Chemical character and origin of organic acids in streams and seepage lakes of central Maine

Abstract

Abstract. Organic acids and inorganic chemistry were examined in seventeen seepage lakes, seven streams, and one seep in central Maine. The objectives of this analysis were to determine the quantity and quality of dissolved organic carbon (DOC), and to assess the relationship between organic and inorganic surface water chemistry. Lakes and streams sampled were dilute (average conductivity of 20.3 pScm-') with a wide range of DOC (125-2593 pmol C L-'). Organic acids in DOC were evaluated by:-DOC fractionation (hydrophobic acids and neutrals, and hydrophilic acids, bases, and neutrals); -DOC isolation followed by FT-IR, base titration, and chemical analyses; -adsorption on solid phase extraction columns; and charge balance studies.All lakes and streams were dominated by hydrophobic and hydrophilic acids (60 to 92% of DOC). Lakes and streams with low DOC had low hydrophobic to hydrophilic acid ratios (ca 1.2-1.3), regardless of pH and acid neutralizing capacities (ANC), compared to lakes and streams with moderate to high DOC concentrations (ca 1.9-2.4). Based on FT-IR spectroscopy and chemical analysis, organic acids were found to be dominated by a strong carboxylic character. Titration data of isolated DOC allowed accurate prediction of organic anions, which were strongly pH dependent (organic anions ranged from 14 to 198peq L-' ). Exchange acidity averaged 11.3, 13.6, and 8.7 peq mg C-' for lake hydrophobic acids, lake hydrophilic acids, and stream hydrophobic acids, respectively.Overall evidence suggested that DOC and organic acid characteristics were related to their carboxylic functional group content and that the nature of these constituents was similar despite the source of origin (upland soils, wetlands, or Sphagnum deposits). Also, contact of soil leachates with B horizons seemed to be a controlling factor in DOC quantity and quality in the lakes and streams studied.

The chemistry of streams in southwestern and central Nova Scotia, with particular reference to catchment vegetation and the influence of dissolved organic carbon primarily from wetlands

“…Peterson (1990) suggested that a low color/DOC quotient also indicates poorly humified, less complex organic material from streams and lakes rather than from peatlands. In this same connection, David and Vance (1991) observed that those waters from streams and seepage lakes in Maine that were low in DOC also had small ratios of hydrophobic to hydrophilic acids. In those cases where DOC exceeded 10 mg L -~, the color/DOC quotients in Halifax County lakes sampled in December 1985 (Gorham et al 1986) were generally lower than those of the streams examined in December 1988, suggesting that colored organic matter in the lakes may have undergone relatively more breakdown than that in the streams, either photochemically or biochemically (Engstrom 1987).…”

The episodic acidification of a stream with elevated concentrations of dissolved organic carbon

“…This input of DOC was mainly in the form of hydrophobic acids, which have low charge density (Wellington and Driscoll, unpublished results). David and Vance (1991), in studying the origin of stream organic acids in Maine, found that DOC from wetlands and organic soil horizons had similar characteristics, both having high hydrophobic acid content and low charge density.…”

Modelling the effects of acid deposition: refinements, adjustments and inclusion of nitrogen dynamics in the MAGIC model

“…McKnight et al, 1985;David and Vance, 1991). Organic acids are effective H ion buffers and can form complexes with inorganic Al.…”