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This year I dug a 30-foot creek and a foot deep, 4 x 6 foot pond in my back yard, and named it the Frogs' Mitigation Area. I wanted to encourage frogs there, so I didn't put any fish in the pond. I figured without nitrogen-rich fish poop in the water to feed algae, that pond would remain clear and unclouded.
Nature had other ideas, as demonstrated in the pictures and text below the orange tracing of a killdeer's mating flight.
The pond and stream are between a 60-foot-tall sequoia redwood, and a 40-foot-tall sugar maple. A couple of smaller firs, cedars and pines are also nearby. All of these have shedded needles and leaves. The maple leaves especially have visibly fallen into the pond and stream.
These leaves contain tannin, which is a chemical called a polyphenol. Tannins are in many kinds of plant life. One of their purpose is to make the plant taste astringent or "puckery" and unpalatable to predators.
Also, if certain types of wood, or leaves fall into water, the tannins leach out and turn the water dark, as shown in the following picture;
The above photo is in lighthouse mode, and you can click on it for more detail. I drew mainly on Wiki for my following narrative on leaves and related issues.
Tannin is a powerful darkening agent. Large pulp and paper mills remove thousands of pounds daily of these dark tannins and other materials from the wood feedstock. Some of these mills discharge high concentrations of tannins into nearby rivers, creating an ink-dark flow of effluent.
Travis Williams of Riverkeepers took the above picture where the Halsey pulp mill discharged tannin-rich waste water into the Willamette River, for instance.
I was stuck by how much leafy material fell into my own Frogs' Mitigation Area. I wondered then about the heavily wooded and shallow wetlands at the golf course where I work, and why the autumn leaf falls don't simply fill up those shallow water bodies after a decade or two.
When I clean out my own backyard ponds every ten years or so, I find a couple of inches of blackened leaves on the bottom, apparently not decomposed very much. My own pond probably has some bog-like characteristics, like a low-oxygen "reducing" chemistry. When I start up the water circulation pumps after a long haitus, the pumped water yields a sulfury scent, probably the result of the very slow acidic leaching of minute traces of sulfur from the submerged vegetation.
The water stays cold in my pond's bottom, and the temperature may never rise enough to activate nature's microbes to heartily chew the leaves into fertile mulch.
However, in the golf course's shallow wetlands, when the foot of water dries up every summer and the mercury hits 90, then the leaves probably decompose every season.
I still wonder about shallow water bodies in cool heavily forested areas, and whether leaf fall eventually fills them up, perhaps reducing them to bogs, as described in Old Jack Pine's recent, fine Bucket on Bogs:
http://www.dailykos.com/...
The tannins, and another constituent of leaves and woods called lignin, perform other important natural functions. These materials can determine the speed by which leaves decompose, which is a crucial step in the great carbon cycling that makes the earth what it is. Probably about 100,000 tons of leaves fall annually just in Portland Oregon, to provide some estimates about the bulk of fallen leaves on our world, and the magnitude of nutrients and carbon those leaves harbor.
Meanwhile, I wonder if I should rake the leaves out of the Frog Mitigation Area, or just watch and wait and see. I could just be lazy, do nothing, and claim to be conducting backyard science.
"Spotlight on Green News & Views" will be posted every Saturday at 1pm and Wednesday at 3:30 pm Pacific Time on the Daily Kos front page. Be sure to recommend and comment in the diary.
Now It's Your Turn What's interesting to you? Please post your own observations and your general location in the comments.
Thank you for reading. I'll work this morning so I'll respond to comments before lunchtime,