Download Biogeochemical cycles

Ecosystem Ecology
Serengeti at Sunrise
Biogeochemistry
Energy and Material Flow in Ecosystems
Biogeochemical Cycles
Nutrients exist in pools of chemical elements - 3
main compartments where these nutrients exist
are:
1) atmosphere - carbon in carbon dioxide, nitrogen in
atmospheric nitrogen
2) lithosphere - the rocks - phosphates, calcium in
calcium carbonate, potassium in feldspar
3) hydrosphere - the water of oceans, lakes, streams
and soil - nitrogen in dissolved nitrate, carbon in
carbonic acid
Atmosphere
Living Organisms
Lithosphere
Hydrosphere
Nutrients are input to ecosystems via:
1) from atmosphere - direct uptake such as carbon dioxide
(photosynthesis) and nitrogen (taken up and fixed by
bacteria and blue-green algae);
Wetfall (rain, snow, fog) carrying the nutrients and
washing them out of the atmosphere;
Dryfall - particles directly settle out of the air;
2) from lithosphere - from weathering of rocks - some due to
mechanical weathering by freezing and thawing and
erosion, most due to chemical weathering by water running
over the rocks;
3) from hydrosphere - streamflow carries nutrients into new
areas
Living Organisms and Nutrient Cycles
• Living organisms are a compartment in which
carbon exists in carbohydrates (mainly cellulose)
and fats, nitrogen in protein, and phosphorus in
ATP
Nutrient Fluxes
• For some nutrients in some ecosystems,
nutrient fluxes may be in balance so that
inputs = outputs
• But for other ecosystems and nutrients, the
cycle may be out of balance from too much
input so that
input > output
storage
• or too much output
output > input
loss
General Scheme for Biogeochemical Cycles
Consumers
Producers
Decomposers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Hydrologic Cycle
Hydrologic Cycle
• Evaporation determines the flux of water through
the cycle because it is in evaporation that energy is
input
• The atmosphere holds about 2.5 cm of water
spread evenly over the earth's surface at any one
time
• 65 cm of rain falls across the earth each year water cycles through atmosphere 25 times a year,
each transit takes about 2 weeks
• Most of the evaporation on land is due to losses by
plants during respiration - 55 x 1018 g while total
for land is 59 x 1018
Carbon Cycle
Some Carbon Cycle Numbers
• World's terrestrial biota respires about 120 x 109
metric tonnes of carbon per year
• Human activities release about 5.1 to 5.9 x 109 metric
tonnes per year
• The observed increase in atmospheric CO2 is due to
about 2.9 x 109 tonnes per year - which is 39 - 57% of
human input
• The rest is probably dissolved in the oceans though
some is absorbed by terrestrial plants and put into
extra biomass.
• 1750 atmospheric CO2 was 280 ppm, 400 ppm in
May 2013
• Current estimate is that by 2050 atmospheric CO2
will reach 660 ppm
Increase in Atmospheric CO2
and Global Temperature
Global Carbon Emissions
CO2 Last 400K years
Projected Temperature Changes –
B1 low, A1 medium, A2 high
Changes in NPP due to Global
Climate Change
Nitrogen Cycle
Ammonia in Agriculture
Nitrogen Cycle
• To become a part of an organism, nitrogen must first be
fixed or combined with oxygen or hydrogen.
• Nitrogen cycle is mainly an atmospheric cycle – Nitrogen
fixation mainly occurs by atmospheric N being fixed by
microbes in soil; 3 - 4% of annual influx is fixed by
lightning and brought to earth by wetfall.
• When plants and animals eventually die, their nitrogen
compounds are broken down giving ammonia
(ammonification).
• Some of the ammonia is taken up by the plants; some is
dissolved in water or held in the soil where bacteria
convert it to nitrates (nitrification).
• It may also be converted to free nitrogen (denitrification)
and returned to the atmosphere – especially in low oxygen
environments.
Phosphorus Cycle
Phosphorus Cycle
The global Phosphorus budget:
Pools of available
phosphorus, in 1012
grams P
• Sediment 4 x109
• Soils 200,000
• Sea 90,000
• Mineable rock 10,000
• Terrestrial 3,000
Fluxes (x1012 g P/yr)
• Terrestrial cycle 60
• Mining extraction 12
• Transport airborne
dust 1
• Transport rivers 21
• Marine cycle 1000
• Burial 2
Cultural Eutrophication
• Eutrophication means well
fed and in natural situation
is okay
• Cultural eutrophication –
human sources introduce
nutrients, especially
phosphorus or nitrogen, to
a body of water leading to
very high concentrations
of the nutrient causing
increased growth of algae.
Lake Washington, Seattle
Seattle
Oscillatoria –
Cyanobacteria
Cyanobacteria
Blooms
Eutrophication Timeline
• Late 1800’s – Seattle starts to grow to city size –
raw sewage dumped into Lake Washington
• 1926 – Seattle builds sewage treatment plant –
sewage sent to Puget Sound
• 1940’s – area grows – suburbs build 10 treatment
plants that dump treated sewage in Lake
Washington between 1941-1954
• 1955 – Oscillatoria found growing in lake
• Action taken to clean lake – 1963 sewage diverted
to Puget Sound, 1964 water quality improves,
1968 no sewage dumped into lake; 1975 – back to
pre-pollution state
Lake Washington – Reduction in Phosphorus
followed by reduction in growth of cyanobacteria
measured as amount of chlorophyll in the water