Export of dissolved organic carbon and acidity from peatlands

Abstract

Because of the vast areal extent and high rates of organic matter production of peatlands, such ecosystems have a significant but poorly quantified impact on large numbers of lakes. This study reports the export of dissolved organic carbon (DEC) and acidity from two bogs and one fen in north central North America. Rates of export of Dec are high for all three peatlands (8-40 g m -2 yr-•), and variations are largely dependent on water yield. Dissolved organic matter from all sites exhibits a charge density between 7 and 24/xeq (mg Dec) -l, and rates of acidity export from all three sites are similar (100-200 meq m -2 yr-•). Variation in elemental composition of dissolved organic matter suggests a seasonal change in relative proportions of organic matter fractions and indicates direct incorporation of microbially reduced sulfur into organic matter. Current definitions and measurement techniques for alkalinity are inappropriate for such high Dec waters, and fixed end point titration to pH 4 is suggested as an alternative. organic carbon (DEC) from a bog, 8.6 g m -2 yr-• [McKnight et al., 1985], is high relative to Dec export from either mineral soils or southern swamps [e.g., Mulholland and Kuenzler, 1979; Tate and Meyer, 1983; Naiman, 1982]. Concentrations of Dec typically are higher in midwestern bogs relative to fens [Verry, 1975; Sparling, 1967; Glaser et al., 1981] or to maritime bogs [Gorham et al., 1985], but the relative magnitudes of export from these peatland types are not known. Variability in rates of Dec export among peatlands of a single type has not been assessed, and little is known about seasonal dynamics. Kerekes et al. [1986] observed peak concentrations of Dec in summer in Nova ScotJan streams receiving drainage from peatlands, but Glover and Webb [1979] reported maximum weak acid concentrations in spring in a river in southern Norway. On the basis of the few existing measurements and without knowledge of factors controlling the magnitude of DOM export, we cannot predict the export from a single wetland type much less generalize about other wetland types. Second, lack of knowledge about differences in the nature of DOM from peatlands and other sources renders unclear the extent of characterization that is necessary. Thurman [1985] reported that DOM from bogs typically is composed of a greater fraction as fulvic acids (60%) than DOM from other surface or ground waters. McKnight et al. [ 1985] found DOM in Thoreau's bog to be dominated by hydrophobic acids (60% of Dec, primarily as fulvic acids), while hydrophilic acids accounted for 30% of the Dec. Bourbonniere [ 1987] reported generally similar results from fractionation of bog and fen waters in Quebec and Nova Scotia, but he found that hydrophobic and hydrophilic neutral fractions also were important components of the DOM. Oliver et al. [1983] and Steinberg and Muenster [1985] reported that humic acids from bogs tend to have low carboxyl contents and high phenolic contents. Thurman [1985] reported that humic and fulvic acids from bogs are defici...

Fluorescence characteristics and biodegradability of dissolved organic matter in forest and wetland soils from coastal temperate watersheds in southeast Alaska

“…For example, the greater DOC concentrations in the bog and forested wetland could result from seasonal water table drawdown in combination with greater rates of organic matter decomposition and subsequent DOC production in the aerobic surface horizons (McKnight et al 1985;Fraser et al 2001). The fen in contrast had signiWcantly lower DOC concentrations than the bog and forested wetland and suggests that continuous soil Xushing in fens results in low pore water DOC concentrations (Urban et al 1989). Seasonal changes in DOC and DON concentrations have been previously documented in both wetland (Devito et al 1989;Fraser et al 2001) and forested landscapes (Qualls and Haines 1991;Yano et al 2004).…”

Sources, Sinks, and Fluxes of Dissolved Organic Carbon in Subarctic Fen Catchments

“…bicarbonate and ca 2 i") which dilute the organic acids, raising pH and decomposition rates and providing nutrients to the plant community. As the peatland thickens the influence of ground water decreases, inputs of bicarbonate decrease, and H+ concentrations increase since theyare no longer diluted (Moore and Bellamy 1974;Urban et al 1989). …”

“…Little is known about the variability and seasonality of DOC export from peatlands (Urban et al 1989). It is estimated that there are more than 2 million km 2 of peatlands in the world (Moore and Bellamy 1974) including 1.1 million km z , or 12\ of the land surface, jn Canada (National Wetlands Working Group 1988).…”

Sustaining Aquatic Ecosystems in Boreal Regions

“…Much of the DOC (dissolved organic carbon) entering lakes and streams, which, as I shall discuss later, has very important effects on physical, chemical, and biological properties, originates in wetlands rather than uplands (Engstrom 1987, Urban et al 1989. Also, wetlands intercept and sequester much of the sulfate and nitrate entering catchments in precipitation, whether the origins are natural or anthropogenic.…”