For the first time, an international group of scientists has come up with a way to estimate river basin phosphorus flows over many decades.

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

The researchers studied three river basins where food and water security are directly linked to phosphorus. The analysis included the UK’s Thames River basin, the Maumee River Basin in the mid-western section of the US and the Yangtze River Basin in China.

Co-author Professor Helen Jarvie of the Centre for Ecology & Hydrology said, “The Thames is unique amongst these three river basins. While the Maumee and Yangtze basins continue to accumulate phosphorus, in the late 1990s, the Thames basin actually shifted from phosphorus accumulation to net phosphorus depletion, associated with a long-term decline in fertiliser use. This is the first time we have observed this landmark change in river-basin phosphorus storage, and it provides important historical context for our work on the Thames Initiative, an intensive study of changes in water quality of the Thames from the Cotswolds to Windsor.”

River Thames in London photographed from the Shard
River Thames in London. See an overview of CEH's Thames Initiative project

The world’s total human population has jumped to more than 7.4 billion just this year. Feeding the world’s population takes a tremendous toll on natural resources including water, soil and phosphorus — a chemical element in fertiliser essential for food production. Phosphorus from agriculture and sewage can leak into waterbodies such as rivers, lakes and oceans. This stimulates algae blooms and then, when the algae die and decompose, causes dead zones and death of fish. But large amounts of phosphorus also accumulate in the landscape. Until now, scientists have not fully understood the magnitude of this accumulation.

Legacy phosphorus

The River Thames had the longest historical phosphorus records, dating back 70 years. These data were used to examine 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 results showed that massive amounts of phosphorus have accumulated in the landscape — a form of “legacy phosphorus” that can affect water quality and aquatic ecosystems for decades or even centuries.

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.

Phosphorus from agriculture and sewage can leak into waterbodies such as rivers, lakes and oceans...But large amounts of phosphorus also accumulate in the landscape. Until now, scientists have not fully understood the magnitude of this accumulation.

Dr Stephen Powers, postdoctoral researcher with Washington State University and lead author of the paper, said, “Somewhat of a surprise is that 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. Until recently these waste flows have been largely ignored in catchment studies that involve phosphorus.”

Dr James Elser, research scientist with the Arizona State University School of Life Sciences and School of Sustainability, and co-author of the study, added, “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.”

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

Additional information

Paper link: Long-term accumulation and transport of anthropogenic phosphorus in three river basins by Stephen M Powers et al in Nature Geoscience

Staff page of Prof Helen Jarvie, Centre for Ecology & Hydrology

CEH Thames Initiative project overview

The research was funded by the NSF Research Coordination Network Science, Engineering, and Education for Sustainability Program (RCN-SEES, award #1230603); the University of Notre Dame Environmental Change Initiative, the National Basic Research Program of China (973-2015CB150405); the National Natural Science Foundation of China (31330070); and the Washington State University Center for Environmental Research, Education, and Outreach (CEREO).

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