Influence of Bioturbation on Hyporheic Exchange in Streams: Conceptual Model and Insights From Laboratory Experiments. Issue 2 (23rd February 2021)

• Record Type: Journal Article
• Authors: Shrivastava, S.; Stewardson, M. J.; Arora, M.
• Is Part Of: Water resources research. Volume 57:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-23
• Subjects: bioturbation -- hyporheic exchange -- lotic environment; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2020WR028468
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Bioturbation occurs in streambeds by the action of a range of faunal species, but little is known about how it could modify the hyporheic exchange in streams. Previous experimental work investigating the effects of sediment‐biota interaction on exchange across the sediment‐water interface has been largely conducted in small mesocosms or infiltration columns that do not represent the lotic environment adequately. Therefore, the experimental findings from these studies may not be transferable to flowing water environments (e.g., streams). In this work, we first present a conceptual model demonstrating the causal pathways through which the sediment reworking and burrow ventilation processes (together referred to as bioturbation) could potentially modify the hyporheic flow regime. Next, to study the role of activities of faunal organisms in lotic environments and test some of the arguments presented in the model, laboratory experiments are conducted in re‐circulating flumes. The experiments involved investigating the modification of dune‐induced hyporheic flow due to the activities of a model bioturbating organism, Lumbriculus variegatus, following a control (without organisms) and treatment (with organisms) based experimental design. The sediment reworking activities such as surficial deposition of fecal pellets and burrowing by L. variegatus caused significantly higher hyporheic flux, longer mean residence times, and deeper solute penetration in the treatment flumes relative to the control flumes. We advocate that more intensive laboratory experiments and field investigations must be conducted to test the propositions put forward in the conceptual model and advance our understanding of the role of bioturbation process in fluvial ecosystems. Plain Language Summary: The exchange between surface and groundwater underpins several stream ecosystem services such as biochemical cycling of nutrients and attenuation of contaminants. In this regard, a comprehensive understanding of the in‐stream processes influencing the exchange across sediment‐water interface is essential for holistic stream management. Detailed research has been undertaken in the past to investigate the effects of physical variables such as flow velocity or flow depth on surface and groundwater exchange. However, little is known about how the activities of faunal organisms such as macroinvertebrates that inhabit streambeds affect the surface and subsurface exchange. In this work, we advance the conceptual understanding of how activities such as feeding and excretion, locomotion, and construction of galleries by macroinvertebrates could alter the two‐way exchange across sediment‐water interface. We also conduct laboratory experiments by forming streambeds in Perspex built long channels to perform preliminary testing of the propositions presented in the conceptual model. The results reveal that activities of sample macroinvertebrates significantly modified the rate of transfer of water across the sediment‐water interface, the time it resides in the bed, and to what depth it is exchanged. This modification in the exchange characteristics has direct consequences for the overall functioning of stream ecosystems. Key Points: Causal pathways through which sediment reworking and burrow ventilation processes could modify hyporheic exchange are presented Effect of sediment‐biota interaction on hyporheic exchange is investigated by conducting experiments in re‐circulating flumes Sediment reworking by model organisms significantly altered the hyporheic flux, residence times, and penetration depth of solutes