
complexes.  These latter groups of rocks generally contain sufficient
calcium-rich feldspar or other calcium-magnesium silicate minerals to
generate acid-neutralizing soils upon weathering. Dominantly siliceous
clastic rocks (sandstones, shales) were
shown by Webb and others (1994) to be associated with areas of high
acid-precipitation susceptibility.  These rocks release little or no
acid-neutralizing components; indeed sulfidic shales and sulfidic
schists may be acid generators.  These and their metamorphic
equivalents, as well as siliceous mylonites, were rated as high
susceptibility areas.

Areas of felsic volcanic rocks , granitic rocks (granite, granodiorite,
quartz diorite), volcanic and volcaniclastic rocks, felsic paragneiss
and schist, alkalic rocks and anorthosite are characterized by the
presence of alkali (potassium and sodium)

<Water in the humid, water rich eastern parts of the US would have other

                   minerals dissolved in them, especially due to acid
rain.  The lime has long
                   since departed.  The minerals now present are
compounds of heavy metals,
                   responsible for the damage to life in lakes and
streams in the areas most
                   affected.   Neil Mogensen    z 7  in the mountains of
western NC>

--
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
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online R&I <http://www.irisregister.com>

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