By: Matt Scholz
I’ve noted in the past that it’s ironic that the Sustainable Phosphorus Alliance is located in Arizona, when Arizona really doesn’t have much of a phosphorus problem. However, I had to eat crow (the bird, not the president) this summer when I noticed what appeared to be an algal bloom on Tempe Town Lake, featured here.
Algal blooms are typically driven by phosphorus pollution in fresh water system, though nitrogen plays a role too, and are indicative of an ecosystem gone horribly awry. Algal blooms can be toxic and those toxins have been known to kill dogs and wildlife that drink from and live in the water, and can have non-lethal health impacts on people too. Equally important, it’s now believed that freshwater systems are the second largest natural contributor to greenhouse gas emissions to the atmosphere, just after wetlands. Phosphorus limits primary productivity in freshwater systems, and its pollution is rapidly productivity, leading to greater biomass decomposition and consequent production of methane, carbon dioxide, and nitrous oxide–methane being the most critical source. Conservative estimates are that by 2100, phosphorus pollution will drive up these emissions to an extent that is equivalent 18-33% of all current fossil fuel emissions (CO2eq).
Being an admitted nerd, I have to confess I was wildly excited by the prospect of algal blooms on Tempe Town Lake. Here was a chance to connect my work with a problem in my local community, a problem that our organization could help solve through some of its members’ work.
I care a lot about Tempe Town Lake. It gets short shrift from people who don’t like the fact that it is a human construct, but those people might consider living in another state, as Arizona only has only a few natural lakes. Clearly, those people are not birds because birds love Tempe Town Lake, and I love birds. In addition to the recreational opportunities that the lake affords and the increased property values and, therefore, taxes that the city collects because of it, wildlife depends on the lake for a break from the dry desert heat–wildlife that is under severe stress because its habitat has been decimated (literally) by the ceaseless development of Phoenix metro.
It turns out that the bloom I observed on the lake is not algae at all, but duckweed! Unlike algae blooms, which can be toxic, duckweed is actually cultivated in certain parts of the country any used as food or forage. On one hand, this is great news—it’s not toxic algae. On the other hand, the reason the duckweed is blooming is almost certainly related to phosphorus pollution. In other words, this is a harbinger of what’s to come, a canary in the coal mine.
My boss, Jim Elser, years ago warned the developers of Tempe Town Lake that the lake would someday become a green stew if they didn’t take phosphorus pollution seriously. They haven’t, and the stew is simmering. (Annoyingly, Jim is almost always right.) One thing we could do right now is harvest the duckweed, which would remove the phosphorus it contains.
“So Mr. Smarty Pants Scientist”, you might ask, “what are the phosphorus levels in Tempe Town Lake?” That’s a fantastic question, and one for which we have no answer. Astoundingly, no one measures this. The Town Lake is supplied with water by the Central Arizona Project, water that comes from the Colorado River and is transported South and West. After talking to the people who manage the CAP LTER, an NSF funded long- term ecological research program that studies the ecological impacts of Arizona’s water management, I was surprised to learn phosphorus data are not captured. Why don’t they monitor it? Because they lack funding.
So do we have toxic algal blooms lurking within that duckweed? Who knows? No one measures the algae either. This is a major problem across all domains of sustainability science. It’s often said that you cannot manage a sustainability problem unless you can measure it. We desperately need to invest a lot more money into ecological monitoring then we do.
More than 10 years ago, EPA surveyed a sample of our national lakes, rivers, streams, reservoirs, and coasts for various pollutants. 46% of US rivers and streams and 40% of lakes had unacceptably high levels of phosphorus, and the trend was towards rapid deterioration. I think it is safe to say that now most of our freshwater is polluted with excess phosphorus, yet we don’t measure it in the vast majority of systems.
I refer to phosphorus pollution as the biggest environmental problem that no one has heard about. This phosphorus comes from sources such as farms that use it as for fertilizer, from wastewater utilities that discharge it in effluent, from cities who lose it in storm water and runoff, and from soil erosion all along the waterways.
It’s unfortunate, but I believe that Jim Elser’s predictions will ultimately come true. Without a concerted effort—difficult to achieve as state and local budgets are slashed as a result of covid–we will have algal blooms on Tempe Town Lake, and they may sicken or kill pets and wildlife and perhaps make people ill. Businesses that depend on the lake (e.g. the boat rental companies) will take a hit as will property values for lakefront properties, resulting in decreased city tax revenue. This story has played out in city after city across the world for decades, and it won’t stop until people realize what phosphorus pollution is–the most important pollution problem of our most important natural resource and commodity—and budget accordingly.
What steps can you take to reduce our collective phosphorus footprint? Spread the word, eat less meat, which is a P-intensive food source, reduce or eliminate use of P lawn fertilizers, pick up your P-rich pet waste, make sure your yard trimmings don’t enter the city’s storm water (e.g. compost them), make sure your car wash detergent is P-free, and, whatever you do—don’t urinate.
OK, that last one is a joke.
Program Manager, Sustainable Phosphorus Alliance Senior Sustainability Scientist, ASU’s Julie Ann Wrigley Global Institute of Sustainability