title: Evaluation of different approaches to quantify strong organic acidity and acid-base buffering of organic-rich surface waters in Sweden.
abstract: The role of organic acids in buffering pH in surface waters has been studied using a small brownwater stream (26mg L(-1) TOC) draining a forested catchment in Northern Sweden. Under the conditions of elevated pressure of CO2 stream field pH was changed between 3.5 and 6.1 during the acidification and alkalinization experiment. Acid-base characteristics of the natural organic matter were also determined using a high precision potentiometric method for a concentrated sample from the same stream. We compared the predictions from the Windermere Humic Aqueous Model (WHAM Model V), a model derived from the potentiometric titration (diprotic/monoprotic acid model) and a previously derived triprotic acid model which only uses alkalinity and TOC as input variables. The predicted buffering characteristics of all three models are very similar in the pH range 4.5-7 which suggests that during routine analysis alkalinity and TOC are sufficient to give a good estimate of organic acid anion charge contribution in a large range of surface waters. A slightly adjusted version of WHAM V successfully describes the organic charge contribution in a large number of sampled surface water lakes, which were previously used to calibrate the triprotic model.
authors.affiliation: Laboratoire de Geochimie CNRS, UMR 5569, Université Paul Sabatier, Toulouse, France. skohler@lmtg.ups-tlse.fr
authors.forename: Stephan
authors.initials: S
authors.lastname: Köhler
authors.forename: Jakub
authors.initials: J
authors.lastname: Hruska
authors.forename: Jörgen
authors.initials: J
authors.lastname: Jönsson
authors.forename: Lars
authors.initials: L
authors.lastname: Lövgren
authors.forename: Stephen
authors.initials: S
authors.lastname: Lofts
mesh_terms: D015258:Acid Rain; D004784:Environmental Monitoring / Q000379:methods*; D005544:Forecasting; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D013548:Sweden; D014197:Trees; D014867:Water / Q000737:chemistry; D014881:Water Supply
chemical_list: D015258:Acid Rain; D014867:Water