TheHydroEcoSedimentarytool: An integrated approach to characterise interstitial hydro‐sedimentary and associated ecological processes

Abstract

Increased deposition of fine sediments in rivers and streams affects a range of key ecosystem processes across the sediment-water interface, and it is a critical aspect of river habitat degradation and restoration. Understanding the mechanisms leading to fine sediment accumulation along and across streambeds and their effect on ecological processes is essential for comprehending human impacts on river ecosystems and informing river restoration. Here, we introduce the HydroEcoSedimentary tool (HEST) as an integrated approach to assess hydro-sedimentary and ecologically relevant processes together. The HEST integrates the estimation of sedimentary processes in the interstitial zone, as well as hydraulic, geochemical and ecological assessments, with a focus on brown trout early life stages. Compared to other methods, the HEST expands the possibilities to monitor and quantify fine sediment deposition in streambeds by differentiating between vertical, lateral and longitudinal infiltration pathways, and distinguishing between the depth (upper vs. lower layers) at which interstitial processes occur within the sediment column. By testing the method in two rivers with different degrees of morphological degradation, we detail the possible measurements and uses of the HEST, demonstrate its feasibility and discuss its reliability.

Hydropeaking impairs upstream salmonid spawning habitats in a restored Danube tributary

“…The HEST compartments were opened carefully, data loggers and larger stones were removed, and the sediment content was emptied into a tray, rinsed with water and examined for larvae and eggs. A distinction was made between live and dead eggs as well as between live and dead larvae, as described in Casas‐Mulet et al (2021). All samples were preserved in a solution of 70% (v/v) ethanol.…”

Contribution of a groundwater-influenced hinterland drainage system to the restoration of salmonid spawning grounds at the upper river Danube

“…Each of the infiltration openings was covered with Jaera ® perforated metallic plates (2 mm diameter round holes, JAERA GmbH & Co. KG, Laatzen, Germany). For full details of the HEST design, see Casas-Mulet et al (2021).…”

“…Each HEST compartment (T and B) was loaded with 30 eggs that were randomly picked and placed by forming a small pit in the HESTs, which was then carefully covered with a 5 cm thick layer of substrate. The full HESTs were kept submerged in a large tank (700 L) with aerated water, so the quality of the eggs was preserved during transport (45 min) and until their exposure the next day (see Casas-Mulet et al, 2021 for further details).…”

“…Each HEST was then inserted so that its top was even with the gravel surface, and the rivers natural coarse sediment was used to fill up the gap to the same level. The HESTs were installed in closed mode and after fines were settled, they were opened to start the experiment (Casas-Mulet et al, 2021). After exposure, the HESTs were retrieved and immediately assessed in the laboratory for egg and larvae survival.…”

“…The HEST compartments were opened carefully, data loggers and larger stones were removed, and the sediment content was emptied into a tray, rinsed with water and examined for larvae and eggs. A distinction was made between live and dead eggs as well as between live and dead larvae, as described in Casas-Mulet et al (2021). All samples were preserved in a solution of 70% (v/v) ethanol.…”