lecture 10: pathways of elements in ecosystems huang he phone: 18972127775 qq:105367750 e-mail:...

Lecture 10: Pathways of Elements in Ecosystems Lecture 10: Pathways of Elements in Ecosystems

Huang He

Phone: 18972127775 QQ:105367750 E-mail: [email protected]

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23/4/18 1

Burning of fossil fuels and forests has increased atmospheric CO2 concentrations from 280 ppm to 385 ppm since the Industrial Revolution. Understanding why and how ecosystem responses depends a basic understanding of carbon sources and sinks and processes involved.

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College of Chemistry and Environmental Engineering Huang He

Outline :Biogeochemical cycles

10.1 Energy transformations and element cycling are intimately linked

10.2 Ecosystems can be modeled as a series of linked compartments

10.3 Water provided a physical model of element cycling in ecosystems

10.4 Carbon cycle is closely tied to the flux of energy through the biosphere

10.5 Nitrogen assumes many oxidation states in its cycling through ecosystems

10.6 Phosphorus cycle is chemically uncomplicated10.7 Sulfur exists in many oxidized and reduced forms10.8 Microorganisms assume diverse roles in element cycles

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10.1 Energy transformations and element cycling are intimately linked

Assimilatoiry process: transformation of inorganic forms of elements into the molecules of organisms, such as photosynthesis

Dissimilatory process: transformation of organic form of elements back to inorganic form, such as respiration.

Chemical transformations of elements occurs in the soil, air, and water, with and without organisms involved (weathering, lightning)

Biochemical transformation involves oxidation and reduction.

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10.2 Ecosystems can be modeled as a series of linked compartments

Compartment models

Carbon, Inorganic forms to organic forms

Within each compartment, we can reorganize subcompartments

Organic forms: animals, plants, microbes, detritus

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10.3 Water provides a physical model of element cycling in ecosystems

Major processes involved in water cycling: evaporation, transpiration and precipitation

Solar energy drives evaporation

Condensation forms precipitation

Unit in the chart: 10^18 g, teraton (a trillion metric tons)

Biosphere: 1,400,000

97% in oceans

Residence times:Air: 1/26 =2 weeksEarth surface: 2,800 yrs

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10.4 Carbon cycle is closely tied flux of energy

Processes: 1.Photosynthesis and respiration

2.Ocean-atmosphere exchange

3.Precipitation of carbonates in aquatic systems

4.Methanogenesis in swamps, marshes wetlands

Gigaton (10^15 g, billion metric ton)

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Carbon cycle

Tightly linked to energy flow

Difference between production and loss

NPP=GPP-Ra Net ecosystem

productivity• NEP=GPP-Ra-

Rh• NEP=NPP-Rh

Note storage• Carbonates

Coral reefs Limestone

• Coal• Oil• Gas• Peat

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Global carbon cycle

Carbon budget of Earth is closely linked to atmosphere, land and ocean and mass movement around planet.

Unit in gigatons (Gt= 10^9 metric ton=10^15 g)

Earth contains 10^23 g of C (100 m Gt )

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Global Carbon Cycle

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4CH3OH (methanol) CH4 + CO2 +2 H2O

CH4 can absorb about 25 times as much as infrared radiation as one CO2.

Cattle farm

The global carbon cycle involves diverse biochemical and chemical transformations.

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Atmospheric CO2 concentration change

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10.5 Nitrogen assumes many oxidation states in its cycling through ecosystems

Unit: 10^12 g N yr-1, GT N or GT N yr-1

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Nitrogen cycle Nitrogen is essential to life

Two uptake forms:• Ammonium (NH4+) and

nitrate (NO3-) Starts with nitrogen fixation

from atmosphere

Plants can only utilize nitrate or ammonia• Atmospheric deposit

Dryfall+wetfall• Nitrogen fixation

High energy (lightning, 0.4 kg N ha-1) in NH3 and HNO3 (nitric acid)

Biological • Bacteria, 10 kg N

ha-1.

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N fixation: N2 is converted into NH3 (NH4+ then ) by bacteria.

Ammonization: a process that organic N is converted to NH4+

Nitrification: a process that NH4+ is oxidized to NO2- and to NO3-

Denitrification: under anaerobic condition, NO3- is reduced to N2O and N2 and returned to atmosphere.

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Nitrogen assumes several different oxidation states as it cycles through ecosystems

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Nitrogen movement after fertilization in forests17


Global nitrogen cycle

Unit: 10^12 g N yr-1

3.9x 10^9

120 x 10^3

3.5 x 10^3

NxO

Nitrous oxide (N2O)

Nitric oxide (NO)

Nitrogen oxide (NO2)

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10.6 The phosphorus cycle is chemically uncomplicated

Phosphorus does not enter the atmosphere in any form other than dust, so little phosphorus cycles between the atmosphere and other compartments of ecosystems

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No atmospheric reservoir (rock and natural phosphate deposits) Follow water path, permanent loss of phosphorus to oceans Input limited to weathering of rocks Terrestrial systems can be limited by phosphorus availability (natural

ecosystems) Phosphorus is more abundant in marine and freshwater systems

Particulate organic P (contained in bacteria, algae, detritus) Dissolved organic phosphorus

Rapidly utilized by zooplanktonSecrete inorganic

Dissolved inorganic phosphorus Rapidly utilized by phytoplankton

Phosphorus can sink as particulate phosphorus and become locked in bottom sediment Depletion of surface layers, only return due to upwelling

Phosphorus cycle has no atmospheric pool

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Phosphorus cycle has no atmospheric pool

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Global phosphorus cycle

Unit 10^12 g P yr-122

10.7 Sulfur exists in many oxidized and reduced forms cycle

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Sulfur cycle is both sedimentary and gaseous (hybrid)

Hydrogen sulfide (H2S)Sulfur dioxide (SO2)Sulfuric acid (H2SO4)

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Global sulfur cycle (poorly understood)

Unit: 10^12 g S yr-1

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10.8 Microorganisms assume diverse roles in element cycles Heterotrophs: obtain carbon in reduced ( organic) form by consuming

other organisms or organic detritus. All animals and fungi, and many bacteria, are heterotrophs.

Autotrophs assimilate carbon as carbon dioxide and expend energy to reduce it to an organic form.

Photoautotrophs use sunlight as their source of energy for this reaction ( photosynthesis). All green plants and algae are photoautotrophs, as are cyanobacteria.

All of these organisms use H2O as an electron donor ( reducing agent) and are aerobic. Purple and green bacteria are also autotrophs, but their light- absorbing pigments differ from those of green plants, they use H2S or organic compounds as electron donors, and they are anaerobic.

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Microorganisms assume diverse roles in element cycles Chemoautotrophs use CO2 as a carbon source, but they obtain energy for

its reduction by the aerobic oxidation of inorganic substrates: methane ( for example, Methanosomonas and Methylomonas); hydrogen ( Hydro- genomonas and Micrococcus); ammonia ( the nitrifying bacteria Nitrosomonas and Nitrosococcus); nitrite ( the nitrifying bacteria Nitrobacter and Nitrococcus); hydrogen sulfide, sulfur, and sulfite ( Thiobacillus); or ferrous iron ( Ferrobacillus and Gallionella).

Chemoautotrophs are almost exclusively bacteria, which are apparently the only organisms that can become specialized biochemically to make efficient use of inorganic substrates in this way and dispose of the resulting waste products.

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Bacteria use oxygen from seawater to oxidize the hydrogen sulfide in vent water ( H2S SO42 + energy), which provides them with a source of energy for the assimilatory reduction of inorganic carbon and nitrogen from seawater ( e. g., NO3 NH4+).

Chemoautotrophic sulfur bacteria form the base of the food chain in hydrothermal vent communities.

Other vent organisms, such as these tubeworms ( Riftia pachyptila) at a Pacific hydrothermal vent, rely on these bacteria to produce food.

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The cycling pathways of carbon and phosphorus differ in temperate lakes.

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10.9 Two major types of biogeochemical cycles

All nutrients follow biogeochemical cycles Two major types of cycle

GaseousMajor reservoirs are atmosphere and oceansGlobal in nature, important gases

– Oxygen 21%– Nitrogen 78%– Carbon of carbon dioxide 0.03%

SedimentaryMajor reservoirs are soil, rocks and mineralsRock phase and salt solution phaseSalt solution is the available form

– Phosphorus– Metals, eg Calcium, Magnesium, etc

Some cycles are hybrid Sulfur (S) Major pools in Earth’s crust and atmosphere

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Two major types of biogeochemical cycles

Common features: Involve biological and non-biological processes Driven by the flow of energy through ecosystem Tied to water cycle (water is the important medium;

Without water cycle, biogeochemical cycle would cease).Share three basic components:

inputs, internal cycling outputs.

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10.10 Inputs and outputs

Nutrients enter the ecosystem via inputs Gaseous cycle from atmosphere (C,N) Sedimentary from rocks and minerals (P, Ca)

Wetfall and dryfall Precipitation -- wetfall Airborne particular and arsenal (rainfall on the forest floor

is nutrient rich than on the bare soil) -- dryfallNutrient in aquatic ecosystem

From surround lands in the form of drainage water, detritus, sediment and precipitation.

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Outputs

There are also outputs to the biogeochemical cycles Carbon to carbon dioxide, release back to atmosphere Nutrient to gaseous form (denitrification) Loss of organic matter from ecosystem by washout (from terrestrial to aquatic) Herbivores between aquatic and terrestrial

Moose (feed on aquatic plants, deposit nutrient in terrestrial ecosystem in the form of feces) Hippopotamus (move organic matter from terrestrial to aquatic)

Harvesting may be replaced by fertilization Loss of nutrient (e.g.Leaching) may be balanced by inputs (weathering of rocks and minerals)

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Internal cycling

Nutrients are recycled within the ecosystem Internal recycling is important within ecosystem Some systems have large amount of short term recycling

Lakes Other have most stored as biomass

Forests Long term storage in water systems is in the sediment

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A generalized biogeochemical cycle

Note input, internal cycling, and output

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Pools and fluxes

Three calcium pools:

Plants, dead OM and soil

Pool size: 290, 140, 440 kg ha-1

Fluxes (kg ha-1 yr-1)

F1: uptake

F2: litterfall

F3:leaching from plants

F4:net mineralizationTurnover time: t=P/f steady-state t_p=4.8, t_OM=2.3, t_s=7.3 (years)

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10.11 Various biogeochemical cycles are linked

All elements are components of living organisms and constituents of organic matter

Thus all cycles are linked: ChemicallyEnergeticallyBiologically

Stoichiometry: quantitative relationship of elements in combination.

Example: C:N ratio, 8 to 15 for microbes, 30 for leaf, etc C:N:P ratio

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23/4/18 39

lecture 10: pathways of elements in ecosystems huang he phone: 18972127775 qq:105367750 e-mail:...

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