Influence of Bedrock Geology on Water Chemistry of Slope Wetlands and Headwater Streams in the Southern Rocky Mountains

Abstract

We characterized the water chemistry of nine slope wetlands and adjacent headwater streams in Colorado subalpine forests and compared sites in basins formed on crystalline bedrock with those formed in basins with a mixture of crystalline and sedimentary bedrock. The pH, Ca2+, Mg2+, NH4+, acid neutralizing capacity, and electrical conductivity of wetland porewater and streamwater were higher in the basins with mixed geology. Bryophyte cover was higher in lower pH, crystalline basins, and vascular plant cover was higher in the mixed bedrock basins. On average, wetland porewater had lower pH and higher concentrations of dissolved organic carbon (DOC) and nitrogen and several other ions than streamwater; however, because discharge from these small wetlands is low, their direct influence on stream solute concentrations was generally undetectable. Dilution altered stream solute concentrations during peak flow in both basin types, but had little effect on wetland chemistry. In contrast to other solutes, the concentration of DOC in streams increased marginally during peak runoff and its concentration in wetland porewater was stable throughout the year. These findings further knowledge of the influence of watershed characteristics on wetland and stream chemistry and will inform future decisions regarding conservation and management in headwater basins.