Monday, July 13, 2009

7-13-09 A note about the red tint, or tea color, in some streams in the White Mountains.

This is a note to Phil W. who asked about the reddish, tea-like color of the water in side streams in the Zealand Valley. When I first asked someone the same question years ago about the reddish color (and if was it okay to drink, etc.) I got a brusque answer that it was "the tannin". So your analogy to the tea color is right on as there is tannin in tea. There is tannin in myriad species of plants. The photo above is of a small branch stream of the Zealand River where it flows out of a series of beaver ponds and the water has the characteristic tannin color.

The tannin is leached out of the leaves, stems and other tissues of plants growing in or near the streams and in and around the ponds and lakes that are the sources of the streams. The plant tissues contain the tannin that eventually turns the water the reddish, tea color. If you notice you will see organic matter growing in the stream beds as well as along the stream edges. Last week when I was wading in Zealand Pond looking for Sundews the bottom of the pond had a 6-inch thick "ooze" consisting of organic matter all or most of which contains tannin.

There are a number of factors influencing the presence and amounts of tannin in the water: the water source, the season, the temperature of the water, the amount of precipitation, the flow rate of the stream, and what I call the "Drop Rate." The first five will impact the concentration of tannins in the water. I‘ve observed that more tannin is seen in slow moving streams towards the middle to end of summer and the least in the spring after snow melt when the water is cold and moving rapidly. If it’s a rainy summer with a resulting increase in volume of water and rate of stream flow there's less tannin. The "Drop Rate" effect is when a stream “drops” over waterfalls or down rapids and rills and gets aerated in the process. I’ve observed that the tannin decreases markedly in these streams. I would guess that the air (oxygen) removes the tannin and that there is an inverse relationship between the amount of tannin and amount of oxygen in the water. Phil (or anyone reading this), it might be worth while to Google "tannin" and see what comes up. Thanks for your nice comments, Alex.


Jon said...

It is, of course, safe to drink, or at least as safe as any other mountain water. However, having just about anything in the water will change the efficiency of most water treatment. To be safe, it's probably a good idea to increase treatment time when the water is highly tannic.

Philip Werner said...

Alex - thanks for the great explanation!

Sandy said...

Tannins are complex organic compounds manufactured by plants primarily as biological "warfare" agents. They have anti-bacterial, anti-digestive properties and are often used by the plants to promote interspecific allelopathy.
Look it up in wikipedia.

The tannin in stream and lake water is the breakdown product of plant material. The amount of tannin concentration in water is largely a function of plant material quantity, tannin concentration in that material, and "steep-time" where water in contact with decomposing organic matter for longer periods will have higher concentrations, just as you would see when steeping tea. Therefore, generally, tannins are more obvious in swampy, boggy, terrain where water is in contact with decaying plant material for long periods.

The color of the tannins is a function of the TYPE of tannin. You can google a bit on this but tannins are very complicated organic chemicals and vary tremendously by plant species.

Tannins in stream-water colloidal suspensions are removed by oxidation, flocculation, etc.

I would not drink heavily tannin stained water for long periods but a couple of bottles full won't hurt too much. It will interfere with digestive processes in humans just as it does in the animals targeted by the plant.