Biogeochemical cycles, abundance and distribution

• Biogeochemical cycles


  Recycling of matter involving both biotic and abiotic components of the ecosystem
• Biogeochemical cycles covered


  • Water
  • Carbon
  • Nitrogen
  • Phosphorus
• Importance of biogeochemical cycles

  • Most ecosystems have an inexhaustible amount of solar energy
  • Some chemical elements are available in limited amounts
  • In living organisms, chemical elements are absorbed as nutrients
  • The waste produced is released back into the ecosystem
• Decomposition


  1. Waste or dead organisms are reduced to simpler compounds and atoms by decomposers

  2. These compounds are released into the atmosphere, water bodies or stored in soil

  3. Decomposition is vital as it replenishes the pool of inorganic nutrients that plants and other autotrophic organisms require to build new organic matter
• Biogeochemical cycles


  There are two models of chemical cycling: globally and locally
• Elements cycled globally


  • Carbon
  • Oxygen
  • Nitrogen
  • Sulfur
• Water cycle


  • Biological importance: A key solvent in transport of nutrients, essential for producer organisms and decomposition in terrestrial ecosystems
  • Reservoir: 97% in the ocean, 2% in glaciers and 1% in lakes, rivers and groundwater
  • Forms available in life: Liquid water is the primary form used by most living organisms, while some organisms can use vapour form. Solid form in soil limits availability to plants
• Water cycle


  1. Evaporation moves water from the ocean and land to the atmosphere as precipitation (cloud)

  2. Transpiration via plants also remove water from soil

  3. Water returns to surface as rainfall

  4. Run-off from the ground enters rivers and lakes or back into the ocean
• Carbon cycle


  • Biological importance: Carbon is the framework for all organic molecules in living things
  • Reservoirs: Major reservoir is CO2 in the atmosphere. They exist as carbon compounds in fossil fuels, sediments in aquatic ecosystem, and biomass in plants and animals
  • Forms available in life: CO2 is converted by plants and autotrophic organisms into usable forms by consumer and heterotrophic prokaryotes
• Carbon cycle


  1. Photosynthesis by plant and other autotrophic organisms converts CO2 to glucose or other nutrients, removing a large amount from the atmosphere

  2. Burning fossil fuels also releases CO2 into the atmosphere

  3. Some material is stored in soil as fossil fuel

  4. CO2 is returned to atmosphere by consumer organisms during respiration and decomposition
• Nitrogen cycle


  • Biological importance: A crucial component in living things forming amino acids, proteins, and nucleic acid
  • Reservoirs: 80% of nitrogen exists as gaseous form (N2) in the atmosphere. The rest is bound in soil, sediments of lakes, rivers and the ocean. Some are dissolved in water and in biomass of living organisms
  • Forms available to life: Plants and algae use two organic forms ammonium (NH4+) or nitrate (NO3-). Animals can utilize it in organic form only as protein
• Nitrogen cycle


  1. Nitrogen fixation is the main pathway for nitrogen to enter the ecosystem from the atmosphere

  2. Bacteria converts N2 from the atmosphere via nitrogen fixation to forms that can be synthesized into nitrogenous organic compounds

  3. Ammonification decomposes organic nitrogen into NH4+

  4. Nitrification converts NH4+ to NO3- by nitrifying bacteria

  5. Denitrifying bacteria use NO3- instead of O2 in anaerobic conditions producing N2 (Returns nitrogen back into the atmosphere)

  6. Animals obtain nitrogen from eating plants or other animals
• Phosphorus cycle


  • Biological importance: Phosphorous is a major constituent of nucleic acid, phospholipids and ATP
  • Reservoirs: Large amounts in soil, some in ocean and living organisms
  • Forms available to life: Biologically important in inorganic form phosphate, PO4 3- where its easily absorbed by plants
• Phosphorus cycle


  1. Phosphate leeched into water during soil erosion and sediment run-off

  2. Only a small amount of phosphorous is lost to the atmosphere in dust or sea spray, since there are no significant phosphorous containing gases

  3. Dissolved phosphate is absorbed by plants and other producers which is eaten by consumer organisms
• Disturbance


  An event that can change the abiotic conditions in an ecosystem, resulting in changes on how organisms interact
• Resistance


  The ability of the ecosystem to resist change from a disturbance and return to its initial state
• Resilience


  How quickly the ecosystem returns to its initial state after the disturbance
• Biodiversity


  • Species richness: Number of different species
  • Species abundance: Number of each species
• Distribution


  Number of different species and how they are "spread" throughout the ecosystem
• Factors affecting distribution of species

  • Area of expansion – including geographical barriers
  • Behaviour of animals and habitat selection
  • Biotic factors – how species interact and change their numbers
  • Abiotic factors – amount of water, light, oxygen and soil condition
• Abundance


  • The number of organisms of each species
  • Dominant species – Species in the area of study with the highest biomass
  • Keystone species are organism that may not be abundant but play a crucial role by controlling the abundance of certain species
  • Dominant species exerts control by limiting the occurrence and distribution of other species in the ecosystem
• Techniques used for determining distribution and measuring abundance

  • Quantitative sampling: Capture-mark-release-recapture, Random quadrats
  • Qualitative sampling: Transects
• Transect sampling


  1. Line transect – Only organisms that touches the line are recorded

  2. Belt transect – Organisms between two lines are recorded

  3. Interrupted belt transect – A quadrat (square frame) is placed along random intervals of the belt transect. Only organisms in the square frame is recorded
• Random quadrats


  • Photographic data of the area of investigation can be used and small quadrats are dropped randomly on the image, then counted
  • The quadrats are placed in areas of high and low density at random locations in the area of study
  • The total number of organisms is divided by the total number of quadrats placed in the area of investigation
• Limitations of random quadrats
• Capture-mark-release-recapture


  1. Traps with bait are placed within the boundary of the area of investigation

  2. The captured organisms are counted, marked and then released

  3. Traps are placed in the same locations of the area of study and left for the same period of time. The total number of organisms captured are counted as well as the ones that are marked
• Capture-mark-release-recapture


  To determine the number of mobile organisms in a sample: Total number marked in the sample population (N3) = Original number marked (N1) x Total population sampled (N2) / Number recaptured (N3)
• Conditions for capture-mark-release-recapture to be viable
• Limitations of capture-mark-release-recapture
• Summary of biogeochemical cycles

  • Water: Biological importance as a solvent, forms available in life as liquid, vapour and solid
  • Carbon: Biological importance as the framework for organic molecules, forms available as CO2 gas and glucose/starch
  • Nitrogen: Biological importance as a component of proteins and nucleic acids, forms available as ammonium, nitrates, nitrites and proteins
  • Phosphorus: Biological importance as a component of nucleic acids, phospholipids and ATP, forms available as phosphate
• Biogeochemical cycles


  Recycling of matter in ecosystems involving both biotic and abiotic components
• Biogeochemical cycles covered


  • Water
  • Carbon
  • Nitrogen
  • Phosphorus
• Importance of biogeochemical cycles

  • Most ecosystems have an inexhaustible amount of solar energy
  • Some chemical elements are available in limited amounts
  • Chemical elements are absorbed as nutrients in living organisms
  • Waste and dead organisms are reduced to simpler compounds and atoms by decomposers
• Biogeochemical cycles


  Involve both biotic (living) and abiotic (non-living) components of the ecosystem
• Models of chemical cycling

  • Globally
  • Locally
• Globally cycled elements


  Carbon, oxygen, nitrogen, sulfur
• Locally cycled elements


  Phosphorus, potassium, calcium
• Water cycle


  1. Evaporation

  2. Transpiration

  3. Precipitation

  4. Runoff
• Biological importance of water cycle

  Key solvent in transport of nutrients, essential for producer organisms and decomposition
• Reservoir of water


  97% in the ocean, 2% in glaciers, 1% in lakes, rivers and groundwater