1Ecosystem fluxes and cycles• Ecosystem “efficiency” and trophictransfers• Tipping points between “blue water”and “green water” states in lakes andrivers• Ecosystem cycles of water, carbon,phosphorus, and nitrogen2Ecosystem ecology• Energy flowsand nutrientscycle throughecosystems• Humans areincreasinglychangingEarth’sbiogeochemicalcycles3Materials cycle—atoms (O, C, N, Ca, P ) created in stars, used again andagain, end up in different pools, fluxes transfer atoms between pools.Energy flows—a small fraction of solar radiation is fixed byphotosynthetic organisms, but once energy is dissipated as heat, it is neverrecovered by ecosystem (except as passive energy savings fortransport—e.g. ocean or air currents driven by heat and used byorganisms)."We Are Stardust..."Science Daily (June 25, 1999) — When Joni Mitchell, in her song"Woodstock," sang, "We are stardust..." she was being factualas well as poetic. Every element on earth, except for the lightest,was created in the heart of some massive star.45PhotosynthesisInputsChange in storageOutputs6Terrestrial (bottom-heavy) pyramid of trophic level biomass7Trophic levelefficiency (PN/PN-1)often ~ 10%)PN-1 = Resource Production= Not consumed + ingestedIngested = feces excreted+ assimilatedAssimilated = used formaintenance (respired)+ used for production (ofnew tissue or offspring) =PNP N-1PNNotconsumedDeadorganicmatterANINENRNFood producedconsumer8 Herbivore Carnivore Microbivore DetritivoreVert endotherm Vert ectotherm InvertI = ingestionA = assimilationF = egestionR = respirationP = productionEfficiency oftrophictransfer forsecondaryproductionAllocationsthatcompetewith growthandreproduction(defense,stress)P n / ( P n-1)Food quality is an important factor affecting production efficiency9Stocks (pools, compartments) and flows (fluxes)Input - Output = Change in Storage (= 0 atequilibrium)Turnover time: if system is in equilibrium,input (vol time-1) = output (vol time-1) = qResidence time, T = Volume/qTurnover rate (fraction of storage that is replacedin a given unit of time) = 1/Tstorageinput outputstorageinput outputYellow system hasshorter turnover timethan blue system.10Inverted pyramid of Trophic level Biomass-->Clean water, and fish—suppresssustain11Or “bottom heavy” trophic pyramid dominated by Cyanobacteria in a eutrophied lake?12Stabilized by: *nutrient sequestration in long-lived top predators; *upslope vectoring of nutrients by scavengers and predators(salmonids, birds, bats, bears) *terrestrial vegetative cover; *frequent scour and flushing thatmaintain edible prey taxaClear water state:Green water,eutrophic state:13Switch from oligotrophic to eutrophic state: Land conversion -loss of wetlands, forests -erosion, fine sediment loading -sewage, agrochemicals Water management (extraction, impoundment, diversion): -loss of flushing flows, habitatN214Eutrophic state stabilized by: *internal nutrient cycling enhanced by hypoxia; *loss of higher trophic levels due to hypoxia and inedible algae *more bank erosion with loss of rooted terrestrial vegetation; *nitrogen fixation by cyanobacteria that dominate under high P N215Ecosystem “healthier” with longer foodaquatic chains, if predators native.• Zero trophic levels: “drinkingtheir own automobile exhaust”• One trophic levels: nutrientassimilation and retention, buteutrophication• Two trophic levels:vegetation grazed down, butpestiferous insect emergence• Three trophic levels: smallfish• Four trophic levels: biggerfish• Five trophic levels: really bigfish, anglers, and wildlife16Waterextracted,fine sediments,solutes,and heat added.What are we doing torivers?Flow regulation,diversion andextraction17Bioaccumulation of DDT, PCBs, Hg, and other toxins18SF Chronicle Nov. 23 2003Double-edged swordfish:top of their food chains,and very long lived species19The Californiawater system:“The most massiverearrangement ofNature everattempted”(Kahrl et al.1978)Disturbance removal;Habitat simplification fragmentation 20River networkfragmentation:blue lines onmaps haven’tbeenconnected onground for 50yearsTerminus of Cowchilla R.should be a tributary ofthe San Joaquin, butdies in an agriculturalfield.Photos, W.E. Rainey21Most serious consequence of greenhouse warmingwill be the redistribution of water in space andtime:reduced snowpack storage in Sierraincreased intensity of stormsflashy, erosive runoffHydrologic cycle:Evaporation = PrecipitationTransfer processes:atmospheric transport,runoff22Hydrologic (water) cycle23Permeability of the surface: path that water takesfrom land to rivers determines time interval forstorage, and “flashiness” of floods24Evapotranspiration: Evaporation andtranspiration (loss of water through stomates ofplants)25Plants: changes in stomate behavior and roots willaffect evapotranspiration and storage of waterLess evaporation ! less precipitation26Campbell,p. 1209CO2NH4+NO3-CO (NH2) 2C6H12O6(Organic compoundscontain C and H)Available to biotaUnavailableInorganicCarbon27Carbon cycle (Campbell p. 1211)28Unavailableuntil mined2930Phosphorus cycle: No gaseous, atmospheric component31Fig. 27.3,KrebsP residence time:algae: days-weeksanimals: days-yearssoils: months-milleniaocean sediments: millions of yearsPhosphorus32Nitrogen cycle: more complex than P cycle33http://www.physicalgeography.net/fundamentals/9s.htmlHuman activities (fossil fuel combustion, syntheticfertilizers, cultivation of legumes, industrial meat production)have more than doubled the natural input rate of fixed(bioavailable) nitrogen (Vitousek 1997).The Nitrogen Cycle34Vitousek 1997 Ecol. Applicns35V. Smil 1997. Scientific American. Curiousfate of Franz Haber* German chemist,awarded Nobel Prize 1919 for ammoniasynthesis. Haber-Bosch synthesis of ammoniafrom nitrogen and hydrogen, combined at hightemps and pressures! explosives for WWIbut world fertilizers soon thereafter, allowinghuman population to exceed 6 billion….*also developedweaponizedchlorine gasused in WWI,hoping to limitoverallsuffering bybringing abouta quickerresolution tothe war.36Importance of forest cover in retaining N high in thelandscape—Hubbard Brook ExperimentGeneLikensp. 1214 CampbellTreecuttingcompletedcontroldeforestedstreamLosses during floods37Ecosystem efficiency:organic production/nutrient flux(mass time-t / mass time-t )38Stream Ecosystem
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