Building knowledge for healthy northern Australian catchments and coasts

Economic development in northern Australia brings the greatest benefits to northern communities when there are no adverse effects on river catchments, estuaries and marine waters. To achieve this, the potential environmental impacts of developments must be understood, predicted, and included in economic and regional planning deliberations and decisions.

There is limited scientific understanding of how further development of industries such as irrigation and grazing could affect northern catchments and their downstream marine ecosystems. At the same time, climate change is increasing temperatures, changing coastlines and causing more extreme weather events, but our understanding of the impacts is still limited. Without this knowledge, decision-makers cannot predict the environmental and associated outcomes of developments with a high degree of certainty, nor accurately plan for mitigation.

This project examined existing information and undertook field and desktop analyses aimed at improving our understanding of how runoff from key northern catchments (Flinders, Gilbert, Daly, and Keep Rivers) affects downstream estuaries and marine systems. The goal was to support informed, science-based decisions about future land and water use.

Approach and findings

The project employed multiple research approaches to gain a deeper understanding of the relationships between catchment activities and downstream coastal ecosystems.

Literature review

A literature review examined the current knowledge on the functioning of estuaries, coastal floodplains, and coasts in northern Australia, as well as the potential impacts of catchment development on these areas, focusing on grazing, irrigation, mining, and urban development. It also examined the potential effects of climate change. The review provided a summary of the potential impacts of different development types on the four catchments, identifying sedimentation, reduced flows, changes in nutrient loads and increased pollutant loads as key risks to estuarine and marine health.

Flood plume mapping

Satellite imagery and flow data were utilised to map flood plumes over a 20-year period, showing the relationship between plume size, sediment and nutrient distribution, and river flow. This analysis helped assess how future development and climate change might affect plume extent. Larger flows produced wider plumes, which were closely linked to increased marine productivity (measured as chlorophyll-a). This highlighted the role of wet season flows in fuelling fisheries productivity, such as commercially caught prawns. Climate models predicted a future reduction in rainfall for all river catchments.

Mangrove condition

The study found a disconnect or no apparent relationship between river flow and rainfall, on the one hand, and mangrove extent and forest composition, on the other. Instead, observed changes in mangrove canopy cover were more strongly linked to sea level fluctuations and cyclones.

Primary productivity in estuaries

Experiments tested the effect of nutrient additions and removal on algal growth on mudflats in four estuaries. All sites showed similar levels of oxygen flux rates (as a measure of primary productivity), but importantly, all showed significant increases in primary productivity with nutrient inputs. The implications of this study are that all estuaries in this study were nutrient-depleted, and therefore, a reduction in nutrient loads from increased freshwater extraction will ultimately decrease primary production on mudflats.

Stakeholder engagement

Throughout the project helped identify gaps and priorities for future monitoring and modelling.

Outcomes

This project provides a knowledge base for understanding how water extraction, land use and the interaction with climate change affect northern Australia’s catchments. It reinforces the importance of maintaining seasonal freshwater flows to sustain coastal productivity and fisheries.

By drawing on lessons from better-studied regions, such as the Great Barrier Reef, the project offers practical insights to guide sustainable development and protect the ecological integrity of northern Australia’s coasts.

The findings of this project can help inform state and Commonwealth water planning processes, such as Queensland’s Gulf Water Plan review. The research also supports efforts to improve development assessment tools by highlighting the cumulative and climate-sensitive nature of catchment pressures.

Project location