Sulfur Biogeochemical Cycle

Transcription

1 Sulfur Biogeochemical Cycle Chris Moore 11/16/

2 Sulfur Why is it important? 14 th most abundant element in Earth s crust Sulfate is second most abundant anion in rivers (after bicarbonate) and in ocean after chloride Development of an oxygenated atmosphere facilitated this Aerosols (cloud condensation nuclei) Perturbed cycle Anthropogenic emissions of sulfur into the air are double natural emissions Acid rain, AMD From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 2

3 From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) Active Reservoirs From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 3

4 Essential steps in the cycle Mineralization of organic sulfur to the inorganic form, hydrogen sulfide: (H 2 S) Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate, (SO 4 2- ) Reduction of sulfate to sulfide Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 4

5 From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) Overall Cycle (an evolution in understanding) 5

6 Cycle from the 1970s Treatise on Geochemistry (2 nd Edition), Holland and Turekian Eds Note may be as high as 120 dry deposition poorly understood WH by W.H. Schlesinger Schlesinger, / modified by S and B LOOK at table

7 From Schlesinger and Bernhardt (3 rd edition) Treatise on Geochemistry (2 nd Edition), Holland and Turekian Eds. 7

8 Biogeochemistry of a Forested Ecosystem (3 rd edition), Likens G. Sources Biological (microbial) sources Volatile forms SO42- reduction Sulfate reduction can also lead to production of pyrite FeS2. Volcanic emissions SO2 Oceans Fossil fuel burning Dust and sea salt 8

9 Anthropogenic sources Troposphere Residence time days SO 4 (2-) 1-2 Days DMS Regional impacts Upper troposphere Aerosol S0 4 increasing over time Suggested due to aircraft. 9

10 Dry deposition is poorly understood 10

11 Essential steps in the cycle Mineralization of organic sulfur to the inorganic form, hydrogen sulfide: (H 2 S) Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate, (SO 4 2- ) Reduction of sulfate to sulfide Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur Wetlands: brief introduction 11

12 Wetland types From Mitch and Gosselink 2000 Example Types of Wetlands 12

13 Biogeochemistry of Wetlands, Reddy and Delaune (2008) From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 13

14 Redox potential Measure of electron availability in a solution (negative more Used to quantify reduction Measured as Eh and is a quantitative measure of the soils ability to oxidize or reduce chemicals Redox Potential From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 14

15 From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) 15

16 From: Biogeochemistry of Wetlands, Reddy and Delaune (2008) Biogeochemistry of Wetlands, Reddy and Delaune (2008) 16

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18 COS Carbonyl sulfide Most abundant sulfur species in the remote troposphere Not reactive long atmospheric residence time ~5 years In stratosphere important for maintaining sulfate aerosol Derived from abiotic photolysis of organic S compounds in seawater Oxidation of carbon disulfide-cs 2 emitted from anoxic soils and industry Table 13.3 Ocean is a sink Soils and vegetation are a sink New work COS uptake through plant stomata may be a useful indicator of gross primary productivity COS due to long residence time-mixed to stratosphere Where, reactions with OH produce SO4 SO4 combines to produced aerosols Not increasing in atmosphere 18