Direct observations of the effect of fine sediment deposition on the vertical movement of Gammarus pulex (Amphipoda: Gammaridae) during substratum drying

Abstract

Benthic macroinvertebrates inhabit the streambed sediments of temporary streams during drying events. Fine sediment (\ 2 mm in diameter) deposition and clogging of interstitial pathways reduces the connectivity between benthic and subsurface habitats, potentially inhibiting macroinvertebrate vertical movements. Direct observations within subsurface sediments are, however, inherently difficult. As a result, confirmation of macroinvertebrate vertical movement, and the effect of fine sediment, is limited. We used laboratory mesocosms containing transparent gravel sized particles (10-15 mm) to facilitate the direct observation and tracking of vertical movements by Gammarus pulex in response to water level reduction and sedimentation. Seven sediment treatments comprised two fine sediment fractions (small: 0.125-0.5 mm, coarse sand: 0.5-1 mm) deposited onto the surface of the substrate, and a control treatment where no fine sediment was applied. We found that G. pulex moved into the subsurface gravel sediments in response to drying, but their ability to remain submerged during water level reduction was impeded by fine sediment deposition. In particular deposition of the coarser sand fraction clogged the sediment surface, limiting vertical movements. Our results highlight the potential effect of sedimentation on G. pulex resistance to drying events in streams.

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

“…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).…”

“…To date, we are aware of only two studies that have sought to quantify the real-time activity levels of fauna within subsurface sediments, but these are associated with limitations and did not employ lotic flow conditions. Vadher, Leigh, Millett, Stubbington, and Wood (2017), and Vadher, Millett, and Wood (2018) Mathers et al, 2014). We selected the three flow treatments as vertical hydrological exchange has been shown to affect the distribution of macroinvertebrates but to date monitoring the behavioural attributes of individuals continuously within the subsurface has not been possible.…”

“…To date, we are aware of only two studies that have sought to quantify the real‐time activity levels of fauna within subsurface sediments, but these are associated with limitations and did not employ lotic flow conditions. Vadher, Leigh, Millett, Stubbington, and Wood (2017), and Vadher, Millett, and Wood (2018) utilised transparent acrylic particles to monitor the vertical migration of a freshwater amphipod in response to surface dewatering. In their experiments, the vertical distribution of amphipods was manually classified into 1mm and 5 cm intervals respectively, every 15 min prior to incremental water drawdown, providing a general vertical distribution profile over time.…”

Body size affects the vertical movement of benthic amphipods through subsurface sediments in response to drying

“…The ability of fauna to access the subsurface habitat reflects both sedimentary characteristics (Gayraud & Philippe, 2003;Vadher et al, 2018b) and faunal traits (Wickson et al, 2012;Loskotová et al, 2019). Sediment characteristics such as pore size, ratio of gravel framework to fine sediment matrix, and particle size and heterogeneity have been highlighted as key abiotic factors affecting the ability of invertebrate fauna to access subsurface sediments (Mathers et al, 2014;2019b;Vadher et al, 2017;Loskotová et al, 2019).…”

Understanding the effect of catchment characteristics on suspended sediment dynamics during flood events

“…In this context, studying the temporal dynamics of catchment sediment delivery during run‐off events is of value for several reasons: (a) identifying the provenance of fine sediment in catchments in terms of distance upstream and erosion processes generating the sediment and (b) identifying the sources responsible for delivering sediment late in the hydrograph, which is when many issues occur—such as fine sediment deposition and extended recession turbidity. Cobbly substrate embedding with fine sediment degrades benthic habitat (Anderson, Barrett, & Morrisey, ; Bryce, Lomnicky, & Kaufmann, ; Larsen, Vaughan, & Ormerod, ; Vadher, Millett, & Wood, ). Such deposition tends to occur in catchments with relatively high sediment concentrations late on event recessions, when more low energy zones become available to trap sediment and there is waning re‐entrainment potential (Hicks & Hoyle, ; Park et al, ).…”