Quality control of pore water chemical analyses is intrinsically difficult. To the best of authors' knowledge, there are no specific certified international standards, and replicate analyses were seldom possible.
Preliminary release tests with deionised water on new lysimeters and rhizometers indicated negligible (below detection limits for ICP–OES) amounts of released elements, except for Ba. For this element, high values were recorded in lysimeter blanks, therefore data for Ba were not included in this study. Field blanks were obtained by introducing deionised water in the same devices used for pore water samples, and treating the collected volumes as independent samples. The accuracy of ICP–OES analyses was checked with calibration standard solutions. A further check of quality of analysis for major elements is ionic balances. From data in Table 3b, it is possible to calculate ionic balances: most are within ±10%, and only two are within ±15%. Overall, it is estimated that most of analyses are within ±20% error for both accuracy and precision.