I agree with James Elser and Elena Bennett that we should recycle phosphorus (Nature 478, 29–31; 2011). However, there are situations in which the natural recycling of phosphorus is not ecologically desirable.

As the authors note, excess phosphorus in water bodies can feed algal blooms and create anoxic zones. What is less well known is that these waters can become permanent dead zones, stuck in an oxygen-deprived, nutrient-rich state. This happens when the algae die, sink and are decomposed by anaerobic bacteria that need only limited amounts of phosphorus. Most of the algal phosphorus is released back into the water to feed further blooms. In the Baltic Sea, for example, reductions in phosphorus pollution from rivers have not yet led to ecosystem recovery because of this effect.

We have disturbingly little insight into major phosphorus fluxes in the marine realm. This is the legacy of decades of research priority being given to the microbial complexities of the nitrogen cycle over the methodologically challenging investigation of phosphorus cycling.