The study of three river basins where food and water security are directly linked to phosphorus - a chemical element in fertiliser essential for food production - included the Thames River basin in the U.K., the Maumee River Basin in the mid-western section of the U.S. and the Yangtze River Basin in China.

For the first time, the international group of scientists have discovered a way to estimate on a large scale how phosphorus flows through an environment over many decades.  By doing so, researchers are gaining a better understanding of how and where phosphorus accumulates.

The results showed that massive amounts of phosphorus have accumulated in the landscape — a form of "legacy P" that may affect aquatic ecosystems for decades or even centuries. Of the three sites, only one showed clear improvement over several decades — the Thames River in the U.K.

Professor Phil Haygarth of Lancaster Environment Centre said: “This study was very important because for the first time we have long-term data from these big rivers from around the world and we can see the scale of the problem and it is quite compelling. The information from the Thames shows there is hope, but we can’t be complacent.  Phosphorus is vitally important to farming – and it is a finite resource - but it is ending up in our rivers and estuaries where it is causing serious problems.”

Feeding the human species takes a tremendous toll on our natural resources including water, soil and phosphorus. In modern agriculture, fertiliser often leaks into waterways such as rivers, lakes and oceans. The phosphorus in the runoff stimulates algae blooms and then, when algae die and decompose, dead zones develop and fish die off.  Until now, scientists have not had a good handle on the magnitude of this accumulation.

The study areas ranged in size from approximately 5,000 to 700,000 square miles. Historical records dating back 70 years were used to measure the human impact on the flows of phosphorus into and out of each catchment through trade, food waste, human waste and agricultural runoff, comparing these flows to losses of phosphorus from each river's discharge.

The study’s findings by Washington State University, International Plant Nutrition Institute, Universities of Arkansas, Bristol, Durham, Lancaster, Arizona State University, Centre for Ecology and Hydrology, China Agricultural University and Minnesota Department of Agriculture are published in Nature Geoscience.

“After we understand how human activity affects the accumulation of phosphorus in the environment, we can then focus our research efforts on reducing its long-term impact, even on figuring out how to recycle it. This will help secure food and water supplies for future generations,” said James Elser, research scientist with the ASU School of Life Sciences and School of Sustainability, and co-author of the study.

The study’s novel analyses illustrate the challenges researchers face in figuring how to manage the storage, exploitation and reactivation of phosphorus that is already present in our environment.

“In populated landscapes, there is a huge amount of phosphorus in food waste, such as animal bones, and in sewage sludge removed during wastewater treatment,” said Stephen Powers, postdoctoral researcher with Washington State University and lead author of the paper. “Until recently these waste flows have been largely ignored in water flow studies that involve phosphorus.”

Powers said the U.K. is using less fertiliser to grow food and that both historically and currently, it is a world leader in modern wastewater treatment. By following the U.K.’s lead, Powers said other countries might improve their ability to manage phosphorus.

Elser and Powers said the next step is to develop strategies that will reduce the impact of this “legacy P.” The pair added that it is important to create new technologies and policies that recycle P for re-use as fertiliser, rather than allowing it to escape and build up in the landscape.