Phosphorus: Are We Part of the Solution or Part of the Problem?

The Devil’s Element by author Dan Egan is a never-ending story that offers readers insight into the “overuse-scarcity” paradox of phosphorus—a looming environmental crisis that impacts our long-term future. 

In the December newsletter of the Friends of Pheasant Branch Conservancy, Rick Eilertson wrote about the effects of two pollutants, sediment and phosphorus, on the water quality of Pheasant Branch Creek and the DNR’s decision to place the creek on the Impaired Waters list. Dan Egan describes the phosphorus cycle transformed into a straight line that now runs from oversupply in waterways to an increasingly limited supply in terrestrial reserves. The story intrigued me as a dietitian nutritionist who had not contemplated the scarcity issue or fully investigated the implications of overuse.

At the Friends of Pheasant Branch Annual Membership Meeting on January 10, Dan enthusiastically discussed with John Reimer (Assistant Director of the Dane County Land and Water Resources Department) the imbalance among the earth’s limited reserves, our need for phosphorus, and its overuse, which poisons our lakes and rivers. 

The biological sciences majors among us know phosphorus as a key component of human energy production, metabolism, and bone health. Adults with well-functioning kidneys need about 700 milligrams of dietary phosphorus each day; teens need about 50 percent more. Phosphorus is present in significant amounts in meat, milk, legumes, nuts, and grains, and it’s also a component of many commonly used food additives, so assuring adequate intake is rarely a concern unless you are an individual with failing kidney function. 

Many of us also know phosphorus as a component of plant fertilizer, supporting root, flower, stem, and seed development, as well as photosynthesis. For plants, it is as essential as water. The primary source of this phosphorus is mined phosphate rock, a finite resource found primarily in a few countries, such as Morocco and China, which control 85 percent of the world’s phosphorus. It is also present in soil. It is required for crop growth, and its depletion poses a serious threat to future food production. Soil depletion due to erosion and other factors is a major concern in other parts of the world (Eastern Europe, Africa, and South America). Fertilizer scarcity, already experienced by these countries, is another major concern for us all as phosphate reserves dwindle and supply chain disruptions and rising energy costs make it expensive or unavailable.

Dan and John’s primary concern about phosphorus is twofold. First, only 30 to 40 percent of phosphorus-containing fertilizer is absorbed by the soil, leading to phosphorus-containing runoff that promotes algae growth in our lakes and waterways, resulting in fish kills and aquatic dead zones. Egan emphasized a hard truth: “Food on the table is at cross purposes with clean water.”

Second: Natural phosphorus reserves are limited, and if we continue using it at our current rate, our future food system cannot be sustained. However, phosphorus is also present in biological waste (human and animal) and in plant residues left on fields. In his book, Dan notes that more than 3 million tons of phosphorus are produced in human urine and feces alone and describes methods used and being developed to reclaim phosphorus from these biological products. John Reimer’s extensive work on the Yahara River Sediment Removal Project, featured in the September 1, 2021 and May 16, 2025, issues of the Cap Times, has already had significant environmental effects, including improved stormwater flow during flooding, improved navigation, and benefits to fish spawning. 

Both John and Dan are optimistic that we can meet the challenges of the overuse-scarcity paradox

Herb Garn, the chair of the Friends’ Watershed Committee, leads a citizen-science project that monitors, among other things, the amount of phosphorus in the Pheasant Branch Creek tributary resulting from runoff from the former Acker dairy farm addition to the Conservancy. Restoration of this farm to platinum prairie was completed in 2024, resulting in a greater than 90 percent reduction in phosphorus washing into the Creek as runoff flows to Lake Mendota. These promising findings are the result of collaboration between Dane County Parks and Recreation and the Friends, underscoring our mission to restore, protect, and promote the Conservancy as an ecological whole.