Microbial Community Composition Correlates with Metal Sorption in an Ombrotrophic Boreal Bog: Implications for Radionuclide Retention

Merja Lusa,Malin Bomberg

doi:10.3390/soilsystems5010019

Abstract

Microbial communities throughout the 6.5 m depth profile of a boreal ombrotrophic bog were characterized using amplicon sequencing of archaeal, fungal, and bacterial marker genes. Microbial populations and their relationship to oxic and anoxic batch sorption of radionuclides (using radioactive tracers of I, Se, Cs, Ni, and Ag) and the prevailing metal concentrations in the natural bog was investigated. The majority of the detected archaea belonged to the Crenarchaeota, Halobacterota, and Thermoplasmatota, whereas the fungal communities consisted of Ascomycota, Basidiomycota, and unclassified fungi. The bacterial communities consisted mostly of Acidobacteriota, Proteobacteria, and Chloroflexi. The occurrence of several microbial genera were found to statistically significantly correlate with metal concentrations as well as with Se, Cs, I, and Ag batch sorption data. We suggest that the metal concentrations of peat, gyttja, and clay layers affect the composition of the microbial populations in these nutrient-low conditions and that particularly parts of the bacterial and archaeal communities tolerate high concentrations of potentially toxic metals and may concurrently contribute to the total retention of metals and radionuclides in this ombrotrophic environment. In addition, the varying metal concentrations together with chemical, mineralogical, and physical factors may contribute to the shape of the total archaeal and bacterial populations and most probably shifts the populations for more metal resistant genera.

Highlights

Heavy metals and radionuclides polluting the environment originate mainly from anthropogenic sources, including uranium mining, coal combustion, and accidental or purposeful release of radionuclides
We suggest that the metal concentrations of peat, gyttja, and clay layers affect the composition of the microbial populations in these nutrient-low conditions and that parts of the bacterial and archaeal communities tolerate high concentrations of potentially toxic metals and may concurrently contribute to the total retention of metals and radionuclides in this ombrotrophic environment
Ni Kd values varied from 190 L/kg DW detected in the clay layer to 19,900 L/kg DW in the gyttja layer after one week equilibrium time

Summary

Introduction

Heavy metals and radionuclides polluting the environment originate mainly from anthropogenic sources, including uranium mining, coal combustion, and accidental or purposeful release of radionuclides. Heavy metals and radioactive isotopes may present variable threats to biota, due to, e.g., atmospheric deposition and enrichment in soils and sediments, build-up into water bodies, and their high toxicity [1,2,3,4,5,6]. Radioactive isotopes and heavy metals can have toxic effects on soil microorganism activity if bioavailable and present in sufficient concentrations [7]. The land uplift will result in a formation of new bogs in the area on which the first possible releases from the deep nuclear repository to the upper biosphere (through the clay, gyttja and peat layers in this order) would, based on biosphere safety assessment calculations, be possible if some of the copper canisters would leak. The Lastensuo Bog, sampled in our study, approximates the bog type likely to form in this area and has been used as an analogue biotope in the biosphere safety assessments of the disposal of spent nuclear fuel in Finland [9]. 59Ni, 108mAg, 135Cs, 79Se, and 129I, with calculated potential geosphere release rates between 101 and 103 Bq/a starting 103 years after the start of disposal, are among the most important radionuclides, as the potential radiation doses for humans in the biosphere safety assessment calculations of spent nuclear fuel are considered [10]

Methods

Results

Discussion

Conclusion