Characterizing hyporheic exchange processes using high‐frequency electrical conductivity‐discharge relationships on subhourly to interannual timescales

Abstract

Concentration‐discharge (C‐Q) relationships are often used to quantify source water contributions and biogeochemical processes occurring within catchments, especially during discrete hydrological events. Yet, the interpretation of C‐Q hysteresis is often confounded by complexity of the critical zone, such as numerous source waters and hydrochemical nonstationarity. Consequently, researchers must often ignore important runoff pathways and geochemical sources/sinks, especially the hyporheic zone because it lacks a distinct hydrochemical signature. Such simplifications limit efforts to identify processes responsible for the transience of C‐Q hysteresis over time. To address these limitations, we leverage the hydrologic simplicity and long‐term, high‐frequency Q and electrical conductivity (EC) data from streams in the McMurdo Dry Valleys, Antarctica. In this two end‐member system, EC can serve as a proxy for the concentration of solutes derived from the hyporheic zone. We utilize a novel approach to decompose loops into subhysteretic EC‐Q dynamics to identify individual mechanisms governing hysteresis across a wide range of timescales. We find that hydrologic and hydraulic processes govern EC response to diel and seasonal Q variability and that the effects of hyporheic mixing processes on C‐Q transience differ in short and long streams. We also observe that variable hyporheic turnover rates govern EC‐Q patterns at daily to interannual timescales. Last, subhysteretic analysis reveals a period of interannual freshening of glacial meltwater streams related to the effects of unsteady flow on hyporheic exchange. The subhysteretic analysis framework we introduce may be applied more broadly to constrain the processes controlling C‐Q transience and advance understanding of catchment evolution.

The Role of Hyporheic Connectivity in Determining Nitrogen Availability: Insights From an Intermittent Antarctic Stream

“…Surprisingly, our data suggest that variations in streamflow did not result in a shift from transport‐to reaction‐limitation for remineralization and nitrification in the hyporheic zone as concentrations remained fairly stable. It is notable that, even in well‐studied perennial systems, there is conflicting evidence of how hyporheic exchange scales with discharge across geomorphologies (Lee et al., 2020; Ward et al., 2012; Wondzell, 2006; Wondzell & Gooseff, 2013; Zimmer & Lautz, 2014) and how N uptake rates are affected (Webster et al., 2003), although evidence from MDV streams suggests hyporheic turnover increases during periods of higher flow (Singley et al., 2017). While we cannot constrain actual rates on any particular process from the data, it is notable that cycling of autochthonous N in the hyporheic zone of Von Guerard Stream must occur on timescales sufficiently fast to counteract transport losses, or shifts in residence time, that can occur due to successive flow pulses (Singh et al., 2020).…”

Hydrological regulation of chemical weathering and dissolved inorganic carbon biogeochemical processes in a monsoonal river

“…Numerous studies have demonstrated that most dissolved solute concentrations negatively correlate with discharge, which can be represented as a power‐law function (Ali et al, 2017; Clow & Mast, 2010; Diamond & Cohen, 2018; Godsey, Kirchner, & Clow, 2009; Gwenzi, Chinyama, & Togarepi, 2017; Kim, Dietrich, Thurnhoffer, Bishop, & Fung, 2017; Koger, Newman, & Goering, 2018; Musolff, Schmidt, Selle, & Fleckenstein, 2015; Rose, Karwan, & Godsey, 2018; Rue et al, 2017; Singley et al, 2017): where a is a constant, and b reflects the index of the deviation from chemostatic behaviour (Clow & Mast, 2010). When b is close to 0, there is a weak relationship between solute concentrations and discharge, implying chemostatic behaviour (Godsey et al, 2009); when b > 0, solute concentrations increase with increasing discharge (Musolff et al, 2015); however, when b = −1, the solute contents decrease with increasing discharge, when Q is the only control on C (Godsey et al, 2009).…”

Transit Times and Rapid Chemical Equilibrium Explain Chemostasis in Glacial Meltwater Streams in the McMurdo Dry Valleys, Antarctica

“…Along these lines, temporal changes in reactive surface area have also been hypothesized to control C‐q dynamics (Godsey et al, ). In MDV streams, highly unsteady flows can influence the connectivity of hyporheic flow paths and storage/flushing of solutes (Koch et al, ; Singley et al, ). Similarly, expansion and contraction of the wetted perimeter between high and low flows may cause the dissolution and precipitation of channel‐margin salt crusts.…”