Effects of shallow and deep sediment disturbance on whole-stream metabolism in experimental sand-bed flumes

Abstract

Water flow causes complex patterns of sediment disturbance in sand-bed streams, but effects on stream metabolism resulting from different depths of sediment scour and fill are poorly known. We assessed such effects by manually disturbing sandy sediments of 16 experimental outdoor flumes to two different depths (1 and 4 cm) during an early and a more advanced stage of stream community succession. To separate effects on heterotrophic and autotrophic metabolism, half of the flumes were permanently covered. At the early successional stage, sediment disturbance did not affect net community production (NCP), while sediment mixing reduced production independent of disturbance depth in the later stage. Microbial respiration, in contrast, was significantly stimulated when sediment was mixed to greater depth. These results suggest that disturbing sediments during early successional stages has no effect on whole-stream metabolism, whereas at later stages, deep sediment disturbance can lead to a transitory shift toward heterotrophy. The recovery time of NCP from perturbation was independent of disturbance depth. Similar trajectories observed after deep and shallow sediment disturbance indicate that delayed recovery was not simply due to mixing algae into deeper sediment layers but primarily a result of disrupting the fine structure of the surface sediment.

Periodic sediment shift in migrating ripples influences benthic microbial activity

“…comparably low flow causing sand ripple migration [Baas, 2003]. Gerull et al [2012] found that a single disturbance of a sand bed in flumes did not affect respiration of the microbial community. The sediment in these flumes was disturbed once only by mixing the upper 1 cm of the sand bed, generating a mechanical disturbance that was similar in depth and nature to the disturbance during one cycle of sediment shift in migrating sand ripples.…”

Fungal importance extends beyond litter decomposition in experimental early‐successional streams

“…After inoculation, the stream channels ran in complete recirculation mode for 24 h with filtered (5 μm pore size) Chicken Creek water to facilitate establishment of the added microorganisms. Subsequently, the channels received well‐oxygenated groundwater from a subterranean tank (Gerull et al ., ) to replace 5% of the water volume during each cycle in the now partially recirculating channels. The current velocity was 1.7 ± 0.3 cm s −1 at a water depth of 1 cm.…”

“…We conducted a full factorial experiment in outdoor channels simulating early-successional sand-bed streams. The channels (4.0 ¥ 0.12 ¥ 0.12 m) were set up next to a recently created experimental catchment (referred to as Chicken Creek) near Cottbus in eastern Germany (51°36′N, 14°16′E) situated in a former brown-coal mining area (Gerwin et al, 2009;Gerull et al, 2012). The channels were filled with a 4 cm layer of sterilized (combustion overnight at 160°C) sandy sediment collected from a dry stream reach in the catchment and supplied with well-oxygenated groundwater originating from the catchment.…”

“…after 4, 18, 25 and 32 days). To this end, the tops of the stream channels were sealed with Perspex lids and changes in oxygen concentration were recorded with optodes (10-channel Minisensor Oxygen Meter, Oxy 10 mini, PreSens GmbH, Regensburg, Germany; Gerull et al, 2012). Water in the channels was flowing in closed-circulation mode during the measurements.…”

Shifts in microbial community structure and function in stream sediments during experimentally simulated riparian succession

“…S1). Dissolved organic carbon (DOC) was abundant, averaging 9.8 mg L À1 , but hardly bioavailable (Gerull et al, 2012). This ensured natural light, temperature and other environmental conditions.…”