Organic solutes and recovery of a bog stream from chronic acidification

Natural organic acids are important in the acid-base chemistry of many natural waters. However, field studies suggest that the degree of acid neutralization provided by natural organic acids is smell, even in organic- rich waters. We added sulfuric acid and sodium bicarbonate separately to a bog stream in the Czech Republic to evaluate the role of organic acids in the acidification and subsequent recovery of brown waters subjected to chronically high acid deposition. Despite naturally high organic acid concentrations (dissolved organic carbon [DOC] concentration, 48.9 mg L^-1; total carboxyl group concentration [C(T)], 344 μequiv L^-1; organic acid anion concentration [RCOO^-], 176 μequiv L^-1), only 10% of the added acid and base were neutralized by the protonation or deprotonation of carboxylic functional groups. Approximately 80% of the acid and base additions remained unbuffered. Release of aluminum and basic cations to solution accounted for the remainder of the added acid and base. A Gaussian model of organic acid dissociation, fitted to our experimental results, explained the variations in RCOO^- and the minimal buffering offered by organic solutes. Sulfate and hydrogen ion (H⁺) concentrations at the study site declined sharply (ca. 50%) in 1992-1996, but DOC, C(T), and RCOO^- were unchanged. Our experimental and monitoring results suggest that organic acids are not likely to hinder significantly the recovery of brown water streams in the region from chronic anthropogenic acidification).