This is the second in a series of “standing issue” posts that I plan to morph into standing pages on the Conservation portion of the website. But since pages can’t receive comments easily, I thought I’d post the drafts, as it were, in case anyone out there had anything to add to our pages.

Phosphorus, chemical symbol P, atomic number 15. (Please don’t spell it “phosphorous.”)

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