Phosphorus: What exactly is it doing to our oceans?

What is Phosphorus?

Phosphorus is known as the "miracle mineral" and more often than not, it is exactly that. It is an essential mineral that is vital to the bones in your body and is also a key element in modern agriculture. Phosphorus is essential for plant life and is very commonly used in fertilizers because it helps to regulate plant functions like photosynthesis.

How is it cycled through the environment?

Phosphorus is cycled through the environment via the phosphorus cycle, a slow biogeochemical cycle, where the element is passed through living matter, land, and water. To put it simply, rain and weathering releases phosphate ions (PO4^3-) from rocks over time and spreads them to rivers and streams. Plants uptake the phosphate and terrestrial food chains continue this distribution. Phosphate eventually ends up in waterways and reaches the ocean, where it aides the production of microbes and phytoplankton, which is the foundation of the marine food web. Naturally, because phosphorus availability is limited in the phosphorus cycle and the natural environment, both terrestrial and aquatic plant growth is also limited, making it a limiting factor in these ecosystems.

Deoxygenation of the Oceans

As the anthropogenic sources of phosphorus, namely synthetic fertilizers, increase, its mishandling thus becomes more prevalent. When crop fields and other agricultural areas are overfertilized, excess phosphorus either runs off into streams, rivers, and nearby bodies of water or leaches from the soil, inevitably flowing to the ocean. This leads to increased growth of algae (algal blooms) and eutrophication (see image). For one, this disrupts the nutrient balance of the marine ecosystems as the concentration of phosphorus in the oceans and other bodies of water continually increases. In addition, phosphorus pollution also leads to the deoxygenation of the ocean because the increase in autotrophs causes more rapid rates of photosynthesis, which depletes the available oxygen. The algae form a thick layer that makes it difficult for marine animals to find food and creates massive dead zones in the water. In some cases, the algal blooms can produce algal toxins that are harmful to human and animal health.

Although the buildup of phosphorus and phosphate ions in the oceans is not an immediate concern, ocean deoxygenation will undoubtedly have lasting effects on longer time scales.