A Century of Legacy Phosphorus Dynamics in a Large Drainage Basin

Michelle L. McCrackin, Bärbel Muller-Karulis, Bo G. Gustafsson, Robert W. Howarth, Christoph Humborg, Annika Svanbäck, Dennis P. Swaney
  • Global Biogeochemical Cycles, July 2018, American Geophysical Union (AGU)
  • DOI: 10.1029/2018gb005914

How "leaky" is accumulated phosphorus in the Baltic Sea drainage basin?

What is it about?

We developed a model to understand phosphorus (P) dynamics for the entire drainage basin of the Baltic Sea since 1900. This model included a rapid transport pathway that represented sources such as runoff from cropland and a slow pathway that represented leakage from mobile legacy sources. The model suggests that loss from the mobile pool contributes about half of current waterborne inputs to the sea; as a result, it could be difficult to make substantial near-term reductions. However, there are opportunities to meet environmental goals by slowing the accumulation of P in the landscape and by implementing measures that address the rapid transport pathway, such runoff from cropland, and the mobile stores, such as cropland with large soil-P reserves.

Why is it important?

All life depends on phosphorus (P), which is why it is an important crop fertilizer. Humans generally consume more P than needed and the excess ends up in sewage systems. Past management of P in fertilizer and human sewage has led to the accumulation of P in soils and sediments of lakes and streams. This accumulation is called “legacy” P because it can leak for decades to downstream lakes and coastal areas where it contributes to environmental problems.


Dr Michelle L McCrackin
Stockholm University

For me personally, this paper is exciting because it is the first model (that I know of) that describes the extent to which legacy phosphorus can "leak" into surface waters, in this case, the Baltic Sea. A number of scientific studies have discussed the potential for phosphorus to accumulate and leak, but modeling these dynamics has been challenging. Our findings show the importance of having a long term perspective (i.g. being patient), when managing nutrients.

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The following have contributed to this page: Dr Michelle L McCrackin

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American Geophysical Union (AGU)