Ammonium threshold values for groundwater quality in the EU may not protect groundwater fauna: evidence from an alluvial aquifer in Italy

The European Union (EU) threshold values for NHþ4 in groundwater range from a minimum of 0.084 mg l-1 to the maximum allowed of 5 mg l-1. The aim of our study was to determine whether these values are adequate to protect groundwater copepods in alluvial aquifers underlying intensive agriculture. To this end, we analyzed abiotic (including NHþ4 concentration) and biological patterns (copepod assemblages) in an alluvial aquifer in an area of intensive agriculture. Groundwater was collected from pre-existing farmer-owned bores. Abiotic and biological patterns were not related to seasonal variation in agricultural practices, and pollutant concentrations were typically below the legal maximum threshold values. However, both abiotic and biological variables differed significantly between two groups of bores, with high and low NHþ4 conditions based on separate ecotoxicological assays that set the NHþ4 toxicity threshold for stygobiotic copepods at 2.59 below the current EU lowest legal threshold. In particular, phosphorus concentration was higher, and oxygen and copepod abundance and richness were lower in high NHþ4 bores. Our results suggest that the present threshold value range for NHþ4 adopted by EU Member States may not protect stygobiotic copepod assemblages in alluvial aquifers underlying densely cultivated areas.