Groundwater and surface water flow to the Merced River, Yosemite Valley, California: super(36)Cl and Cl super(-) evidence

• Published in: Water resources research 2014-03, Vol.50 (3), p.1943-1959
• Main Authors: Shaw, Glenn D, Conklin, Martha H, Nimz, Gregory J, Liu, Fengjing
• Format: Article
• Language: English
• Subjects: Freshwater
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2013WR014222

Our current understanding of water fluxes and flow paths within the mountain block is limited, and improved understanding is necessary to assess hydrology more accurately above the mountain front. Source waters and the processes controlling their mixing were characterized in the Merced River basin within Yosemite National Park, California, using super(36)Cl and Cl super(-), supported by super(222)Rn, [delta] super(18)O, [delta]D, and streamflow data. Streams, snow, groundwater, and springs were sampled seasonally from July 2004 to October 2007. Three source water end-members were identified: (i) near surface runoff of recent meltwater containing bomb-pulse super(36)Cl ( super(36)Cl sub(BP)), (ii) shallow, evapotranspired groundwater, and (iii) groundwater containing Cl super(-) derived through extended rock interaction. Both groundwater end-members mix in Yosemite Valley and then later discharge to the Merced River. Near surface runoff dominates all stream hydrographs during snowmelt, whereas the two groundwater end-members become significantly more important during base flow. Tributaries consist of mixtures of the shallow evapotranspired groundwater and near surface runoff, whereas the Merced River is composed of the mixture of all source water end-members. Snow is not an obvious end-member, and elevated super(36)Cl sub(BP) in the near surface runoff suggests that super(36)Cl sub(BP) was retained efficiently, and is being slowly released as meltwater interacts with the soil. The use of super(36)Cl as a natural tracer is important in revealing the processes controlling streamflow generation in large montane catchments and the results will be helpful in configuring and calibrating hydrologic models. Key Points * Chlorine-36 is used to investigate groundwater and surface water interactions * Complex mixing of source waters is observed in a large mountain catchment * Significant retention of chlorine is observed within high alpine catchments