Factors limiting the vertical movement and use of subsurface sediments by lotic macroinvertebrates in response to dewatering and surface drying

Climate change projections suggest increased frequency and duration of streambed drying in many regions across the globe. These predictions even apply to streams in temperate environments, which are typically characterised by perennial river flow. The subsurface sediments of streams are an important refuge for benthic invertebrates during streambed drying; this role may become more important given the predicted increased future extent and duration of stream drying. However the vertical movement of organisms into subsurface and hyporheic sediments, and factors affecting this movement, has received limited attention historically. The research in this thesis employed a series of laboratory experiments to examine the impact of sedimentological characteristics (particle size, porosity, sedimentation) on the vertical movement of macroinvertebrates. This research also used tightly controlled flume and field experiments to examine how the duration of drying events affected macroinvertebrate survival. Specifically, the laboratory studies used direct observation in transparent artificial mesocosms containing different sediment sizes and interstitial pore space volumes to examine the subsurface vertical movements of five lotic taxa displaying different biotic traits in response to water level reduction. The results indicated that lotic macroinvertebrates actively moved into subsurface sediments in response to water level reduction. The extent to which taxa moved vertically through sediments was: i) species-specific, and ii) restricted by sediment porosity. In addition, the research examined the effect of varying loads of fine sediment (particles < 2 mm) on the vertical movement of the freshwater shrimp, Gammarus pulex, through transparent mesocosms during water level reduction. The results demonstrate the limiting effect of fine sediment load and size on the ability of G. pulex to remain submerged as sand particles (0.5 - 1 mm) capable of bridging interstitial pathways into the subsurface impeded and prevented the movement of individuals into the subsurface. Finally, this thesis presents the results of flume and field mesocosm studies which examine the effect of surface water loss duration on the survivorship of G. pulex within the subsurface. These experiments demonstrate how increasing drying duration and variability in water quality can significantly reduce faunal survival within subsurface sediments. The results and synthesis illustrate the value of laboratory / mesocosm-based research and effective riverbed management to ensure instream ecology can access and utilise the vital hyporheic refuge in the face of increased drying due to climate change and anthropogenic management

Disaster risk management and cultural heritage: The perceptions of European world heritage site managers on disaster risk management

peer reviewedResearch into the sustainable management of the world's cultural heritage (CH) is increasing. This is due to the vulnerability of CH to climate-related disasters and the perceived contribution of CH to the achievement of broader sustainability goals. Despite the perceived benefits of bringing together CH and sustainability, researchers have identified barriers that slow integration. These barriers are theoretical and practical, and targeted research would help improve the resilience of our CH. This article aims to explore the perceptions of a group of UNESCO world heritage site managers (WHSM) on disaster risk management. A questionnaire was sent to WHSM via professional email boxes. The questionnaire consisted of 26 questions designed to explore the perception of WHSM. In total, 58 responses were received, and the results produced findings worthy of discussion. WHSM still have limited access to disaster risk management strategies or practical implementation experience. Practitioners in this field perceive multiple risks, not just those related to climate change. The researchers noted that there was a tendency to focus on the most immediate problem, rather than the full range of risks they might face. It is clear that there is an opportunity to improve resilience through knowledge sharing and better communication across all CH. This is also true of individual world cultural heritage sites, with opportunities to engage more effectively with local stakeholders. This article pinpoints the current perceptions of WHSM for the academic community and highlights critical avenues of research that will aid in the overarching theoretical and operational integration of CH and sustainability.The SHELTER Projecthttps://shelter-project.com

The duration of channel drying affects survival of Gammarus pulex (Amphipoda: Gammaridae) within subsurface sediments: an experimental flume study

Field studies have demonstrated that benthic fauna use hyporheic sediments during drying events in temporary rivers, but the factors influencing the survival of fauna in subsurface sediments remain poorly quantified. Laboratory mesocosm experiments were conducted to determine how the length of drying events (1, 7, 14 and 21 days) influenced the survivorship of Gammarus pulex (L.) (Amphipoda: Gammaridae). The water level was reduced to 5 cm below the substrate surface during drying experiments and held at 5 cm above the sediment surface during control experiments. The results demonstrate that G. pulex survivorship was reduced with increasing length of the experiment, particularly in the drying treatment compared to the control treatment. We show that G. pulex can persist in subsurface sediments for up to 21 days during surface drying. In view of interacting climatic drivers and water resource pressures that are increasing the spatial and temporal occurrence of streambed drying, our results have important implications for stream management. Our results also highlight the utility of mesocosm-based studies for elucidating the abiotic controls of macroinvertebrate survival during stream drying events

Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances

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

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

The effect of increasing fine sediment load and drying duration on the re-emergence of Gammarus pulex (Amphipoda: Gammaridae) from the subsurface following flow resumption

peer reviewedEnvironmental change and growing anthropogenic pressure on water resources is increasing the duration and intensity of drying events in streams in many geographical locations. Favourable sediment characteristics (e.g. high porosity and low fine sediment load within the substrate matrix) may facilitate benthic macroinvertebrate use of subsurface sediments in response to drying. However, the influence of sedimentary characteristics on the use and subsequent recovery of macroinvertebrates from initial vertical migration into, survival during unfavourable conditions within, and subsequent re-emergence from subsurface sediments have not been directly observed. Transparent mesocosm tanks were used to directly observe the vertical movement and subsequent re-emergence of Gammarus pulex from subsurface sediments in response to increasing dry period (1, 7, or 21 days) and fine sediment load (0.5–1 mm particle diameter used for light and heavy sediment treatment) and following rehydration and resumption of flowing conditions. Increasing volumes of fine sediment addition limited the ability of G. pulex to access subsurface sediment in response to drying and re-emerge following rehydration. The longest dry period (21 days) reduced the ability of G. pulex to re-emerge from the subsurface sediments following rehydration and flow resumption. Increasing fine sediment load negatively affects taxa using subsurface sediments as a refuge. Increased fine sediment deposition has the potential to reduce both access to the sub-surface and re-emergence once surface flow resumes. As many rivers are beginning to dry out, or are showing prolonged drying due to global warming, it is increasingly important that river management reduces the input of fine sediment into rivers and increase sediment porosity of riverbeds to facilitate access into the subsurface refuge by benthic fauna

The effect of increasing fine sediment load and drying duration on the re-emergence of <i>Gammarus pulex</i> (Amphipoda: Gammaridae) from the subsurface following flow resumption

Environmental change and growing anthropogenic pressure on water resources is increasing the duration and intensity of drying events in streams in many geographical locations. Favourable sediment characteristics (e.g. high porosity and low fine sediment load within the substrate matrix) may facilitate benthic macroinvertebrate use of subsurface sediments in response to drying. However, the influence of sedimentary characteristics on the use and subsequent recovery of macroinvertebrates from initial vertical migration into, survival during unfavourable conditions within, and subsequent re-emergence from subsurface sediments have not been directly observed. Transparent mesocosm tanks were used to directly observe the vertical movement and subsequent re-emergence of Gammarus pulex from subsurface sediments in response to increasing dry period (1, 7, or 21 days) and fine sediment load (0.5–1 mm particle diameter used for light and heavy sediment treatment) and following rehydration and resumption of flowing conditions. Increasing volumes of fine sediment addition limited the ability of G. pulex to access subsurface sediment in response to drying and re-emerge following rehydration. The longest dry period (21 days) reduced the ability of G. pulex to re-emerge from the subsurface sediments following rehydration and flow resumption. Increasing fine sediment load negatively affects taxa using subsurface sediments as a refuge. Increased fine sediment deposition has the potential to reduce both access to the sub-surface and re-emergence once surface flow resumes. As many rivers are beginning to dry out, or are showing prolonged drying due to global warming, it is increasingly important that river management reduces the input of fine sediment into rivers and increase sediment porosity of riverbeds to facilitate access into the subsurface refuge by benthic fauna.</p