April Presentation: The Missing Carbon Link in the Carbon Cycle is in Freshwater

Assoc. Professor Peter C. Pollard PhD, Australian Rivers Institute, Griffith University presented his findings at our April meeting. Here is a review of his presentation.

In the beginning:

3.8 billion years ago, cyanobacteria oxygenated the Earth’s atmosphere over the following 2 billion years. The Stromatolites in Shark Bay, and Thrombolites in Lake Clifton, Western Australia are remnants of this distant past. Thus began photosynthesis and set us on the path to the Carbon Cycle.


Carbon Cycle

In the Carbon Cycle there are two processes- photosynthesis and respiration. Plants and cyanobacteria use CO2 from the atmosphere to make their own biomass. The carbon moves through the ecosystem as plants are eaten by animals and dead animals and plants are decomposed by bacteria. Plants, animals and microbes all respire to obtain their energy they need and give off CO2 into the atmosphere.

Some carbon can be diverted from the cycle for longer periods such as in the wood of trees. Coal and oil are products which remove carbon from the short term cycle for billions of years.

Levels of CO2 in the atmosphere started to increase in the Industrial Age and have continued to rise to over 400 parts per million. CO2 is going back into the atmosphere faster than the rate at which it can be removed naturally. This is happening because oil and coal are being burnt and the carbon locked up for billions of years is being released back into the atmosphere.

Microbes in aquatic environments

Most aquatic climate change research has been based on how the oceans cycle carbon. This is because the volume of fresh water in lakes and streams is very small in comparison.  Dr Pollard has spent 14 years doing research in freshwater environments and has found that they are source of very large quantities of CO2 production, far greater than that produced by the oceans.  For instance, for each 1 km of the Bremer River, 0.5 tonnes of CO2 are produced per day.

In our society, microbes have a bad reputation, bringing to mind disease and death. Yet the vast majority are beneficial, essential to our very existence. We need bacteria and viruses. It is through them that material is recycled through land, water and air.  In aquatic environments bacteria feed on Dissolved Organic Carbon (DOC) and then release CO2 to the air. Viruses invade these bacteria and replicate themselves. In the viral life cycle, the viruses ‘control’ the bacteria. The virus attaches to the outside of the bacteria (host) and injects its own DNA into the host. The viruses replicate, the host dies, and the viruses move on to another host. These dead bacteria then are the source of more DOC to feed more bacteria and so the cycle perpetuates. The CO2 released with each pass of the cycle is lost to the atmosphere and does not pass up the food chain.

At this point, Dr Pollard showed a test tube containing 1 ml of water from a local dam. It contained approx. 10 million bacteria and 100 million viruses, nearly all of the beneficial kind.

It was argued by some researchers that these findings were due to the sub-tropical environment of S.E. Qld so Dr Pollard undertook further research in Panama, Boston and many other places. Despite the climatic differences between these environments all freshwater was found to produce large quantities of CO2.


Scientists at the Smithsonian Research Institute in Panama showed that they could not balance the amount of CO2 taken up during photosynthesis by rainforest plants with the amount returned to the atmosphere. The budget did not balance. Dr Pollard’s research proposed that as the rainforest plant matter decays, the resulting carbon finds its way into freshwater streams and lakes, where it is released as CO2 through the bacteria- viral cycle. The Amazon River alone could produce 3GT of CO2 per year, which is as much as all the oceans together bury yearly.


  • Dr Pollard suggests that rainforests are not the climate change ‘get -out-of-jail-free’ card that we would like.
  • Deforestation may be an even bigger problem. As well as the loss of the trees which photosynthesize and remove carbon from the air, the erosion of soil into waterways will result in feeding this bacteria-viral loop and result in greater return of CO2 to the atmosphere.
  • In our waterways the importance of reducing both point and diffuse sources of pollution eg don’t wash the car with detergents which flow into the waterways as storm water. Even biodegradable detergents feed bacteria in rivers and result in more CO2 going skywards and suffocating the fish populations as the bacteria use up the oxygen in the water.
  • At the conclusion of the talk Dr Pollard showed a picture of a suburban drain with the message “DUMP NO WASTE; FLOWS TO CREEK” to which he added “ÄND ATMOSPHERE”. (Picture courtesy Peter Pollard)

Dump no waste


April Presentation: The Missing Carbon Link in the Carbon Cycle is in Freshwater — 1 Comment

  1. Thanks for the great summary- I missed the talk but it sounds like it was fascinating. I really appreciate this new take on the CO2 cycle. I have been experimenting with solar panels and pumps to clean water, by promoting plant growth. I’d be really interested in learning more- well done!

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