Environmental water needs for the Fitzroy River

This project aimed to determine environmental water requirements of key plants and animals for the Fitzroy River in the Kimberley region of Western Australia.

An initial conceptual model was developed (from literature reviews) to describe hydro-socio-ecological relationships to encourage more integrated and inclusive water allocation planning. This included 10 key considerations for water planning which fed into the development of initial water-planning documents by the Western Australian Government.

The ecological relationships in this conceptual model were largely based on evidence from elsewhere in northern Australia (and even further afield), as there was very little data on the relationships between flow and biota or habitats for the Fitzroy itself. This helped to identify key ecological knowledge gaps for the Fitzroy River. These knowledge gaps guided research design and data collection for on-ground studies focusing on freshwater biota (algae, fish, cherabin) and riparian vegetation in the Fitzroy, conducted in partnership with Traditional Owners and Indigenous rangers.

This new research details five flow-biota relationships and 14 habitat-biota relationships, including studies on algal biomass, fork-tailed catfish, cherabin and riparian vegetation. Flow-biota relationships are particularly useful for environmental water planning because they provide a direct link between river flow and an ecological outcome – such as cherabin population size and catfish body condition – indicating potential implications of water extraction.

The initial conceptual model was updated and refined with new ecological evidence that emerged during the project, resulting in a model that is populated largely by knowledge generated from research undertaken in the Fitzroy instead of elsewhere. This model is more defendable and provides stronger evidence for water planning, but with less ecological breadth than the initial version.

We recommend that both models be used to guide management decision-making and policy development for the river.

The Fitzroy River in the Kimberley region of Western Australia.

The initial hydro-socio-ecological conceptual model of the impacts of water abstraction in the Fitzroy River. The model is centred on four flow phases and the potential impacts of abstraction during each flow phase. Small inner circles describe impacts on hydrology and physical habitats, large outer circles describe impacts on habitat availability and quality, and water-dependent biota and ecological processes. Impacts of particular interest to Indigenous people are in bold type. The quotes illustrate Indigenous perspectives on hydro-socio-ecological relationships. The outer circle encompasses the key social factors and conditions that affect water allocation planning. Taken from Douglas et al. (2019) and available in pdf format here.

The revised conceptual model using only research undertaken in the Fitzroy River. Black text = evidence from this project, published; black text italicised = evidence from this project, unpublished. Grey text = evidence from other sources, published. Available in pdf format here. 

• Links were identified between flow velocity and algal biomass – biomass which is important for riverine productivity.
• Local food sources supported fish in the main channel at the end of the dry season.
• The body condition and intramuscular fat of fork-tailed catfish were greater in years following moderate to high wet-season flow, and decreased as the dry season progressed.
• Larger wet-season flows increased the cherabin population.
• The duration of inundation from flood flows was a strong predictor of the occurrence of woody riparian plant species, which may be used to predict species response to water-take scenarios.
• There is a zonation in the composition and structure of riparian tree species from the edge of the river and across the floodplain.
• The water sources used by riparian trees reflects the local hydrology, with trees using regional groundwater sources where it is available.
• There is a relationship between some physiological traits of riparian trees and their distribution along a hydrological gradient.

A representation of the zonation of riparian woody plants, including photographs representative of each zone.

This project generated new ecological evidence to support water planning in the Fitzroy River, increasing our knowledge of riparian vegetation, fish and cherabin, the aquatic food web, the water chemistry of pools and hydrological connectivity. The most direct flow-biota relationship generated by this project is the link between the duration of floodplain inundation and the probability of occurrence of different riparian tree species. The relevance of this research to water policy decision-making was maximised by using this flow-biota relationship to predict tree occupancy for the different water-take scenarios that were used in a discussion paper by state government water managers. Spatial mapping across the lower Fitzroy River highlighted areas most vulnerable to water extraction. The species most vulnerable to wet-season water harvesting are Melaleuca argentea (silver-leaved paperbark), M. leucadendra (weeping paperbark), Nauclea orientalis (Leichhardt tree) and Barringtonia acutangula (freshwater mangrove), which may make them good candidates for monitoring to assess environmental impacts.

Other flow-biota relationships generated by this project can also inform and support water management decisions. For instance, the positive link between years with high wet-season flows and the energy stores of fork-tailed catfish in dry-season pools reinforces the importance of flow/water availability as a critical force shaping the ecology of riverine biota. Protecting wet-season flows during years with low river discharge will be particularly important for fork-tailed catfish so that they can accumulate the energy stores needed to survive during the subsequent dry season.

Habitat-biota relationships are also useful for water planning because they can reveal the changes likely to arise if the availability and quality of habitats change due to water extraction. For instance, knowledge generated by this project about the importance of the floodplain for fish recruitment and growth indicates the importance of protecting within-bank flows that fill flood-runner channels and replenish flood-runner pools. Similarly, flood flows are important for maintaining wetlands in the floodplain, which are important habitats for the recruitment of riparian plant species.

Researchers Leah Beesley, Chris Keogh and PhD student Thiaggo de Castro Tayer sampling fish and algae in collaboration with Yimardoo-Warra Rangers Jeremiah Green and Shaquille Millindee. Photo: Michael Douglas.

Although it wasn’t a key objective of the research, our research findings highlight the need for an effective monitoring program to protect the ecological assets of the Fitzroy River and support water allocation decisions. A monitoring program must:

• assess ecologically appropriate indicators – spot measurements of water quality are unlikely to be sufficient
• measure relevant hydrological variables and other influential but non-target variables
• be undertaken at both local and system-wide scales (i.e. the lower Fitzroy River)
• use appropriate methods for data collection
• generate data that is publicly available, analysed regularly and independently reviewed
• be incorporated into management (i.e. adaptive management), so that a clear link exists between monitoring outcomes and decision-making, and monitoring data must be able to trigger a management action.

For monitoring to successfully assess the impacts of water extraction, a baseline dataset must be amassed that accurately describes natural range of conditions experienced by plants and animals. The data set collected by this project helps to identify critical features to monitor, but it is relatively short-term and is insufficient as a baseline dataset.

This project has markedly increased the ecological knowledge related to flow and riverine habitats in the Fitzroy River. It has also identified key knowledge gaps that should be the target of further research, including:

• the importance of river flows for the growth, recruitment and survival of many plants and animals, including fish, cherabin and vegetation (woody or herbaceous)
• the ecological role of recessional flows
• the potential for off-stream water storage to trap and cause mortality for fish
• the energetics of the river system, including the role of large-bodied fish in transferring energy through space and time
• the life history of cherabin, especially their reliance on an estuarine nursery, and the wet-season flows that promote larval transport to the estuary
• the reliance of riparian trees on groundwater, especially the aquifers identified for water-take
• modelling of how groundwater take will affect water table height
• mapping and ground-truthing of groundwater dependent ecosystems, including springs and aquifers, as well as baseline data on those identified as ‘at risk’ from pumping.