Acid neutralisation capacity measurements within natural waters: towards astandardised approach

Detailed hydrochemical data for an extensive survey of streams draining sma ll acidic and acid sensitive forested and felled catchments across Wales ar e used to assess the relationship between Gran alkalinity and acid neutrali sing capacity (ANC). The waters vary in their ANCs from relatively high (15 00 mu Eq./1) to low values (-319 mu Eq./l) thus covering a range which enco mpasses good quality bicarbonate bearing to highly acidic waters. The resul ts show a good relationship when allowance is made for aluminium and organi c anion charge associated with dissolved organic carbon. The relationship t akes the form: ANC approximate to [Alk(Gran)] - [Al-Total] + Delta{DOC} whe re [] denotes equivalent and {} molar concentrations, while Delta, a stoich iometric constant, has a value of approximately 0.07 which relates to the d eprotonation of hydrogen ions from the DOG. The relationship is of importan ce to acidification studies as it provides a means of assessing the critica l measure of ANC which is infrequently determined from routinely and much m ore easily measured determinands. The work shows that both aluminium and or ganic anion charge can make up a substantial part of the ANC and that neith er can be ignored. (C) 1999 Elsevier Science B.V. All rights reserved.