Effects of Heterogeneous Stream‐Groundwater Exchange on the Source Composition of Stream Discharge and Solute Load

Log jams alter gradients in hydraulic head, increase the area available for hyporheic exchange by creating backwater areas, and lead to the formation of multiple channel branches and bars that drive additional exchange. Here, we numerically simulated stream‐groundwater interactions for two constructed flume systems—one without jams and one with a series of three jams—to quantify the effects of interacting jam structures and channel branches on hyporheic exchange at three stream flow rates. In simulations without jams, average hyporheic exchange rates ranged from 2.1 × 10−4 to 2.9 × 10−4 m/s for various stream discharge scenarios, but with jams, exchange rates increased to a range of 1.3 × 10−3–3.5 × 10−3 m/s. Largely due to these increased hyporheic exchange rates, jams increased stream‐groundwater connectivity or decreased the turnover length that stream water travels before interacting with the hyporheic zone, by an order of magnitude, and drove long flow paths that connected multiple jams and channel threads. Decreased turnover lengths corresponded with greater reaction significance per km, a measure of the potential for the hyporheic zone to influence stream water chemistry. For low‐flow conditions, log jams increased reaction significance per km five‐fold, from 0.07 to 0.35. Jams with larger volumes led to longer hyporheic residence times and path lengths that exhibited multiple scales of exchange. Additionally, the longest flow paths connecting multiple jams occurred in the reach with multiple channel branches. These findings suggest that large gains in hydrologic connectivity can be achieved by promoting in‐stream wood accumulation and the natural formation of both jams and branching channels.

Section: Resultssupporting

confidence: 89%

Laboratory Flume and Numerical Modeling Experiments Show Log Jams and Branching Channels Increase Hyporheic Exchange

Wilhelmsen

Sawyer

Marshall

et al. 2021

“…However, beyond modeling uncertainties in the lowland loess areas, this mismatch is most likely explained by an effect of the interactions between stream water and the nearby mining lake water (impacted by open water evaporation) through complex groundwater dynamics in this region (Z.‐Y. Zhang et al., 2021). Note that the well‐matched two depleted observations at HG were sampled during the first flow‐events after dry summers, likely before stream‐lake hydraulic connectivity was re‐established.…”

Section: Discussionmentioning

confidence: 99%

Upscaling Tracer‐Aided Ecohydrological Modeling to Larger Catchments: Implications for Process Representation and Heterogeneity in Landscape Organization

Yang

Tetzlaff

Müller

et al. 2023

Ecohydrological partitioning strongly influences the provision of water resources in terms of quantity, quality, location, and timing; thus, fundamentally affecting water-related ecosystem services (Brauman, 2015). In larger scale catchments (>100 km 2 ), ecohydrological functioning often exhibits strong spatio-temporal variability due to small-scale process heterogeneity and non-linearity, both of which result in often marked catchment-wide contrasts in landscape organization (Hunt et al., 2021;Skøien et al., 2003;Tetzlaff et al., 2011). Process-based models have been widely adopted for capturing such catchment functional heterogeneity, as well as its responses to environmental changes (Thirel et al., 2015). Efforts of the catchment modeling community have been progressively improving the physical realism of process conceptualization (Beven, 2002;Clark et al., 2017;Tetzlaff et al., 2008). As part of this trend, stable isotopes of water (i.e., 𝐴𝐴 𝐴𝐴 2 H and 𝐴𝐴 𝐴𝐴 18 O ), as ideal tracers, have received more attention and been increasingly integrated into process-based modeling . As complementary to the use of more traditional hydrometric data (Fenicia et al., 2008), isotopic tracer information has provided more direct evidence of the velocity of water particle transport and allowed inference of catchment-scale water age distributions (

“…Zhang et al. (2021) could evaluate the interplay of stream‐groundwater exchange and in‐stream solute loadings with their model for an extended version of hydrologic turnover. They obtained ratios of 20/80 for contributing reach length to catchment outlet water composition.…”

Section: Discussionmentioning

confidence: 99%

“…Exchange flows in the forested streams with their coarse streambed and complex morphological structures seem to be dominated by larger‐scale morphological features and subsurface structures that remain independent of flow over extended periods (e.g., Schmadel et al., 2017). There is increasing evidence that general patterns of losing or gaining stream reaches tend to be spatially persistent (Frye, 2013; Ward et al., 2016; Zhang et al., 2021). In contrast, the lowland agricultural streams were characterized by temporarily variable exchange patterns (Figure 5).…”

Section: Discussionmentioning

confidence: 99%

Hydrologic Turnover Matters — Gross Gains and Losses of Six First‐Order Streams Across Contrasting Landscapes and Flow Regimes

Jähkel

Graeber

Fleckenstein

et al. 2022

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