2.3 - Flows of energy and matter

Gross Productivity

The total gain in energy or biomass per unit area per unit time

It is the biomass that could be gained by an organism before any deductions

Net Productivity

The gain in energy or biomass per unit are per unit time that remains after deductions due to respiration

Biomass

The living mass of an organism or organisms, but sometimes referred to as dry mass

Gross Primary Productivity

The total gain in energy or biomass per unit area per unit time by green plants

It is energy fixed by green plants by photosynthesis

Net primary productivity

Calculated by subtracting respiratory losses from GPP

An ecosystem’s NPP is the rate at which plants accumulate dry mass usually measured in g m^-2. The glucose produced in photosynthesis has 2 main fates

• Some provides for growth, maintenance, and reproduction

• The remainder is deposited in and around cells as new material

NPP = GPP - R

Gross Secondary Productivity

The total energy/biomass assimilated by consumers and is calculated by subtracting the mass of fecal loss from the food eaten

GSP - food eaten - fecal loss

Net Secondary Productivity

The total gain in energy or biomass per unit area per unit time by consumers, after allowing for losses to respiration Calculated by subtracting respiratory losses (R) from GSP

Different things happen to the energy

• Some of the assimilated food energy is used in cellular respiration to provide energy for life processes

• Some is removed as nitrogenous waste, in most animals as urine

• The rest is stored in dry mass of new body tissue

• Some will be released as feces

NSP = GSP - R

Pathways of energy through an ecosystem include

• Conversion of light energy to chemical energy

• Transfer of chemical energy from one trophic level to another with varying efficiencies

• Overall conversion of ultraviolet and visible light to heat energy by an ecosystem

• Re-radiation of heat energy to the atmosphere

Storages in the carbon cycle include:

• Organisms and forests (both organic)

• The atmosphere, soil, fossil fuels, and oceans (all inorganic

Flows in the carbon cycle

• Consumption

• Death and decomposition

• Photosynthesis

• Respiration

• Dissolving and fossilisation

Storages in the nitrogen cycle include:

• Organisms (organic)

• Soil, fossil fuels, atmosphere, and water bodies (all inorganic)

Flows in the nitrogen cycle include:

• Nitrogen fixation by bacteria and lightning

• Absorption

• Consumption (feeding)

• Excretion

• Death and decomposition

• Dentrification by bacteria in waterlogged soils

Solar Radiation

Made up of visible wavelengths (light) and those wavelengths that humans cannot see (ultraviolet and infrared). Almost all energy that drives processes on Earth comes from the Sun

• Some 60% of this is intercepted by atmospheric gases and dust particles.

Solar radiation hitting the Earth diagram

• In the Sky/Atmosphere

  • 31% - Total Reflection

  • 69% - Total Absorption

Entering Solar Radiation

• 49% is absorbed by the Earth’s ground

• 17% is absorbed by molecules and dust

• 3% is absorbed by clouds

• 19% is reflected by clouds

• 9% is reflected by the ground

• 3% is reflected by scatter

Productivity

The conversion of energy into biomass over a given period of time.

It is the rate of growth or biomass increase in plants and animals.

It is measured per unit area per unit time, eg. per metre² per year

About carnivores and energy

• On average they assimilate 80% of the energy in their diets

• They egest less than 20%

• Usually have to chase moving animals, so higher energy intake is offset by increased respiration during hunting

• Biomass is locked up in prey foods - non-digestible skeletal parts, such as bone, horn, and antler

About herbivores and energy

• They assimilate about 40% of the energy in their diet

• They egest 60%

• They graze static plants

Flows of energy and matter table

Carbon Stores

Organic locations

• Organisms (biomass) - living plants and animals

• Fossilized life forms ex. fossil fuels

Inorganic locations

• Sedimentary rocks and fossil fuels

• The oceans

• Soil

• The atmosphere

Carbon flows

It cycles between biotic and abiotic chemical cycles

• Fixed by photosynthesis and released back to the atmosphere through respiration

• Released back to the atmosphere through combustion of fossil fuels and biomass

• Respire through the death of organisms

• It’s oxidized to become carbon dioxide when fossil fuels are burnt

• Plants recapture it through carbon fixation and lock it up in their bodies as glucose

• When plants are harvested or cut down, it gets released into the atmosphere

Nitrogen Cycle

For plants to take up nitrogen, it must be in the form of ammonium ions or nitrates

It can be throught of in three basic stages: nitrogen fixation, nitrification, denitrification

Nitrogen Storages/sinks

• Organisms

• Soil

• Fossil fuels

• The atmosphere

• Water

Flows in the nitrogen cycle

• nitrogen fixation

• nitrification

• denitrification

• feeding

  • absorption

  • assimilation

  • consumption

• excretion

• death and decomposition

Nitrogen Fixation

When atmospheric nitrogen is made available to plants through the fixation of atmospheric nitrogen. It can be carried out in 5 ways

• By nitrogen-fixing bacteria free-living in soil (Azotobacter)

• By nitrogen-fixing bacteria living symbiotically in root nodules of leguminous plants (Rhizobium)

• By cyanobacteria that live in soil or water. Cyanobacteria are the cause of high productivity in Asian rice fields

• By lightning also causing the oxidation of nitrogen gas to nitrate which is washed into the soil

• The industrial Haber process is a nitrogen-fixing process used to make fertilizers

Nitrification

Nitrifying bacteria are able to convert ammonium to nitrates (Nitrosomonas) while other bacteria convert the nitrites to nitrates (Nitrobacter) which are then available to be absorbed by plant roots

Denitrification

Denitrifying bacteria in waterlogged and anaerobic conditions reverse this process by converting ammonium, nitrate, and nitrite ions to nitrogen gas, which escapes to the atmosphere

Assimilation

Once living organisms have taken in nitrogen, they assimilate it or build it into more complex molecules.

Decomposition in the nitrogen cycle

Provides nitrogen uptake by plants. Supplies the soil with much more nitrogen than nitrogen fixation processes. Important organisms in decomposition are animals (insects, worms), fungi, and bacteria.

Efficiency of assimilation equation

gross productivity x 100/ food eaten

Efficiency of biomass productivity

net productivity x 100/ gross productivity

Trophic efficiency

The efficiency of transfer from one trophic level to the next, is considered, on average, to be about 10%

Trophic inefficiencies occur because:

• Not everything is eaten

• Digestion is inefficient (food is lost in feces because the digestive system cannot extract all the energy from it)

• Heat is lost in respiration

• Some energy assimilated is used in reproduction and other life processes

Energy budget

For an individual animal/population, we can measure the quantities of energy entering, staying within, and leaving the animal or population

Maximum Sustainable Yield

The largest crop or catch that can be taken from the stock of a species (ex. a forest, a shoal of fish) without depleting the stock. It is often used in managing fisheries

Gersmehl’s Model

Illustrates how nutrients are transferred/and or cycled between nutrient sinks via environmental inputs and output as represented by the arrow in and around each nutrient sink