Microbial activity and sediment disturbance modulate the vertical water flux in sandy sediments

Abstract

Little research has been conducted on the influence of microbial communities, sediment disturbances, and their interaction on the Vertical Water Flux (VWF) across a hydraulically complex streambed. Our study was aimed at the effects of microbial activity and shallow-sediment disturbance on VWF in sandbed flumes. We assessed the dynamics of VWF and the development of a microbial community during 30 d (June-July 2010) in 16 outdoor flumes with 2 types of bedform shape (level and ripple). We operated 8 flumes in constant darkness (no-light), and 8 in daylight to gain information on the relative significance of algae and heterotrophic microorganisms. We simulated a shallow-sediment disturbance after 21 d and compared microbial activity and VWF before and after the disturbance. We measured organic matter content, abundance of organisms, microbial activity, precipitation of CaCO 3 , and O 2 bubbles resulting from primary production before and after the disturbance. VWF differed among treatments after 13 d. Algal and bacterial cells embedded in an extracellular polymer network, algal and microbial precipitation of CaCO 3 , and production of O 2 bubbles in the uppermost sediment blocked the sediment pore space and disrupted VWF under daylight conditions, whereas bacterial cells and microbial precipitation of CaCO 3 reduced VWF in no-light flumes. Microbial activity and organic matter were not affected by the shallow-sediment disturbance, but VWF was restored. VWF can be controlled by microbial activity and shallow-sediment disturbances and should be seen as spatially heterogeneous and fluctuating in time on small scales.

Behind the Scenes: Mechanisms Regulating Climatic Patterns of Dissolved Organic Carbon Uptake in Headwater Streams

“…Whereas bioassays typically consider DOC consumption only in the water column, whole‐reach approaches include DOC processing rates from the benthic and hyporheic stream compartments. These compartments are well known to increase stream transient storage and are hot spots of biogeochemical processing in streams (Battin et al, ; Mendoza‐Lera & Mutz, ). While decay rates estimated throughout bioassays are the net result of both DOC uptake, transformations, and mineralization, short‐pulse addition methods measure gross uptake fluxes (Mineau et al, ).…”

Variation in reach-scale hydraulic conductivity of streambeds

“…Biofilm growth is likely to enhance clogging (Mendoza-Lera and Mutz, 2013) and root growth and borrowing of biota may create preferential flow paths and increase conductivity (Battin and Sengschmitt, 1999;Mermillod-Blondin and Rosenberg, 2006). For example, tubificid worms can dig networks of galleries in fine sediment, creating preferential flow pathways and increasing hydraulic conductivity (Nogaro et al, 2006).…”

Exploring the role of hydraulic conductivity on the contribution of the hyporheic zone to in‐stream nitrogen uptake

“…Hence, contrary to the common assumption of spatially invariant microbial reaction rates (Li et al, ), our results show that N‐uptake is heterogeneous in the hyporheic zone. Despite hzKf may not be a good predictor of hzN‐uptake or relative connectivity, it may indirectly determine hyporheic N‐uptake by means of driving hyporheic flow, interstitial velocity, and the abundance of the microbial community (noteworthy that microbial community dynamics can also influence hzKf, e.g., bioclogging; Mendoza‐Lera & Mutz, ). Thus, improved predictions of the contribution of the hyporheic compartment to in‐stream N‐uptake require integration of the interplay between the relative hydrological connectivity and microbial community.…”