Phosphorus runoff from farms and other sources is an ongoing problem for Vermont’s lakes. While phosphorus is essential for life, too much of it can lead to toxic algae blooms.

Phosphorus is imported into Vermont’s watersheds by way of feed and fertilizer, and the state is struggling with a phosphorus imbalance in the Lake Champlain Basin. According to a recent analysis by UVM researchers, the state-level imbalance in 2012 was about 1,490 tons, says Michael Wironen, PhD Candidate and Graduate Fellow at the Rubenstein School of Environment and Natural Resources.

In the US EPA’s 2016 Phosphorus Total Maximum Daily Load (TMDL) for the Vermont portion of the Lake Champlain Basin, agriculture accounts for an estimated 41 percent of base phosphorus loading to Lake Champlain, with developed land and wastewater treatment facilities responsible for 18 percent and 4 percent, respectively. Phosphorus can also be lost from stream banks (an estimated 21 percent of base load) and forests (16 percent of base load).

Eric Roy, assistant professor of environmental sciences at the UVM Rubenstein School of Environment and Natural Resources, studies the dynamics of nutrients like phosphorus and nitrogen in food systems and the environment.

We talked to Eric about algae blooms, phosphorus and the food system, and why phosphorus is perhaps the world’s most important natural resource.

We hear a lot about the problem of too much phosphorus in Lake Champlain. What is phosphorus?

Phosphorus is the stuff of life in many ways. It is an element that plays a large number of roles in biochemistry. Phosphorus is in our DNA. Phosphorus is in phospholipids, a major component of all cell membranes. Phosphorus is in our bones and our teeth. Every living organism on Earth, plant or animal or otherwise, is after phosphorus. Therefore, phosphorus plays a critical role in our food systems. Phosphorus is an important component of agricultural soil fertility and health, and is contained within fertilizer, food products and agricultural wastes. When these materials are transported, phosphorus is along for the ride.

Is phosphorus a pollutant? Why is too much of it a problem for our lakes?

As a biogeochemist, I am somewhat reluctant to call phosphorus a pollutant, given its role as an essential nutrient for life on Earth. However, human activity is resulting in the presence of too much phosphorus in many aquatic ecosystems around the world. Cyanobacteria in lakes that are capable of producing harmful toxins need phosphorus just like any other organism, and when a larger amount of phosphorus is available, it can enable the formation of cyanobacteria blooms—often referred to as “harmful algal blooms.” This is a problem in portions of Lake Champlain, as well as smaller lakes including Lake Carmi in Franklin County. Cyanobacteria blooms in Lake Erie have received considerable media attention, due in part to the hazards posed to drinking water supplies. Harmful algal blooms can also hurt lakefront economies by restricting fishing and recreation.

Where does phosphorus come from?

Historically, phosphorus needed in agriculture was obtained from materials including human excrement, farm animal manures, animal bones, and guano, which is the accumulated excrement of seabirds and bats.

In many nations, including the United States, this changed as industrialization proceeded and synthetic chemical fertilizers became available. These fertilizers were shown to boost crop yields and became widely adopted. The phosphorus contained in synthetic fertilizer comes from phosphate rock deposits, which are mined and then processed to create fertilizer products. In the United States, phosphate rock deposits are mined in Florida, Idaho, North Carolina, and Utah.

Globally, over 70 percent of phosphate rock reserves are located in Morocco and Western Sahara. Phosphate rock is a finite resource—deposits form over a relatively very long time. Today’s high global rate of phosphate rock consumption is concerning for several reasons, including the absence of a substitute for phosphorus in agriculture, the finite nature of phosphate rock on Earth, the geographic concentration of phosphate rock reserves and fertilizer industries, potential for fertilizer price spikes, and environmental impacts associated with inefficient phosphorus use.

Are we at risk of phosphate rock depletion?

There have been debates in the scientific literature about when we will reach “peak phosphorus”—that is, when humanity reaches the maximum global mine production rate for phosphate rock, after which production would theoretically decline due to supply constraints. Such an event could cripple food systems around the world. My take on this, based on the latest literature, is that there is no imminent risk of running out of phosphate rock. However, I am still concerned, regardless of the exact timeline of phosphate rock depletion. Phosphorus is perhaps the world’s most important natural resource, and achieving sustainability and intergenerational equity will require transforming our management of phosphorus.

How does phosphorus move through food systems?

Phosphorus entering food systems in fertilizer can be removed from soils by crops, including those grown for animal feed. In many cases, less phosphorus is taken up by crops than is applied as fertilizer, which can contribute to losses of phosphorus to the environment. Furthermore, most of the phosphorus fed to animals in feed ends up in their manure, which can also be an important source of phosphorus losses to the environment depending on handling and land application strategy. Finally, we consume phosphorus in our food, and this phosphorus ends up in our feces and urine, entering wastewater handling and treatment systems, which vary in their ability to remove phosphorus. 

What is currently being done to reduce the amount of phosphorus getting into the lake, and is it working?

There are several efforts underway in Vermont to make progress toward meeting water quality restoration targets outlined in the US EPA’s TMDL for phosphorus. The state’s efforts include Required Agricultural Practices (RAPs), which are practices and management strategies that farms must follow to reduce the water quality impact of agricultural activities. The RAPs establish nutrient, manure, and waste storage standards, make recommendations for soil health and establish requirements for vegetated buffer zones and livestock exclusion from surface water, as well as standards for nutrient management planning and soil conservation. There have also been efforts by The Nature Conservancy and others to conserve river corridors and wetlands. In developed areas, there has been a focus on Green Stormwater Infrastructure, one goal of which is to help mitigate phosphorus runoff. These example efforts are important steps toward enhanced phosphorus stewardship in Vermont. However, we need further research to reduce uncertainty concerning how effective these different strategies are at achieving phosphorus load reductions on the ground.

One concern that I have is what some have referred to as the “mass balance problem.” Briefly, for decades Vermont has imported more phosphorus in fertilizer, animal feed, and human food than has been exported, resulting in a surplus. This surplus phosphorus accumulates in the watershed or receiving lake, including in soils and lake sediments. Over time, this accumulated “legacy phosphorus” can leak out into water and contribute to harmful algal blooms. This means that the full water quality benefits of phosphorus management practices in the basin today may not occur until long after initial implementation. Therefore, I think it is very important to pursue strategies that help Vermont move toward a more balanced phosphorus budget, reducing the buildup of legacy phosphorus.

Vermont Governor Phil Scott promoted the idea of harvesting phosphorus in his recent budget address. What exactly is he suggesting Vermont do? Is phosphorus capture feasible?

Governor Scott and his team are planning to launch a Phosphorus Innovation Challenge, which will “incentivize creation of a commercial operation that captures excess phosphorus (from manure) before it is applied to the land and convert it to a saleable product.” This is not the first challenge that includes an emphasis on phosphorus recovery. Examples include the Nutrient Recycling Challenge hosted by the US EPA and its partners, the George Barley Water Prize, and the Baltic Sea Nutrients and Carbon Reuse Challenge.

If phosphorus in manure is captured and converted into a saleable product, this could contribute to better balancing of Vermont’s phosphorus budget. Using the product within Vermont would ideally offset phosphorus fertilizer imports and reduce the net phosphorus surplus. Additionally, if the product could be transported and sold out of state, this would help better balance phosphorus imports and exports, thereby reducing the net surplus. In general, the hope is that phosphorus recovery and reuse strategies can help direct phosphorus away from areas where water quality impacts driven by excess phosphorus are a concern and toward places within the food system where phosphorus is needed. Remember, phosphorus is required for the production of all crops—some soils have received too much, but other soils still require phosphorus input to remain productive.

I think increased attention to phosphorus recycling is warranted, and that innovations in this area can contribute to progress on phosphorus stewardship. The design of manure phosphorus recovery and reuse programs that are economically feasible and sustainable is challenging and will require creative solutions in Vermont. Furthermore, phosphorus recycling is not a panacea, and we need to also make progress on other aspects of phosphorus stewardship.

Where do you see the most potential for lake conservation efforts going in the future?

Vermont has an opportunity and, in my opinion, a responsibility as a leader in the sustainability movement to help pave the way forward for phosphorus stewardship that supports both water quality and food systems.

I think we need an integrated approach to phosphorus stewardship that includes complementary efforts focused on three R’s:

  • Reduce excessive phosphorus use and import into watersheds—by using phosphorus efficiently on farms so it ends up in food and is not lost to the environment. This includes good nutrient management planning on farms and eliminating unnecessary phosphorus inputs to non-farm landscapes.
  • Recycle “waste” phosphorus safely to locations in the food system where it is needed, offsetting fertilizer inputs derived from phosphate rock. This includes phosphorus contained in animal manures, wasted food, and human excreta.
  • Retain phosphorus on the landscape to protect water. This includes on-farm best management practices, well targeted phosphorus control structures, green stormwater infrastructure with enhanced phosphorus removal capabilities, and restoring landscapes to enhance phosphorus retention.


Reposted with permission from the UVM Food Systems Food Feed blog.


Alison Nihart
Eric Roy
Eric Roy studies nutrient biogeochemistry and management, ecological engineering and design, aquatic ecology, and food systems.