Response of lake chemistry to changes in atmospheric deposition and climate in three high-elevation wilderness areas of Colorado

• Published in: Biogeochemistry 2011-04, Vol.103 (1-3), p.27-43
• Main Authors: Mast, M. Alisa, Turk, John T, Clow, David W, Campbell, Donald H
• Format: Article
• Language: English
• Subjects: Air temperature; Alpine; Atmosphere; atmospheric deposition; Biogeochemistry; Biogeosciences; Climate; Climate change; Climate models; Climatic data; climatic zones; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Elevation; Engineering and environment geology. Geothermics; Environmental Chemistry; Exact sciences and technology; Freshwater; Geochemistry; Global warming; hydrochemistry; Hydrology; Hydrology. Hydrogeology; Lakes; Life Sciences; Limnology; Mineralogy; Mountain regions; Nitrogen; Pollution, environment geology; Precipitation; Pyrite; Silicates; Sulfates; Sulfur; Sulfur dioxide; Surface water; Trends; Water geochemistry; Watersheds; Weathering; Wilderness; Wilderness areas
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-010-9443-4

Trends in precipitation chemistry and hydrologic and climatic data were examined as drivers of long-term changes in the chemical composition of high-elevation lakes in three wilderness areas in Colorado during 1985-2008. Sulfate concentrations in precipitation decreased at a rate of −0.15 to −0.55 μeq/l/year at 10 high-elevation National Atmospheric Deposition Program stations in the state during 1987-2008 reflecting regional reductions in SO₂ emissions. In lakes where sulfate is primarily derived from atmospheric inputs, sulfate concentrations also decreased although the rates generally were less, ranging from −0.12 to −0.27 μeq/l/year. The similarity in timing and sulfur isotopic data support the hypothesis that decreases in atmospheric deposition are driving the response of high-elevation lakes in some areas of the state. By contrast, in lakes where sulfate is derived primarily from watershed weathering sources, sulfate concentrations showed sharp increases during 1985-2008. Analysis of long-term climate records indicates that annual air temperatures have increased between 0.45 and 0.93°C per decade throughout most mountainous areas of Colorado, suggesting climate as a factor. Isotopic data reveal that sulfate in these lakes is largely derived from pyrite, which may indicate climate warming is preferentially affecting the rate of pyrite weathering.