National Wetlands Update September 2012
Issue No. 21, September 2012
The hydroecology of the Lower Burdekin River floodplain wetlands
Queensland Department of Science, Information Technology, Innovation and the Arts and the Queensland Wetlands Program
How do you manage an ecosystem when you don't understand how the natural drivers or human pressures control what happens to its biophysical conditions? You can't! A conceptual understanding underlies all natural resource management and scientific investigations.
Presentation of this understanding as a conceptual model or diagram allows for compilation of information and review of propositions made. A set of conceptual models has been developed for describing the Lower Burdekin Floodplain Wetlands with the specific aim of providing information on groundwater dependent ecosystems (GDEs) for water resource management.
The Lower Burdekin River Floodplain
The Burdekin River catchment in North Queensland spreads into a broad floodplain of highly productive ecosystems and agricultural systems before flowing into the Great Barrier Reef lagoon.
Much of this productivity relies on water from river flows and groundwater from a large underlying aquifer, which are highly connected and therefore difficult to manage separately. For example, groundwater is managed to ensure irrigation is available throughout the dry season and also to prevent saltwater intrusion.
To ensure reliable irrigation water, an extensive network of irrigation channels and groundwater recharge is used to transport water across the floodplain. While there are numerous threatening processes to wetlands in the Lower Burdekin, irrigation works present the major threat.
In the Lower Burdekin floodplain four GDE types are present:
- shallow non-permanent palustrine wetlands
- non-permanent riverine wetlands
- permanent riverine wetlands
- shallow estuarine wetlands.
All wetland types present have changed significantly because of altered hydrology. The conceptual models below detail these changes for non-permanent riverine wetlands.
Conceptual model of a pre-development wetland
Non-permanent riverine wetlands, such as Barratta Creek, carry floodwater away from the Burdekin River. In the wet season, they are connected to the ocean allowing fish to migrate up and down the system.
In large wet seasons, streams flood and recharge the aquifer. During the dry season, waters recede creating a series of isolated deep water refuges characterised by clear tannin stained water. The water table also drops and becomes disconnected from the wetlands.
A model of the pre-developed conditions and functions in wet and dry seasons. (Queensland Department of Science, Information Technology,
Innovation and Arts)
Current conceptual model
Many of these wetlands no longer dry out in the dry season with water inputs from irrigation tailwater and discharge from raised water tables.
Combined with grazing and fire this increased water has negatively impacted remnant vegetation. The water in these wetlands is commonly anoxic (low dissolved oxygen) and nutrient rich.
The effect of the increased stressors has aided the spread of invasive aquatic and semi-aquatic vegetation. These plants can restrict water flow and block light in the water column which in turn reduces habitat quality for native fish and aquatic macroinvertebrates and promotes an increase in invasive fish species.
The current conditions of non-permanent palustrine and riverine wetlands. (Queensland Department of Science, Information Technology,
Innovation and Arts)
Compilation of the information available on an ecosystem (including expert opinions and community knowledge) is essential for fully understanding the structure, processes and functions of ecosystems.
Presenting information as conceptual models assists in synthesising and communicating this information to a wide range of stakeholders including natural resource managers, scientists and the community. The development and use of conceptual models will ultimately result in broader engagement and better evidence-based decision making on ecosystem management.
This case study was created by the Water Planning Ecology Group in the Queensland Department of Science, Information Technology, Innovation and the Arts. The models are based on the outcomes of a project funded by the National Water Commission.
Models will be available in the future on the Queensland Wetlands Program's WetlandInfo website.
Perna, C. O'Connor, R. and Cook, B, 2012, Hydroecology of the lower Burdekin River alluvial aquifer and associated groundwater dependent ecosystems, Department of Environment and Resource Management, Queensland Government.