Presentation on theme: "Outline Approaches to study ecosystems What is a “global” biogeochemical cycle? Why are they studied? Basics of the C cycle and its links to O A counterintuitive."— Presentation transcript:
Outline Approaches to study ecosystems What is a “global” biogeochemical cycle? Why are they studied? Basics of the C cycle and its links to O A counterintuitive idea about atmospheric O 2 What role to freshwater systems play in the global C balance? The regulation of a global cycle depends on the time frame considered.
Global C balance in Gt y -1 rough numbers after Schimel et al. 2001 Emissions to atmosphere 6.5 Increase in atmosphere 3.1 Oceanic gas exchange -1.5 (physical) Net “terrestrial sink” -1.9 ( biological) How are these numbers validated?
Suess Effect Change in 14 C (and 13 C) in the atmosphere due to human process. Named for Hans E. Suess What changes and why?
Past 10,000 years of atmospheric CO 2 Relatively stable. Not decreasing. (Falkowski and Raven) If organic C was stored on land, where did CO 2 come from? Oceanic source, not larger than ~0.75 Gt y -1 Maybe terrestrial sink is 0.75 larger than the sink from modern atmospheric budget.
Atmosphere Increasing slowly 0.02 Gt y -1 Ocean ocean sediment Post glacial (10,000 y) 0.09 to 0.75Gt y -1 Values after Sundquist 1993 0.09 to 0.75Gt y -1
Atmosphere Increasing rapidly 3.1 Gt y -1 Ocean ocean sediment Modern (50 y) 1.3Gt y -1 ~1.9Gt y -1 Values after Schimel et al 2001 6.3 Gt y -1
Review standing stocks Before we get in deep- What are the large and small reservoirs of C on Earth?
Components of Productivity CO 2 GPP NPP Detritus and exudates Not decomposed Exported Buried (Sediments and SOM) Consumers RaRa Decomposers RhRh Plant biomass accumulation NEP (R t = R a + R h)
GPP review GPP = total photosynthesis (> 0) R = total respiration (> 0) NEP =GPP-R (may be + or -) When NEP is +, equals burial plus export When NEP is -, net heterotrophy
NEP algebra. External Import from Outside ( I e ) Export from ecosystem (E) Burial (export to sediments) (B) GPP (gross primary production) R (total respiration in the system) Total Inputs = GPP + I e Total losses = R+E+B Total Inputs = Total Losses (conservation of matter)
NEP Algebra Continued Since NEP = GPP-R, we can rearrange (GPP-R) = E+B-I e or: NEP = E + B – I e So you do not need to measure GPP or R to get NEP. If I e is > (E+B), NEP is NEGATIVE
Terrestrial Biosphere 500 -1000 Gt Terrestrial detritus 1000-2000 Gt Marine Biosphere 2 - 4 Gt Marine detritus 500 -1000 Gt Marine sediments, organic 20,000,000 Gt Atmosphere 760 Gt ~48 Gt/y photosynthesis ~52Gt/y photosynthesis Biological parts of the C cycle (after Holland, 1993). -2 y 0.12 Gt/y 0.4 Gt/y river transport whole ocean net heterotrophy is Burial + Export - Import 0.12 –0.4 = -0.28 Gt/Y or OR ~0.8 g C m burial R ~100-0.12 99.8Gt/y
Terrestrial GPP (slightly) > R; NEP > 0 Aquatic GPP (generally) < R; NEP < to << 0 Positive NEP on land subsidizes aquatic R
1 2 3 4 Billions of years before present pO 2 (atm) cyanobacteria eucaryotes Land plants mammals
Where does oxygen come from? Photosynthesis Balance between GPP and R GPP-R=NEP= org C burial. Atmospheric Oxygen comes from org C burial. If atmospheric O 2 has been “flat” for the past 500,000 years, what does that imply?
What ever controls organic C burial controls atmospheric O 2 O 2 >> 0.2 atm leads to increased fire. O 2 << 0.2 atm unsuitable for most aerobes What controls C burial? – Mayer hypothesis – Oxygen hypothesis.
GAIA (Lovelock, 1991) Hypothesis: Earth is kept in a state favorable to living organisms by (in part) living organisms. Theory: sees Earth as system in which evolution of organisms is tightly coupled to evolution of the environment. Self regulation of climate and chemistry are emergent properties of this system
Thank you. Jan 10 th - think about Coupled Biogeochemical Cycles and Geoengineering
Organic C burial in lakes is large Natural lake organic C burial – 0.065 Gt y-1 (Mullholland and Elwood 1982) – 0.034 Gt y-1 (Dean and Gorham 1998; Stallard 1998) Lakes sequester 28 to 54% as much organic C as does the global ocean! Oceanic organic C burial ~0.12 Gt y -1 See Cole et al. 2007, Ecosystems
Why do lakes bury so much organic C? Rich theory of C preservation in the sea – Oxygen exposure time hypothesis – Sorptive preservation hypothesis Poorly developed theory in freshwaters. – Low oxygen (a real possibility) – Low sulfate (especially compared to ocean) – High lignin (plus low O 2 ) – can be dismissed Certainly not close to a universal law of C burial in freshwaters.
High organic C content in freshwater sediments. This Danish man from 500 BC (so somewhat older than our St. James) was preserved in bog sediment.
Dr. Morten Sondergaard a living Dane and scientist.
Why did Morten’s progenitor preserve – or why do freshwater sediment have so much organic C? (From the Tollund man web site) No oxygen, therefore no bacteria, and no rotting. Sphagnum inhibits bacteria Special acids inhibit bacteria Tannins ‘tan’ the hide.
Burial Efficiency- Oxygen exposure time Hartnett et al. 1998 Nature Burial Efficiency = Burial / Input = Burial / (Burial + Respiration) DI-MICTIC LAKES HERE? Oxygen exposure time (yr) Organic C Burial Efficiency (%)
An empirical organic content model Hakanson 2003 IG = loss on ignition (%DW) SMTH= 52 week smoothing function ADA = drainage area; A lake area Drel = relative depth; color = water color Drel is the relative depth (= Dmax · √π/(20 · √Area),
Whole-lake areation experiment Engstrom and Wright 2003 10 lakes in Minnesota Cores taken before and after aerating 5 5 lakes as ‘control’ Areation was from 8 to 18 Years. Near continous. Irregular effect of aeration on total sed accumulation Areated lakes did not decrease in organic content.
Carbon in freshwaters – summary so far Globally, lakes bury about 40% as much organic C as does the ocean. We do not have good models for C preservation in lake sediments. Research opportunity. River delivery of organic and inorganic C to the ocean is an important term in the global C balance. Lakes and rivers tend to be net heterotrophic – must respire some terrestrial C. Does this terrestrial C move up the food web? Research opportunity.
GPPR sedimentation Net gas flux transport Do Freshwater systems matter in the global C balance?
NCEAS working group Cole et al. Ecosystems 2007 Integrating Terrestrial and Aquatic C Cycles (ITAC) Rob Streigl, Nina Caraco, Lars Tranvik, Bill McDowell, Carlos Duarte, Jack Middleburg, John Melack, Yves Prairie, Pirkko Kortalainen, John Downing, Jon Cole
Rivers also transport “atmospheric” C Terrestrial OC in rivers to the ocean (units are Gt y -1 (from Meybeck 87; Sarmiento and Sundquist 92; Stallard 98: Dissolved organic C - 0.23 Particulate organic C - 0.30 Total organic transport 0.53 Note implied loss from land is larger by 0.23 number or ~ 0.75 Gt y -1 to balance riverine gas flux.
Dissolved inorganic C (DIC) DIC is CO 2 +H2CO 3 + HCO 3 +CO 3 DIC in rivers is dominated by HCO 3 At pH 7.3 HCO 3 is 10X CO 2 and 100X CO 3 Where does riverine HCO 3 come from? How does the transport of HCO 3 fit into the terrestrial C balance?
Riverine HCO 3 is soil respiration in disguise The ultimate source of C in HCO 3 is (mostly) the atmosphere. Alkalinity comes from rock weathering which either consumes atmospheric CO 2 directly or consumes CO 2 from soil respiration. Terrestrial NEE (flux tower) is overestimated by the amount of HCO 3 lost
for carbonates CO 2 + H 2 O + CaCO 3 Ca ++ + 2HCO 3 - 2CO 2 + 2 H 2 O + CaMg (CO 3 ) 2 Ca ++ + Mg ++ + 4HCO 3 - Carbonate weathering – half the CO 2 is atmospheric for silicates 2 CO 2 + 3 H 2 O + CaSiO 3 Ca ++ + 2 HCO 3 - + H 4 SiO 4 2 CO 2 + 3 H 2 O + MgSiO 3 Mg ++ + 2 HCO 3 - + H 4 SiO 4 Silicate weathering – all the CO 2 is atmospheric
Riverine HCO 3 transport units are Gt C y -1 Total river DIC flux - 0.3 Gt y -1 From carbonate weathering 0.14 “atmospheric” C from carbonate weathering 0.07 From silicate weathering 0.15 Total atmospheric C as DIC 0.22
Rivers – summary units are Gt y -1 CO 2 efflux 0.15 Organic C delivery 0.5 Atmospherically derived HCO 3 (disguised soil R) 0.23 Burial – assumed ~ 0 Loss of terrestrial NEP in rivers 0.87 Note some organic C may be of riverine origin.
Nearly half of the “terrestrial” C sink is in riverine transport. Net Terrestrial C sink 2-3 G t/y ___________________________ Riverine transport 0.87 Burial in lake sediments0.05 Reservoir burial 0.22 ___________________________ Freshwater components 1.14
Lake, holocene Reservoir L. Malawi All rift lakes Terrestrial Biomass Soil Organic C stores on “land” Organic C (Pg)
Lake Reservoir Ocean sediment Terrestrial pre- industrial Terrestrial, industrial Net Storage (Pg y -1 ) Annual Rates of net organic C storage
Lake, holocene Reservoir River Flood plain Ocean abiotic Terrestrial biomass increase CO 2 flux (Pg y -1 ) To atmosphere from atmosphere Note: pre-industrially biomass increase approaches 0 and ocean CO 2 flux has opposite sign
Ocean Sediment storage Inland waters Ocean Terrestrial NEP (1-4 Pg C y -1 ) Inland waters CO 2 evasion 0.9 1.9 0.75 0.23 Passive Pipe Model Active Pipe Model Cole et al. Ecosystems 2007
Ecosystem An ecosystem is defined as a spatially explicit unit of the Earth that includes all of the organisms, along with all components of the abiotic environment within its boundaries – Likens 1992 Boundary definition is a big problem! Ideally, boundaries should represent the plane at which short-term exchanges of matter are irreversible relative to the functional ecosystem, ie, where cycling becomes a flux. Likens et al. 1974