High spatial resolution of distribution and interconnections between Fe‐ and N‐redox processes in profundal lake sediments

Abstract

The Fe and N biogeochemical cycles play key roles in freshwater environments. We aimed to determine the spatial positioning and interconnections of the N and Fe cycles in profundal lake sediments. The gradients of O2, NO3 − , NH4 + , pH, Eh, Fe(II) and Fe(III) were determined and the distribution of microorganisms was assessed by most probable numbers and quantitative polymerase chain reaction. The redox zones could be divided into an oxic zone (0-8 mm), where microaerophiles (Gallionellaceae) were most abundant at a depth of 7 mm. This was followed by a denitrification zone (6-12 mm), where NO3 − -dependent Fe(II) oxidizers and organoheterotrophic denitrifiers both reduce nitrate. Lastly, an iron redox transition zone was identified at 12.5-22.5 mm. Fe(III) was most abundant above this zone while Fe(II) was most abundant beneath. The high abundance of poorly crystalline iron suggested iron cycling. The Fe and N cycles are biologically connected through nitrate-reducing Fe(II) oxidizers and chemically by NOx − species formed during denitrification, which can chemically oxidize Fe(II). This study combines high resolution chemical, molecular and microbiological data to pinpoint sedimentary redox zones in which Fe is cycled between Fe(II) and Fe(III) and where Fe and N-redox processes interact.

Sedimentary archaeal amoA gene abundance reflects historic nutrient level and salinity fluctuations in Qinghai Lake, Tibetan Plateau

“…The Qinghai Lake water column currently is oxic, but within a few centimeters below the water-sediment interface, the sediments become anoxic as determined from pore water chemistry 51 , consistent with a recent study which indicated that oxygen concentration was zero below one centimeter into lake sediments 59 . Furthermore, all known AEA require oxygen for growth, although previous studies indicated some AEA might prefer low oxygen environments 20 60 .…”

Microbial anaerobic Fe(II) oxidation – Ecology, mechanisms and environmental implications

“…Another study showed that chemolithoautotrophy was dominant in an organic poor aquifer and that high fractions of the denitrifying communities were represented by OTUs closely related to the Fe(II)-oxidizer Sideroxydans lithotrophicus ES-1 (Herrmann et al, 2017). Recent studies have investigated the abundance and distribution of NRFeOx bacteria in freshwater lake sediments (Melton et al, 2012(Melton et al, , 2014c and in coastal marine sediments (Laufer et al, 2016b). In the freshwater lake sediments, the results indicate that NRFeOx bacteria are likely to be in competition for Fe(II) with phototrophic Fe(II)-oxidizers in the presence of light (Melton et al, 2012).…”

Mineralogical Diversity in Lake Pavin: Connections with Water Column Chemistry and Biomineralization Processes

“…For instance, anaerobic Fe(II)-oxidizing bacteria at sediment redox interfaces contribute actively to the biomineralization of diverse Fe-oxyhydroxides and to Fe and N cycling [42]. Moreover, multiple studies evidenced the presence of sulfur-cycling microorganisms (e.g., sulfate reducing and sulfur oxidizing microbes) at redox boundaries in anoxic sediments [43,44].…”