This research project is one of five components delivered by the Goyder Institute for the Department for Environment and Water’s Healthy Coorong, Healthy Basin Scientific Trials and Investigations Project.
The project will provide scientifically defensible advice on how to use existing and new management interventions to reduce nutrient availability and conditions that promote excessive filamentous algal growth in the Coorong. The data and knowledge generated will also improve and validate biogeochemical models that are critical to support evidence-based decisions on flow management and infrastructure options.
The Nutrient Dynamics Component will provide a holistic understanding on how the nutrient load in the Coorong could be lowered to improve management by assessing the relative importance of external and internal nutrient sources and processes within the Coorong.
This Component involves field, laboratory and data analysis tasks across multidisciplinary areas (water, sediment, ecology) with a need to resolve temporal and spatial nutrient dynamics and processes that are contributing to poor ecosystem health. A collaborative team involving all of South Australia’s key research universities, CSIRO, and national and international experts has been formed. State-of-the-art techniques such as isotope tracers and high-resolution sediment geochemical measurements will be used to resolve the key questions surrounding nutrient cycling.
The data and knowledge collected through this Component are also required to improve and validate biogeochemical models of the Coorong. This is critical to support evidence-based decisions on flow management, including barrage releases from Lake Alexandrina, releases from the South-East via Morella Basin and Salt Creek, and the Murray Mouth dredging regime. This will also support investigations into options for improving system flexibility such as long-term infrastructure options. Combined with knowledge of the effectiveness of complementary management actions aimed at reducing nutrient inputs and controlling nutrient concentrations in the South Lagoon, this will ultimately lead to reduced nutrient availability and limit excessive growth of filamentous algae.
The Coorong South Lagoon has been considered to be in a degraded and hyper-eutrophic state (Mosley et al. 2017, Aldridge et al. 2018) with elevated concentrations of total nitrogen and phosphorus, phytoplankton (as measured by chlorophyll a), and an increased presence of filamentous algae at the expense of the keystone aquatic plant Ruppia. Without a shift from a phytoplankton and algal dominated system to aquatic plants, the Coorong cannot support the abundance of food that makes this wetland productive for birds and fish. The presence of algae and high levels of organic matter also increases the frequency and scale of suspended sediment and an anoxic water column, exacerbating the nutrient problem and increasing the build-up of sulfidic materials (i.e. black oozes), which are also toxic and of concern to the community. A Conceptual model has been developed of the nutrient sources in the Coorong that shows how the Nutrient Dynamics Component will address uncertainties in the relative importance of these sources in order to provide sound management guidance.
Figure 1. Conceptual model of potential nutrient dynamics in the South Lagoon of the Coorong that the project will elucidate.
Key Knowledge Gaps and Management Questions
There is uncertainty in current knowledge of how South-East flows influence nutrient concentrations in the Coorong. These flows bring in some bioavailable nutrients (dissolved nitrogen, phosphorus and silica), but also increase flushing of the system and appear to induce lower salinity, total nutrients and chlorophyll in the water column of the South Lagoon (Mosley et al. 2017). Internationally, increased eutrophication of estuarine systems is linked to a lack of flushing as well as external nutrient sources, and warming temperatures due to climate change. The fate of water from the South-East, as well as how this drives export of dissolved and suspended material from the South to North Lagoon, is unknown at present. This is a critical question that needs answering to manage South-East flows in order to influence nutrient levels and cycles, as well as salinity and water levels. This knowledge is required to support evidence-based decision-making to protect and restore the South Lagoon ecosystem.
Four tasks are being delivered by the Nutrient Dynamics Component (Figure 2).
Figure 2: Diagram showing the main Component activities which are interlinked, and which also link to other T&I Research Components.
The Nutrient Dynamics Component will collate existing data and knowledge (Activity 1.1) and then undertake targeted research to understand: the sources and fate of external nutrients entering the system (Activity 1.2); the internal nutrient cycling processes and fluxes within the system including a sediment quality survey (Activity 1.3); the most appropriate nutrient removal strategies (Activity 1.4).
Specifically, this Component is designed to address the following research question(s):
Aldridge, K., Mosely, L. and Oliver, R. (2018). Water quality in the Coorong, Lower Lakes and Murray Mouth. In Natural History of the Coorong, Lower Lakes and Murray Mouth (Yarluwar-Ruwe). Eds: L. Mosley, S. Shepherd, Q. He, S. Hemming and R. Fitzpatrick.
Mosley L.M., Hamilton B., Busch B., Hipsey M., and Taylor B. (2017). Assessment and modelling of the effects of the 2013-2016 Morella Basin releases on Coorong water quality. Report to the Department of Environment, Water and Natural Resources (DEWNR). University of Adelaide, South Australia.