Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
1
Energy Flows open system
sun earth
Nutrients cycle closed system
earth
poolpool
flux
flux
Classes of nutrients
Major nutrients: carbon,nitrogen, oxygen, water
Minor (but biologicallyimportant) nutrients:phosphorous, calcium,sodium , sulfur,magnesium, iron …
earth
poolpool
flux
flux
Types of transfer processes
Meteorological (rain, snow, wind)
Geological (volcanism, drainage)
Biological (transfers involving
microbes, plants or animals)
pool
earth
Nutrients cycle closed system
Pools =amounts
Fluxes =transfer rates
Rates of cycling
are dependenton pool sizesand flux rates
pool
flux
flux
Hydrologic cycle
The Amazon river
moves not onlywater, but nutrients
The Amazon river floods seasonally inundating 20% of theAmazon basin, depositing nutrients and enriching the soil
Many planned dams threaten thenatural flooding of the Amazon
2
The rich nutrientsmean the river isteeming with life
(high productivity) The sediment
laden waterselects foradaptationsin fish tosurvive inmurky water
pools = 1018 grams, fluxes = 1018 grams/yr
Hydrologic cycle
Evaporation from the sea (1/5th of all energy used to evaporate water)
Small atmospheric pool (13) Precipitation over sea (flux=283)
Flux to land (36=319-283) : flux into atmosphere must equal flux out
Large pool in ocean (1,380,000)
pools = 1018 grams, fluxes = 1018 grams/yr
Hydrologic cycle
Rainfall to land (95=36+59) : flux into atmosphere must equal flux out;evaporation from land contributes large fraction of rainfall to land
Runoff (36) balances 36 net which left oceans
Evaporation from land (flux = 59)
pools = 1018 grams, fluxes = 1018 grams/yr
Hydrologic cycle
Humans are altering the hydrologic cycle: a) 50% of the surface water is used by humans
(already a shortage, will get worse)
b) mining “fossil water” - pumping aquifers faster than they are beingreplenished (e.g. AZ and NV)
c) deforestation reduces evapo-transpiration and rainfall(50% of rainfall in amazon from evapo-transpiration)
Deforestation affects local rainfall - Panama
Forest cover in Panama
1910 1960 2010
Ra
infa
ll
3
Nitrogen cycle ( a simplified version)Nitrogen is one of the 2 most limiting plant nutrients
Inorganic nitrogen(nitrate and ammonium)
Atmospheric N2
Dead plants and animals
Organic nitrogen in proteins (live plants and animals)
1
2
4
3
Atmospheric N is a huge poolnot available to plants
1. Nitrogen fixation: <5% fixed bylightening, 95% by bacteria in soil orsymbionts, limiting step, expensive
2. Assimilation: rapid
small pool
3. Denitrification: bacteria convertorganic nitrogen back toelemental form
4. Many steps involving bacteria (some stepsare called ammonification and nitrification),slow step
Nitrogen fixation is the most limiting stepHumans now use fossil fuels to make fertilizerFertilizers have doubled the global input
Impacts of increasing nitrogen inputs : Mississippi
Humans have increase N input into the Mississippi by 8 fold in 50 yrs
7 million metric tons of N in fertilizer is applied in the river basin/yr1.8 million metric tons (26%) are lost down the river/yr = $750 million
This causes temporary algal blooms in the Gulf, which die, decompose
and deplete the water of oxygen, killing all other life
The “dead zone” in the Gulf is larger than the size of New
Jersey (20000 km2) and growing larger every year
Differences in the nitrogen cycle between temperate and tropical regions
Inorganic nitrogen(nitrate and ammonium)
Atmospheric N2
Dead plants and animals
Organic nitrogen in proteins (live plants and animals)
1
2
4
3
Distribution of nitrogen soil plants
Tundra 99% 1%Temperate 70% 30%Tropics 30% 70%
c) Leads to most nutrients being in the soil(dead plants) in cold climates and mostbeing in the live plants in warm climates
d) Deforestation in the tropics removes most ofthe nutrients, less impact in temperateforests
b) Decomposition (steps 3 & 4) are slow incold climates (experiment?)
a) Pool sizes differ. What steps arelimiting in the tundra?
Variation in nutrient availability
Andes are new and nutrient rich, as arethe rivers draining them (Amazon)
The Guyanashield is old,
highly weatheredand nutrient poor
Variation in nutrient availability
Black water river draining white sands (nutrient poor)
White-water river draining nutrient rich Andes
Burning for agriculture causes a pulse of nutrients, most of which are
washed downstream (majority of nutrients are in plants not the soil)
In white sands forests, plots sustain
agriculture for ~2 years before nutrientsare completely depleted and plotsabandoned
4
Despite nutrient poor soils (white
sands), forests grow very big.
How do they do it?
many adaptations to acquirenutrients and lose less
Plant adaptations for nutrient poor soils
Investments in roots, many at the surface
Plant adaptations for nutrient poor soils
Symbioses with nitrogen fixing bacteria and mycorrhizal fungi
Plant adaptations for nutrient poor soils
Carnivorous plants
Plant adaptations for nutrient poor soils
Defend the nutrients already acquired(toughness, secondary metabolites
such as tannins)
Tannins in leaves leach intothe water turning it dark
(black water rivers)
White sands are nutrient poor
Black water rivers are nutrient poor becausethey drain nutrient poor white sands
Plants on white sands are selected to be welldefended against herbivores (protect thenutrients)
Black water rivers are black becausethey are full of tannins leached from
the well defended leaves
Black water rivers have lower animal
abundance and diversity than white water rivers (nutrient rich)
White versus black water rivers