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The Environmental Protection Agency of the Campania region in Italy (ARPAC) manages a groundwater quality monitoring network. For almost all the polluted waters, the key parameter driving the classification is the concentration of nitrate; hence, the Campania region, in coherence with the EU regulations, outlined the vulnerable areas and undertook remediation policies. The best groundwater quality is recorded for carbonate aquifers of the Apennine chain; on the contrary, the Tyrrhenian coastal plains are affected by severe contamination, with a locally very contaminated groundwater of the shallow and also the deeper aquifers. The study is especially focused on a large coastal plain of Campania region, where nitrate concentration sometimes exceeds 200 mg/L. The study, based on almost 200 sampling points for the whole region during the period 2003-2015 (approx two samples per year), verified the effectiveness of the groundwater monitoring network, the present distribution of nitrate in groundwater, and the evolution of nitrate trends at different scales: regional, groundwater body, and single well, using spatial and time series statistical approaches. Significant variations in contamination evolution within the study area have been observed and the correlation with land use has been highlighted.

Nitrate is a worldwide pollutant in aquifers. Shallow aquifer nitrate concentrations generally display vertical stratification, with a maximum concentration immediately below the water level. The concentration then gradually decreases with depth. Different techniques can be used to highlight this stratification. The paper aims at comparing the advantages and limitations of three open hole multilevel sampling techniques (packer system, dialysis membrane samplers and bailer), chosen on the base of a literary review, to highlight a nitrate vertical stratification under the assumption of (sub)horizontal flow in the aquifer. The sampling systems were employed at three different times of the year in a shallow aquifer piezometer in northern Italy. The optimal purge time, equilibration time and water volume losses during the time in the piezometer were evaluated. Multilevel techniques highlighted a similar vertical nitrate stratification, present throughout the year. Indeed, nitrate concentrations generally decreased with depth downwards, but with significantly different levels in the sampling campaigns. Moreover, the sampling techniques produced different degrees of accuracy. More specifically, the dialysis membrane samplers provided the most accurate hydrochemical profile of the shallow aquifer and they appear to be necessary when the objective is to detect the discontinuities in the nitrate profile. Bailer and packer system showed the same nitrate profile with little differences of concentration. However, the bailer resulted much more easier to use.

& Nitrogen Use Efficiency or NUE should read as Nitrogen Efficiency or NE throughout the text (except in Abstract, paragraph 2, line 3 and paragraph 4, line 6), as well as in Table 1 and Fig. 1. & On page 3 of the original article, paragraph 3, the formula ‘NUE =shoot weight/total nitrogen content of shoot’ should read as ‘NE = [Biomass accumulation at low N level/Biomass accumulation at high N level] × 100’. & On page 3 of the original article, 5th paragraph, lines 16–17, “nanomoles NO2 produced per milligram protein per minute” should read as “micromole NO2 produced per gram dry weight per hour”. & On page 3 of the original article, 6th paragraph, lines 15– 16, “micromoles NO2 utilized per milligram protein per hour” should read as “micromole NO2 utilized per gram dry weight per hour.” & On page 3 of the original article, 8th paragraph, lines 10–11, “micromoles γ-GH formed per milligram protein per minute” should read as “micromoles γ-GHA formed per gram dry weight per minute.” & On page 4 of the original article, 6th paragraph, lines 3– 4, the sentence “six cultivars varied from 0.008 to 0.43 mM,” should read as “six cultivars varied from 0.008 to 0.043 mM,”.