Pelagic boundary conditions affect the biological formation of iron‐rich particles (iron snow) and their microbial communities

Abstract

We studied the formation of iron-rich particles at steeply opposing gradients of oxygen and Fe(II) within the redoxcline of an acidic lignite mine lake (pH 2.9). Particles formed had a diameter of up to 380 mm, showed high sedimentation velocity (, 2 m h 21 ), and were dominated by the iron mineral schwertmannite. Although the particles were highly colonized by microbial cells (, 10 10 cells [g dry weight] 21 ), the organic carbon content was below 11%. Bathymetry and the inflow of less acidic, Fe(II)-rich groundwater into the northern basin of the lake results in two distinct mixing regimes in the same lake. The anoxic monimolimnion of the northern basin had higher pH, Fe(II), dissolved organic carbon, and CO 2 values compared with the more central basin. Particles formed in the northern basin differed in color, were smaller, had higher organic carbon contents, but were still dominated by schwertmannite. Microcosm incubations revealed the dominance of microbial Fe(II) oxidation.

Insights into the Structure and Metabolic Function of Microbes That Shape Pelagic Iron-Rich Aggregates (“Iron Snow”)

“…The central basin undergoes mixing in autumn and spring. Sampling sites were the same as in the study of Reiche et al (6), and their designations are abbreviated as follows: central basin redoxcline, CR; central basin anoxic bottom water, CB; northern basin redoxcline, NR; and northern basin anoxic bottom water, NB.…”

“…The acidic Lake 77 located in the Lusatian mining area in east-central Germany has two basins with different stratification patterns caused by a bank that separates the bottom water of the northeastern basin from the rest of the lake (6,15). The northern basin is meromictic, has a pH of 5.9, and shows higher Fe(II) and sulfate concentrations in the bottom part of the lake due to the inflow of less acidic, contaminated groundwater (16).…”

“…The initial step of iron snow formation, the oxidation of Fe(II), was shown to be a microbial process in an acidic lignite mine lake in which Fe(II) concentrations can reach 10 mM in the anoxic bottom water layer (6). Lignite mine lakes are characterized by low pH and high concentrations of Fe(II) and sulfate (12).…”

“…Opposing gradients of oxygen and Fe(II) are critical for the formation of iron minerals in streams, lakes, and marine habitats (4)(5)(6). These minerals can be the nucleus for pelagic aggregate formation either by adsorption or coprecipitation of organic matter (7) and rapid microbial colonization.…”

A paleolimnological archive of metal sequestration and release in the Cumberland Basin Marshes, Atlantic Canada

“…Processes that sequester or release metals in lakebed sediments include sediment-water interface redox conditions (Davison 1993;Johnson 2008;Reiche et al 2011) and sediment resuspension (Kalnejais et al 2007;Terry 2011), but the degree to which these affect the availability of metals in the CMR is not known (Loder et al 2016). Finally, stratigraphic variability in metal concentration in lakebed sediments can have significant consequences for bioavailability and may influence habitat management practices.…”