Transcript Chapter 22 Biogeochemical cycling

Chapter 22
Biogeochemical cycling
The Universe
When?
How?
15 X 109 years ago
Matter existed in its most fundamental form.
Elements formed as universe expanded and
cooled.
13.8 sec post ‘Big Bang’ –formation of H and He
nuclei
700,000 years later—electrons attached to nuclei
Formation of elements
Elemental formation is linked to evolution
of stars.
Stars derive energy from nuclear
reactions that synthesize elements.
4He + 4He  8Be
8Be + 4He  12C
1H + 4He  5Li
12C + 4He  16O
Ecosystems are linked
Input and output of nutrients link ecosystems
Gaseous cycle—
atmosphere and ocean
Sedimentary cycle—
soil, rocks and minerals
dissolved salts and rock phase
Carbon
Basic element of all organic compounds
Inseparable with energy flow
Source of CO2
atmosphere/water
Primary producers decomposers
Net ecosystem productivity
Rate at which C is taken up in
photosynthesis and lost due to
respiration.
Determined by
Primary production
Decomposition
Terrestrial ecosystems—slower
in cooler climates—
slower decomposition and
production
Aquatic C cycling
Phytoplankton uses CO2 or carbonate
CO2 enters back into system through
respiration and decomposition
Variation in C cycling
Varies with time of day—
photosynthesis highest in afternoon
respiration highest just before daylight
Seasonal variation—
varies according to weather
varies with climate
varies with seasonal
More pronounced in
terrestrial ecosystems
Carbon stores
1023 grams of C = 100 million Gt
(1 Gt = 109 tons)
55,000 Gt in C pool
Oceans –38,000 Gt
dead organic matter –1500 Gt
living biomass – 750 Gt
Terrestrial –
dead organic matter – 1500 Gt
living biomass – 560 Gt
Atmosphere – 750 Gt
Carbon exchange
Ocean exchange site — surface water
Circulates via currents and movement
through food chain
Terrestrial exchange site – governed by
photosynthesis / respiration
Large stores in soil
increases from tropics poleward
Nitrogen cycle
Essential in proteins rubisco
Usable forms = NH4+ and NO3N stores in atmosphere = N2
N enters ecosystem through:
wetfall/dryfall
N fixation
Cosmic radiation/lightening/meteor trails
biologically— N fixing bacteria
Biological N fixation
Provides 90% of available N to ecosystems
Splits N2 into 2 N + H+  NH3
For each gram NH3 use 10 grams glucose
Agents
Legumes/symbiotic bacteria
free-living aerobic/anaerobic bacteria—
Azotobacter/Clostridium
Cyanobacteria (blue-green algae)—
Nostoc/Calothrix
Lichens
N availability
Ammonification –process of breaking
down organic matter and producing NH3
Soils slightly acidic
Quickly converts to NH4+
Nitrification –converting NH4+ to NO2- and
then to NO3Denitrification—reduction
of NO3- to N2O and N2
N export & stores
NO3- most common form exported
High demand for N
ecosystem and global cycling similar
N stores
Atmosphere –largest pool 3.9 X 1021
Biomass and soils –
3.5 X 1015 / 95-140 X 1015
Oceans—inputs from rivers and atmosphere
36 X 1012 / 30 X 1012
Biomass—15 X 1012
Denitrification returns 110 X 1012 to atmosphere
Phosphorus cycle
No atmospheric input--follows hydrological
cycle only
Often in short supply
Reservoirs – Rock + natural phosphate
deposits
Internal cycling important—3 states
organic P, dissolved organic P & inorganic P
Inorganic P taken up by primary producers
eaten by zooplankton—excreted or retained
P used by bacteria not recycled
P can be deposited into sediments
Global cycling unique—no atmospheric
inputs /
river inputs important in oceans
High turnover rate
Sulfur cycle
Sedimentary and gaseous phases
Carried in salt solutions
tied up in deposits—released by weathering
Atmospheric input—fossil fuels, volcanic
eruption, ocean surface water,
decomposition
Enters as H2S—oxidized to SO2 carried as
H2SO4 –result = acid rain
Important in amino acids
Decomposition—released as HSO4- or SO42Presence of Fe, S precipitates out as FeS2
Global cycling of S
Least understood of nutrients
Gas phase allows global cycling
Inputs:
Oceans contain large pools, but do not
contribute much
Input into atmosphere:
Forest fires
Volcanic
Industrial
Oxygen cycle
Complex cycle—linked to other nutrients
Sources of O2
photosynthesis
breakup of H2O in atmosphere
Presently --balance of
photosynthesis
and respiration
O2 produced as byproduct of
anaerobic respiration
O2 released by weathering of rocks
O available in water and carbon dioxide
Redfield ratio
Cycles of nutrients are linked
Stoichiometry—quantitative relationships of
elements in combination
Redfield ratio—constant atomic ratio despite
ambient nutrient concentrations
C:N:P
106:16:1
106CO2 + 16NO3- + HPO42- + 122 H2O + 18H+
(CH2O)106(NH3)16(H3PO4) + 139 O2