Carbon Cycling or. perspective. CE5508 Biogeochemistry

Transcription

1 Carbon Cycling or the importance of methods & perspective CE5508 Biogeochemistry Spring 2006

2 Topics to cover GPP vs. NPP vs. NEP (NCP) Carbon flow paths Allochthonous (exogenous) vs. autochthonous (endogenous) Cycles within cycles (net vs. gross)

3 NEP CO 2 NPP Autotrophic respiration GPP Photosynthesis Heterotrophic respiration DOC export NEE

4 Human Effects Global plant harvesting = ~6% of global NPP; Pollution, fires reduce global NPP 25-40%; Anthropogenic CO 2 emissions of 6.9 Pg/yr represent ~10% of total t terrestrial t NPP or emissions (respiration ~ NPP within 3%); Global biomass reduced by ~13% in 100 yrs. Biodiversity loss: 1000-times normal rate

5 How do we define efficiency? Plants fix only about 2% of incident solar radiation (GPP) but only 1% is stored as NPP; how much could be fixed without altering earth s temperature? Typical fossil fuel power plant efficiency 33%; high-efficiency LP or NG furnaces have efficiency 85-94%; Ethanol production: 1% solar conversion efficiency x 50% respiration loss x 95% (herbivory) x 10% biomass used x 50% fermentation efficiency x production efficiency < 0.02% U.S. ethanol production: BTU in ethanol per BTU required for production ( ) Photovoltaics: 12-17% solar conversion efficiency x 19.8yr-life/0.2- yr EPBT = ~140% (1000 BTU received for 1 BTU to mfr) eff = output input

6 Energy Flow, Trophic Pyramid

7 Organic Matter Cycle to Geologist Atmossphere 2.5 CO O 2 Biosphere 25CHO CO O 2 Ocean 2.5 CH 2 O 2.5 CH 2 O Deep Rocks Terramole/yr

8

9 Total Cycle Atmossphere 5.37 CO O 2 Biosphere CO 2 537CHO CO 2 44MgCO O 2 Ocean 4.92 SiO SiO CaSO SiO Mg CaSO CaCO Ca HCO CaCO MgSiO MgSiO CH 2 O 4.93 FeSiO 3 27NaCl Na 2 SiO K 2 SiO FeS 2 Deep Rocks 1.0 Na K NaCl 2.74 Fe 2O H 2 SO CH 2 O 2.74 Fe 2 O NaCl 05N 0.5 Na 2 SiO K 2 SiO 3

10 Organic Matter Cycle Atmossphere 10,000 CO 2 (GPP) Terrestrial Biosphere 500 CO 2 Fossil Fuel 10,000 O CH 2 O 500 O 2 Ocean 2.5 CH 2 O Deep Rocks 2.5 CH 2 O < 5% of NPP Terramole/yr

11

12 Phosphorus Cycle Average turnover time of PO 3-4 in L. Victoria is 5-10 minutes; In L. Superior, a P atom is cycled more than 500 times in water column before settling into the sediments; i.e., although residence time is about 4 years from net budget, the actual turnover time is only about 3 days in summer.

13 GPP vs. NPP GPP is instantaneous SUMMER rate of CO 2 fixation; NET NPP is GPP less OXYGEN PRODUCTION WINTER autotrophic respiration. NEP is NPP minus HR NEP (NCP) is GPP minus RATE LIGHT, GPP Community respiration PHOTORESPIRATION (CR) Time (hour of day) 2-hr 8-hr Basal RESPIRATION 24-hr

14 Aquatic GPP vs. NPP Rate 14 Δ PO C DIC = t DI 14 Δ C DI 14 C GPP DIC POC DOC

15 Tropical Rainforest Temperate Deciduous forest Boreal forest Grassland

16 On what does terrestrial NEP depend? Arrow height proportional to annual emissions/uptake

17 Leakage from terrestrial systems

18 Rivers as conduits

19 16% 10% 10% Global Terrestrial ecosystem DOC export (annual) ~400 Tg In-lake respiration ~80 Tg 16% In-river respiration ~120 Tg 19% Delivered to ocean 200 Tg Missing carbon sink 1300 Tg/yr

20

21 Does allochthonous C support lake food webs?

22 Peter & Paul Lakes

23 In both lakes, particulate organic carbon (POC) is quickly labeled with 13 C indicating that phytoplankton fixation of H 13 CO 3- occurred. Zooplankton also quickly pick up label.

24 Modeling of POC pool suggests that data can be fit only when POC includes both new algal production, old algal production, and terrestrial components. Terrestrial component represents 50% of POC.

25 Model with terrestrial carbon component, old algal component, and new algal component fits best for zooplankton as well. Fish also showed label; not modeled, but if 50% of zooplankton C is terrestrially-derived, so must 50% of fish carbon.

26 Same experiment, 13 C appears first in DIC, then quickly appears in POC, DOC, bacteria.

27 55-70% of bacterial carbon was allochthonous

28 Most DOC is allochthonous (terrigenous or exogenous). Although bacteria are feeding on DOC, they have less allochthonous org C than does DOC. Evidently, bacteria preferentially utilize small pool of (labile) autochthonous (algal-derived or endogenous) DOC.

29

30 WATER TABLE PREDICTION

31

32

33

34