Understanding particulate organic nutrient dynamics in the Coorong, South Australia – part of the Healthy Coorong, Healthy Basin Action Plan

Dr Stacey Priestley¹, Jonathan Tyler¹, Savannah Liebelt¹, Luke Mosley¹, Wei Wen Wong², Yuexiao Shao¹, Zara Woolston¹, Mark Farrell³, David Welsh⁴, Justin Brookes¹, Alan Collins¹, Juraj Farkas¹

¹University of Adelaide, Adelaide, Australia, ²Monash University, Melbourne, Australia, ³CSIRO Agriculture & Food, Adelaide, Australia, ⁴Griffiths University , Southport, Australia

Abstract:

The Coorong is a unique estuarine lagoon system at the terminus of the largest river system in Australia draining the Murray-Darling Basin catchment. It has experienced declining ecological health due to the combined effects of progressive hypersalinisation and eutrophication as a result of declining freshwater inputs. To restore the health of the Coorong the “Healthy Coorong, Healthy Basin Action Plan” outlines scientific experiments and investigations to address knowledge gaps. One of these is to trace the major external sources of nutrients, as well as nutrient transport processes and cycling in the Coorong. Thus the aim of this project was to characterise particulate organic carbon and nitrogen dynamics in the Coorong using δ¹⁵N and δ¹³C of particulate organic matter (POM) in lagoon waters and sediment. The PON and POC has built-up in the southern end of the Coorong due to increased phytoplankton production and lack of seasonal flushing of lagoon waters. Also, δ¹⁵N-PON and sediment δ¹⁵N values across the Coorong lagoon overlap, suggesting that PON from algal matter represents the main source of nitrogen to the sediment, which is consistent with algal deposition from a highly eutrophic water column. Subsequent release of nutrients from the sediment then favours increased algal production adding to the subsequently larger PON and POC concentrations in the southern end of the Coorong, especially when water flow is low. Locking up nutrients in plant biomass, or removal via increased flushing and dredging, are possible options for addressing legacy nutrient issues in the sediment and restoring the Coorong.

Biography:

Stacey Priestley is an environmental scientist who is passionate about using environmental tracers, especially isotopic tracers, to investigate hydrological systems to help address challenging environmental problems in water resources sustainability and environmental change