10 - Biogeochemical cycle

Global biogeochemical cycle

linked network of biological

and physical processes that moves nutrients through pools

within the environment

Pool

large reservoir of nutrients (e.g., oceans, atmosphere, soil)

Flux

movement of nutrients between pools (e.g., evaporation &

precipitation, carbon-fixation through photosynthesis &

respiration)

hydrological cycle - steps, pools, fluxes

evaporation condensation precipitation

• Major pools: Oceans (97.5% of water), atmosphere, ice sheets.
  
  

• Fluxes: Evaporation, precipitation, transpiration, runoff.

major pools in the carbon cycle

Major pools include atmosphere, oceans, land surface (soils and vegetation), sediments and rock, terrestial organism, surface watrt, marine organism

fluxes in carbon cycle

marine photosynthesis and respiration

terrestrial photosynthesis and respiration

human activty - usually unidirectional

explain this

there is more land north

Respiration is fairly constant throughout the year

Photosynthesis is typically SEASONAL in north

more plants (↑ photosynthesis) in spring- summer so it starts going down

: How does carbon dioxide enter the atmosphere?

1. Geological inputs (volcanoes, mid-ocean ridges)

2. Biological inputs (respiration)

3. Anthropogenic inputs (burning fossil fuels, deforestation)

How does carbon dioxide leave the atmosphere?

1. Geological removal (chemical weathering à CO2 in

rainwater reacts with exposed rocks)

2. Biological removal (photosynthesis)

TERRESTRIAL C-CYCLE

MARINE C-CYCLE

explain this

Trend: Rapid increase in atmospheric CO₂ levels since the Industrial Revolution.

Cause: Human activities, mainly burning fossil fuels and land-use changes (deforestation, agriculture).

how can you find how the atmosphere was years ago

Glacial ice, as it forms, traps air bubbles, and this ice can

last for thousands of years! We can examine ice cores to find out

what the atmosphere was like in the past.

evidence that has led us to identify human activies as a cause

Neither volcanic gases nor dissolved ocean waters have 13C/12C ratios that match the increase in atmospheric carbon

•Additional studies showed that carbon entering in the atmosphere was 14C-depleted ß modern plant vegetation contains too much 14C to be the source

Chemical analyses support hypothesis that carbon

is ANTHROPOGENIC in origin, from burning ancient

organic matter (i.e., from burning fossil fuels)

do all carbon produced by us enter atmospehere

no, only half usually stored in ocean

The largest nitrogen pool is

n2

Nitrogen fixation –

process by which some bacteria and archaea reduce N2 gas to biologically useful NH3 (this is how nitrogen enters food webs)

Assimilation -

process by which primary producers obtain biologically useful nitrogen from surroundings (NO3 - or NH3)

Denitrification –

a form of anaerobic respiration in which NO3 - is terminal electron acceptor

Nitrification –

a process in which NH3 or NO2 - are oxidized to generate energy

Rhizosphere

soil layer surrounding actively growing roots, receives carbohydrates from plants to stimulate growth of soil microbial mutualists

Rhizobium bacteria - Partner, Benefit to Plant, Benefit to Mutualist, Cost to Plant

Legume roots

Biologically available nitrogen (NH₃)

Carbohydrates (sugars) from plant

Provides energy-rich carbon

Ectomycorrhizae - Partner, Benefit to Plant, Benefit to Mutualist, Cost to Plant

netwrok of filamnet surroudning root tips

Access to soil nutrients & water

Carbohydrates

Carbon allocation to fungi

Endomycorrhizae - Partner, Benefit to Plant, Benefit to Mutualist, Cost to Plant

Most plant species

Enhanced phosphorus uptake

Carbohydrates

Energy cost in sugar exchange

Phosphorus Cycle: pools

• Rocks and soil (no atmospheric component).
  
  

Phosphorus Cycle: fluxes

• Fluxes: chemical Weathering of rock and uplift releases phosphate; uptake by plants; returns to soil via decomposition.
  
  

Phosphorus Cycle: entry

• Entry: Uptake by roots, often facilitated by fungal mutualists.
  

Phosphorus Cycle: exit

• Exit: Runoff into aquatic systems; sedimentation.

P leaves terrestrial ecosystems through soil erosion, leaching, and groundwater runoff, and marine ecosystems through sedimentation Can take over 100 millions years for a P atom to return to food webs once enters ocean sediments