Ground and Surface Water Interaction in Ephemeral Wetlands, San Luis Valley, Colorado

Abstract

Groundwater- surface water interactions were studied at Mishak Lakes and Blanca Wetlands, ephemeral wetlands located in the arid San Luis Valley of Colorado. Hydraulic conductivities and hydraulic gradients along with major ion chemistry and stable isotope composition of ground and surface water were determined. At Mishak Lakes, groundwater mounding occurs beneath the basins despite the presence of a laterally consistent low permeability layer, suggesting that recharge occurs through macropores. Isotope enrichment between sampling rounds was used to estimate recharge at approximately 51% of total surface water volume loss. The recharge rate has been estimated to be 4.3 mm/day. The estimated evaporation rate over the same time was estimated at 4.1 mm/day. At Blanca Wetlands, higher elevation basins receive a nearly constant supply of water, and recharge creates a locally high water table equal to the elevation to surface water near the basin margins. Isotope data indicates that recharge primarily occurs below the higher basins. As surface water flows into lower elevation basins more distant from the source, chloride replaces bicarbonate as the dominant anion, resulting in salt precipitation as the basins evaporate to completion.