Supporting Information
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High spatial resolution of distribution and interconnections
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between Fe- and N-redox processes in profundal lake sediments
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Melton E.D.1, Stief P.2, Behrens, S.1, Kappler A.1 & Schmidt C.1*
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1.
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2.
Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
Microsensor Research Group, Max Planck Institute for Marine Microbiology, Bremen, Germany
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(2.Department of Biology, University of Southern Denmark, Odense, Denmark)
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*corresponding author:
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Caroline Schmidt, Geomicrobiology, Center for Applied Geosciences
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University of Tübingen, Sigwartstraße 10, D-72076 Tübingen, Germany
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Phone: +49-7071-2974790, Fax: +49-7071-295059
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Email: caroline.schmidt@uni-tuebingen.de
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Running Title: Microbial Fe and N redox cycling in lake sediments
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Supporting Information
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Figure S1: Geochemical gradients in profundal Lake Constance sediments.
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The grey filled black squares represent the fit of the measured concentration profiles obtained by
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diffusion-reaction modelling with Profile 1.0 (Berg et al., 1998). The measured concentration profiles
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are shown as open black squares. A) Oxygen (O2). B) Nitrate (NO3-). C) Ammonium (NH4+).
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Material & Methods
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Diffusion-reaction modelling of microsensor concentration profiles
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The average concentration profiles of O2, NO3-, and NH4+ were used to derive the vertical sequence
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of production and consumption zones of these solutes in the sediment (Fig. S1). Diffusion-reaction
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modelling was carried out using the program Profile 1.0 (Berg et al. 1998). The calculation domain
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was set to reach from the sediment surface to the maximum depth at which microsensor profiling
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resulted in reliable readings (O2: 20 mm, NO3-: 17.5 mm, and NH4+: 16.5 mm). A few obvious outliers
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were manually removed from the concentration profiles (NO3-: 4 out of 39 measuring points, NH4+: 1
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out of 60 measuring points). Boundary conditions were selected according to the availability of data
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(O2 and NO3-: concentration at the top and flux at the bottom of the calculation domain, NH4+:
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concentrations at the top and bottom of the calculation domain). The diffusivities of O2, NO3-, and
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NH4+ in water (D0) at 15°C were taken as 1.80 · 10-5 cm2 · s-1, 1.47 · 10-5 cm2 · s-1, and 1.54 · 10-5 cm2 ·
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s-1, respectively (Stief et al. 2002). The effective diffusivities in sediment (Ds) were calculated by the
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program as Ds = D0 · ϕ2, where ϕ is the sediment porosity of 0.806. Model runs were repeated with
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different numbers of equally spaced conversion zones allowed until the modelled concentration
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profiles fitted satisfactorily the measured concentration profiles. The vertical sequence of
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production and consumption zones of O2, NO3-, and NH4+ obtained in the best model run is
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presented.
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Thermodynamic calculations
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The Gibbs free energy was determined based on the geochemical concentrations measured at each
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depth in the profile and the sediment pore water DOC. Dissolved ferrous iron concentration were
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taken from preliminary voltammetric microsensor measurements in the profundal sediments of Lake
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Constance (data not shown). Solid compounds, gases and water were considered to be 1 in the
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calculations. The H+ concentration was based on the pH microelectrode measurements.
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theoretical energetic budget ∆G at 25°C was determined by:
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∆𝐺 = ∆𝐺0 − 𝑅𝑇 𝑙𝑛𝑄
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where ∆G0 is the standard Gibbs free energy at 25°C and pH 0 for the respective reaction equation, R
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is the ideal gas constant, T is the temperature (in K) and Q expresses the equilibrium conditions for
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the respective reaction equation:
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𝑄=
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for the general reaction equation:
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𝑎𝐴 + 𝑏𝐵 ↔ 𝑐𝐶 + 𝑑𝐷
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The considered reactions for the energy computation and the respective ∆G0 values are as follows:
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𝐹𝑒 2+ + 𝐻 + + 𝑂2 →→ 𝐹𝑒 3+ + 𝐻2 𝑂
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𝐹𝑒 2+ + 4 𝑂2 +
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𝐹𝑒 2+ + 5 𝑁𝑂3− + 5 𝐻 + → 𝐹𝑒 3+ + 10 𝑁2 + 5 𝐻2 𝑂
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𝐹𝑒 2+ + 5 𝑁𝑂3− +
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8𝐹𝑒(𝑂𝐻)3 + 𝐶𝐻3 𝐶𝑂𝑂− + 17𝐻 + → 8𝐹𝑒 2+ + 2𝐶𝑂2 + 22𝐻2 𝑂
The
{𝐶}𝑐 {𝐷}𝑑
{𝐴}𝑎 {𝐵}𝑏
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4
1
10
𝐻 𝑂
4 2
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2
∆G0 = -44 kJ.mol-1
→ 𝐹𝑒(𝑂𝐻)3 + 2𝐻 +
∆G0 = -36 kJ.mol-1
1
6
1
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𝐻 𝑂
5 2
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→ 𝐹𝑒(𝑂𝐻)3 +
3
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𝑁
10 2
∆G0 = -46 kJ.mol-1
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+ 5 𝐻+
∆G0 = -38 kJ.mol-1
∆G0 = -72 kJ.mol-1
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