Drought conditions and recovery in the Coorong wetland, south Australia in 1997–2013

Abstract

Between 2004 and 2009, South Australia suffered its longest period of below average annual rainfall. This impacted riverine ecosystems and particularly the Murray-Darling Basin (MDB), the largest river system in Australia. The MDB combines 30,000 wetlands of which the Coorong wetland is of significant importance for the reproduction of bird and fish species, and is listed under the Ramsar Convention. We sampled water in the Coorong wetland between 2011 and 2013 and compiled additional data from 1997 to 2013 to assess the impact of the drought and subsequent recovery of the environment. The salinity levels of the Coorong wetland increased dramatically during the drought because of the lack of freshwater inflow from the Murray River. The changes in water flow observed from 2002 to 2009 had an impact on the number of habitats present along the Coorong wetland. In addition, a shift in community composition was observed between the freshwater habitat (<5) dominated by chlorophytes to the hypersaline habitat (>85) dominated by diatoms. It is evident that during the drought, the Coorong wetland was dominated by diatoms and dinoflagellates. After the drought, the North Lagoon was dominated by chlorophytes up to a salinity level of 20. However, over 20 and in the South Lagoon, diatoms dominated the community. This study highlights how salinity levels drive the phytoplankton community. Based on the complementary data obtained for salinity between 1997 and 2010, there is a significant difference between the salinity levels observed during the drought and those observed before and after the drought. It appears that salinity levels are now recovered to what they were in the late 1990s.