Sensitivity to acidification of subalpine ponds and lakes in northwestern Colorado

Abstract/Summary

The chemical composition of 97 lakes and ponds in and near the Mount Zirkel Wilderness Area (MZWA) was studied during snowmelt of 1998 and 1999 to determine the magnitude of episodic acidification and the effects of acidification on amphibian reproductive success. Within the areas identified as sensitive to acidification based on granitic bedrock types, there was substantial variability in ANC that was likely related to differences in hydrologic flowpaths that control delivery of weathering products to surface waters. Many of the lakes are sensitive to acidification (summer and fall ANC< 100 eq/l), however, none of them appeared to be immediately threatened by episodic or chronic acidification. 22 ponds had minimum ANC of < 30 ueq/l, indicating that they are extremely sensitive to acidic deposition, however net acidity (ANC < 0) was not measured in any of the ponds. The lowest measured pH value was 5.4 and pH generally remained less than 6.0 throughout early summer in the most sensitive ponds, indicating that biological effects of acidification are possible at levels of atmospheric deposition measured during the study.