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Re: Iron adn TMG etc

What a load of typing, James!  I have a few comments.
> 3.4.6 Nutrient Supply through Nutrient Springs
> "We also discovered that although the amount of water varies considerably at
> different times of year...had little effect on the chemical composition of
> the waters we have been analyzing."

In most records I've seen there are substantial variations in water
composition through wet a dry seasons.  That may not be true in wet areas
where even the "dry" season is wet by most standards, but in other areas
there are changes in chemical composition.  And plants do just fine.

> The Challenge of Nutrient Springs
> "The discovery of nutrient springs, and the observation that certain
> critical nutrients are continually replenished in plant water, led us to
> certain conclusion for the aquarium. These critical nutrients are
> principally iron, manganese and other trace elements which are needed by
> plants only in very small quantities, but which when absent...lead to severe
> plant damage.

Streams, rivers, ponds and lakes are usually (not always) the drain for
their local ground water system.  Ground water flows toward the stream,
through the stream bed material and into the water.  Not just at isolated
springs, but virtually everywhere along the stream.  The stream bed
material is often loaded with labile organic material so the groundwater
passing through it becomes depleted of oxygen, often depleted in nitrate
and frequently enriched in iron, manganese and phosphorus. Not always, but
quite frequently.  As a result in many areas where plants grow along
streams their roots are provided with a constantly-renewed nutrient bath.  
Some of the nutrients make it on into the water column and for the most
part they are rapidly precipitated.

> An Fe content of 0.1 mg per liter is
> desirable, whereby it is important to remember that small traces of iron are
> available even in the avsence of light. We believe that higher levels of
> iron such as 1.0 or even 2.0 mg per liter which is commonly suggested are
> too high and quite unnatural."

Most natural water has iron levels in the range of a few parts per
billion.  "Black water" from marshy areas can have iron content over 5

> >From The Complete Book of Aquarium Plants, Allgayer & Teton:
> [anything in square brackets is me......]
> Iron additives/chelators
>  "Hard water generally has an average [iron] concentration of 2.0
> mg/L........where iron is naturally present in a concentration higher than
> 1.5 mg/L, there will be no need to supplement it.

Could the authors have meant micrograms/liter instead of mg/l?

Very few people on public water supplies will have more than a few parts
per billion of iron in their water.  A part per billion (ppb) is a
microgram per liter or 0.001 mg/l.  My tap water, for instance averaged 1
ppb through the year 2000 and the highest test was 7 ppb.  The standard in
the US for public water supplies is 0.3 mg/l (300 ppb).  I think Canada,
the EU and the rest of the civilized world maintain similar standards.  
Private well water will often have more than that, and the well owners
complain and/or treat their water.

Further, I don't think there's a positive relationship between hardness
and iron content.  If anything, the iron content should drop in hard
water.  The highest iron contents I've seen in surface waters have been a
few mg/l in very soft water from marshy areas.  Anoxic ground water (often
hard) can have quite a bit of iron in it.  Maybe that's what the authors
were thinking of.  On the other hand, not many of us use that water.

Incidentally, in looking up the EPA standard for iron in drinking water I
came across their standard for the protection of freshwater aquatic life.
The US standard is that iron should not exceed 1.0 mg/l for freshwater
aquatic life.  The little bit of summary material I have includes a nice
little summary of iron chemistry and occurence, but *no* justification for
the 1.0 mg/l standard

Roger Miller