Effects of Macrofaunal Recolonization on Biogeochemical Processes and Microbiota—A Mesocosm Study

Annika Fiskal,Dejan Malcic,Michael Sander,Prachi Joshi,Carsten J Schubert,Mark Alexander Lever,Aixala Gaillard,Sebastien Giroud

doi:10.3390/w13111599

Annika Fiskal, Dejan Malcic + Show 6 more

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https://doi.org/10.3390/w13111599

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Abstract

Macroinvertebrates are widespread in lake sediments and alter sedimentary properties through their activity (bioturbation). Understanding the interactions between bioturbation and sediment properties is important given that lakes are important sinks and sources of carbon and nutrients. We studied the biogeochemical impact of macrofauna on surface sediments in 3-month-long mesocosm experiments conducted using sediment cores from a hypoxic, macrofauna-free lake basin. Experimental units consisted of hypoxic controls, oxic treatments, and oxic treatments that were experimentally colonized with chironomid larvae or tubificid worms. Overall, the presence of O2 in bottom water had the strongest geochemical effect and led to oxidation of sediments down to 2 cm depth. Relative to macrofauna-free oxic treatments, chironomid larvae increased sediment pore water concentrations of nitrate and sulfate and lowered porewater concentrations of reduced metals (Fe2+, Mn2+), presumably by burrow ventilation, whereas tubificid worms increased the redox potential, possibly through sediment reworking. Microbial communities were very similar across oxic treatments; however, the fractions of α-, β-, and γ-Proteobacteria and Sphingobacteriia increased, whereas those of Actinobacteria, Planctomycetes, and Omnitrophica decreased compared to hypoxic controls. Sediment microbial communities were, moreover, distinct from those of macrofaunal tubes or feces. We suggest that, under the conditions studied, bottom water oxygenation has a stronger biogeochemical impact on lacustrine surface sediments than macrofaunal bioturbation.

Highlights

IntroductionBioturbation is defined as the translocation of particles (reworking) and movement of water (ventilation) through sediments by living organisms [1]
We study the impact of oxygenation and bioturbation based on (1) biogeochemical properties of solute and solid phases, (2) microprofiling of O2, redox potential, pH, and H2 S, and (3) microbial community analyses based on 16S
We found that the presence of O2 alters pore water and solid phase geochemical conditions in surface sediments and leads to a gradual but clear change in microbial community composition over time

Summary

Introduction

Bioturbation is defined as the translocation of particles (reworking) and movement of water (ventilation) through sediments by living organisms [1]. Ventilation causes the advective and diffusive exchange of solutes between sediments and overlying water (bioirrigation). This leads to input of oxygen (O2 ) into otherwise anoxic sediment layers and can cause fluctuations between anoxic/oxic conditions within sediments [1,2]. Reworking due to macrofaunal burrowing, feeding, and defecation activities moves sediment particles in an undirected or directed manner and can thereby mix, oxidize, and introduce organic matter to surface sediments [1,2]. The dominant mode of bioturbation, and the

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