2Biogeochemical Cycles A biogeochemical cycle is the complete path a chemical takes through the four major components of Earth’s system.AtmosphereHydrosphereLithosphereBiosphere
3Chemical ReactionsA process in which new chemicals are formed from elements and compounds that undergo a chemical change.E.g. rain water and carbon dioxideH2O + CO2 H2CO3Weak carbonic acid reacts w/ rock and soil
4Chemical Reactions Another example Chemical reaction for photosynthesis6CO2 + 6H2O C6H12O6 + 6O2The two reactions start with same compounds but end up with very different products.
6Biogeochemical cycles The simplest way to think of BGC cycles is a “box and arrow” diagramSometimes useful to consider a global perspective.Global climate changeOther times may need to viewed at local scaleLake Washington
8Chemical ReactionsChemicals in the four major components have different average storage timeLong in rocksShort in the atmosphereIntermediate in the hydrosphere and biosphere
9Environmental Questions and Biogeochemical Cycles Biological QuestionsWhat factors place limits on the abundance and growth of organisms and their ecosystem?What toxic chemicals might be present…?How can people improve the production of a desired biological resource?What are the sources of chemicals required for life?What problems occur when a chemical is too abundant?
10Environmental Questions and Biogeochemical Cycles Geologic QuestionsWhat physical and chemical processes control the movement and storage of chemical elements in the environment?How are chemical elements transferred from solid earth to water, atmosphere and life-forms?How does the long term storage of elements in rocks and soils affect ecosystems on local to global scales?
11Environmental Questions and Biogeochemical Cycles Atmospheric QuestionsWhat determines the concentrations of elements and compounds in the atmosphere?Where the atmosphere is polluted how might we alter a biogeochemical cycle to reduce pollution?
12Environmental Questions and Biogeochemical Cycles Hydrologic QuestionsWhat determines whether a body of water will be biologically productive?When a body of water becomes polluted, how can we reduce the pollution and its effects?
13Biogeochem Cycles and Life Of the 103 known elements only 24 required for life.Macronutrients- required in large amountsBig six = C, H, N, O, P, SMicronutrients- required either in small/ moderate amountsFor life to persist elements must be available at right time, right amount, and right concentrations relative to one another.
14Biogeochem Cycles and Life For life to persist elements must be available at right time, right amount, and right concentrations relative to one another.When this does not happen chemical can become a limiting factor
16General Concepts Central to Biogeochemical Cycles Some chemical cycle quickly and are readily regenerated for biological activity.They typically have a gas phase, are soluble and carried by the hydrologic cycle.Other chemical elements are relatively immobile and returned by geological processes.Typically lack a gas phase and insoluble
17General Concepts Central to Biogeochem Cycles Chemical w/ gas phase, that are stored in atmosphere cycle rapidly.Those w/o atmospheric phase end up in deep-ocean sediment and recycle slowly.Since life evolved it has altered biogeochem cycles.The continuation of processes that control biogeochem cycles essential for maintenance of life.
18General Concepts Central to Biogeochem Cycles Through modern technology transfer rate of elements into air, water, and soil altered.May improve crop production but pose enviro hazardMust recognize the + and – consequences of altering cycles
19The Geologic CycleOver the last 4.6 billion years rocks and soils has been continuallyCreated, maintained, changed, and destroyedBy physical, chemical, and biological processesGeologic cycle- group of cycles that is responsible for formation and changeTectonic, hydrologic, rock, and biogeochemical
23** mya = million years ago; bya = billion years ago Geologic History: Formation of the Earth: 4.57 bya1st life forms evolve: 4.00 byaOxygen Catastrophe: 2.50 byaAtmosphere becomes oxygenated: 2.05 byaEarliest fossils of multicellular life: 635 myaCambrian explosion, 1st chordate fossils: mya1st land plants: 470 myaTrilobites are common and diverse: 430 mya1st land vertebrates: 331 myaFormation of Pangea, creating the Appalachian mountains: 254 myaDissolution of Pangea: 174 myaDinosaurs ruled the land, mammals are common but small: 152 myaMammals are diverse and common: 59 myaEvolution of humans: mya
24The Tectonic CycleInvolves creation and destruction of the lithosphere (outer layer of Earth)~100 km thick and broken in to several platesThe movement of plates called plate tectonicsPlate tectonics has large scales effectsAlterations in climateEcological islandsAreas of volcanic activity and earthquakes
25The Tectonic Cycle Three types of plate boundaries Divergent, convergent, transform faultsDivergent plate boundaryOccurs at a spreading ocean ridge, where plates moving away from one anotherNew lithosphere producedKnown as sea floor spreading, produces ocean basins
27The Tectonic Cycle Convergent plate boundary Occurs when plates collideWhen heavier ocean plates meet lighter continental plates a subduction zone is present.When two lighter continental plates collide a continental mountain range may form.
31The Hydrologic CycleThe transfer of water from oceans to the atmosphere to the land and back to the oceans.Involves evaporation of water from oceansPrecipitation on landEvaporation from landRunoff from streams, rivers and subsurface groundwater
32The Hydrologic Cycle Driven by solar energy 1.3 billion km3 of water on Earth97% in oceans2% in glaciers and ice caps0.001% in atmosphereThe rest in fresh water on land
33The Hydrologic CycleAt the regional and local level, the fundamental unit of the landscape is the drainage basin.The area that contributes surface runoff to a particular stream or riverVary greatly in sizeUsually named for main stream or river
40Biogeochemical Cycling in Ecosystems An ecosystem is a community of different species and their non-living environment in which energy flows and chemicals cycle.Chemical cycling in an ecosystem begin w/ inputs from outside.RainDustVolcanic ash
41Biogeochemical Cycling in Ecosystems Chemicals cycle internally within ecosystem throughAir, water, rocks, soil and food chainsBy way of physical transport and chemical reactionsEcosystem can lose chemical elements to other ecosystemsE.g. river transport from land to sea
42Ecosystem Cycles of a Metal and a Nonmetal Different chemical elements have very different pathways.Calcium cycle is typical of a metallic elementSulfur cycle typical of a nonmetallic elementMetals do not have a gaseous phase.Elements with a gas phase can be returned to ecosystem rapidly.Annual input of S 10x that of CaCa more likely to be a limiting factor
45The Carbon CycleCarbon is the element that anchors all organic substances.Carbon has a gaseous phraseEnters atmosphere (CO2 and CH4) through respiration, fires and diffusion.Removed from the atmosphere by photosynthesis
46The Carbon Cycle Carbon occurs in the ocean in several forms Dissolved CO2, carbonate and bicarbonateMarine organisms and their products, CaCO3Enters the ocean bySimple diffusion then dissolvesTransfer from land in rivers as dissolved carbonWind
47The Carbon CycleCarbon enters the biota through photosynthesis and then returned by respiration or fire.When organism dies decomposition releases carbon.If buried under certain conditions carbon is not be releasedTransformed into fossil fuels
50The Missing Carbon Sink Carbon forms two greenhouse gasesCarbon dioxide and methaneAt a global level some key issues remain unanswered.8.5 units of CO2 release each year3.2 units remain in atmosphere2.4 units diffuse into ocean2.9 units unaccounted for
51The Missing Carbon Sink Inorganic processes don’t account for the fate of the carbon sink.Either land or marine photosynthesis.No agreement on whichTwo major uncertainties areRate of land use changeAmount of carbon in ecosystem storage compartments affected by human use
53The Carbon-Silicate Cycle The cycling of carbon intimately involved with the cycling of silicon.Weak carbonic acid falls as rain and weathers silicate rich rocksReleases Ca2+ and HCO3-Transferred to oceans and used by marine animals to construct shellsShells deposited on sea floor become part of sed rock layer and return to surface in subduction zones
54The Carbon-Silicate Cycle Affects the levels of CO2 and O2 in the atmosphere
56The Nitrogen CycleN essential to life because it is necessary for the production of proteins and DNA.Free N2 makes up 80% of atmosphereBut most organisms can’t use it directlyRelatively unreactive element must be converted to NO3- or NH4+Done by bacteria
57The Nitrogen CycleNitrogen fixation- process of converting atmospheric N to NO3- or NH4+Denitrification- process of releasing fixed N back to molecular NAlmost all organisms depend on N converting bacteriaSome have formed symbiotic relationships in the roots of plants or stomach on animals
58The Nitrogen CycleIndustrial process can now convert molecular N into compounds usable by plants.Main component of N fertilizersN in ag runoff potential source of water pollutionN combines w/ O at high temperaturesOxides of N a source of air pollution
60The Phosphorus Cycle P one of the “big six” required for life Often a limiting factor for plant and algal growthDoes not have a gaseous phaseRate of transfer slow
61The Phosphorus CycleEnters biota through uptake as phosphate by plants, algae and some bacteria.Returns to soil when plants die or is lost to oceans via runoffReturned to land via ocean feeding birds (guano)Guano deposits major source of P for fertilizers