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The Redox ladder H2O H2 O2 NO3- N2 MnO2 Mn2+ Fe(OH)3 Fe2+ SO42- H2S CO2 CH4 Oxic Post - oxic Sulfidic Methanic Aerobes Dinitrofiers Maganese reducers Sulfate reducers Methanogens Iron reducers The redox-couples are shown on each stair-step, where the most energy is gained at the top step and the least at the bottom step. (Gibb’s free energy becomes more positive going down the steps)
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Microbes, e- flow Catabolism breakdown of any compound for
energy
Anabolism consumption of that energy for biosynthesis Transfer of
e- facilitated by e- carriers, some bound to the membrane, some
freely diffusible The Redox ladder H2O H2 O2 NO3- N2 MnO2 Mn2+
Fe(OH)3 Fe2+ SO42- H2S CO2 CH4 Oxic Post - oxic Sulfidic Methanic
Aerobes Dinitrofiers Maganese reducers Sulfate reducers Methanogens
Iron reducers The redox-couples are shown on each stair-step, where
the most energy is gained at the top step and the least at the
bottom step.(Gibbs free energy becomes more positive going down the
steps) Profiles and microbial habitats
Minerals Expected? 3 2 Fe2+ depth H2S 4 H2S 1 Org. C Org. C
Concentration Diffusion, Fickian Diffusion from high to low
levels..
Where D is the diffusion coefficient, dc/dx is the gradient, and J
is the flux of material Other nutrients needed for life
Besides chemicals for metabolic energy, microbes need other things
for growth. Carbon Oxygen Sulfur Phosphorus Nitrogen Iron Trace
metals (including Mo, Cu, Ni, Cd, etc.) What limits growth??
Nutrients Lakes are particularly sensitive to the amount of
nutrients in it: Oligotrophic low nutrients, low photosynthetic
activity, low organics clear, clean Eutrophic high nutrients, high
photosynthetic activity, high organics mucky, plankton /
cyanobacterial population high Plankton growth: 106 CO NO3- + HPO
H2O + 18 H+ + trace elements + light C106H263O110N16P O2 (organic
material composing plankton) This C:N:P ratio (106:16:1) is the
Redfield Ratio What nutrients are we concerned with in Lake
Champlain? Nutrient excess can result
in blooms Lake Champlain Phosphorus limited? Algal blooms What
controls P?? Nutrient cycling linked to SRB-IRB-MRB activity
Blue Green Algae blooms FeOOH PO43- Org C + SO42- H2S FeS2 Sulfate
Reducers Redox Fronts Boundary between oxygen-rich (oxic) and more
reduced (anoxic) waters Oxygen input through entrainment (wind,
wave action, photosynthesis) Oxygen consumption from heterotrophic
consumption, reaction with reduced forms of Fe, Mn, S Anoxic Oxic
Methods Voltammetric microelectrodes In-situ pore water
measurements to determine redox front by real time analysis of O2,
Fe2+/Fe3+, Mn2+, H2S DGT (Diffusive Gradients in Thin films) to
monitor P fluxes through sediment Gravity Coring and chemical
extractions of iron, manganese, and phosphorus in the sediment
Inductively-coupled plasma optical emission spectroscopy (ICP-OES)
to measure iron, manganese, and phosphorus from extractant
Voltammetric data - St. Albans Bay Sediments
Mn2+ + 2e- --> Mn0(Hg) H2O2 + 2e- + 2H+ 2H2O O2 + 2e- + 2H+ H2O2
Fe3+ + 1e- Fe2+ FeS(aq) Results: Sediments generally become more
reduced as summer progresses
Redox fronts move up and down in response to temperature, wind,
biological activity changes This movement of the redox front
invokes changes in mineralogy and nutrient dynamics on short time
scales Seasonal Phosphorus mobility
Redox front movement mobilizes P in the sediment over time Movement
is EVENT based fluxes should vary significantly in time. We
currently have little idea what P fluxes are out of the sediment
Profiles show overall enrichment of P, Mn, and Fe in upper sections
of SAB sediment Fe and Mn would be primarily in the form of Fe and
Mn oxyhydroxide minerals transformation of these minerals is key to
P movement P Loading and sediment deposition
Constantly moving redox fronts affect Fe and Mn minerals, mobilize
P and turn ideal profile into what we actually see Redox changes
and Nutrients
We have linked at least some component of P dynamics to redox
changes and Fe, Mn mineralogy this is one of several processes that
would affect nutrient balance in these bay systems however.
Nitrogen speciation and availability may also be affected by these
processes, but potentially in very different ways hence there may
be some background control on N/P ratio which may affect algal
community dynamics Geochemical niches and microbial community
changes in Saint Albans Bay, Lake Champlain, sediments
PCA analysis of Restriction Fragment Length Polymorphism analysis
from DNA extracted from 4 geochemically distinct zones and a 1mm
buffer zone between 1 Oxic, top mm of sediment 2 Buffer 1 mm 3
Nitrate reduction 4 buffer 2 1 mm 5 manganese reduction 6 buffer 1
mm 7 iron reduction 8 -bottom of sediment column Can reducing
conditions force P out of the sediment and into the overlying water
column?Incubation experiments: Oxic Anoxic From the volumetric
analyses and visually (red is FeOOH oxidized iron, black is FeS
reduced iron and sulfur) we see the difference in the redox
condition between the two cores. DGT films in incubation
experiments
Diffusive Gradients in Thin films (DGT) probes put into sediment (
in sediments, in water above) to measure time-averaged P release in
2 incubation experiments DGT films definitively show potential for
significant release of P into pore water and overlying water column
on reduction of the Fe minerals present
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