Strange River Colours 2009

If you were a child whose experience of a river were that it was green, pink, red, black, brown and smelt bad for months on end, like the river photos below, how would that colour your attitude to the environment? 

 

 

    

 

 

Well at Jeparit, from 2007  - 2009,  that was the situation for the Wimmera River.    By then, it had been a decade since the last good flow of water.

You can get a good idea from this in the article  on the web called “A French eye on the Wimmera” at the Wimmera CMA websites archived media articles Feb 2009.  or link to

http://www.wcma.vic.gov.au/index.php?option=com_content&task=view&id=148&Itemid=119

From 2003, the remnant water was stagnant—able to change only with:

·  evaporation— concentrating the salts and leaving a white crust on the banks

· rainfall runoff dissolving the salt on the banks and bringing it back into the water, ironically raising the salinity as the rainfall was so little

· salty seepage from the banks, as the lowered water level exposed a salty aquifer that was free to run downhill into the water. 

So the net effect of the remnant water was that the salinity rose, to seawater salinity levels and then up to triple that by the time these colours were cycling through.

 

What could survive here? The colours tell the story:

The green came first— it was water rich with algae. The algae had an offensive odour.  It could be seen growing in the water on hot days.  It was also able to rise and fall in the water column, so some times it was very bright green when it was photosynthesizing.

The pink and the bright reds were from water rich with growing purple sulphur bacteria instead. The bacteria was breaking down the black hydrogen sulphides in the decayed matter on the bed of the River, some of which could have been from the algae completing its life cycle, some of which may have been deposited in silt over the years, including some possibly from sewerage 40+ years old  from a time when upstream towns used to release directly to the River.

This cycle involved the release of sulphides which made the water a darker colour. When this process dominated the water went browns and blacks, and also had an offensive odour. 

This sulphide release had another unseen effect on the water which was getting shallower.  It changed the pH– to a more acidic one. Now because the River was so salty it had been more alkaline,  around the 8.5 level, but when this sulphate reaction kicked in, the pH suddenly started dropping.

Then something more surprising happened, when the pH reached neutral levels. Our ‘dead’ river developed new life, life in abundance, well of one species only—brine shrimp. They carpeted the shallow River bed in another shade of red and ate up the algae! They lasted for several months.

Jeparit Waterwatch tracked them from one remnant pool to another and, as it’s pH fell, the shrimp bloomed! Our 80 year old members had never seen this happen before, and it became apparent that the eggs must have been dormant here for a very long time. 

The brine shrimp showed us that something wonderful can appear in extreme  environments. When it did, we were so excited! What an expression of hope!

 

This page was last updated on 2 August 2011.

© J. Clark, environmental educator, enviroed4all, Warracknabeal, 2011. All Rights reserved.

To contact us:                            E-mail:                      enviroed4all@skymesh.com.au

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photo of red water at weirphoto of red waterphoto of black water at weirphoto of green water at weirphoto of weir coloursphoto of black and brown water at weirphoto of weir coloursphoto of brine shrimp

National Science Week 2011

Strange River Colours 2009

Jeparit Primary School 2010

WEEC Roundtable paper

WEEC news release

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