Flows of Energy & Matter

human influences on biogeochemical cycles

• chemical run off leads to eutrophication

• atmospheric emissions emit excessive nutrients

• deforestation alters water/carbon cycles

• urbanisation disrupts ecosystems

description of the carbon cycle

• carbon circulated between atmosphere, oceans, soil, and organisms.

• forms organic molecules

• part of energy transfer and climate regulation

• carbon sinks sequester carbon

• human activities increase carbon

• Carbon dioxide absorbed by plants, animals consume plants

• carbon released through respiration and decomposition

• carbon returns to atmosphere

definition of nitrogen fixation

Converting atmospheric nitrogen (N2) into ammonia (NH3) to make it accessible.

3 methods of nitrogen fixation

1. biological fixation: bacteria (Rhizobium/cyanobacteria) fix it; they live in legumes, and exchange carbohydrates and nitrogen.

2. atmospheric fixation: lighting creates nitrogen oxides that dissolve in rain, forming nitrates.

3. industrial fixation: Haber-Bosch process synthesises ammonia under high pressure/temperature to create fertilisers

definition of nitrification

nitrifying bacteria convert nitrites into nitrates

description of nitrification of ammonia

• nitrosomonas oxidise ammonia to form nitrite; ammonia is toxic to plants in high concentrations

• nitrobacter convert nitrite to nitrate, which plants absorb

description of assimilation

• plants take it up an convert them into amino acids, proteins, etc.

• animals consume plants

description of ammonification

decomposers decompose organisms, turning nitrogen back into ammonia in the soil

description of denitrification

pseudomonas convert nitrates/nitrites in the soil back into nitrogen gas/nitrous oxide, re-releasing it into the atmosphere

human impacts on the Nitrogen cycle

• use of fertisilers = excessive nitrogen

• irrigation causes leaching into groundwater/water bodies

• combustion of fossil fuels releases nitrogen oxides, causing air pollution, acid rain, climate change

• Haber-Bosch = excessive nitrogen in biosphere

• sewage treatment can release nitogen into oceans/rivers

example: Gulf of Mexico Dead Zone

• oxyegn plummets due to excessive nutrient pollution from Mississippi River

• agricultural & urban runoff; fertilisers & stormwater/wastewater drainage

• hypoxia kills/forces migration of marine life

• fisheries impacted

• Riparian Buffers = vegetated river banks to aborb/filter excess nutrients

• wetland restoration also filters nutrients

why is nitrogen important?

Nitrogen is essential for the formation of amino acids, which are needed to form proteins

sources of energy

• energy from insolation is unavailable due to:

  • being absorbed by inorganic matter

  • reflected back into the atmosphere

  • 51% energy never reaches producers

energy transfers

• coversion of light energy to chemical energy

• transfer on chemical energy between trophic levels

  • 10% efficiency

• UV & visible light → heat energy

• re-radiation of heat energy into atmosphere

definition of gross primary productivity - GPP

total rate of photosynthesis: biomass + respiration; a comprehensive measure of ecosystem's capacity to capture/store energy

definition of net primary productivity - NPP

Energy stored as biomass available to herbivores/decomposers AFTER accounting for respiration; represents energy available for next trophic level

definition of maximum sustainable yield

• maximum amount of a renewable natural resource that can be harvested annually without comprommising long term productivity of the resource

• equivalent to the net primary productivity (NPP) or net secondary productivity (NSP) of a system (as these values represent the amount of energy stored and new plant or animal biomass per year)

definition of gross secondary productivity - GSP

• total energy/biomass assimilated by consumers

• GSP = food eaten - fecal loss

definition of net secondary productivity - NSP

• total gain in energy/biomass per unit area per unit time by consumers; accounting for respiration

• NSP = GSP - R

3 factors affecting secondary productivity

1. food quality

2. food quantity

3. metabolic rate (body size, temperature, activity level)

definition of trophic efficiency

% energy/biomass transferred from one trophic level to the next 10%, but can range between 5-20%

reasons for trophic inefficiency

• Not everything is eaten

• Digestion is inefficient

• Heat is lost in respiration

• Some energy assimilated is used in life processes

stores of carbon

• solid forms; sedimentary rocks/fossil fuels

• oceans (dissolved/shells of crusteaceans)

• soil (humus/respiration of soil organisms)

• atmosphere

• organisms (biomass; cellullose)

• fossilized life forms (fossil fuels)

importance of biogeochemical cycles

• ensure nutrients/vital elements are consistently available

• support biodiversity

• ecosystem service; aids soil fertility, water purification, and climate regulation

• entwined with energy flow e.g. photosynthesis

• food webs transfer nutrients across trophic levels

description of phosphorus cycle

• used in ATP, nucleic acids, and cell membranes

• cycled through water, soil, organisms; NOT atmosphere

• released into environment through rock weathering; accelerated by human activities

description of water cycle

• medium for transport of nutrients within ecosystems

• precipitation & evaporation are continuous processes

• influences climate/weather patterns

• translocation/transpiration