17.0147.014Lecture 20: Limiting Factors and Lecture 20: Limiting Factors and Biogeochemical CyclesBiogeochemical CyclesMarch 30, 2005March 30, 2005Global Nutrient Cycling - Biogeochemical CyclesUseful Conversion Factors1012 g = 1 teragram = 1 Tg109 g = 1 gigaton = 1 gt106 g = 1 metric ton = 1 tonneMean Residence Time (MRT)= pool size / mean flux in or out of poolFractional Turnover = 1 / MRT= fraction that is removed and replaced per unit timeOCEANDead Organic MatterMarine BiomassSinkingDead Organic MatterBioelements in SolutionUptakeWeatheringVolatile ElementsVolatile ElementsPrecipitationDecompositionRunoff LossesTerrestrial BiomassDeathEvaporationH2O and volatile elements only2Solar Energy BudgetSolar Energy BudgetTotal From Sun 100%(1.3 x 1021kcal per year)Reflected 30%Absorbed (heat) 47%Used in Evaporation 23%Used in Winds & Currents 0.2%Used in Photosynthesis 0.002%Used to Drive the CyclesSolar RadiationUV radiationAbsorbed by ozoneAbsorbed by earthVisible lightReflected by atmosphereRadiated by atmosphere as heatGreenhouse effectEnergy In = Energy OutSource of energy to most ecosystems on Earth is Solar RadiationHeat radiated by earthThe Geologic CyclePowered by Solar & Geothermal EnergyGEOTHERMALMagmaMetamorphic RocksSedimentary RocksSoilsSurface RocksIgneous (Lava)IgneousMeltingWeathering ErosionUplifting UncoveringSOLARCritical for Critical for Driving the Driving the CycleCycle3The Global Water CycleIce 33,000,000Soil Waters 122,000Groundwater 15,300,000Atmosphere 13,000Oceans 1,350,000,000111,00071,000River flow40,00040,000385,000 425,000Net transport to landReference: Schlesinger, 1997Pools (km3)Fluxes (km3/yr)The Global Phosphorus CycleDust Transport1.0Soils 200,000Mineable rock 10,000P- MinesLand plants 300060Internalcycling12Sediments 4x109Riverflow211000InternalcyclingOceans 90,0002Fertilizers & DetergentsPools (1012g P)Fluxes (1012g P/yr)Geologic Time Scales (108years)Reference: Schlesinger, 1997crops4Global Nitrogen- TransformationsReducedReducedOxidizedOxidizedAnoxicAnoxicOxicOxicOrganic - N NH4+NO2-NO3-N2N2ONOAmmonificationNitrogen FixationDenitrification (anaerobic respiration)Nitrification(chemosynthesis)AssimilatoryNitrate ReductionReleases EnergyRequires EnergyRequires EnergyThe Global Nitrogen CycleN-fixation in lightening <3Land plants 3,5001200Soil organic – N 12,000Industrial N-fixation80InternalcyclingGroundwaterRiverflow368000InternalcyclingOceans 570,000Permanent Burial 10Atmosphere 4x109Biological Fixation 140Denitrification<200Denitrification110Fluxes (1012g N/yr)Pools (1012g N)Reference: Schlesinger, 1997Fertilized crops20Cultivated legumes405Natural sources Human sourcesAmount of nitrogen (gigatons/year)160140120100806040200Nitrogen FluxesLightningBiologicalfixationFossil fuelsNitrogenfertilizerNitrogen-fixing cropsFigure 51.13bHubbard Brook Experimental Forest, New HampshireChoose two similar watersheds.Document nutrient levels in soil organic matter, plants, and streams.Figure 51.10a upper6Figure 51.10a lowerClearcutControlDevegetate one watershed and leave the other intact.Monitor the amount of dissolved substances in streams.DevegetatedNet dissolved substance (kg/ha)1965–66 1966–67 1967–68 1968–69 1969–70Control10008006004002000YearFigure 51.10bNutrient runoff results7Burning fossil fuelThe Global Carbon CycleBurial 0.1Ocean 40,00092 90Atmospheric Pool 750 Measured annual increase +3.5Soils 1500Net destruction of vegetation1.510250GPPR50Rivers 1Land plants 560Pools (1015g C)Fluxes (1015g C/yr)See Freeman, Figure 51.1R6YearCO2concentration (ppm)3603503403303203101960 1970 1980 1990Figure 51.12bAtmospheric CO28-450 -350-400 -300 -250 -100-150-200 0-50 50Thousands of years400150200350300250Atmospheric CO2(ppmV)Ice Core Data Showing Changes in Ice Core Data Showing Changes in Atmospheric COAtmospheric CO22ConcentrationsConcentrationsBiosphere II ExperimentBiosphere II Experiment9Photosynthesis OPhotosynthesis O22Cement infrastructureCement infrastructureRich soilRich soilCa(OH)2+COCO2 2 →CaCO3+ H20Why didn’t CO2increase?RespirationRespirationCOCO22Photosynthesis COPhotosynthesis CO22RespirationRespirationOO22gasp!∆ O2∆ CO2Understandable Understandable only in only in hindsighthindsight““Biosphere I” ExperimentBiosphere I” ExperimentPopulation size (billions)Population size (billions)COCO22NN22O (310 x COO (310 x CO22))CHCH4 4 (21x CO(21x CO22))Population sizePopulation size38038034034030030026026018001800140014001000100060060000100010005005001500150020002000COCO22and Nand N22O O ppmVppmVTime, Calendar years (A.D.)Time, Calendar years (A.D.)CHCH44ppbVppbV66442200Falkowski and Tchernov
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