Experimental desiccation indicates high moisture content maintains hyporheic biofilm processes during drought in temperate intermittent streams

Laura E Coulson,Christian Griebler,Jakob Schelker,Katrin Attermeyer,Gabriele Weigelhofer,Thomas Hein

doi:10.1007/s00027-021-00799-3

Laura E Coulson, Christian Griebler + Show 4 more

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https://doi.org/10.1007/s00027-021-00799-3

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Abstract

Droughts are expected to become more common with climate change resulting in more frequent occurrences of flow intermittency in temperate streams. As intermittency has deleterious effects on fluvial microbial biofilms, there is a need to better understand how droughts affect the microbial functioning and thereby nutrient and organic matter processing in temperate stream ecosystems. Here, the hyporheic zone is of particular importance as it has been shown to be a hot spot for biogeochemical activity under flow intermittence. This study evaluates how drought duration affects microbial biofilm dynamics in the hyporheic zone of intermittent temperate streams. To do so, we used outdoor hyporheic flumes that were subject to periods of drought ranging from 4 to 105 days. Sediment was sampled before and during the drought, and at several occasions after rewetting. Samples were analyzed for extracellular enzymatic activity, bacterial respiration, and bacterial abundances including live to dead cell ratios. The high moisture content remaining in the hyporheic zone of the flumes allowed for the sustained microbial functioning during drought, regardless of drought duration. This can be attributed to cooler temperatures in these climate zones and shading by riparian forests. The high moisture content inhibited the local habitat and community changes that the biofilm might have undergone during more severe desiccation. However, the change in the hyporheic flow regime (flow cessation and resumption) may stimulate microbial processing in these moderate drought conditions. We suggest that the hyporheic zone may act as a buffer against drought and the factors determining this buffer capacity, such as sediment characteristics and climatic regions, need to be analyzed in more detail in future.

Highlights

Introduction14, 1090 Vienna, Austria et al 2018)
Despite their relatively small surface area, streams and riv‐ ers play a globally important role in the transformation and transport of organic matter (Allen and Pavelsky 2018; DrakeWasserCluster Lunz–Biologische Station, Dr Carl Kupelwieser Promenade 5, 3293 Lunz am See, AustriaInstitute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences (BOKU), Gregor‐Mendel‐Str. 33/DG, 1180 Vienna, AustriaDivision of Limnology, Department of Functional and Evolutionary Ecology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria et al 2018)
Microbial biofilms in streams are crucial in the biotic processing, storage, and release of organic matter and nutrients (Battin et al 2016; Leff et al 2016; Pusch et al 1998)

Summary

Introduction

14, 1090 Vienna, Austria et al 2018). Stream biofilms inhabit a large surface area in the streambed as well as in the hyporheic zone and both interact significantly with solutes in the water passing through this interface (Battin et al 2016; Boano et al 2014). These biofilms improve the water quality and contribute to the transformation of carbon compounds and the recycling of nutrients (Battin et al 2008). As droughts are expected to become more common in the future with

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