Ecology - Nutrient Cycling and Carbon Cycle

Nutrients and Recycling

  • All living things require nutrients and energy for survival. Nutrients are materials required by an organism (e.g., C, H, O, N, P).
  • Nutrients are finite and limited, thus they are recycled within ecosystems.
  • Autotrophs: Obtain inorganic nutrients from their environment (water, soil, air) and convert them into organic compounds.
  • Heterotrophs: Ingest organic compounds and release inorganic compounds as a byproduct.
  • Saprotrophs: Decompose organisms and release inorganic materials back into the environment.
  • These inorganic compounds are then used again by autotrophs, completing the recycling process.

The Carbon Cycle

  • Carbon exists in three main forms:
    • In the air as carbon dioxide (CO_2) - inorganic.
    • In living organisms as organic compounds (primarily C6H{12}O_6 produced during photosynthesis).
    • In water as dissolved CO_2 and hydrogencarbonates - inorganic.
  • Carbon Cycle: A biogeochemical cycle where carbon is exchanged between the different spheres of the Earth (atmosphere, lithosphere, hydrosphere, and biosphere).
  • Carbon is essential for life, forming the backbone of the four macromolecules: carbohydrates, lipids, proteins, and nucleic acids.
  • Flux: Transfer of an element (like carbon) from one pool/sphere to another.

Key Processes in the Carbon Cycle

  • Photosynthesis: Conversion of CO2 (gas) to C6H{12}O6 (solid) using light energy.
    • 6CO2 + 6H2O + {light energy} \rightarrow C6H{12}O6 + 6O2
  • Cellular Respiration: Conversion of C6H{12}O6 (solid) to CO2 (gas), transferring chemical energy into making ATP.
    • C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + {ATP}
  • Feeding: Transfer of carbon compounds through consumption of organic matter.
  • Combustion: Burning of organic materials (e.g., fossil fuels, biomass) releasing CO_2 into the atmosphere. Moves solid forms of C into the atmosphere.
  • Decomposition: Breakdown of organic matter by decomposers, releasing CO_2 into the environment.
  • Incomplete Decomposition: Leads to the formation of fossil fuels (coal, oil, and natural gas) and peat.

Carbon Sinks and Sources

  • Carbon Sink: An ecosystem that absorbs more carbon than it releases (net carbon uptake - stores carbon).
    • Photosynthesis > Respiration Example*: Peatlands - acidic soil and anaerobic environment due to dense vegetation and water, leading to slow decomposition.
      • Peat: Partially decomposed vegetable matter; a good carbon sink due to acidic soil & anaerobic environment caused by dense vegetation + water.
      • Sequestration is the removal of carbon from the carbon cycle - a bog or bogland is a wetland that accumulates peat, a deposit of dead plant material.
  • Carbon Source: An ecosystem that releases more carbon than it absorbs (net carbon release).
    • Photosynthesis < Respiration
  • Fossil Fuels: Coal, oil, and natural gas formed from partially decomposed organic matter from past geological eras (non-renewable energy sources).
    • Oil and natural gas: formed from buried marine plankton and algae.
    • Coal: formed from buried peat.
      Example*: Forest fires or burning of fossil fuels (combustion).

Analysis of the Keeling Curve

  • The Keeling Curve is a graph showing the concentration of CO_2 in the atmosphere.
  • Annual Fluctuations:
    • Low atmospheric CO2 in summers: More plant life in the Northern Hemisphere leads to increased photosynthesis, pulling CO2 out of the air.
    • High atmospheric CO2 in winters: Many plants die, leading to less photosynthesis and increased decomposition, releasing CO2 into the air.
  • Long-Term Trends: Carbon dioxide concentrations have drastically increased over time due to human activities, primarily the burning of fossil fuels.

Production and Biomass

  • Biomass: The amount of living matter found in a space (measured in mass of carbon).
    • Crucial for ecosystems as it serves as a foundation for food webs and energy transfer.
      Example*: Rainforests have an estimated biomass of 400-700 metric tons/hectare.
  • Ecological Production: Rate of generation of biomass in an ecosystem (mass per area per time).
    • Expressed in g / (m^2 \cdot year)
  • Primary Production: Rate at which producers (autotrophs) convert energy into biomass through photosynthesis.
    • Accumulation of carbon compounds in biomass by autotrophs.
  • Secondary Production: Formation of biomass by heterotrophs.
    • The percentage of energy converted to biomass depends on the respiration rate.

Gross Primary Production (GPP) vs. Net Primary Production (NPP)

  • Gross Primary Production (GPP): Total biomass of carbon compounds made by plants via photosynthesis.
  • Net Primary Production (NPP): Biomass left after respiration (what is passed on to the next trophic level).
    • NPP = GPP - Respiration
  • Both GPP and NPP are generally measured as grams of carbon per square meter per year (gCm^{-2}y^{-1}).

Biomes and NPP

  • Biomes: Large geographical areas characterized by similar climates, landscapes, and types of plants and animals.
  • Biomes vary in their capacity to accumulate biomass (accumulated when organisms group and reproduce).
    Note*: biomes are larger than ecosystems and influenced by physical factors, mostly temperature and rainfall.

Calculations

*If the gross primary productivity of a coastal wetland was measured to be 20 kg C/m² - year. The respiration for the system is measured as 8 kg C/m² - year, then the Net Primary Productivity for this wetland in terms of its carbon biomass is calculated as below:

*NPP = GPP - R
*NPP= 20 - 8 = 12

*If the total solar energy received by a grassland is 5 x 10^5 kJ m^{-2} year^{-1}. The gross production is 4.35 x 10^3 kJ m^{-2} year^{-1}. The net production of the grassland is 1.95 x 10^3 kJ m^{-2} year^{-1}. Then:

The percentage of solar energy converted into chemical energy by photosynthesis is:
*% Conversion = (\frac{Gross \ Production}{Total \ Solar \ Energy}) * 100
*% Conversion = (\frac{4.35 x 10^3}{5 x 10^5}) * 100 = 0.87 \%$%

The energy lost by plant respiration is:
*R = GP-NP
*Respiration = (4.35 x 10^3) - (1.95 x 10^3) = 2400 kJ m^{-2}y^{-1}

Secondary Production

  • Secondary Production = accumulation of carbon compounds in biomass by heterotrophs.
  • These carbon compounds are both:
    • Ingested from foods and used to build up macromolecules.
    • Used in cellular respiration where carbon compounds get lost when they are converted to CO2 and H2O$$.
  • Secondary production is lower than primary production in an ecosystem.
  • There is a decline of secondary production with each successive trophic level.
  • Application: Production of crops will produce more per unit area than the production of meat (more humans can be fed per hectare of farmland if they eat plant products rather than meat).