1Announcements• Homework #5 to be assigned later today, due next Tuesday• Midterm Exam in two weeksGlobal Change: Terrestrial ecosystems & biogeochemistry #1Global Change Lecture #10, S. Saleska, 2-Oct-2007I. Definitions: Biogeochemistry & Ecosystem EcologyII. Example: the global carbon cycle through timeIII. Ecosystem Development paradigmIV. StoichiometryNext lectures: -N & P cycles - the water cycleBiogeochemistry = the study of how the cycling of elements through the earth system (water, air, living organisms, soil and rock) is governed by physical, chemical, geological and biological processesKey NamesVladimir Vernadsky (1863-1945): Russian scientist known as the “father of biogeochemistry”, invented the terms geosphere, biosphere, and “noosphere”G. Evelyn Hutchinson (1903-1991): famous limnologist (considered to be founder of limnology) (also studied the question of how biological species coexist)hydrosphereatmospherebiosphere pedosphere lithosphereI.(a) What is Biogeochemistry?• Ecosystem - all organisms in an area and the physical environment in which they interact– (abiotic and biotic characteristics of an area)• Ecosystems are characterized by energy flow and structural linkages (trophic structure)• Ecosystem ecology is the study of interactionsamong organisms and their physical environmentas an integrated systemI.(b) What is Ecosystem Ecology?2“The ecosystem stands as a basic unit of ecology, a unit that is as important to this field of natural science as the species is to taxonomy and systematics.”Francis Evans (1956) Ecosystems as the Basic Unit in Ecology, Science, 123: 1127-28I.(b) What is Ecosystem Ecology?II. Example: the global carbon cycle through timeWhat controls atmospheric CO2?Long-term trendsControlled by: Timescale:A. Geology (500 Myr)B. Oceanography (500 Kyr)C. Ecosystem Ecology (500 yr)Stocks of Carbon in the Earth SystemMass, Pg CLocation(=1015g)Lithosphere• carbonate in rocks 60,000,000• organic C in rocks 15,000,000ocean HCO-3+ CO-2342,000Biosphere/Atmosphere• soil carbon 1,500• atmospheric CO2 750• Living organic matter 600• Long-term atmospheric CO2 is the balance of volcanism (input) and chemical weathering/transfer to oceans/subduction(removal):CO2+ {Ca,Mg}SiO3Æ {Ca,Mg}CO3+ SiO2 • Shorter-term is the balance between Photosynthesis and Oxidation:H2O + CO2ÅÆ CH2O + O2(Silicate rock)(Cabonate rock)Chemistry of Carbon Dioxide3Weathering of rock• Weathering = physical and chemical decomposition of rock material•Weathering ≠ erosion• Weathering + erosion = denudation(in situdecompostion)(physical removal)CO2– Carbonate cycleSchlesinger 1997CaSiO3+ 2CO2+ H2O Æ Ca2++ 2HCO-3+SiO2SubductionCaCO3+ SiO2Æ CaSiO3+ CO2(weathering + erosion of silicate rocks, Æ riverinetransport to oceans)Ca2++ 2HCO3-Æ CaCO3(e.g. organisms build seashells)CO2from Volcanism(~ 0.1 Pg/yr)Berner, 1997A. Long-term trends in atmospheric CO2(geology controls)Ratio of ancient to modern pre-industrial CO2The rise of vascular plants with rootsBerner, 1997With a big assist from evolutionary ecosystem ecology!Ratio of ancient to modern pre-industrial CO2A. Long-term trends in atmospheric CO2(geology controls)4The rise of vascular plants with rootsBerner, 1997Ratio of ancient to modern pre-industrial CO2Amt of carbon in plant biomassWith a big assist from evolutionary ecosystem ecology!A. Long-term trends in atmospheric CO2(geology controls)Large scale ocean circulation (timescale ~1,000 yrs) driven by winds and fluxes of heat and salt (i.e. the “thermohaline circulation”)Ocean: 40,000 Pg CAtm: 750 Pg CVariations in thermohaline circulation (probably forced by solar Milankovich cycles) drive variations in CO2 – temperature pattern across glacials and interglacialsB. Medium-term trends in atmospheric CO2(ocean circulation controls)Ocean currents carry dissolved CO2 between deep ocean and surface mixed layer (where it can exchange readily with the atmosphere)Ice Cores Preserve the History of Atmospheric CO2 and climate over recent ice agesBarnola, et al.Vostok Ice core, AntarcticaB. Medium-term trends in atmospheric CO2(ocean circulation controls)Ice Cores Preserve the History of Atmospheric CO2 and climate over the recent ice ages(Ocean circulation controls)Barnola, et al.Current CO2 (375 ppm)Doubled pre-industrial CO2 (~550 ppm)plus human activity!5Ice cores + instruments record the recent (~100 yr) record of atmospheric CO2Uptake by= land and oceans(ecosystem ecology)(a) What mechanisms cause it?• Long-term forest regrowth? (not a feedback)(e.g., IPCC 2001; Goulden et al, 1996)• CO2 fertilization effect? (Bazzaz, Field) (a negative feedback)• N-deposition fertilization effect? (partial negative feedback)(probably not, say Nadelhoffer, et al. 1999)• Overestimation of deforestation source? (not a feedback)(b) Where and what kind of ecosystems?• Northern mid-lattitude forests? (atmospheric inversion models: e.g. Tans et al., 1990; Fan et al., 1998)• Tropical forests? (forest surveys: Phillips et al., 1998; plant physiological models of CO2 enrichment: Lloyd & Farquhar, 1996; Tian et al, 1998)More details in later lecture on fate of anthropogenic CO2– but ecosystem ecology controlsTerrestrial Uptake of excess atmospheric CO2• Carbon•Nutrients – (N, P, in inorganic forms)–Cations(Ca+, Mg+, K+ , ...)– Trace metals (Fe, Cu, Mn, Zn, …)•WaterWhat ingredients are needed to build a terrestrial ecosystem?Plants need:On average, plants are made (roughly) of:CH2Oor, more precisely:C106H263O110N16P1 + 21 other elements(of which element 53, Iodine, is heaviest)95% of bio-sphereIII. Biogeochemistry and terrestrial ecosystem development6How do necessary ecosystem ingredients get assembled?• Carbon•Nutrients –N–P–Cations(Ca+, Mg+, K+ , ...)– Trace metals (Fe, Cu, Mn, Zn, …)•WaterPlants need:Atmosphere (CO2)Atmosphere (N2 is 80%)Ultimate sourceOceanUnderlying Rock material(via evaporation & recon-densation as precip.)(via chemical weathering)(via biological fixation)(via biological photosynthesis)III. Biogeochemistry and terrestrial ecosystem developmentSimple ecosystem development model• Rock weathering is fundamental supply of P and cations that plants require: Ca, K, Mg• Atmosphere supplies N and mineral dust (cations and P)• Plants fundamentally create organic matter (Corgfrom CO2); recycle nutrients from all sources; promote weathering by making soil more acidic (adding