Acid neutralisation capacity measurements within natural waters: towards a standardised approach

Detailed hydrochemical data for an extensive survey of streams draining small acidic and acid sensitive forested and felled catchments across Wales are used to assess the relationship between Gran alkalinity and acid neutralising capacity (ANC). The waters vary in their ANCs from relatively high (1500 mu Eq./1) to low values (-319 mu Eq./l) thus covering a range which encompasses good quality bicarbonate bearing to highly acidic waters. The results show a good relationship when allowance is made for aluminium and organic anion charge associated with dissolved organic carbon. The relationship takes the form: ANC approximate to [Alk(Gran)] - [Al-Total] + Delta{DOC} where [] denotes equivalent and {} molar concentrations, while Delta, a stoichiometric constant, has a value of approximately 0.07 which relates to the deprotonation of hydrogen ions from the DOG. The relationship is of importance to acidification studies as it provides a means of assessing the critical measure of ANC which is infrequently determined from routinely and much more easily measured determinands. The work shows that both aluminium and organic anion charge can make up a substantial part of the ANC and that neither can be ignored. (C) 1999 Elsevier Science B.V. All rights reserved.