How Freshwater Transformed the Coorong's Microbial World
Image: Darcy Whittaker
Environment Institute membersÌýÌý²¹²Ô»å in their newly published piece for , and alongside they have explored how microorganisms in aquatic ecosystems, specifically sediments, respond to changes in water salinity and flooding, both of which are directly impacted by climate change and human activity.
was initially conducted in 2022, during the largest flood the Coorong Lagoon in South ÐÓ°ÉÖ±²¥ had faced since 1956. This area is hypersaline, essentially a very salty part of the Murray-Darling Basin. Beyond its ecological role, the Coorong Lagoon holds cultural significance for the Ngarrindjeri people and serves as a critical habitat for migratory birds and various wildlife, including pelicans, terns, and the endangered orange-bellied parrots. This unique wetland is a vital indicator of the overall health of the Murray-Darling Basin. Samples were collected across six sites before and during the flood, varying in salinity gradient from low to high salinity.
Chris, Justin and their team aimed to examine how microbial communities (types of microbes) and their functions changed due to the flood. The study not only sought to understand microbial responses to changes in salinity and flooding but also to assess how such environmental shifts might help restore ecological balance in the Coorong, which has faced long-term health challenges. Methods used included:
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16S rRNA gene sequencing – a method to identify which microbes are present.
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LC-MS metabolomics – a way to detect small molecules (metabolites) produced by these microbes, giving clues about their activities.
revealed a decrease in microbial diversity during flooding, mainly in areas with higher salinity. Before the flood, microbes adapted to salty environments and were thriving, which is common. These microbes include various types such as osmolytes (compounds that help organisms survive salty conditions) and methane producers. Metabolites like glycine betaine and choline (osmoprotectants) were also common. A key finding of the study was the reduction of methane-producing microbes, which play a significant role in greenhouse gas emissions. This decrease, driven by the influx of freshwater, highlights a positive environmental impact of the flood.
Image:ÌýÌýChris Keneally taken byÌýTyler Dornan
During the flood, the influx of freshwater reduced salinity. While this shift may seem disadvantageous, it allowed other microbes, such as Halanaerobiaceae and Beggiatoaceae, to flourish. These microbes also play crucial roles in nutrient cycling, reducing harmful compounds like methane and sulfide. These changes underscore the importance of maintaining balanced microbial populations for ecosystem health. The new, now dominant communities showed activity related to sulfate and nitrogen reduction, which are key biogeochemical processes.
Sustained high freshwater flows from 2022 to 2023 allowed native fish populations and aquatic plants to recover, which in turn improved habitats for waterbirds such as black swans. This highlights the ongoing positive impact of consistent environmental flows on the Coorong's biodiversity. The research also provided valuable insights into predicting and managing ecosystem changes caused by climate events or human impacts. Microbes are essential for nutrient cycling and ecosystem health, showing rapid responses to environmental changes like flooding.
Although the types of microbes changed, their roles remained consistent, continuing to perform important functions such as breaking down sulfur and nitrogen compounds. Combining genetic and chemical analyses provided a greater understanding of how ecosystems respond to disturbances. To ensure the long-term health of the Coorong, it is crucial for policymakers to maintain adequate freshwater flows, especially as the Murray-Darling Basin Plan undergoes review. Balancing human water needs with ecological preservation remains a pressing challenge for the region.
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To read the full article, .
To read his piece in The Conversation,
Chris KeneallyÌý
Justin Brookes
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