Architects under the streams: influence of macroinvertebrate sediment
reworking on hyporheic exchange in clogged streambeds
Abstract
The mobilization and mixing of sediments by the activities of streambed
inhabitants, referred to as sediment reworking, constantly modify the
physical and hydraulic properties of streambeds. However, limited
progress has been made to explore the influence of this
sediment-organism interaction on hyporheic exchange. In this work, we
advance the understanding of the role of macroinvertebrate sediment
reworking in altering the hyporheic exchange flows in clogged
streambeds. Laboratory experiments are conducted in re-circulating
flumes following a control (clogging) and treatment (clogging + sediment
reworking) 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 model streambeds comprising fine sand, coarse sand,
and gravel sediments. We observe that model organisms burrowed
extensively into the clogging layer, mixed the clay particles with
underlying grains, and eventually eroded or disintegrated the clogging
layer at the bed surface in the treatment flumes. As a consequence, the
treatment flumes exhibited greater solute penetration depth, shorter
median and mean residence times, and higher hyporheic 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 including both fine and substrate sediments. The
alteration of hydro-physical properties of streambeds and subsequently
the hyporheic flow regime due to sediment reworking has direct
implications for the biogeochemistry of hyporheic zones and may impact
the overall quality of surface and sub-surface waters, particularly in
low flow environments.