Embed Size (px)
Citation preview
BIO 3072 !Ecology !Eric L. Peters!
Topic 12 !Biogeochemical Cycles!
Biogeochemical Cycles! Exchanges of the various chemical elements that make up living
cells that occur between the nonliving (abiotic) and the living (biotic) components of the biosphere!
The source for each cycle generally has two parts:! A reservoir pool (or sink): a larger, slow-moving, usually abiotic portion
(atmosphere, hydrosphere, lithosphere). Slowly exchanges with:! An exchange (nutrient cycling) pool: a smaller but more active portion
with more rapid exchange between the biotic and abiotic ecosystem components!
Autotrophs and some heterotrophs obtain some of their nutrient elements from aqueous solutions in the environment!
Heterotrophs acquire many of their chemical elements from the foods that they consume!
After the death of an organism, the elements in its tissues are returned to the exchange pool through the action of decomposer organisms!
Biogeochemical Cycling!!In gaseous cycles, the reservoir is the air (in aquatic systems, the gases are dissolved in water)!
Tend to cycle more rapidly and adjust more quickly to changes in the biosphere, e.g., local accumulations of carbon dioxide are soon dissipated by winds or taken up by plants!
Examples: N, O, and C!!In sedimentary cycles, the reservoir is the Earth’s crust (or sometimes, the magma)!
Varies from one element to another, but each cycle consists fundamentally of a solution phase and a rock (or sediment) phase!
Weathering releases minerals from the rocks as salts, some of which dissolve in water, pass through a series of organisms, and ultimately reach the deep seas and are not recycled for long periods (sinks)!
Other salts deposit out as sediment and rock in shallow seas, eventually to be weathered and recycled!
Examples: S, Ca, and P!
Heat!
Producers! Primary!Consumers!
Secondary!Consumers!
Detritivores!Nutrient!Exchange Pool!
Energy and!Nutrient Sink!
Nutrient Flow!
Heat! Heat!Heat!
Energy Flow!
Detritus!
Decomposers!
Heat!
Nutrient Sources and Cycling! Biotic Components of Biogeochemical Cycles! Producers capture nutrients contained in abiotic sources, and
convert them into a form that can be used by consumers! Consumers digest some of this macromolecular material for food, use
monomers of macromolecules to build tissues! Certain consumers (detritivores) break down dead organic
matter and wastes (detritus) into small pieces! Like consumers, they digest some of this macromolecular material for
food, use monomers of macromolecules to build tissues! Detritivore wastes and leftovers are broken down still further
by other consumers (decomposers) for food! Decomposer bacteria usually required to convert elements
contained in organic molecules back into their original inorganic forms (thus, returning them to nutrient pool), e.g.,! Releasing N in amino/nucleic acids back into the environment as N2! Releasing P in nucleic acids back into the environment as PO4
2-! Releasing S in amino acids back into the environment as H2S!
Sources and Sinks in the Carbon Cycle!
A large fraction of C in the oceans precipitates as carbonates, and is converted into carbonate rocks. This C is eventually returned to the atmosphere after a long period of time by subduction of Earth’s crust, which carries the rocks down into the magma and vaporized, and resultant outgassing of CO2 by volcanism !
The Carbon (C) Cycle! !
BIO 3072 !Ecology !Eric L. Peters!
Topic 12 !Biogeochemical Cycles!
The Carbon (C) Cycle! Source of carbon is CO2 in the atmosphere or dissolved in H2O (as
bicarbonate anions, HCO3-)!
Autotrophs fix C into energy-bearing and structural organic compounds by photosynthesis or chemosynthesis. Most of these carbon compounds are metabolized by the the producers and is returned to the abiotic environment as CO2 as the end product of their respiration.!
C passes into heterotroph food webs via food consumption (and most of this ingested C is returned to the environment as CO2 as the end product of their respiration)!
When organisms die, C is returned to the abiotic environment by detritivores and decomposers (and again, most their ingested C is returned to the abiotic environment as CO2 as the end product of their respiration)!
A small amount of organic C is not decomposed, and accumulates as as peat and fossil fuels (coals, petroleum, and methane), becoming sequestered for 1000s to 100s of millions of years. Since 1820, humans have vastly increased the combustion of these fuels, which is releasing this long-buried C back into the atmosphere as CO2.!
Biotic Components of the Carbon Cycle! !
Distribution of the Earth’s water! The Water (Hydrological) Cycle!In thousands of km3 y-1 (1 km3 = 109 m3 = 109 T = 1012 L)!
The Water (Hydrological) Cycle!!The recirculation of water between the atmosphere, land, and oceans of the Earth!
Solar heat causes water to evaporate from the oceans and other water bodies on Earth to form atmospheric water vapor !
Atmospheric water vapor may condense to form clouds, which (depending on climate and the presence of nucleating agents) may allow it to be returned to the Earth’s surface as precipitation (rain, sleet, hail, and snow)!
A variable amount of precipitated water is quickly returned to the atmosphere through evaporation, or is taken up through the roots of plants and subsequently released through their leaves (transpiration)!
Water also runs off of the land surfaces due to gravitational flow, and is eventually returned to the oceans via rivers!
The remaining water infiltrates the ground and forms groundwater (which is also subject to flow)!
World Water Supply!! !Percent !Mean"
!Volume !of !Residence "Location !(km3) !Total ! Time!"
Oceans !1.23 × 109 !97.2 !1000s y!Ice caps and glaciers !2.80 × 107 !2.15 !>10,000s y!Groundwater (to 1 km) !4.00 × 106 !0.28 !days-1000s y!FW lakes and reservoirs !125,000 !0.009 !1-100s y!SW lakes !104,000 !0.007 !10-1000s y!Biota !65,000 !0.005 !7 d!Soil !65,000 !0.005 !14 d to 1 y!Swamps and marshes !3,600 !0.003 !months to y!Atmosphere !12,700 !0.001 !9 d!Rivers and streams !1,700 !0.0001 !10-30 d!Total !1.40 × 109 !100 !2800 y!
BIO 3072 !Ecology !Eric L. Peters!
Topic 12 !Biogeochemical Cycles!
Water Budgets!Distribution of water is very heterogeneous, and most precipitation occurs over the oceans!
!Precipitation !Evaporation ! !Runoff !"Location !(cm y-1) !(cm y-1) !(cm y-1) ! !(km3 y-1)!Africa !69 !43 !26 ! !7,700!Asia !60 !31 !29 ! !13,700!Australia !47 !42 !5 ! !380!Europe !64 !39 !25 ! !2,200!N. America !66 !32 !34 ! !8,100!S. America !163 !70 !93 ! !16,600!Total !469 !257 !212 ! !47,980!All of this comes from the 0.001% of the Earth’s water that is in the atmosphere!!
The Nitrogen Cycle! !
The Nitrogen (N) Cycle! Source of nitrogen is the atmosphere"
(79% N2, which is biologically inert)! N2 must undergo fixation before it"
can be used by biota! Small amount (4-9%) is abiotic:"
cosmic radiation, meteorites"entering atmosphere, and"lightning.!
Combines with O2 and H"(in H2O) to form ammonia"(NH3) and nitrogen oxides"(NOx, mostly nitrate, NO3)!
About 8.9 kg/ha/y "is produced this way!
Most N-fixation (ca. 100-200 kg/ha/y)"is biological!
Biological Nitrogen Fixation! Biological fixation is"
accomplished by:! Symbiotic bacteria living in"
association with legumes and"root-noduled non-leguminous"plants!
Cyanobacteria! Free-living aerobic soil bacteria!
These organisms split N2 into free N atoms, which combine with H to produce NH3 (under non-alkaline conditions, NH3 is generally in the form of ammonium ions, NH4
+)! Requires a lot of energy (about 10 g worth of glucose/g N fixed)!
NH4+ and NO3 are taken up by autotrophs and converted into
N-containing organic molecules (primarily amino acids and some nucleic acids)!
Heterotrophs obtain their N in these forms from their food!
Nitrogen Decomposition!Dead organic matter and wastes are broken down by decomposers! Ammonification: decomposer "
bacteria break down amino "acids for energy, and release"NH4
+ as a waste product"(which can be taken up"again by plants)!
Nitrification: bacteria"oxidize NH4
+ for energy:! Nitrosomonas bacteria use soil NH4
+ as their only energy source, converting it into nitrite (NO2) and H2O!
Nitrobacter bacteria convert nitrite (NO2) into nitrate (NO3)! Denitrification decomposer bacteria (Pseudomonas) and some
fungi convert NO3 into gaseous forms for energy! Produce N2 in high O2, pH 6-7, optimal (60 °C) temperature conditions! Also produce nitrous oxide (N2O), a ‘greenhouse gas’!
The Sulfur (S) Cycle! !
BIO 3072 !Ecology !Eric L. Peters!
Topic 12 !Biogeochemical Cycles!
The Sulfur (S) Cycle! Most of the S in the abiotic environment is found in rocks!
A small (but significant) amount is present in the atmosphere as sulfur dioxide (SO2), produced by combustion of fossil fuels!
Also release of hydrogen sulfide (H2S) into air by volcanoes! Sulfate (SO4
2-) is released from weathering and oxidation of rocks! Taken up by autotrophs and incorporated into S-containing amino
acids (e.g. methionine)! In this form, S is passed along food chains to heterotrophs!
Decomposition of dead organic matter and feces by anaerobic sulfate-reducing bacteria returns S to the abiotic environment as H2S! H2S can be converted back to sulfate or to elemental S by different
groups of photosynthetic and sulfide-oxidizing bacteria! Elemental S (S°) becomes incorporated into rocks!
Sulfur Bacteria!!Several unrelated groups of bacteria utilize sulfur, sulfide, or sulfate in their metabolisms!
Anaerobic photoautotrophic green sulfur bacteria and purple sulfur bacteria can use H2S an electron source in photosynthesis, producing S° as a by-product:"!
2H2S + CO2 >> H2O + CH2O + 2S°"!
Aerobic hyperthermophilic Archaea also use H2S as a source of electrons in chemosynthesis and produce S° as a by-product!
Chemoautotrophic sulfur-oxidizing bacteria derive energy from oxidation of S or S compounds (e.g. sulfide), producing SO4
2-! Anaerobic heterotrophic sulfate-reducing bacteria require SO4
2- for respiration, deriving energy from reducing it to S° or H2S!
Aerobic filamentous sulfur bacteria can grow by oxidizing sulfides to sulfates!
The Calcium (Ca) Cycle! Found in igneous rocks as calcium silicates and in
sedimentary and metamorphic rocks as calcium carbonates! Weathering of rocks, especially where some acid is present (e.g., CO2
dissolved in water, or released from growing lichens), are able to free some calcium (as a cation attracted to a water molecule)!
Flows of freshwater carry Ca2+ cations to the oceans! Concentrations of Ca2+ in fresh water range from 0.01- 0.1 mM (high
concentrations of Ca2+and/or Mg2+in fresh water create hard water)! Seawater Ca2+ concentrations are ≈10 mM (slightly greater in deeper,
colder water)! Absorbed by autotrophs from soil and water, and passes into
heterotrophs through food chains (or in drinking water)! Ca salts used as structural materials (e.g., calcium carbonate shells of
mollusks and in exoskeletons of crustaceans, calcium phosphate in cartilage, bone, eggshells)!
Used in variety of biochemical reactions (e.g., muscle contraction, enzyme activation)!
The Calcium (Ca) Cycle! Ca2+ remains in the sea water until it is precipitated out as
calcium carbonate (CaCO3) or (more rarely) as CaSO4 (gypsum)! Upper levels of the oceans are supersaturated with Ca2+ and carbonate,
(CO32-) ions (varies with different locations and conditions, with
greatest saturation in warm shallow water with high photosynthesis)! CaCO3 precipitates readily, either inorganically or with the help of
organisms, e.g., in tests of protists (biomineralization)! Precipitated Ca sinks to the ocean bottom Some is dissolved and
returned to the water column! The mechanisms which cause CaCO3 accumulation in water are
not fully understood! Microscopic life, heterotrophic and photoautotrophic, is responsible for
much of the deposition! Many aquatic plants occurring in alkaline waters release CaCO3 as a
byproduct of photosynthetic assimilation (100 kg of Anacharis canadensis can precipitate 2 kg of CaCO3 in 10 h in sunlight)!
Zooxanthellae of stony corals also release CaCO3 as a byproduct of photosynthesis, producing reefs!
The Calcium (Ca) Cycle! Each Ca atom spends an average of 1 million years in the
ocean before returning to land! Some is brought back when birds, animals and man
harvest seafoods and eat them on land, discarding or eliminating the shells and skeletons!
Most, however, comes back because of the movements of crustal plates and land masses! Various geological upthrusts have brought many accumulated
CaCO3 deposits to or near the surface as limestone or (after metamorphosis by heat and pressure) as marble!
For example, much of Europe and the U.S. east of the Mississippi River are underlain with limestone !
Ca also makes it back to land through the evaporation of brackish inland seas!
The Phosphorus Cycle! !
BIO 3072 !Ecology !Eric L. Peters!
Topic 12 !Biogeochemical Cycles!
The Phosphorus (P) Cycle! !
The Phosphorus (P) Cycle! Most P in the abiotic environment is found in rocks: elemental
(metallic) P (P°) does not exist on Earth (explosively oxidizes)! Inorganic phosphates (PO4
3-, HPO42-, or H2PO4-) gradually weathered
from rock into soils, oceans, rivers, and lakes! Absorbed by autotrophs from soil and water, and passes into
heterotrophs through food chains! Phosphates are incorporated into organic molecules (e.g., nucleic acids) ! Used as structural material (e.g., calcium phosphate in cartilage, bone,
eggshells)! Used in phosphorylation reactions (e.g., ADP → ATP)!
When organisms die, phosphates are released and returned to the abiotic environment by bacterial decomposition! On a geological time scale, phosphates in aquatic environments
eventually become incorporated into rocks! P-containing rocks are mined for use in fertilizers, the use of which
provides an additional source of inorganic phosphates to the abiotic environment which can also produce eutrophication!
Biogeochemistry of Radioactive Fission Products! Radioactive products of nuclear "
reactions have been released into "the environment by reactor (e.g.,"Chornobyl) and waste disposal"accidents (e.g., Kyshtym), and from "nuclear weapons detonations!
More than 200 different radioisotopes"(radionuclides) of 35 elements can be"generated during nuclear fission of "Pu or U into lighter elements! Each kT worth of energy produced"
generates about 1.5 × 1013 Ci (5.6 × 1023 Bq)"of radioactive ‘fission products’ (mainly short half-lived gases)!
Other radionuclides are generated by neutron activation and radioactive decay! Half-lives of these radionuclides range from < 1 ms to 17 My!
Many of these are radionuclides of natural nutrients or their biochemical analogs, e.g., 90Sr (T1/2 = 28 y) is an analog of Ca, 137Cs (T1/2 = 30.2 y) is an analog of K!
These radionuclides become part of the biogeochemical cycles of the natural elements that they resemble!
U.S. Nuclear Weapons Testing Fallout!
Biomagnification! Biomagnification can occur whenever toxicants are
easily absorbed from diet or water but, once taken up, are not as easily eliminated from the body!
An organism’s ‘body burden’ therefore reflects both its own exposure"history " AND "the exposure history of "lower trophic levels!
The result can be toxic"effects on organisms"at higher trophic levels!
DDT in water: 2.5 parts per trillion!
DDT in zooplankton: 40 ppb!
DDT in small"fishes: 500 ppb!
DDT in large"fishes: 2 ppm!
DDT in piscivorous" birds: 25 ppm!
DDT increases !10 million times"
Biogeochemistry of Persistant Organic Pollutants (POPs)! Chlorinated hydrocarbons such as PCBs and DDT also cycle
biogeochemically! Can be transported great distances through the oceans and atmosphere! Break down very slowly!
