Topics 2.3 & 2.4 Flows of energy and matter ★ The fate of solar radiation reaching the Earth ★ Productivity ★ Flows of energy and matter Main concepts: ➔ As Solar radiation enters the atmosphere some energy becomes unavailable for ecosystems as it is absorbed by organic matter or reflected back ➔ The loss of radiation is through reflection and absorption ➔ Pathways of energy: ◆ Light energy to chemical energy ◆ Transfer of chemical energy from one trophic level to another, with different efficiencies ◆ ultraviolet and visible light to heat energy ◆ Reradiation of heat energy to the atmosphere ➔ Conversion of energy into biomass for a period of time = productivity ➔ Gross secondary productivity = total energy / biomass assimilated by consumers. (food eaten - fecal loss) ➔ Net primary productivity = GPP - respiratory losses ➔ Net secondary productivity = GSP - respiratory losses ➔ Maximum sustainable yields = net primary/net secondary productivity of a system ➔ Flows of matter: transfers and transformations ➔ Carbon and nitrogen cycles: illustrate flow of matter using flow diagrams ➔ Storages in the carbon cycle: organisms, forests , atmosphere, soil, fossil fuels and oceans Organic Inorganic ➔ Flows in the carbon cycle: consumption, death and decomposition, photosynthesis, respiration, dissolving and fossilisation. ➔ Storages in the nitrogen cycle: organisms , soil, fossil fuels, atmosphere and water bodies ➔ Flows in the nitrogen cycle: nitrogen fixation, absorption, assimilation, consumption, excretion, death and decomposition, denitrification ➔ Human activities: burning fossil fuels, deforestation, urbanization and agriculture impact energy flows as well as the carbon and nitrogen cycle Key points Almost all energy comes from the sun Solar radiation is made up of visible wavelengths (lights) and those invisible to humans (ultraviolet and infrared) 60% of energy is absorbed by atmospheric gases and dust particles Nearly all ultraviolet light is absorbed by ozone Infrared light (heat) is absorbed by carbon dioxide, clouds and water vapours Ultraviolet and visible light energy (short wave) are converted to heat energy (long wave) The systems depend on the amount of energy that reaches the ground, not the atmosphere. This amount varies according to time, season, clouds, etc Most energy is reflected or absorbed and re radiated as heat 35% of energy is reflected back to space by ice, snow, water and land Some of the energy absorbed heats up the land and seas Only 1-4% of energy is available to plants on the surface Green plants: light energy to chemical energy Chemical energy: one trophic level to another