Abstract

Montane meadows are often areas of groundwater discharge. In this study we characterized the groundwater - surface water interactions of two meadow systems and their connectivity to the surrounding catchment . We analyzed groundwater elevation data in 24 wells in two meadows located in the southern Sierra Nevada. Well transects extended from the meadow centers near the stream, to the meadow edged, and into the adjacent forest—where wells were drilled into the weathered granite saprock layer. Water samples were collected from the monitoring wells and from streams associated with the meadow systems and analyzed for major ions and stable water isotopes. Ground water elevations in the monitoring wells were used to calculate daily evapotranspiration (ET) values. These values show that locations on the meadow slopes and near the meadow edges are losing water to the atmosphere at near potential evapotranspiration rates during the height of the growing season. ET signals from wells near the meadow streams are muted, likely due to the vegetation utilizing the available surface water at these locations. Wells installed in the saprock layer, outside of the meadow boundaries, show diurnal fluctuations in sync with fluctuations observed at the meadow edge. This trend persists after the meadow vegetation senesces, indicating that groundwater elevations in the meadow, especially near the meadow edge, are significantly influenced by the adjacent hillslope saprock layer and forest ET. Geochemical sampling results indicate that the meadow streams are predominantly fed by snowmelt in the spring and early summer, moving toward more influence from base flow in the late summer and early fall. Results from the geochemical analysis established the connections of the hillslope to the meadow water tables and of the meadow subsurface waters to the down-gradient streams. Our results indicate that the these meadows are directly connected to the shallow sub-surface processes in the up gradient sap rock layers and movement through the meadow systems plays a significant role in the timing of the release of subsurface water into the down gradient streams.

Citation

Conklin, M.H., Lucas, R.G. (2011): Hillslope and stream connections to water tables in montane meadows of the southern Sierra Nevada, California . Fall meeting, American Geophysical Union, December 2011. Abstract H43N-07..