Notes on Kite Aerial Photography: Photo Gallery
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A true color satellite image, or near
true color anyway, of salt evaporation ponds in the South Bay. The lighter color
areas surrounding the bay are urban buildup while the wetlands devoted to salt production reflect
the vivid colors of halophilic algae and bacteria (image courtesy of MapQuest).
I always asks for a window seat when traveling by air (and this despite my 6'-4" frame) because it is simply to much fun to gaze out the window to ponder the terrain below. One of my favorite subjects for aerial voyeurism is the southern portion of San Francisco Bay. Here the wetlands were co-opted a hundred years ago to support the evaporation of sea water for the production of salt. It is a process that produces a remarkably vivid landscape.
For reasons I cannot fully explain, it took until 2002 for me to seek photographic access to the evaporation ponds that fascinate so from the sky. I guess I just assumed they were inaccessible and/or lacked a strong sense of how to find them. In any event Thomas' recent work on a term paper about Bay Area wetlands and a bit of time on the 4th of July motivated a search for salt pond access on the WWW. There I found directions to the Don Edwards National Wildlife Refuge, located about a 30 minute drive south of Berkeley. This, it turned out, was a splendid discovery.
Plan view of a salt pond shoreline featuring my lovely wife Claudia lending a bit of scale (Canon Digital Elph, July 2002)
There were remarkably few folks evident as Claudia and I took the five-mile
long stroll around a salt pond accessible to the public.
Fodder from Cargill: The palette of colors that makes the salt ponds such a vibrant sight reflects a complex ecosystem. Colors in salt ponds range from pale green to deep coral pink, and indicate the salinity of the ponds. Microorganisms create these spectacular colors, changing their own hues in response to increasing salinity.
In low-to mid-salinity ponds, green algae proliferate, lending the water a green cast. As the salinity increases, an algae called Dunaliella out-competes the other microorganisms in the pond, and the color shifts to an even lighter shade of green.
In mid-to high-salinity ponds, high salt concentrations actually cause the Dunaliella to produce a red pigment. Millions of tiny brine shrimp in mid-salinity ponds contribute an orange cast to the water. Halophilic (salt-loving) bacteria such as Stichococcus also contribute red tints to high-salinity brine.
Weather can affect the colors of the ponds. When wind creates choppy conditions, the colors appear murkier. Heavy rain can dilute the brine, causing the colors to shift toward the hues found in lower-salinity ponds or even turn the water clear.
When the brine is fully saturated, we call it "pickle." At that point, the brine is holding as much salt as it can, and the salt begins to crystallize in flakes. Our watermen pump the pickle into large crystallizer beds at our plants in Newark and Redwood City, which have been carefully leveled and packed to create flat, even bottoms.
Here, the brine will undergo its final evaporation, yielding pure salt crystals. This is where the art and science of salt making are put to the test. If the days are too hot and the breeze is too gentle, small flakes called "drift salt" can form - to avoid that, our watermen may add brine to the crystallizers. On the other hand, untimely rain could dilute the brine and delay harvest for weeks - even a whole season.
Ultimately, though, evaporation continues and the salt crystals form at the pond surface, dropping to the bottom when they grow heavy enough to overcome the water's surface tension.
After five long years of gentle coaxing, the bay water has yielded a crop of beautiful salt crystals. The first step in preparing for harvest is draining off the red "bittern," a solution of minerals other than sodium chloride that has concentrated during the evaporation process. Bittern, which is high in magnesium, can be used as a low-corrosive de-icer during the winter, as well as a dust control agent in the summer months.
Now the bed of salt - 5 to 8 inches deep and glistening in the September sun - is ready for harvest. It's already more than 99 percent pure. We're in a race against winter rains as we bring out our harvesting equipment to collect 700,000 tons of salt at our Newark plant and 300,000 tons at our Redwood City plant. We'll work 24 hours a day, five days a week, to bring in our harvest by mid-December.
Our crews harvest the salt off the clay floor of the crystallizers with a mechanical harvester that breaks up the salt with a rotating "pickroll" and scrapes the pieces up with a blade that operates something like a snowplow. Our skilled harvester operators can scrape salt within a fraction of an inch of the clay, yielding very pure salt. On the harvester, conveyors lift the salt and place it into hopper cars that are pulled by diesel locomotives along temporary tracks laid on the crystallizer floor. Each hopper car carries about two tons of salt.
The locomotives pull the salt to the wash house - the first step in further purifying the Bay's bounty.
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All rights reserved. Revised: Saturday, June 26, 2010