Mesocosm experiments reveal the direction of groundwater–surface water exchange alters the hyporheic refuge capacity under warming scenarios

Abstract

Climate change is expected to affect hydrologic and thermal regimes of river ecosystems. During dry periods when river flows decrease and water temperatures increase, the hyporheic zone (HZ) can provide a refuge to surface aquatic invertebrates and enhance the resilience capacity of riverine ecosystems. However, shifts from up‐ to downwelling flow conditions in the HZ could jeopardise this capacity. Using laboratory mesocosms and high‐resolution fibre‐optic distributed temperature sensing, we explored the combined effects of five different increased surface water temperature treatments (from 15 to 27°C at 3°C intervals) and the direction of water exchange on the ability of Gammarus pulex (Crustacea: Amphipoda: Gammaridae) to migrate into the HZ as a response to warming. We determined the survival rates of this ubiquitous hyporheic dweller and its rates of consumption of alder (Alnus glutinosa; Betulaceae) leaf litter in the HZ. Results showed that at increasing surface water temperature, leaf‐litter breakdown was observed at a greater depth in the sediments under downwelling flow conditions, that is, G. pulex migrated deeper into the HZ compared with upwelling conditions, resulting in greater survival rates (64 ± 11 vs. 44 ± 10%). However, under both upwelling and downwelling conditions, we found evidence for potential use of the hyporheic zone as a thermal refuge for G. pulex. Below sediment depths of 25 cm, temperatures remained low (<22°C) even when surface waters were at 27°C, so temperatures deep in the hyporheic zone never exceeded critical thermal thresholds for G. pulex. This study provides evidence that alterations to the direction of groundwater–surface water exchange can alter the capacity of the HZ to provide a refuge for benthic invertebrates, thereby affecting the resilience of river communities to warming under climate change.

Solute Transport and Transformation in an Intermittent, Headwater Mountain Stream with Diurnal Discharge Fluctuations

“…One tool that has proven effective in assessment of combined transport and transformation is the Resazurin-Resorufin (hereafter Raz-Rru, respectively) tracer system, in which Raz undergoes an irreversible transformation to Rru in the presence of metabolically active microbial communities [70][71][72][73]. The Raz-Rru system has broadly been used to identify the portion of transient storage that is metabolically active, and has been used to assess reactivity in biofilms [74], the benthic zone [75,76], vegetation beds [77], stream-and lakebed sediments [78][79][80][81], and whole stream reaches [82][83][84][85]. Interpretation of Raz-Rru information commonly relies upon inverse modeling that enforces a conceptual model with binary divisions of the system into zones such as channel or storage (based on the importance of advection and relative timescales of storage) or metabolically active or inactive storage (based on transformation rates) [83,86].…”

Beneath the surface: Application of transparent super absorbent polymer substrates to track faunal activity within the sediment layer

“…It has been hypothesised that the hyporheic zone may act as a nursery and refugium for benthic invertebrates during adverse surface conditions such as supra seasonal drought conditions (Boulton, 2003; Wood et al., 2010), ephemeral and intermittent streams (Datry, 2012; Loskotová, Straka, & Pail, 2019), and high flows (Dole‐Olivier, Marmonier, & Beffy, 1997); however, evidence is still equivocal. Recently the hyporheic zone has also been demonstrated to act as a thermal refuge from warming surface waters (Folegot et al., 2018) associated with the cooler temperatures often located in the deeper substrates. It is likely that subsurface sediments may also provide some protection from hydropeaking activities that instigate sharp thermal changes in the water temperature regime.…”

“…Gammarus fossarum was selected as the focal organism for the experiments. Gammaridae are commonly used in experimental studies including those examining faunal behaviour in the hyporheic zone (Folegot et al., 2018; Little & Altermatt, 2018; Vadher et al., 2018), and G. fossarum is a widespread and abundant model organism in Switzerland where the experiments were conducted (Altermatt et al., 2014). It is known to colonise benthic and hyporheic habitats, thereby enabling observation of a taxa that crosses habitat boundaries freely and, in many communities, dominates in terms of biomass (Robinson, Uehlinger, & Monaghan, 2003).…”

“…Studies that have investigated the behaviour of organisms to environmental cues (e.g. vertical hydrological exchange, streambed drying events) within subsurface sediments have focussed on the vertical distribution of biota by measuring their final position (Foy & Thistle, 1991; Mathers, Hill, Wood, & Wood, 2019; Mathers et al., 2014; Stumpp & Hose, 2013), by using a proxy such as leaf litter breakdown rates (Folegot, Krause, Mons, Hannah, & Datry, 2018), or by assuming use of subsurface sediments when individuals are not observed above surface substrates (Vadher, Stubbington, & Wood, 2015). Stumpp and Hose (2017) employed transparent laboratory columns to assess the burrowing ability of a freshwater amphipod in redistributing fine sediment thereby creating migration networks.…”

Evaluating a Coupled Phenology‐Surface Energy Balance Model to Understand Stream‐Subsurface Temperature Dynamics in a Mixed‐Use Farmland Catchment

“…Stream temperature is an important variable that affects ecosystem functioning and controls biogeochemical processes in aquatic systems (Allan & Castillo, ; Baranov et al, ; Folegot et al, ; Webb et al, ). Increased stream temperature can negatively impact water quality and the health of aquatic ecosystems (Calow & Petts, ; Folegot et al, ; Roth et al, ), while water temperature at the outlet of catchments controls water quality in receiving waters such as lakes and the coastal ocean (Safaie et al, ). Stream thermal regimes are primarily driven by climatic conditions and are also influenced by a host of other factors, including topographic conditions, stream discharge, riparian vegetation and land use near the stream, and interactions with the subsurface environment (Caissie, ; Hannah & Garner, ).…”