Acid-Induced Changes in DOC Quality in an Experimental Whole-Lake Manipulation

Abstract

Fluorescence analyses of archived water samples were used to typify dissolved organic carbon (DOC) quality in experimentally acidified lakes and reference lakes at the Experimental Lakes Area, in northwestern Ontario. Carbon-specific DOC fluorescence (CSF) during peak acidification (pH 4.5) was 40−50% of that for a high-DOC reference lake and similar to a low-DOC reference lake. Reference lakes showed similar but smaller decreases in CSF during several years of prolonged drought in the late 1980s. During the 1990s, recovery from acidification resulted in increased CSF, whereas reference lakes remained unchanged during the same time period. In addition to causing decreased [DOC], acidification causes changes in fluorescence-peak geometry that indicate a switch in DOC quality from allochthonous to “autochthonous-like” during acidification. The acid-induced change in DOC quality was likely due to increased chemical oxidation or precipitation of the UV-absorbent aromatic portions of allochthonous DOC molecules, leaving more UV-transparent aliphatic chains. The change in the nature of DOC following acidification and drought may have an important role in physical, biological, and chemical processes within these lakes. With recovery from acidification, DOC quality has also recovered.

Functional variability of dissolved organic matter from the surface water of a productive lake

“…These results are consistent with the findings of Donahue et al (1998) and Waiser and Robarts (2004). In addition, the present data show that DOM AUT is more hydrophilic, and possesses fewer acid-dissociating groups than DOM ALL .…”

“…given extra impetus by the apparent sensitivity of DOM to environmental change, as shown by long-term increases (Hongve et al, 2004;Evans et al, 2005) or decreases (Schindler et al, 1996) in DOM concentration, and changes in DOM quality (Curtis, 1998;Donahue et al 1998), attributed to climatic warming and/or declining acid deposition.…”

“…"Autochthonous-like" DOM may be produced from DOM ALL , due to in-lake chemical alterations, for example, acidification (Donahue et al 1998) and photobleaching (Waiser and Robarts, 2000). Typically, DOM AUT absorbs less UV light, is poorer in aromatic residues, and is more enriched in nitrogen than DOM ALL (Tipping et al, 1988;Curtis and Adams, 1995;Curtis 1998).…”

“…Typically, DOM AUT absorbs less UV light, is poorer in aromatic residues, and is more enriched in nitrogen than DOM ALL (Tipping et al, 1988;Curtis and Adams, 1995;Curtis 1998). There are also differences in fluorescence properties, for example Donahue et al (1998) reported that, with excitation at 370 nm, the peak emission of DOM ALL was at 462 nm, whereas that of DOM AUT was at 443 nm. The relative contributions of DOM ALL and DOM AUT in a lake depend upon hydrological factors and the biological and physico-chemical characteristics of the water body and its surrounding catchment (Thomas, 1997).…”

Chemical composition of the Tatra Mountain lakes: Recovery from acidification

“…Concentrations of dissolved organic carbon in the Tatra forest lakes have been increasing during recovery (Fig. 8) similarly to other European sites (e.g., surface waters A recovery in DOC quantity (and also quality) with recovery from acidification was observed also in the Experimental Lakes Area (Donahue et al, 1998). Of the 10 Tatra forest lakes sampled both in the 1994 and 2004 surveys, DOC concentrations increased in 8 (on average by 120 µmol L −1 ) and decreased in two lakes.…”