VERMONT — Phosphorus, an element on the periodic table like iron and gold, is an essential part of all living beings. It’s part of the structure of DNA and RNA, molecules that carry genetic instructions for all organisms, and ATP and ADP, molecules in our cells that store and transport energy. Phosphorus exists in our cell walls and in our bones.
In “The Role of Phosphorus in Lake Champlain Pollution,” a chapter in a 2016 edition of the Vermont Journal of Environmental Law, University of Vermont Professor William Bowden explains that phosphorus was discovered long ago for its value in growing plants and crops.
Carbon, nitrogen and phosphorus are the basic building blocks of all life. Generally, organisms require lots of carbon, moderate amounts of nitrogen, and a small amount of phosphorus. When one element is limited, life is limited. It’s a lot like baking cakes, according to Bowden:
“Let us say you need two cups of flour, one cup of sugar, and a single egg for each cake,” he writes. “The flour is carbon, the sugar is nitrogen, and the egg is phosphorus. You do not need that many eggs to make a cake, but if you do not have enough, it will not matter if you have an abundance of sugar or flour; you cannot use them. But, if you have lots of eggs and a limitless supply of sugar and flour, you could bake as many cakes as you wish. The same is true for algae (biomass) in lakes. If you provide plenty of carbon, nitrogen, and phosphorus—in the correct ratios—you can grow a lot of biomass.”
In nature, phosphorus exists in small quantities, leaching slowly from rocks and minerals. But humans mine phosphorus from rocks and minerals, like apatite, for fertilizer. Today, phosphorus often abounds in environments near human activity, particularly around developed land and agriculture.
“The annual report on the phosphate mining industry produced by USGS notes tersely that there are ‘no substitutes for phosphorus in agriculture,’” Bowden writes.
If the phosphorus supply in the lake is endless, the next limiting element is nitrogen—the sugar in our cake recipe. Nitrogen becomes available in the environment through natural events, like fire and lightning; it’s not available everywhere. But some microbial organisms have developed a protein called nitrogenase, which allows them to extract usable nitrogen from nitrogen gas, which is abundantly available in the atmosphere.
In water bodies like Lake Champlain, organisms with nitrogenase have endless access to carbon, nitrogen and phosphorus. Like a super villain with infinite powers—Voldemort with the invisibility cloak, the elder wand and the resurrection stone—nothing limits their growth.
Most types of blue-green algae, and some types of regular algae, have developed nitrogenase. That means, as long as phosphorus is abundant in the lake, those types of algae will be almost impossible to control.