HR: 1340h
AN: U53A-0703    [Abstracts]
TI: Impact of Retreating Glaciers in an Intermontane Andean Watershed: Hydrochemical Analysis From the Callejon de Huaylas, Per\'{u}
AU: * Mark, B G
EM: mark.9@osu.edu
AF: Department of Geography, The Ohio State University, 154 N Oval Mall, Columbus, OH 43210 United States
AU: McKenzie, J M
EM: jeff_mck@yahoo.com
AF: Department of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AU: Welch, K A
EM: welch.189@osu.edu
AF: Byrd Polar Research Center, 1090 Carmack Road The Ohio State University, Columbus, OH 43210 United States
AB: The Callejon de Huaylas, Per\'{u}, is a well-populated 5000 km$^{2}$ watershed of the upper Rio Santa river draining the glacierized Cordillera Blanca. This tropical intermontane region features rich agricultural diversity and valuable natural resources, but currently receding glaciers are causing concerns for future water supply. A major question concerns the relative contribution of glacier meltwater to the regional stream discharge-from first order basins to the whole watershed. In July, 2004, we collected 37 water samples from streams, springs and precipitation over a 2000 m vertical range within the watershed and analyzed them for major dissolved ions and isotopic (\delta$^{18}$O) composition. The water chemistry is used to establish the extent of variability in the surface waters, and to identify different hydrologic end-member components. \delta$^{18}$O values for the waters range from -4.29\permil to -5.28\permil. There is a consistent trend towards lighter isotopes with greater percentage of glacier coverage in tributary stream catchments of the Rio Santa, with some exceptions due to evaporative enrichment in lakes. Samples taken along transects of these glacierized tributary streams become more isotopically enriched with lower elevation and greater distance from the glaciers. However, waters from the Rio Santa become less enriched with lower elevation. We hypothesize that the distribution of glacier mass in the mountain range causes a greater volume of glacial meltwater to join the Rio Santa at lower elevations. The water generally has a Ca-Mg-HCO$_{3}$ chemical signal. Samples along transects of tributary valleys show an increase in TDS and the Na:Mg concentration ratio with decreasing elevation. We see geochemical evidence for a small groundwater source in the tributaries and the Rio Santa. We propose that distinct chemical signatures of source water end-members may provide a means of quantifying the volumetric contribution of glacier meltwater over time.
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1863 Snow and ice (1827)
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
SC: Union [U]
MN: 2004 AGU Fall Meeting