‘Fundamentals’ of biogeochemical cycles • All matter cycles...it is neither created nor destroyed... • As the Earth is essentially a closed system with respect to matter, we can say that all matter on Earth cycles . • Biogeochemical cycles: the movement (or cycling) of matter through a system
by matter we mean: elements (carbon, nitrogen, oxygen) or molecules (water) so the movement of matter (for example carbon) between these parts of the system is, practically speaking, a biogeochemical cycle The Cycling Elements: macronutrients : required in relatively large amounts "big six": carbon , hydrogen , oxygen , nitrogen , phosphorous sulfur
other macronutrients: potassium , calcium , iron , magnesium micronutrients : required in very small amounts, (but still necessary) boron (green plants) copper (some enzymes) molybdenum (nitrogen-fixing bacteria)
6 of the most important cycles are the water, carbon, nitrogen, sulfur, phosphorus and oxygen.
HYDROLOGIC CYCLE CONNECTS ALL OF THE CYCLES AND SPHERES TOGETHER
HUMAN IMPACTS TO WATER CYCLE • Water withdrawal from streams, lakes and groundwater. (salt water intrusion and groundwater depletion) • Clear vegetation from land for agriculture, mining, road and building construction. (nonpoint source runoff carrying pollutants and reduced recharge of groundwater) • Degrade water quality by adding nutrients(NO2, NO3, PO4) and destroying wetlands (natural filters). • Degrade water clarity by clearing vegetation and increasing soil erosion.
Carbon in Oceans • Additional carbon is stored in the ocean. • Many animals pull carbon from water to use in shells, etc. • Animals die and carbon substances are deposited at the bottom of the ocean. • Oceans contain earth’s largest store of carbon.
IMPORTANCE OF CARBON CYCLE CARBON IS THE BACKBONE OF LIFE!
Sources • Lightning • Inorganic fertilizers • Nitrogen Fixation • Animal Residues • Crop residues • Organic fertilizers
Forms of Nitrogen • Urea CO(NH2)2 • Ammonia NH3 (gaseous) • Ammonium NH4 • Nitrate NO3 • Nitrite NO2 • Atmospheric Dinitrogen N2 • Organic N
Roles of Nitrogen • Plants and bacteria use nitrogen in the form of NH4+ or NO3- • It serves as an electron acceptor in anaerobic environment • Nitrogen is often the most limiting nutrient in soil and water.
Nitrogen is a key element for • amino acids • nucleic acids (purine, pyrimidine) • cell wall components of bacteria (NAM).
Nitrogen Cycles • Ammonification/mineralization • Immobilization • Nitrogen Fixation • Nitrification • Denitrification
Ammonification or Mineralization N2 N2O NH4 NO2 R-NH2 NO NO2 NO3
Mineralization or Ammonification • Decomposers: earthworms, termites, slugs, snails, bacteria, and fungi • Uses extracellular enzymes initiate degradation of plant polymers • Microorganisms uses: • Proteases, lysozymes, nucleases to degrade nitrogen containing molecules
Plants die or bacterial cells lyse release of organic nitrogen • Organic nitrogen is converted to inorganic nitrogen (NH3) • When pH<7.5, converted rapidly to NH4 • Example: Urea NH3 + 2 CO2
Immobilization • The opposite of mineralization • Happens when nitrogen is limiting in the environment • Nitrogen limitation is governed by C/N ratio • C/N typical for soil microbial biomass is 20 • C/N < 20Mineralization • C/N > 20 Immobilization
Nitrogen Fixation N2 N2O NH4 NO2 R-NH2 NO NO2 NO3
Nitrogen Fixation • Energy intensive process : • N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 + 16ADP + 16 Pi • Performed only by selected bacteria and actinomycetes • Performed in nitrogen fixing crops (ex: soybeans)
Azobacter Beijerinckia Azospirillum Clostridium Cyanobacteria Require the enzyme nitrogenase Inhibited by oxygen Inhibited by ammonia (end product) Microorganisms fixing
Immobilization is the opposite of which process in the cycle? A) Mineralization B) Nitrification C) Immobilization D) Nitrogen Fixation E) Denitrification What process takes place when nitrogen is limiting in the environment? A) Mineralization B) Nitrification C) Immobilization D) Nitrogen Fixation E) Denitrification Which has the highest rate of nitrogen fixation? A) Rhizobium-legume B) Cynaobacteria-moss C) Rhizosphere associations D) Free-living E) Azobacter
Applications to wetlands • Occur in overlying waters • Aerobic soil • Anaerobic soil • Oxidized rhizosphere • Leaf or stem surfaces of plants
Bacterial Fixation • Occurs mostly in salt marshes • Is absent from low pH peat of northern bogs • Cyanobacteria found in waterlogged soils
Nitrification N2 N2O NH4 NO2 R-NH2 NO NO2 NO3
Nitrification Two step reactions that occur together : • 1rst step catalyzed by Nitrosomonas 2 NH4+ + 3 O2 2 NO2- +2 H2O+ 4 H+ • 2nd step catalyzed by Nitrobacter • 2 NO2- + O2 2 NO3-
Optimal pH is between 6.6-8.0 • If pH < 6.0 rate is slowed • If pH < 4.5 reaction is inhibited In which type of wetlands do you thing Nitrification occurs?
Denitrification N2 N2O NH4 NO2 R-NH2 NO NO2 NO3
Denitrification • Removes a limiting nutrient from the environment • 4NO3- + C6H12O6 2N2 + 6 H20 • Inhibited by O2 • Not inhibited by ammonia • Microbial reaction • Nitrate is the terminal electron acceptor
HUMAN IMPACTS TO PHOSPHOROUS CYCLE • Humans mine LARGE quantities of phosphate rock to use in commercial fertilizers and detergents. Phosphorous is NOT found as a gas, only as a solid in the earth’s crust. It takes millions to hundreds of millions of years to replenish. • Phosphorous is held in the tissue of the trees and vegetation, not in the soil and as we deforest the land, we remove the ability for phosphorous to replenish globally in ecosystems. • Cultural eutrophication – ad excess phosphate to aquatic ecosystems in runoff of animal wastes from livestock feedlots, runoff of commercial phosphate fertilizers fro cropland, and discharge of municipal sewage.
IMPORTANCE OF PHOSPHOROUS CYCLE • 1.Phosphorous is an essential nutrient of both plants and animals. • 2. It is part of DNA molecules which carry genetic information. • 3. It is part of ATP and ADP) that store chemical energy for use by organisms in cellular respiration. • 4. Forms phospholipids in cell membranes of plants and animal cells. • 5. Forms bones, teeth, and shells of animals as calcium phosphate compounds.
HUMAN IMPACTS TO SULFUR CYCLE Approximately 1/3 of all sulfur emitted into atmosphere comes from human activities. • 1. Burning sulfur containing coal and oil to produce electric power (SOx = acid deposition). • 2. Refining petroleum – (SOx emissions) • 3. Smelting to convert sulfur compounds of metallic minerals into free metals (Cu, Pb, Zn) • 4. Industrial processing.
IMPORTANCE OF SULFUR CYCLE • Sulfur is a component of most proteins and some vitamins. • Sulfate ions (SO42- ) dissolved in water are common in plant tissue. They are part of sulfur-containing amino acids that are the building blocks for proteins. • Sulfur bonds give the three dimensional structure of amino acids. • Many animals, including humans, depend on plants for sulfur-containing amino acids.