Drought, water extraction and the River Murray

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RESEARCH AREA
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This week’s featured research article has just been published in Marine and Freshwater Research by University of Adelaide researchers and examines whether droughts and over extraction from the River Murray have reduced coastal ocean productivity. The paper describes how water extraction and drought (focused on the “millennium drought” which occurred from about 2001 to 2010) on the River Murray has reduced the primary productivity of the coastal ocean beyond the Murray Mouth. It is well understood that flow drives ecological functions in the river system but this research begins to understand how changing River Murray flows affect the marine environment outside of the Murray Mouth. The study used satellite imagery products taken over a period of almost 15 years (from early 2002 to late 2016) to determine the presence and concentration of phytoplankton (indicated by chlorophyll-a concentration) and particulate organic carbon (POC) in the ocean region beyond the Murray Mouth. Chlorophyll a and POC are good indicators of primary productivity occurring in marine environments, which forms the base of the food web and hence is important for the health of other marine organisms such as fish and shellfish. There was much higher concentrations of both POC and phytoplankton biomass in the coastal water when large river outflows occurred from the Murray Mouth compared to no or low flow periods. During high flows, phytoplankton biomass increased markedly above the seasonal levels up to 60 km from the Murray Mouth which was assumed to be due to delivery of nutrients which provide the “fuel” for phytoplankton growth. The concentrations of phytoplankton and POC were very low during the extreme drought period (2007-2010) as a result of river discharges completely stopping. This likely had negative consequences for many marine species (including mulloway and pipis/Goolwa cockles) and fisheries. The study findings have important implications because water management plans and decisions in the Murray-Darling Basin currently do not consider the requirements of the coastal ocean ecosystem and fisheries. The researchers conclude that the potential implications for a lack of river outflows from the Murray Mouth should be considered in management, especially as there are predictions of increased severity and frequency of droughts in the future, due to climate change. The paper can be downloaded here (or email jennie.fluin@sa.gov.au for a copy).