Acid/base character of organic acids in a boreal stream during snowmelt

Citation
J. Hruska et al., Acid/base character of organic acids in a boreal stream during snowmelt, WATER RES R, 37(4), 2001, pp. 1043-1056
Citations number
43
Categorie Soggetti
Environment/Ecology,"Civil Engineering
Journal title
WATER RESOURCES RESEARCH
ISSN journal
00431397 → ACNP
Volume
37
Issue
4
Year of publication
2001
Pages
1043 - 1056
Database
ISI
SICI code
0043-1397(200104)37:4<1043:ACOOAI>2.0.ZU;2-X
Abstract
In northern regions, spring snowmelt generally results in an episodic decli ne of surface water pH. Natural organic acids may be an important factor in this type of pH change. We studied the variations in the acid/base charact er of aquatic organic acids during spring snowmelt in 1997 at Svartberget, a stream rich in total organic carbon (TOC) that is located in the boreal z one of northern Sweden. Snowmelt at Svartberget was accompanied by a drop i n stream pH of up to 1.8 pH units, as well as the dilution of base cation a nd strong acid anion concentrations. Aluminum and TOC increased or decrease d during snowmelt, depending on the sampling site within the 50-ha catchmen t. Although there were distinct differences in pH, TOC, and major inorganic ions in the runoff from three subcatchments, there was very little variati on in the acid/base character of TOC. Thus organic acids in the Svartberget catchment share a common set of acid/base properties despite markedly diff erent subcatchment drainage patterns, vegetation, and soils. The dissociati on behavior of organic acids at Svartberget could be described with high pr ecision (R-2 = 0.91, P < 0.001, and n = 115) by a triprotic acid analog mod el (pK(al) = 2.5, pK(a2) = 4.0, and pK(a3) = 5.8), together with the measur ed site density of organic acids (8.6 <plus/minus> 0.8 mu eq (mg TOC)(-1)), A Gaussian pK(a) distribution (mu = 4.20 and sigma = 1.43) predicted organ ic acid dissociation with similar precision (R-2 = 0.91, p < 0.001, and n = 94). Variations in site density among the tributary streams could largely be explained by aluminum complexation. Sites with lower measured site densi ties had greater concentrations of organically bound Ai. Thus Al binding re duces the potential release or neutralization of H+ by organic acids.