Hill, KennethÌý1Ìý;ÌýHamann, HillaryÌý2Ìý;ÌýWilliams, MarkÌý3Ìý;ÌýCaine, NelÌý4
1ÌýÀÖ²¥´«Ã½ at Boulder. Department of Geography and INSTAAR
2ÌýÀÖ²¥´«Ã½ at Colorado Springs. Department of Geography and Environmental Studies
3ÌýÀÖ²¥´«Ã½ at Boulder. Department of Geography and INSTAAR
4ÌýÀÖ²¥´«Ã½ at Boulder. Department of Geography and INSTAAR
Solutes are discharged from seasonal snowpacks in the form of an ionic pulse, where up to 80% of the solute load is released in the first 20% of snowmelt. An outstanding question is how the quality of surface waters responds to this ionic pulse. We collected surface waters for chemical and isotopic analysis every 4 hours during the first 30 days of snowmelt runoff from the 8-ha Martinelli catchment, Colorado Front Range. During a one week period at the onset of snowmelt, concentrations of base cations and acid anions peaked at noon each day and followed a diurnal signal. Anions of strong acids displayed the most significant and rapid diurnal variations with nitrate increasing by a factor of 4.0 over a twenty-hour period at the onset of melt (14.5 µeq/L < NO3-Ìý< 57.1 µeq/L). δ18O values also followed a diurnal signal, exhibiting minimum values at noon with differences of almost 2‰ over diurnal cycles. Maximum daily discharges and minimum daily solute values occurred between 12:00 and 16:00, along with the most enriched δ18O values. These results suggest that the release of solutes from the snowpack in an ionic pulse caused concentrations of base cations and anions to increase daily by a factor of 1.5 to 4.0. The inverse relationship between discharge and solute concentration was lost following the first week of snowmelt as flows rapidly increased on the rising limb of the hydrograph.