The current flood is a major gift from Nature to the South Australian River Murray valley, boosting continued recovery from massive damage in the Millennium drought and bringing boom times back to ecosystems. The rich toffee-coloured water is clear water coming from multiple Murray catchments, full of tannins from dissolved leaves, with no water flowing in from Darling catchments which would bring high loads of suspended clay and reduce water clarity.
This extensive flood has spread onto upstream floodplains in the Murrumbidgee, Lachlan and Macquarie catchments which had not been flooded for 20 years, and picked up unprecedented amounts of carbon. This has meant that the first flows down the rivers and into South Australia were totally depleted of oxygen due to the natural process of decomposition of huge volumes of leaves, nutrients and plant debris on floodplains. There were numerous reports of fish kills, sadly including hundreds of adult Murray cod which were trapped between two flows of de-oxygenated water in the anabranch creeks around Lake Victoria.
As the flood progresses downstream, oxygen is returning as the water flows over weirs and spreads out onto Riverland floodplains. The food chains are kicking off, with thousands of dragonflies, insects and microscopic water species, including tiny fish. Waterbirds are starting to feed in floodplain pools, with pelican fishing groups already in action.
Unfortunately, recent news reports about the flood have focussed on the early flows of low oxygen ‘black water’ and the impacts of flooding on shack areas. However, most shacks are designed to allow floods to flow underneath raised structures, and the rewards for shack-owners will come as the water levels fall and increased numbers of fish and yabbies emerge just around the Christmas holidays.
This flood is a major bonus for river health, piggy-backing on the benefits of the 2010-2012 floods and providing the ‘boom’ in the river’s boom and bust ecosystem. The peak level is slightly above the peak of the February 2011 flood, and will boost continued growth of millions of red gum and black box seedlings generated back then. The clear Murray water allows light to penetrate up 10 times further into the water column than in Darling water, boosting photosynthesis. Watch for an explosion of life in coming weeks, as fish, frogs, yabbies, tortoises and plants respond to ideal conditions. This is the time to visit the River Murray and see it burst into life!