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 $C<em>6H</em>{12}O_6$ 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 $CO<em>2$ (gas) to $C</em>6H<em>{12}O</em>6$ (solid) using light energy.
  • $6CO<em>2 + 6H</em>2O + {light energy} \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2$
• Cellular Respiration: Conversion of $C<em>6H</em>{12}O<em>6$ (solid) to $CO</em>2$ (gas), transferring chemical energy into making ATP.
  • $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O + {ATP}$
• 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 $CO<em>2$ in summers: More plant life in the Northern Hemisphere leads to increased photosynthesis, pulling $CO</em>2$ out of the air.
  • High atmospheric $CO<em>2$ in winters: Many plants die, leading to less photosynthesis and increased decomposition, releasing $CO</em>2$ 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}$</p> <h4 id="secondaryproduction">Secondary Production</h4> <ul> <li>Secondary Production = accumulation of carbon compounds in biomass by heterotrophs.</li> <li>These carbon compounds are both:<ul> <li>Ingested from foods and used to build up macromolecules.</li> <li>Used in cellular respiration where carbon compounds get lost when they are converted to$CO2$and$H2O$$.