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2.3. FLOWS OF ENERGY AND MATTER (Productivity (Plant material can either,…
2.3. FLOWS OF ENERGY AND MATTER
Knowledge and Understanding
ecosystems are linked together by energy and matter flows
sun's energy drives these flows and humans are impacting the flows of energy and matter both locally and globally
as solar radiation (insolation) enters earth's atmosphere some energy becomes unavailable for ecosystems as it is absorbed by inorganic matter or reflected back
Solar energy reaching the Earth
Earth's solar constant is 1400 joules per second per square metre
The only way organisms can turn solar energy into food is through photosynthesis from plants
Productivity
Gross primary productivity
: total gain in energy or biomass per unit area per unit time by green plants. It is the energy converted from light to chemical using chlorophyll
Gross secondary productivity
: GSP = food eaten - fecal loss - it is the total energy or biomass assimilated by consumers
Net productivity:
gain in energy or biomass per unit area per unit time that remain after deductions due to respiration - - results from fact that all organisms need to respire to stay alive
Gross productivity:
total gain in energy or biomass per unit area per unit time - biomass that could be gained by any organism before any deductions
Net primary productivity
GPP-R (respiratory losses) - this is the increase in the biomass of the plant, how much it grows, and is the biomass potentially available to consumers that eat the plant
An ecosystem's NPP is the rate at which plants accumulate dry mass ussually measured in grams per metre squared. Glucose produced in photosynthesis has 2 fates
Some for growth, maintenance and reproduction (life processes) with energy being lost as heat from respiration
Remainder is deposited in and around cells as new material and represents stored dry mass - this store is potential food for consumers
Net secondary productivity
: GSP - respiratory losses - it is the total gain in energy or biomass per unit area per unit time by consumers after allowing for losses by respiration
Carnvores: assimilate 80% of energy in diets (on average) egest less than 20% usually have to chase moving animals so higher energy intake is offset by increased respiration while hunting
Herbivores: assimilate around 40%, egest 60%, graze static plants
Plant material can either
be lost from food chains as it dies or decays
be eaten by herbivores and be removed from primary productivity
Amount of biomass produced can vary
Spatially - some biomes have higher NPP rates e.g. rainforest vs tundra
Temporally - many plants have seasonal patterns of productivity linked to changing availability of basic resources - light, water, warmth
Flows of energy and matter
Transfers and transformations
Cycles and flows - biogeochemical cycles - water, carbon and nitrogen
Nutrient cycles
Energy flow diagrams - shows energy entering and leaving each trophic level - allows comparison of various ecosystems
Trophic inefficiencies (only 10% transfer) occur because
Nor everything is eaten
Digestion is inefficient - food is lost as faeces because the digestive system can not extract all the energy from it
Heat is lost in respiration
Some energy assimilated is used in reproduction and other life processes
Human activities and ecosystems
Concept of energy subsidies
Additional energy that we put into the system above that which comes from the Sun'es energy - e.g. human labour, animal labour fertilisers etc. --- Result is some agricultural systems are very productive and have a high NPP
Advantage of this is we can feed more people - increase pop means high food demand
Energy: yield ratio
Input of energy vs output - yield