Original ArticlesThe weighted groundwater health index: Improving the monitoring and management of groundwater resources

•The weighted GHI (wGHI) provides an improved tool to assess and monitor groundwater health.•The framework was tested on 65 sites spanning four catchments over an eight year period.•The framework can classify groundwater ecosystem health into three health categories.

Increased global demand for groundwater has resulted in the need to measure and monitor this resource. Rather than monitoring groundwater simply though water chemistry and levels, which provides a 'snapshot' of the conditions at any given time, a more holistic approach to managing groundwater resources and their changes over time is needed. Korbel & Hose (2011) introduced the first structured framework for measuring groundwater health - the Groundwater Health Index (GHI). This multimetric, two-tiered framework uses biotic and abiotic components of the groundwater ecosystem to measure and identify ecosystem health. The framework can be used to classify impacted from non-impacted groundwaters, however it has certain limitations. With increased research and associated knowledge of groundwater ecosystems in recent times, it is now timely to attempt to build on the GHI framework.This paper refines and improves the GHI by incorporating a weighting system to account for natural factors contributing to variations in biotic distribution and is tested on data within four geologically similar alluvial aquifers in intensively irrigated agricultural areas of New South Wales and Queensland, Australia. Using a combination of microbial, stygofaunal, water chemistry and environmental indicators, the 'weighted GHI' framework was able to discriminate three distinct ecosystem health classifications; that of 'similar to reference'(displaying reference-like condition) 'mild deviation from reference' (sites failing to meet between 2 and 3 benchmarks) and 'major deviation from reference' (sites with more than four benchmarks exceeded). The framework indicated that groundwater health deviated from reference condition in all four catchments studied, with irrigated sites consistently displaying deviations from reference ecosystem health. Tier 2 benchmarks were set using results from the Gwydir River, and were tested on the adjacent Namoi River catchment, the Condamine and Lower Macquarie catchments. Results indicated that ecosystem health benchmarks may be associate with aquifer typology, rather than being applicable only for local areas.