Insights into hydrologic and hydrochemical processes based on concentration‐discharge and end‐member mixing analyses in the mid‐Merced River Basin, Sierra Nevada, California

Abstract

Both concentration‐discharge relation and end‐member mixing analysis were explored to elucidate the connectivity of hydrologic and hydrochemical processes using chemical data collected during 2006–2008 at Happy Isles (468 km2), Pohono Bridge (833 km2), and Briceburg (1873 km2) in the snowmelt‐fed mid‐Merced River basin, augmented by chemical data collected by the USGS during 1990–2014 at Happy Isles. Concentration‐discharge (C‐Q) in streamflow was dominated by a well‐defined power law relation, with the magnitude of exponent (0.02–0.6) and R2 values (p < 0.001) lower on rising than falling limbs. Concentrations of conservative solutes in streamflow resulted from mixing of two end‐members at Happy Isles and Pohono Bridge and three at Briceburg, with relatively constant solute concentrations in end‐members. The fractional contribution of groundwater was higher on rising than falling limbs at all basin scales. The relationship between the fractional contributions of subsurface flow and groundwater and streamflow (F‐Q) followed the same relation as C‐Q as a result of end‐member mixing. The F‐Q relation was used as a simple model to simulate subsurface flow and groundwater discharges to Happy Isles from 1990 to 2014 and was successfully validated by solute concentrations measured by the USGS. It was also demonstrated that the consistency of F‐Q and C‐Q relations is applicable to other catchments where end‐members and the C‐Q relationships are well defined, suggesting hydrologic and hydrochemical processes are strongly coupled and mutually predictable. Combining concentration‐discharge and end‐member mixing analyses could be used as a diagnostic tool to understand streamflow generation and hydrochemical controls in catchment hydrologic studies.

Concentration‐Discharge Relations in the Critical Zone: Implications for Resolving Critical Zone Structure, Function, and Evolution

“…In a study of C‐Q relations in headwater streams of the Sierra Nevada, Hunsaker and Johnson () observed chemostatic behavior for bedrock‐derived solutes and nonchemostatic behavior for biologically active solutes, with the former showing slight dilution and the latter, deriving from soil solutions, showing increased concentration during storm events. Through end member mixing analysis, Liu et al () proposed that C‐Q hysteresis (manifest as a difference in power law exponent between the ascending and descending limbs of the snowmelt hydrographs for Sierra Nevada streams) are attributable to larger deep groundwater contributions on the ascending limb.…”

Hydrologic functioning of the deep critical zone and contributions to streamflow in a high‐elevation catchment: Testing of multiple conceptual models

“…Additionally, changes in the chemistry of groundwater as it traverses the CZ provide insights into geochemical processes regulating long‐term CZ evolution (McIntosh et al, ). Understanding stream water composition, including variation in concentration‐discharge relations across multiple elements (Ameli et al, ; Chorover et al, ; Godsey, Kirchner, & Clow, ; H. Kim et al, ; Liu, Conklin, & Shaw, ; McIntosh et al, ; Trostle et al, ), requires the proper identification of not only geochemically distinct water stores for a given CZ structure but also time‐dependent variation in their relative contributions to streamflow. Most important, this approach enables moving from a “black box” level of understanding, that is, considering the whole CZ structure as a simple well‐mixed bucket, to a “grey box”‐level understanding that acknowledges distinct CZ stores, their time‐variant inputs to surface water, and the residence times of groundwater in different stores.…”

Hydrochemical Changes and Influencing Factors in the Dongkemadi Region, Tanggula Range, China

“…The ion concentration decreased with the increase in runoff, which is mainly affected by the eluviation effect of runoff ions. Some studies have shown that there exists a power function relationship (C = a × Q b ) between runoff and the concentration of the dissolved load in the river water in most rivers [20,21]. C is the ion concentration, Q is the daily average runoff, and a and b are the fitting parameters.…”