Methane CH4 Greenhouse gas 20x more powerful than CO2 Formed biologically methanogenesis Huge reservoir as methane clathrate hydrate in cold soils and ocean bottom stable structure at low T high P 2x1016 kg of C in these deposits What happens if the oceans warm Clathrate gun hyothesis warming seas melt these clathrates CH4 released en masse to atmosphere Microbes and methane production Methanogenesis Reduction of CO 2 or other organics to form CH4 also CH4 generation from special fermentative rxns Only certain groups of Archaea do this specifically with the Euryachaeota subdivision Called methanogens These organisms do not compete well with other anaerobes for e donors thus they thrive where other alternate e acceptors have been consumed Methane cycle Microbial methane oxidation Organisms that can oxidize CH4 are Methanotrophs mostly bacteria All aerobic methanotrophs use the enzyme methane monooxygenase MMO to turn CH 4 into methanol CH3OH which is subsequently oxidized into formaldehyde HCHO on the way to CO2 Anaerobic methane oxidation use SO 42 as the e acceptor this was long recognized chemically but only very recently have these microbes been more positively identified though not cultured Phosphorus cycle P exists in several redox states 3 0 3 5 but only 5 PO43 stable in water 1 microbe to date has been shown to grow on PO33 phosphite P3 as a substrate P is a critical nutrient for growth often a limiting nutrient in rivers and lakes Most P present as the mineral apatite Ca5 PO4 3 F Cl OH also vivianite Fe3 PO4 2 8H2O P sorption P strongly sorbs to FeOOH and AlOOH mineral surfaces as well as some clays P mobility thus inherently linked to Fe cycling P sorption to AlOOH is taken advantage of as a treatment of eutrophic lakes with excess P alum is a form AlOOH AlOOH is not affected by microbial reduction as FeOOH can be P cycling linked to SRB IRB MRB activity PO43 PO43 FeOOH PO43 Org C SO42H2S PO43 Sulfate Reducers PO4 FeS2 3 PO43 PO43 PO43Blue Green Algae blooms Redox Fronts Oxic Anoxic Boundary between oxygen rich oxic and more reduced anoxic waters Oxygen consumed by microbes which eat organic material When Oxygen is gone there are species of microbes that can breathe oxidized forms of iron manganese and sulfur St Albans Bay Sediments Current 0 304 0 106 0 100 0 280 0 260 0 090 0 240 0 080 0 220 0 070 0 200 0 180 0 060 0 160 0 050 0 140 0 040 0 120 H2O2 2e 2H 2H2O 0 100 0 080 0 030 0 020 O2 2e 2H H2O2 0 060 0 040 0 010 0 000 0 020 0 004 1 800 Mn2 2e Mn0 Hg Fe 1e Fe 3 1 600 1 400 1 200 blue 0 00 0 00 red 0 00 0 00 1 000 0 800 0 600 0 400 2 0 010 0 100 0 019 1 800 1 600 1 400 1 200 blue 1 56 0 04 red 1 34 0 01 1 000 0 800 0 600 0 400 0 100 0 341 0 300 0 250 0 200 0 150 FeS aq 0 100 0 050 0 000 0 058 1 800 1 600 1 400 1 200 1 000 0 800 0 600 0 400 0 100 7 19 04 Core 1 Profile 1 10 10 5 5 0 0 5 5 Mn nA 10 O2 nA 15 Fe3 nA 20 20 FeS nA 25 25 30 30 10 O2 nA 15 Depth mm Depth mm 6 23 04 Core 2 Profile 2 35 35 0 20 40 60 80 0 Current nA 10 5 5 0 0 5 5 15 Mn nA Depth mm Depth mm 10 O2 nA 100 8 12 04 Core 1 Profile 1 7 26 04 Core 2 Profile 1 10 50 Current nA 10 15 O2 nA 20 20 Mn nA 25 25 FeS nA 30 30 Fe3 nA 35 35 0 20 40 60 Current nA 80 0 20 40 60 Current nA 80 Results Seasonal Work Sediments generally become more reduced as summer progresses Redox fronts move up and down in response to Temperature wind biological activity changes Seasonal Phosphorus mobility Ascorbic acid extractions of Fe Mn and P from 10 sediment cores collected in summer 2004 show strong dependence between P and Mn or Fe Further profiles show overall enrichment of all 3 parameters in upper sections of 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
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