Sulfur and Silica. Wetzel, Ch. 14

Transcription

1 Sulfur and Silica Wetzel, Ch. 14

2 Nutrient: any element that an organism must take in to live, grow and reproduce. Macronutrients: C, H, N, O, P, S Hydrologic Gaseous Sedimentary water C,N P, S

3 Biosphere Lithosphere H O C N Ca K Si Mg P S Al Elements Hydrosphere Atmosphere

4 Global S Cycle (flux 1012 gs/yr) WRT Lakes -Natural sources -Weathering - Wetlands

5 FORMS OF SULFUR S - = sulfide HS- = Sulfhydral SO 2 = sulfur dioxide SO 3 = sulfur trioxide SO 2-4 = sulfate H 2 S = hydrogen sulfide FeS = pyrite Also Organic S - a) dissolved; b) particulate

6 Wetzel Fig

7 Wetzel Fig

8 The sulfur cycle is regulated by Sulfur oxidizing and reducing bacteria

9 Sulfur Cycle ORGANIC S COMPOUNDS Degradation by bacteria SO 4 2- H S 2 Reduction Oxidation Oxidation ELEMENTAL S 1) Sulfur-oxidizing bacteria a) chemosynthetic b) photosynthetic 2) Sulfur-reducing bacteria

10 Sulfur Cycle ORGANIC S COMPOUNDS Degradation by bacteria Two Steps: E SO 4 2- H S 2 H 2 S O 2 S + H 2 O E Reduction S O 2 + H 2 0 H 2 SO 4 Oxidation Oxidation ELEMENTAL S 1) Sulfur-oxidizing bacteria a) Chemosynthetic Sulfur-oxidizing bacteria (e.g. Beggiatoa, Thiothrix, Thiobacillus)

11 Sulfur Cycle ORGANIC S COMPOUNDS Degradation by bacteria SO 4 2- H S 2 Reduction Oxidation ELEMENTAL S 1) Sulfur-oxidizing bacteria Oxidation CO 2 + H 2 S or LIGHT CH 2 O + 2S LIGHT 2CO 2 + 2H H 2 S 2(CH 2 O) + H 2 SO 4 a) Chemosynthetic sulfur-oxidizing bacteria b) Photosynthetic sulfur-oxidizing bacteria (e.g. green sulfur bacteria, purple sulfur bacteria)

12 Pelodictyon Wetzel Fig. 12-3

13 Sulfur Cycle ORGANIC S COMPOUNDS Degradation by bacteria SO 4 2- H S 2 Reduction Oxidation Oxidation H 2 SO (CH 2 O) 2CO 2 + H 2 O + H 2 S ELEMENTAL S or H 2 SO 4 + 4H 2 2) Sulfur-reducing bacteria (e.g. Desulfovibrio, Desulfotomaculum) 4H H 2 S

14 Wetzel Fig. 13-7

15 Summary Biogeochemical cycling of many macro- and micronutrients are regulated by redox states Cycling can be complex Bacteria can be an important producer as well as decomposer in lakes

16 SILICA CYCLE Si - dissolved (silicic acids) - Particulate silica (organic and inorganic forms) World average 13 mg/l SiO 2 Rock Source Volcanic Plutonic Sandstones Carbonates Si in gw High Low

17 Biosphere Lithosphere H O C N Ca K Si Mg P S Al Elements Hydrosphere Atmosphere

18 LIEBIG S LAW OF MINIMUM The element present in the lowest concentration relative to its demand limits growth - you are only as strong as your weakest link H O C N P Si Biosphere ~0 Lithosphere ~0 ~ Hydrosphere ~0 ~0 ~0 ~0 Atmosphere ~ ~0 ~0 Demand/ Supply (in water) ~Table 13-15

19 Silica mainly important for one dominant algal group: the DIATOMS A major component of their cell walls (= frustules)

20 Chrysophyte algae also have some silica requirements All chrysophytes form siliceous resting stages called stomatocysts

21 Some chrysophyte genera are characterized by external siliceous scales (e.g. Mallomonas) (e.g. Synura)

22 SILICA CYCLE Silica utilization (or uptake) Si that disappears from the water column as the result of production of biogenic Si Silica limitation [Si] where growth becomes limiting (< 0.4 mg/l) Silica depletion long-term biogeochemical decrease in [Si]

23 Wetzel Fig

24 Diatom changes in a lake can often be linked to SiO 2 levels Wetzel Fig

25 Coupling of Silica and Phosphorus Cycles Why are [Si] so low in Lake Ontario and so high in Lake Superior? Have [Si] always been so low in Ontario? Schelske, C.L., E.F. Stormer, G.L. Fahnenstiel, and M. Haibach Phosphorus enrichment, silica utilization, and biogeochemical silica depletion in the Great Lakes. Can. J. Fish. Aquat. Sci. 43:

26 Silica Concentration (mg/l) SUPERIOR 4 ųg/l TP HURON 5 ųg/l TP MICHIGAN 8 ųg/l TP ONTARIO 25 ųg/l TP 150 Moderate changes Not limiting Max. changes After stratification Max. changes Before stratification Small Seasonal Changes Summer Minimum Spring Minimum Winter Maximum

27 Conceptual Diagram relating Phosphorus and Silica Cycles TP Si Diatom Growth Time

28 Summary Silica is important (and potentially limiting for diatoms/chrysophytes) Biogeochemical cycles are often interrelated in complex ways Cycling of Si is rather slow in comparison to phosphorus