Transcript NUTRIENT CYCLES PowerPoint

Nutrient cycles
Ecosphere Photo
Earth Photo
Nutrient cycles
• Nutrient cycles, or “biogeochemical cycles,” involve
natural processes that recycle nutrients in various
chemical forms in a cyclic manner from the nonliving environment to living organisms and back to
the non-living environment again
• Types of nutrient cycles:
– Hydrologic cycle
– Atmospheric cycles
– Sedimentary cycles
The water cycle
• No water, no life
• determines ecosystem structure; water-living (aquatic) communities
important for supporting life on land
• affects nutrient availability
• Evaporation and transpiration lead to condensation, to precipitation, to
percolation and runoff, and all over again
• Powered by energy from the sun and gravity
• 84% of water vapor from the oceans (71% of the Earth’s surface)
• 77% of precipitation falls back into the sea
• Some precipitation locked in glaciers
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runoff, erosion, moves soil and weathered rock
primary sculptor of the earth’s landscape
dissolves many nutrient compounds, transporting nutrients
Percolation dissolves minerals and moves them into groundwater
Times for water to cycle through various pathways:
– Water table: 300-4600 years; Lakes: 13 years; Streams: 13
days; Atmosphere: 9 days; Ocean: 37,000 years; Glaciers:
16,000 years
• Evaporation = natural distillation; also purified by chemical and
biological processes in the soil
• Hydrologic, atmospheric or sedimentary?
The carbon cycle
• Essential to life
• Basic building block of carbohydrates, fats, proteins,
nucleic acids and all other organic compounds
• CO2 is a heat-trapping greenhouse gas; regulates
heat, with major impacts on ecosystem function
• Cycling times for CO2: Atmosphere, 3 years; Soil,
25-30 years; Oceans, 1,500 years
• Hydrologic, atmospheric or sedimentary?
The phosphorous cycle
• essential nutrient of plants and animals, used in DNA, nucleic acids,
fats, cell membranes, and bones, teeth and shells
• from phosphate deposits on land and shallow ocean sediments to
living organisms and slowly back to the land and ocean
• Very little in the atmosphere, only as small particles of dust
• much more rapidly through living components than through
geological formations; animals get by eating producers or animals
that eat producers
• Animal wastes and decay return much of this phosphorous to the
soil, streams, and eventually to ocean bottom and into rock cycle
• Hydrologic, atmospheric or sedimentary?
The nitrogen cycle
• Nitrogen is necessary for vital organic compounds such as
amino acids, proteins, DNA and RNA
• In short supply in both terrestrial and aquatic ecosystems
• N2 = 78% of the volume of the troposphere
• Cannot be directly used by organisms
• Must be converted to compounds that can enter food webs by
the process of “nitrogen fixation”
• Nitrogen fixation:
– Specialized bacteria convert N2 to ammonia (NH3) by the
reaction
N2 + 3H2 = 2NH3
– Cyanobacteria in soils and water, and Rhizobium bacteria in
small nodules in legume root systems
– Nitrification – NH3 converted by specialized aerobic nitrite
(NO2-), toxic
– Converted to nitrate (NO3-) ions, which are easily taken up
by plants as nutrients
• Nitrogen fixation:
– Assimilation – NO3- taken up by plants and used to make
nitrogen-containing organic molecules
– Animals get nitrogen by eating plants or plant-eating animals
– Decomposers convert to NH3 and ammonium (NH4+);
ammonification
– Denitirification - specialized bacteria convert NH3 and NH4+
back into NO2- and NO3, and then to N2 and N2O, released
into the atmosphere
• Easily leached by water, limiting productivity
potential.
• Hydrologic, atmospheric or sedimentary?
Back to the Ecosphere
How do humans affect
nutrient cycles?
Water cycle:
• Drain fresh water from streams, lakes, and underground
sources
• Clear vegetation increasing runoff, reducing infiltration,
increasing erosion and risk of flooding
• Modify water quality by adding nutrients (phosphates) and
changing ecological processes that naturally purify water
Carbon cycle:
• Put more CO2 in the atmosphere than plants can remove
• Deforestation reduces the amount of vegetation to remove CO2
• Burning fossil fuels and wood releases more CO2 than natural
processes
• What happens when we have to much heat-trapping gas?
Phosphorous cycle:
• Mine large phosphate rock for fertilizers and detergents
• Cutting tropical forests; little phosphorous in soil, all bound up in
organic matter which usually rapidly recycles; but we remove the
biomass or burn it, allowing it to be rapidly washed away by runoff,
leaving the land unproductive
• Add excess phosphate to aquatic ecosystems in runoff from
agricultural operations, causing explosive plant growth creating
surface mats which block sunlight; dying plants feed bacteria which
uses up most of the oxygen in the water.
Nitrogen cycle:
• Emit nitric oxide (NO) when burning fuels; leads to acid rain
• Emit heat-trapping nitrous oxide (NO2) into the atmosphere
• Remove nitrogen from the earth’s crust for fertilizers, harvesting nitrogen-rich
biomass, and increase leaching through irrigation
• Remove nitrogen from topsoil when burning grasslands and clearing forests; also
emits nitrous oxides
• Add excess through runoff and sewage – promotes overgrowth of algae, which
dies, breaks down, and decomposition by bacteria depletes the water of oxygen;
disrupts aquatic systems; reduces aquatic biodiversity
• Add excess nitrogen to atmosphere; allowing weedy plants to outcompete other
plants, reducing biodiversity
Experimental
impacts on
nitrogen cycling in
a disturbed habitat
Nitrogen cycles in an experimental
ecosystem