Do benthic invertebrates use hyporheic refuges during streambed drying? A manipulative field experiment in nested hyporheic flowpaths

Abstract

The existence of resilience mechanisms related to a disturbance, such as invertebrate migrations into the hyporheic zone (HZ, saturated subsurface interstices), promotes persistence of benthic communities in river ecosystems. Water exchanges through the HZ, which influence the distribution of biota, are heterogeneous at different scales, determining nested hyporheic flowpaths. The effect of these nested exchanges on the use of the hyporheic refuges by benthic invertebrates is still unknown. We simulated streambed drying in a stream section where hydrological exchanges were considered at riffle (upstream or downstream of riffles) and floodplain (downstream end of a floodplain) scales. Physicochemical indicators determined that local hyporheic flowpaths (up-and downwelling zones) were nested in a large-scale downwelling section of the river. In this situation, the effect of 24 h of experimental drying on the distribution of invertebrates was examined at three sediment depths to follow their migrations into the HZ. Whereas invertebrate assemblages did not change in the control channel, abundance of benthic invertebrate increased in the HZ of the impact channel (up to seven-fold). Changes occurred rapidly (15-24 h) and only upstream of riffle where surface water down-welled. The migration was taxon-specific and concerned the most abundant benthic taxa that temporarily colonize the HZ ("temporary hyporheos," e.g., Leuctra cf. fusca, Baetis sp., Caenis sp., Orthocladiinae, Tanypodinae). In the context of climate change, hyporheic refuge use will promote persistence of communities facing the increasing frequency of extreme hydrological events. Improved knowledge about the distribution and function of these refuges is becoming crucial for river managers. to induce physical and hydrological modifications in rivers and streams (Rolls, Leigh, & Sheldon, 2012). Flow regimes are especially affected with more extended low flows and higher frequencies of extreme events, such as floods and droughts (Dai, 2011;Lehner, Döll, Alcamo, Henrichs, & Kaspar, 2006). During severe events, threats to the aquatic environment are likely to increase, with resistance and resilience becoming crucial properties of communities. Resilience, that is, the return time to a stable state following a perturbation (Gunderson, 2000), may be enhanced by the use of in-stream refuges by benthic invertebrates (Lake, 2003). Refuges are places where the negative effects of disturbance are weaker than in the surrounding area (Lancaster & Belyea, 1997). Refuges that facilitate post-drying resilience include the use of microhabitats available in the streambed (Stubbington, 2012) or within the alluvia. In permeable streambeds, the hyporheic zone (HZ) may offer preferable living conditions for invertebrates during hydrological disturbance (Angelier, 1953;Dole-Olivier & Marmonier, 1992a;Marmonier & Dole, 1986). The hyporheic refuge hypothesis (HRH, Palmer, Bely, & Berg, 1992) proposes that benthic invertebrates increase their survival of adverse condition...

Is the Hyporheic Zone Relevant beyond the Scientific Community?

“…The HZ is considered a refuge for aquatic organisms, especially during adverse environmental conditions, such as floods, droughts, and heat waves [19,20,203] (Figure 2). Disturbances are generally reduced in the HZ compared to the benthic zone due to its capacity for retaining water during drying periods and its greater stability during floods [99].…”

Interplay of hydrology, community ecology and pollutant attenuation in the hyporheic zone

“…Despite the dynamics of rivers, seasonality may result in a set of drastic changes in water flow conditions (Gasith & Resh 1999) and determine the location and extent of the HZ (Wondzell 1993). Nonetheless, the HZ buffers the amplitude of this variation, acting as a potential refuge of riverbed biota during adverse conditions (Maazouzi et al 2017). This has important implications for variations in the composition and abundance of organisms throughout the year (Stubbington et al 2009).…”

The role of fine sediment characteristics and body size on the vertical movement of a freshwater amphipod

“…The sediments immediately below the active riverbed and the hyporheic zone are widely recognised as integral to lotic ecosystem functioning (Bo et al, 2007;Krause et al, 2011;Stanford & Ward, 1988), serving as the ecotone between surface and groundwater ecosystems (Hancock, 2002) and frequently acting as a refugium for benthic fauna during adverse conditions in surface water habitats (Dole-Olivier, Marmonier, & Beffy, 1997;Maazouzi et al, 2017;Wood, Boulton, Little, & Stubbington, 2010). Typically, the hyporheic zone is limited in spatial extent to around 1 m vertically below the riverbed (Williams & Hynes, 1974), although some lotic fauna have been recorded up to 10 m below the riverbed and several kilometres laterally (Stanford & Ward, 1988).…”