Sediment Reworking in Streambeds With Fine Sediment Deposits and Its Influence on Hyporheic Flow Regime. Issue 12 (16th December 2021)

• Record Type: Journal Article
• Authors: Shrivastava, S.; Stewardson, M. J.; Arora, M.
• Is Part Of: Water resources research. Volume 57:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-16
• Subjects: sediment reworking -- fine sediment clogging -- hyporheic exchange; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2021WR030360
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: 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 were filled with sediments to mimic streambeds which were clogged with clay particles (fine sediment). It was observed that the sample organisms could penetrate and disintegrate the clay deposits. This enhances the rate of transfer of water/solute molecules across the streambeds, reduces the time they reside in the bed, and increases the exchange depth. The degree to which exchange characteristics are influenced depends on the interaction of animals with both deposited fine sediments and bed grains. Further research must be conducted to understand how faunal organisms modify exchange processes across streambeds as it has a direct influence on overall stream ecosystem functioning. Key Points: Effect of sediment‐organism interaction on hyporheic flow in streambeds with fine sediment deposits is studied in re‐circulating flumes Sediment reworking by model organisms caused enhanced hyporheic exchange flux, shorter residence times, and deeper solute penetration The extent of modification of hyporheic flow regime depends on interaction of organisms with both substrate and deposited fine sediments