Paper No. 9
Presentation Time: 9:00 AM-6:00 PM
MAINTAINING RIVER FLOW IN AN ALPINE KARST SETTING; THE ROLES OF SNOWMELT AND SHALLOW AND DEEP GROUNDWATER
TOBIN, Benjamin W., Biology, University of California, Merced, Merced, CA 94353 and SCHWARTZ, Benjamin F., Edwards Aquifer Research and Data Center, and Department of Biology, Texas State University, Freeman Aquatic Station, 601 University Drive, San Marcos, TX 78666, bt1171@txstate.edu
Over the last decade, groundwater in alpine basins has been shown to be significant. Due to distinct wet and dry seasons, the ability of these aquifers to store and subsequently discharge water into rivers, is crucial to maintaining stream flows downstream. However, alpine karst within the USA has received little attention in these studies. Using geochemical, stable isotope, and discharge data from a three year period (2010-2012) in the Mineral King Valley of the southern Sierra Nevada, California, USA, this study aims to quantify the relative contributions of snowmelt, shallow non-karst groundwater, and karst groundwater along four stream-aquifer transects. These transects include all the tributaries that form the East Fork of the Kaweah River in the Mineral King Valley. The basin geology consists primarily of granitic bedrock with a series of northwest–southeast trending bands of metamorphic rocks. These bands contain karstified marble, which accounts for 8% of the surface area of the basin.
We used end-member mixing models to assess the relative contributions of each of the three components to discharge over time. In each transect, the contribution of each component to total discharge varies on a distinctly seasonal basis. During high flow conditions, stream flow and chemistry is generally dominated by snowmelt and short-term storage in wet-meadows. Seasonal low flow conditions in 2011 showed snowmelt accounted for 23% of discharge, meadows accounted for 30%, and karst aquifers accounted for 47% of the discharge leaving the Mineral King Valley. During high flow of a dry year (2012), those percentages changed to 35%, 33%, and 32%, respectively. However, during high flow of a wet year (2011), the contributions changed to 38%, 26%, 36 %, respectively. These data suggest that storage in alpine karst systems is very important during both low flow and high flow conditions, and that it plays a substantial and important role in maintaining flow and providing water to the river on a year-round basis.
