Sediment Reworking in Streambeds With Fine Sediment Deposits and Its Influence on Hyporheic Flow Regime

• Published in: Water resources research 2021-12, Vol.57 (12), p.n/a
• Main Authors: Shrivastava, S., Stewardson, M. J., Arora, M.
• Format: Article
• Language: English
• Subjects: Base flow; Burrowing organisms; Burrows; Channels; Clay; Contaminants; Deposits; Ecological function; Ecosystem services; Ecosystems; Energy transfer; Exchanging; Experiments; fine sediment clogging; Flumes; Grains; Gravel; Groundwater; hyporheic exchange; Laboratories; Laboratory experiments; Low flow; Macroinvertebrates; Nutrients; Organisms; Penetration depth; Physical properties; Rivers; Sand; Sediment; Sediment deposits; sediment reworking; Sediments; Solutes; Stream discharge; Stream flow; Streambeds; Substrates; Zoobenthos
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2021WR030360

The mobilization and mixing of sediments by the activities of in‐stream fauna, referred to as sediment reworking, constantly modifies the hydro‐physical properties of streambeds. This sediment‐organism interaction has been increasingly recognized to influence the hyporheic exchange flows in stream ecosystems, particularly in low flow environments (e.g., during base flow). In this work, we advance the knowledge of sediment reworking process by studying its impact on hyporheic exchange flows in streambeds with fine sediment deposits. Laboratory experiments are conducted in re‐circulating flumes following a control (only fine sediments) and treatment‐ (fine sediments + organisms) based design. The experiments involve studying the interaction of model organisms (Lumbriculus variegatus) with fine sediment (clay) deposits, and its subsequent influence on hyporheic flow regime in homogenous streambeds with fine sand, coarse sand, and gravel as substrate sediments. We observe that model organisms burrowed extensively into the fine sediment layer, mixed the clay particles with underlying grains, and eventually exposed the substrate sediments in the treatment flumes. Consequently, the treatment flumes exhibited greater solute penetration depth, shorter residence times, and higher hyporheic exchange flux compared to their respective control flumes. The results also suggest that the modification of hyporheic exchange flows depends on the overall reworking of the beds that is, the interaction of organisms with both substrate material and deposited fine sediments. It is critical to comprehend the influence of streambed inhabitants on mass and energy exchange across the sediment‐water interface as it has implications on the overall quality of both stream and groundwater. Plain Language Summary The exchange of water and solutes between the surface and groundwater in a stream landscape facilitates important ecosystem services such as the natural processing of nutrients/contaminants. This two‐way exchange could be hampered due to the presence of fine sediments on/into the streambed. Besides fine sediments, several faunal organisms such as macroinvertebrates are present in the streambeds. These organisms could move and construct burrows within the fine sediment deposits and potentially enhance the exchange process across streambeds. We explore this idea by performing laboratory experiments in Perspex built long channels to simulate a streamflow environment. These channels we