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 mEq.rl. to low values y319 mEq.rl. 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: ANCfwAlkGranxywAlTotal xqD DOC4 where wx denotes equivalent and 4 molar concentrations, while D, a stoichiometric constant, has a value of approximately 0.07 which relates to the deprotonation of hydrogen ions from the DOC. 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