Previous approaches to assessing vegetation dynamics have largely focussed on responses to rainfall and temperature, with only a brief consideration given to below-ground processes. However, in groundwater dependent ecosystems, such as those found on the Murray River floodplain, SE Australia, vegetation dynamics are also likely to be driven by changes to below-ground biogeochemical processes.
Determining the connections between these aquifers and the pathways through which they are recharged is a key component in sustaining vegetation health in floodplain environments. This approach links climatological, hydrological and soil biogechemical processes to take into account soil-water, regolith-water, and plant-water interactions at a number of time scales in the order of seasons, years and decades. Associations between the hydrogeology, regolith and geomorphology with vegetation can then be elucidated both spatially and temporally. As a result, the primary drivers for land cover and vegetation health change can be determined to aid in developing management strategies on the floodplain.
In the Murray River floodplain, it has been estimated that 70% of the floodplain ecosystems show signs of significant decline as a consequence of changes to the hydrological regime. Targeted environmental flows are planned to attempt to preserve iconic sites, but the success of these actions needs to be guided by improved knowledge of hydrogeology, including surface-groundwater connectivity, and groundwater quality distribution.
This study reports on the use of time series vegetation analysis using ALOS, Landsat and MODIS data, integrated with 3-D mapping of key hydrogeological elements using an airborne electromagnetic (AEM) survey. The latter provides a snapshot of the soil profile and key elements of the hydrogeology including lithology distribution and groundwater quality, at relatively high resolutions. Correlations between vegetation health and soil and geomorphic units, surface salt distribution, saline groundwaters, river flush zones and perched aquifers reveal important associations and drivers of vegetation health.