Stream Centric Methods for Determining Groundwater Contributions in Karst Mountain Watersheds

Abstract

Climate change influences on mountain hydrology are uncertain but likely to be mediated by variability in subsurface hydrologic residence times and flow paths. The heterogeneity of karst aquifers adds complexity in assessing the resiliency of these water sources to perturbation, suggesting a clear need to quantify contributions from and losses to these aquifers. Here we develop a stream centric method that combines mass and flow balances to quantify net and gross gains and losses at different spatial scales. We then extend these methods to differentiate between karst conduit and matrix contributions from the aquifer. In the Logan River watershed in Northern Utah we found significant amounts of the river water repeatedly gained and then lost through a 35‐km study reach. Further, the direction and amount of water exchanged varied over space, time, and discharge. Streamflow was dominated by discharge of karst conduit groundwater after spring runoff with increasing, yet still small, fractions of matrix water later in the summer. These findings were combined with geologic information, prior subsurface dye tracing, and chemical sampling to provide additional lines of evidence that repeated groundwater exchanges are likely occurring and river flows are highly dependent on karst aquifer recharge and discharge. Given the large population dependent on karst aquifers throughout the world, there is a continued need to develop simple methods, like those presented here, for determining the resiliency of karst groundwater resources.

Increasing plant water stress and decreasing summer streamflow in response to a warmer and wetter climate in seasonally snow‐covered forests

“…These two variables were used to calculate HI (Horton, 1933): which is related to the proportion of available water used for vegetation growth and ET (Brooks et al, 2011; Troch et al, 2009; Voepel et al, 2011; Zapata‐Rios et al, 2015). The baseflow separation analyses to quantify potential plant available water (W) used here provide a transferrable and parsimonious approach that is consistent with the growing literature that suggests most precipitation infiltrate soils (e.g., Godsey, Kirchner, & Clow, 2009), that plants are able to access deeper water stores in addition to soil moisture (e.g., Goulden & Bales, 2019; Hu et al, 2010), and that streamflow is composed of a suite variable residence time waters (e.g., Kirchner, 2009; Neilson et al, 2018).…”

A Complicated Karst Spring System: Identified by Karst Springs Using Water Level, Hydrogeochemical, and Isotopic Data in Jinan, China

“…Karst aquifers crop out in approximately 12% of the global land surface and offer water resource for almost 25% of the world population [1][2][3][4]. In the past several decades, karst systems have been widely studied in aspects of the conceptual model [5][6][7], recharge sources [8][9][10], flow types [11,12], hydrogeochemical processes [13][14][15][16][17][18][19][20][21], hydrodynamics [22][23][24], responses to climate changes [25][26][27], and numerical modeling [28][29][30]. However, the heterogeneity and anisotropy of karst conduits and fractures created by uneven groundwater flow give rise to the complex hydrogeological conditions and make it difficult to understand and characterize the karst system [4,31,32].…”

Trace Element Export From the Critical Zone Triggered by Snowmelt Runoff in a Montane Watershed, Provo River, Utah, USA

“…During baseflow, when the river is dominated by groundwater inputs, major ion concentrations increased substantially between Soapstone and Woodland with inputs of solute-rich groundwater from carbonate bedrock. While we did not measure groundwater chemistry as part of our study, previous work in the Provo River watershed (Carling et al, 2015) and the Logan River in northern Utah (Neilson et al, 2018) describes contributions of solute-rich groundwater from carbonate bedrock to rivers during dry-season baseflow. During snowmelt runoff, the major ion concentrations remained low at Soapstone and were diluted at Woodland and Hailstone with the influx of snowmelt-flushed shallow soil water from the upper watershed.…”