Eeewwww!!

Up to now I haven't really looked at the environmental issues which affect the Barwon River, however with Saturday's deluge of rain, pollution has suddenly become a hot topic - well, for the next few days. The Geelong Advertiser informs me that for several days it will be unsafe to swim in either the river or Corio Bay. The reason for this is that the recent downpour caused the sewage system to overflow into the stormwater drains as well as sending a great deal of rubbish into the drains,  meaning that output from the stormwater drains may be contaminated. Not only is this bad news for humans who can suffer a range of unpleasant symptoms, but it is also a problem for the river environment in general.

Stormwater drain near Queen's Park

Large influxes of "nutrients" combined with the right weather and low water levels create ideal conditions for outbreaks of blue green algae along the course of the river. So what is blue green algae? It is actually a type of cyanobacteria, which as a group may well be the most successful micro-organisms on the planet. These tiny bacteria are thought to have given rise to the process of aerobic metabolism used by all higher life forms as well as forming the basis of chloroplasts - the part of a plant which it uses to make food. Cyanobacteria convert water into oxygen and energy by photosynthesis and it is through their actions some 3.8-2.5 billion years ago that Earth's oxygen-rich atmosphere developed. Cyanobacteria are also able to "fix" nitrogen and carbon. That is, they use the nitrogen found in nitrates, nitrites, ammonia and urea as well as carbon as part of their growth cycle.

Jerringot Wetlands

Whilst these effects are vital for the planet as a whole, contributing significantly to a reduction in greenhouse gasses, in a river system such as the Barwon, they can have negative effects. This is because the cyanobacteria use the chemicals which wash into our waterways to multiply. The result is an algal bloom which can result in a reduction in the amount of oxygen available in the water (eutrophication), which harms fish and other fauna. At the same time, cyanotoxins are produced which are toxic to humans and animals which live in and along the river.
Symptoms of poisoning in humans can include skin irritation, dizziness, numbness around the mouth, tingling in fingers and toes (produced by neurotoxins). Longer-term effects can include nausea, vomiting, diarrhoea and liver dysfunction. Animals can experience weakness, staggering, difficulty breathing and ultimately death.
So what are the "nutrients" in question and where do they come from? The primary chemical culprits are nitrogen and phosphorous. In urban areas they can be found in pollutants such as leaf litter from exotic trees (particularly in autumn), human sewage, animal waste, grass clippings, paper, detergent and industrial byproducts while in rural areas crop fertilizers can also impact on the levels of nitrogen and phosphorous in the water.

Pollutants on the surface of water at Jerringot Wetlands

...at Jerringot Wetlands

Other threats to river health and to its flora and fauna come from various sources. Pesticides used to control weeds or insect infestations in crops can be carcinogenic to humans if allowed to build up in drinking water supplies whilst non-biodegradable rubbish can cause physical harm or poison river users and wildlife.

Rubbish in the Barwon near Breakwater

Grass and other rubbish washed up during the recent rain

There are some factors however, which work to counteract the effects of pollution on the river system and one of the most important is the reed beds which filter stormwater runoff before it reaches the river. In the case of the Barwon, this includes not only the reeds and other aquatic plants which line the riverbanks themselves, but also the plant life in the wetlands adjacent to the river.

Reed beds at Balyang Sanctuary

Aquatic plants at Jerringot Wetlands

I have looked at a number of these in previous posts. Much of the stormwater from Belmont is collected by Jerringot Wetlands, whilst that from Newtown flows into Balyang Sanctuary. Most of Leopold's runoff drains into Gateway Sanctuary and Ocean Grove's into Blue Waters Lake. All of these wetlands ultimately drain into the Barwon River. In many places however, Geelong's stormwater flows directly into the Barwon with no intervening wetland to reduce the level of pollutants entering the river.