Among the books I acquired during my recent annual indulgence (read: birthday), perhaps the most exciting is Theodore Gray’s newly released The Elements: A Visual Exploration of Every Known Atom in the Universe (Black Dog & Leventhal, 2009). As you may recall from Marcella’s guest post, we visited Griffith Observatory this summer with our extended family (my dad and my brother and his wife and two sons), where we saw a very interesting display. It was the periodic table, with samples of each element built into the display case:
Well, Theo Gray, frequent guest on one of my favorite radio programs, NPR’s Science Friday, has done Griffith Observatory one better, or at least one more in depth: The Elements is, according to the copy on the foredge flap of the dust jacket, “A mesmerizing photographic display of the 118 elements in the periodic table.” Well, I don’t know about mesmerizing, but, as Marcella and I knew right away when we saw the physical display at the observatory, the very idea of making the periodic table more concrete by using realia is sheer brilliance. And Gray, co-founder of Wolfram Research (Mathematica, anyone), carries out this concept quite well in his book. (And, as you can see from his website, he’s really into periodic tables!)
But enough about Gray and his book. This is not a book review. This is the first in a series of posts about the elements in Florida. Not the weather; I write about that in posts about the weather.
Today’s post is about one of the most important of the elements in the periodic table that is to be found in Florida: phosphorus. As I’ve written elsewhere, phosphorus, chemical symbol P, is the 15th element of the periodic table. It is NOT spelled “phosphorous” (that’s the adjective form).
Commonly found in items like fertilizer, pesticides, match heads and other explosives, phosphorus also exists in important quantities in the human body. Its role in the human body is essential: it is found in the nerves, in bones, and in our RNA and DNA. In fact, phosphorus was first isolated as an extract of human urine. We need phosphorus to survive! However, too much of a good thing can lead to trouble.
Phosphorus plays a very important role in regulating plant growth. It is nearly always found in particulate matter (soil) or bound in other forms, rather than circulating freely in the environment. (Here is the EPA’s explanation of why phosphorus is important.)
Legal limit in the Everglades: 10 parts per billion (10 micrograms per liter). Problems with measurement: the 10mcg/l standard is the “average” amount allowed over a 5-year period. If you measure three or four times a year, it’s pretty easy to cherry-pick your data, to show either high levels (measure right after a storm) or low levels (measure only during drought conditions).
Sugar cane growers like to demonstrate how “dirty” the water that comes off their fields is by drinking a glass full of phosphorus-laden water. It’s not a threat to human health. It’s a threat to ecosystem health. Phosphorus won’t kill you unless you drink an awful lot of it: far, far more than the 10 parts per billion limit enshrined in conservation law.
The problem is, phosphorus encourages plant growth. The plants native to the Everglades ecosystem evolved to tolerate, even thrive in, an environment nearly devoid of phosphorus. Adding water with even 40 parts per billion of phosphorus encourages the growth of non-native plants like cattails, which can grow into huge monoculture stands thanks to the supplemental nutrients. These monoculture stands crowd out native species of plant and animal life and then cause further problems: the cattails bloom, fouling the water.
Satellite photos of the Water Conservation Areas taken over the last decade can serve as a road map for the intrusion of phosphorus into the ecosystem. Where phosphorus levels are high, cattails and other non-native species flourish. Where they are low, the typical Everglades plants appear.
Links:
- SFWMD page on phosphorus
- UM page on phosphorus
- UF/IFAS page on phosphorus in the EAA, purporting that the P in the EAA comes from aquatic weeds (don’t be fooled: even though it’s the aquatic weeds that are the “source” of the phosphorus, the only reason the weeds are able to capture the P is that it’s present in the agricultural runoff. Don’t blame the plants! They just grow where conditions (substrate and nutrients) allow.)
- Legal limits in the Everglades
- A Duke University study suggesting slightly higher limits on phosphorus (12-15 ppb instead of 10)
- EPA facts about phosphorus and water quality
The importance of phosphorus to Florida is manifold.
It is a strong driver of the state’s economy ; according to floridahistory.com, phosphate (the naturally occurring form of phosphorus, found in rocks called phosphorites) mining is the third largest industry in Florida, behind tourism and agriculture. The economics of the situation go up and down, though, with phosphate sometimes commanding a high price, and at other times not so much. The industry is in turmoil, with the deposits in central Florida apparently petering out, and becoming harder and harder to exploit over serious environmental concerns.
Below is a picture of phosphate rock, from the FL department of state website:
The phosphorus in Florida comes from huge deposits of phosphorite (a general term meaning, basically, phosphate rock; also more specifically, a fibrous apatite formed through concretion) that were laid down in the Miocene epoch, “a time of large-scale buildup of ice on Antarctica that resulted in large and rapid changes in sea level” (Compton 197, in Randazzo & Jones 1997).( Sea-level change is important to the formation of phosphorite, because the phosphorus in phosphorite comes from organic sources raining down in warm, shallow seas.) Most of Florida’s phosphorus comes from a carbonate-fluorapatite mineral called francolite, which forms in the upper layers of ocean floors that are being inundated by teeny-tiny phosphorus-containing organic sources like diatoms and foraminifers. But in order for phosphorite fields to be economic, that is, to contain high concentrations of recoverable phosphorus, that organic material must have been removed after it provided the phosphorus to form the mineral. This requires reworking of the substrate, which is where the rapid changes of sea level come in. The sediment reworking that typically takes place during marine regressions is what allows the phosphorite to concentrate to economically viable levels. Yay, climate change!
Although phosphate mining is big business in Florida, it’s not the only type of mining that occurs. Florida also has a lot of plain old “rock mines,” where big industrial companies with big industrial gear gouge huge pits in the limestone of the state and ship it as aggregate to wherever they need it. That would be wherever they’re building roads, which we’ve been doing here for a long, long time. The main chemical in limestone, of course, is calcium carbonate (CaCO3), which I suppose would best be talked about in another post…
Because, as mentioned earlier, phosphorus is one of the main ingredients in fertilizer, this essential element and nutrient comes into direct conflict with one of the most endangered ecosystems in the United States: the Florida Everglades. The plants that dominate the Seldom-ever-shady glades evolved to thrive in an environment low in phosphorus. They are able to outcompete other plants that depend on having more readily available phosphorus to grow, (plants in the Typha genus like cattails). This phosphorus-limited ecosystem is unique in the United States, and is now seriously threatened by uncontrolled releases of phosphorus.