Floodplain vegetation is an important component of the ecology of the Lower Balonne Floodplain system in the northern Murray Darling Basin. Dominant vegetation species in the area (the trees Coolibah, River Red Gum, Black Box, and the shrub Lignum) are all known to depend on flooding to maintain plant condition, with species-specific tolerances for both the maximum period between floods and the duration of inundation during such events. However, most of the knowledge of these requirements is derived from research undertaken in the southern Murray Darling Basin in rivers with climatic and hydrological regimes far removed from those of the Lower Balonne Region. Previous investigations in the Northern Basin have suggested that flooding of a certain frequency to maintain the condition of a particular species to be over-simplifications of a much more variable dynamic.
A multi-year project being undertaken by the Queensland Government as part of the larger Environmental Watering Knowledge and Research (EWKR) project is aiming to better define the water requirements of floodplain vegetation in the Lower Balonne. The overall approach of the project is to combine analysis of long-term time series of vegetation condition, as measured from satellite images, with patterns of water availability from floods, rainfall and groundwater. Vegetation responses to water availability are then being interpreted in relation to mapped landscape characteristics. Results are being validated by detailed field measurements at selected field sites using techniques such as stable isotope analysis and measurement of sap flow to quantify vegetation water use and geophysics to characterise soils, identify shallow aquifers and explain recharge processes of soil water and groundwater.
Preliminary results presented here suggest that some portions of the floodplain landscape, where asset vegetation species dominate, are likely to be utilising shallow groundwater and that flood dependency is mediated by availability of other water sources.