The weighted Groundwater Health Index (wGHI) by Korbel and Hose (2017) in European groundwater bodies in nitrate vulnerable zones

The weighted Groundwater Health Index (wGHI), introduced by Korbel and Hose (2017), is a multimetric, two-tiered framework for measuring and identifying the ecological status of groundwater ecosystems using biotic and abiotic indicators. The wGHI was conceived and tested in unconsolidated alluvial aquifers in Australia. In this study we applied and tested the index in European unconsolidated aquifers located in nitrate vulnerable zones (NVZ). A refinement of the wGHI was necessary to ensure the compliance with the requirements of the European Directives. We called the refined index wGHI where N stands for nitrates. We tested the wGHI in an unconsolidated aquifer (VO_EU_GWB) in the River Vomano catchment (central Italy) that was designated NVZ in 2005 and has since been subject to management measures pursuant to the Nitrate Directive. We also monitored a complex of minor confined unconsolidated aquifers (VO_CON_GWB) located in the same catchment. The wGHI highlighted extensive nitrate contamination in both the VO_EU_GWB and VO_CON_GWB aquifers. Despite the widespread contamination, most of the monitoring sites showed only minor deviations from good ecological status. The index also highlighted the biodiversity of the aquifers which happened to be among the most diverse in Europe. The wGHI proved to be theoretically sounding, concrete, numerical and easily understandable by the public and policy-makers. Finally, the index was economically sustainable. The wGHI has certain limitations that have to be resolved, such as the low correlation of some indicators to the index overall score in the aquifers of the River Vomano and the fact that the index is not "operationally simple" since it requires taxonomic and ecological skills.