Environmental

Phosphate In River Water: An Environmental Chain Reaction That Begins And Ends With Us

Posted on 1 July 2022

Phosphates are everywhere, and they aren’t necessarily your enemy. They’re in your food, your toothpaste, and even your DNA. Phosphates are molecules composed of oxygen and phosphorus, both of which are among the five most common elements found in living organisms. Yet despite being common in nature, phosphates are capable of causing environmental havoc in our water supply, which ultimately impacts humans just as it does the organisms living in our rivers. In this article, we’ll explore the effects of phosphate pollution on nature and how it could impact our own health.

Sources Of Phosphate Pollution

It’s normal to find some phosphates in natural bodies of water, since phosphorus occurs naturally in rocks and other mineral deposits. These rocks gradually release the phosphorus as soluble phosphates, which then enter the food chain as they are taken up by bacteria and plants. Dead organisms decay and release these phosphates back into the water, and eventually some phosphates will find their way back into sediments at the bottom of rivers and oceans.

However, there are many unnatural sources of phosphates that can and do find their way into the water supply:

  • Agriculture: The main sources of phosphate in river water are agricultural fertilisers and manure. Rainwater can wash some of this phosphate off of agricultural land and into ditches, streams and rivers.
  • Waste: Some phosphate pollution comes from organic waste such as sewage and industrial waste.
  • Urban runoff: Rainfall in cities and towns can run across hard surfaces like rooftops and roads, carrying pollutants including phosphorus into local waterways.
  • Mining: Phosphate may enter waterways as a result of phosphate rock mining.
  • Household products: Some household products including some soaps and detergents can contribute to phosphate pollution if not properly disposed of.

Phosphate is only toxic to people and animals if present at extremely high concentrations. Unfortunately, the havoc that phosphate can wreak on the environment has nothing to do with its toxicity, but rather its status as a key nutrient.

Why Is Phosphate Pollution A Problem?

Photo by Liz Harrell on Unsplash

In rivers, phosphate pollution is the main cause of eutrophication, a term that comes from the Greek eutrophos, meaning “well-nourished”. In eutrophication, an excessive supply of nutrients in the form of phosphate disrupts the balance of the ecosystem. This begins at the bottom of the food chain with the microorganisms, specifically the phytoplankton.

Phytoplankton are bacteria and protists that are capable of photosynthesis. These organisms are vital for the health of rivers and oceans because they provide a source of food for aquatic animals. They also contribute to the carbon cycle by absorbing carbon dioxide from the atmosphere, converting it into energy, and releasing oxygen back into the atmosphere. However, when phosphates accumulate in waterways, phytoplankton (as well as aquatic plants) are able to grow and multiply rapidly. This results in a phenomenon called an algal bloom, in which the water takes on the colour of algae pigments. In many cases, the entire surface of the water will become covered in a sea of algae.

Algal blooms may initially benefit larger organisms like fish by providing additional food, but this is short-lived:

  • Algal blooms block off sunlight, causing the death of algae and plants below the surface of the water.
  • Bacteria decompose the organic waste from these dead plants and algae, which consumes large amounts of oxygen and also releases more phosphate back into the water.
  • As oxygen levels decline, anaerobic bacteria begin to take over the decomposition process. These bacteria produce methane gas instead of carbon dioxide.
  • The combination of reduced oxygen and reduced plant life leads to the death of organisms further up the food chain.

How Does This Impact Humans?

Eutrophication can have a significant impact on humans living along affected rivers. That’s because phytoplankton in algal blooms can produce toxins, some of which are capable of causing severe poisoning and even death when ingested at high levels. This makes water and fish from these rivers unsuitable for human consumption, and also damages the terrestrial environment when land animals drink from the river.

What Can We Do About Phosphate Pollution?

Photo by Jon Flobrant on Unsplash

It is possible to remove phosphate from water in treatment plants, usually using a chemical approach, or by using bacteria that are allowed to absorb the phosphate and are then removed from the water. However, it’s always better if we can prevent the entry of phosphate into our rivers in the first place. Here are some things that most people can do to help:

  • Avoid using phosphorus-containing fertilisers on lawns and gardens
  • Keep plant clippings and grass off of the street, as these can wash into gutters and increase the phosphate content of the water.
  • If you live next to the riverbank, plant more deep-rooted plants as these are more effective at absorbing runoff.
  • If you’re a farmer, maintain good soil health to minimise erosion and runoff.

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