Wise Husbandry of the Superabundance of Phosphorus

The Cyano-Biosolids Challenge

I really thought I understood the big picture, I mean the REALLY BIG PICTURE. David Christian’s Big History Project, the 14 billion-year history of human beings, says humans are composed of stardust, the elements derived from the supernova of a preexisting hydrogen/helium star. But the recent article “Did Meteorites Bring Life’s Phosphorus to Earth?” says that Earth has too much phosphorus for this explanation to suffice. The ratio of phosphorus to silicon seen on Earth today cannot be explained by normal astrophysics, but instead by a hypothesis that, early in its formation, the Earth’s surface was bombarded by high-P meteorites originating from a super-supernova elsewhere in our galaxy.  But for the extra injection of phosphorus onto primordial Earth by meteorites, phosphorus would have been too low in concentration to have enable the evolution of life as we know it. Phosphorus, one of six essential elements, constitutes for all life on Earth both the “backbone” of cell structures and the “heart” of its cellular energy systems.

My general take on phosphorus mirrors the position of the Global Phosphorus Research Initiative (Phosphorus Futures): “Without phosphorus, we cannot produce food. As an essential nutrient in fertilisers for food production, phosphorus has no substitute…. At the same time, inefficient use of phosphorus throughout the food systems is polluting our rivers and oceans causing toxic algal blooms.”

The astrophysicists would have us contemplate how life on Earth may be unique, because phosphorus elsewhere in the Universe is so very rare. Yet, nevertheless, here we are, uniquely sentient beings, sitting on this uniquely phosphorus-rich Earth, contemplating, not the miraculous gift of so much phosphorus, but despairing over its excess. How cosmically ironic!

The original beneficiary of high phosphorus was the most ancient of life forms, the cyanobacteria.  These organisms have the unique property within the bacteria domain of capturing solar energy through photosynthesis and in the process releasing oxygen from phosphate minerals. These are the creatures who, over the course of a billion years, were responsible for the Great Oxygenation Event , a necessary first step for evolution of multicellular life and green plants and for sedimentary deposits that are today’s source of the mined phosphorus used in agriculture.

We literally owe our lives to cyanobacteria and the evolution of life that phosphorus has made possible.  But cyanobacteria and excess phosphorus are biting us back. You may recall Toledo in 2011. The city had to shut down its water supply system because of toxin that passed through its filters.  That toxin, microcystin, is from a species of cyanobacteria, the Microcystis. Scientists studying Toledo quickly developed a case that this toxin could be traced to high loadings of phosphorus discharged from farms during spring to tributary streams of Lake Erie. The report by a large science team [Challenges in tracking harmful algal blooms: A synthesis of evidence from Lake Erie ] showed that, while scant rainfall, high air and water temperatures, and quiescent winds were contributors, the root cause of microcystin was excess phosphorus. The finger was wagged at farmlands planted to continuous corn within no-till cultivation systems. A slide deck summary of recommended actions to mitigate farm losses explained this conclusion in Models can support establishment of phosphorus loading targets for Lake Erie.

It is not coincidental that the Sustainable Phosphorus Alliance (SPA), a “nonprofit organization driven to innovate and implement solutions to the phosphorus challenge,” is tied to the Toledo event. The lead researcher in the SPA is Rebecca Muenich, a former post doc at University of Michigan studying control of phosphorus inputs into Lake Erie, and currently Assistant Professor in ASU’s School of Sustainable Engineering.  MABA has been engaged by SPA to chronicle the regulation of P in its seven-state region, so I am boning up on my phosphorus science.

Just as science is overturning astrophysics and Earth’s formation, so is science upending our understanding of soil-phosphorus interaction.  Andrew Sharpley’s review article Phosphorus Legacy: Overcoming the Effects of Past Management Practices to Mitigate Future Water Quality Impairment provides meaningful challenges to the old premise that phosphorus loadings from farmlands were negligible: “the legacy of previous activities can be mobilized directly as particulate P or indirectly as dissolved P and thereby constitute the major source of P in the land–freshwater continuum.”  Despite our earnest agronomic efforts, release of soil phosphorus to surface waters from today’s agricultural practices seems to have increased over the recent decades.

To its credit, the fertilizer industry is responding to this situation. The International Plant Nutrition Institute issued 4R Plant Nutrition Manual: A Manual for Improving the Management of Plant Nutrition: ”The concept is simple – apply the right source of nutrient, at the right rate, at the right time, and in the right place – but the implementation is knowledge-intensive and site-specific.”  IPNI has been sponsoring field research to help improve fertilization practices.  But some results are not what was expected. For instance, in Minimizing Phosphorus Loss with 4R Stewardship and Cover Crops, researchers saw an “increase in dissolved P loss from cover crop treatments.“  The bottom line is that research is still needed to understand soil-crop-phosphorus interactions.  

The driver for research is eutrophication, as the belief is a direct line can be drawn between farm soil P and the P-consuming algae. The research focus is on control of HAB, or “harmful algal blooms.” The consensus (Eutrophication and harmful algal blooms: A scientific consensus) is that nutrient flows from farms are a major contributor to HAB: “nutrients promote the development and persistence of many HABs and is one of the reasons for their expansion in the U.S. and other nations.”

But, the HAB story is more difficult than this simple consensus. In the survey report Anthropogenic nutrients and harmful algae in coastal waters, the authors “find a lack of evidence of widespread significant adverse health impacts from anthropogenic nutrient-generated HABs, [because] the relationship is complex….” Ironically, the microcystin bacteria responsible for this toxin have a competitive advantage with phytoplankton in water bodies where the nitrogen to phosphorus ratio falls too low. When we control nitrogen pollution from our wastewater plants and farming activities, but not so much the phosphorus releases, the risk may be a rise of toxic releases from cyanobacteria.

We can thereby generally agree that less phosphorus release to streams is good and that we need to manage the risk of P release from our biosolids application sites. Over the past two decades, we have discovered that biosolids from different processes vary greatly in their potential for release of phosphorus when land applied. This issue was explored in the early 2000s in seminal Penn State research reports, such as  Phosphorus Runoff Losses from Surface-Applied Biosolids and Dairy Manure. This work was pivotal in leading to a consensus report, Selection of a Water-Extractable Phosphorus Test for Manures and Biosolids as an Indicator of Runoff Loss Potential, which made the case that the WEP test method ought to be deployed in state nutrient regulation programs. 

We can also acknowledge that our choice of wastewater treatment technologies affects phosphorus risks of biosolids use. One biosolids type with a distinctly higher P release risk is the biosolids produced from a treatment technology called Enhanced Biological Nutrient (or Phosphorus) Removal. The WEP test shows that EBPR biosolids measure high in phosphorus extractability, and thereby poses greater risk of P releases than chemically treated biosolids. This aspect of P is under our control.

What are our choices for reducing on-farm risks from P?  Recent research results give us a path forward. We ought to be selective of the soils to which we deliver biosolids. The study Soil phosphorus saturation ratio [PSR] for risk assessment in land use systems suggests that “both the PSR and the SPSC [Soil P Storage Capacity] can be easily adopted by farmers and others who are interested in management practices that minimize the risk of P loss from soils.”   The authors, looking to target biosolids to soils with low P reserves, report in Sustainable management of biosolid phosphorus: a field study that “eutrophication risk on loamy and clayey soils was significantly reduced when OP [Olsen-P soil test results] represented <20% of the soil P sorption capacity. Our results suggest that biosolids could be more sustainably managed by matching biosolid type to soil type and P fertility status.” Researchers and entrepreneurs have been collaborating to find new ways of placing organic-borne phosphorus in the farm fields. Specialized fertilizer machinery, such as offered in the magazine article “Is low-disturbance no-till the future of farming?,” is attracting interest, though experience in the mid-Atlantic to-date is that the prototypes are slow and high maintenance. More work is needed on the equipment side.

We confront a peculiar predicament. Some 14 billion years now into our history, humans still need to learn how to properly manage their own biosolids. We need to choose the right treatment technologies, the right soils, and the right tillage equipment if we are to avoid discharges of nutrients that stimulate cyanobacteria to produce biotoxins deadly to fish, cattle and maybe even humans.

How wonderfully ironic that the Universe, with its first implausible cosmic event supplying a superabundance of meteorite-borne phosphorus, then with its implausible life-generating creation of self-replicating cells of cyanobacteria with phospholipids on the outside and phosphorus-fueled energy system inside, now set us humans up with an implausible challenge of our own. We have today the challenge of living in non-toxic harmony with our ancestral cyanobacteria through wise husbandry of the superabundance of phosphorus emitted by our actions and bodily processes. If we are to perpetuate our own species, we need to meet this Ultimate Cyano-Biosolids Challenge.