Ecosystems are open systems in which energy and matter are exchanged. They are sustained by supplies of energy and matter.

Laws of Thermodynamics And Environmental Systems

Energy exists in a variety of forms (light, heat, chemical, electrical, and kinetic). The behaviour of energy in systems is defined by the laws of thermodynamics.

First Law of Thermodynamics

The first law of thermodynamics states that energy can neither be created nor destroyed - it can only change form. Two examples of the first law in our ecosystem are:

1. Photosynthesis: It is the conversion of light energy to chemical energy in the form of glucose. Glucose can be converted into other carbon compounds contained within biomass. Producers form the first trophic level in a food chain and produce their food using photosynthesis
2. Cellular respiration: Respiration releases energy from glucose by converting it into a chemical form that can easily be used in carrying out active processes within living cells. Some chemical energy released during cellular respiration is transformed into heat.

Second Law of Thermodynamics

The second law of thermodynamics states that energy transformations in ecosystems are inefficient. It relates to the quality of energy and that when energy is transformed, some must be degraded into a less useful form, such as heat.

Entropy

Entropy is linked with the second law of thermodynamics. It is a measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work.

Productivity in Ecosystems

Productivity is a measure of the rate at which energy is converted into biomass over time. There are several important concepts related to productivity:

Gross Primary Productivity (GPP): The total rate of energy capture through photosynthesis.

(HL) Net Primary Productivity (NPP): The energy remaining after the producer's respiratory needs are met.

𝑁𝑃𝑃 = 𝐺𝑃𝑃 − Respiratory losses

(HL) Gross Secondary Productivity (GSP): The total rate of energy assimilation by consumers.

𝐺𝑆𝑃 = Food eaten − Fecal loss

(HL) Net Secondary Productivity (NSP): The amount of energy available for growth and reproduction in consumers after accounting for respiratory losses.

𝑁𝑆𝑃 = 𝐺𝑆𝑃 − Respiratory losses

Maximum Sustainable Yield

The maximum sustainable yield in an ecosystem is equal to the net primary or secondary productivity. This represents the maximum amount of biomass that can be harvested without depleting the resource.

Human Impacts on Energy and Matter Flows

Human activities significantly affect energy flows and biogeochemical cycles:

1. Fossil fuel use: Releases stored carbon into the atmosphere, altering the carbon cycle and global energy balance.
2. Deforestation: Reduces the Earth's capacity to absorb CO₂ through photosynthesis and alters local energy flows.
3. Urbanization: Changes land surface albedo, affecting local energy absorption and reflection.
4. Agriculture: Alters nutrient cycles through fertilizer use and impacts energy flows through land-use changes.

Carbon Cycle

The carbon cycle describes how carbon moves through the atmosphere, biosphere (living organisms), hydrosphere (oceans), and lithosphere (rocks and soil).

Carbon Flows:

Carbon flows between reservoirs (stores) through natural processes:

• Photosynthesis: Plants absorb atmospheric CO₂ and convert it into glucose.
• Respiration: Animals and plants release CO₂ back into the atmosphere by breaking down glucose for energy.
• Decomposition: Dead organisms and waste products are broken down by decomposers, releasing carbon into soil or the atmosphere.
• Combustion: Burning fossil fuels or biomass releases stored carbon as CO₂.