Cycling of Matter in Ecosystems
aka – Nutrient Cycles
How are energy flow and cycling of
matter different?
• Energy flows in one direction through an
ecosystem. Sun  Producers  Consumers
• Energy doesn’t return to sun, it’s “lost”
(unuseable)
• Law of Conservation of Matter: Matter cannot
be created or destroyed, only re-arranged.
• This is why ecosystems must recycle matter
• Nature does this well through nutrient cycles.
The Essential Elements
• Nature tends to use the following raw materials in great
quantity:
• Nitrogen, Carbon, Hydrogen, Oxygen, Phosphorus and Sulfur
• Using their chemical symbols we get the acronym N-CHOPS
• Since natural systems use these so much and dispose of
them so often, they are cycled quite efficiently
• The only way matter can be cycled out of food webs is to
involve detritus feeders and decomposers
Decomposers at work
decomposing rabbit
ants and gecko
Basic Cycle Overview
•
Cycles are basically a series of Reservoirs or
Sinks connected by pathways or fluxes.
• We will trace each nutrient cycle through 5 key
points:
1) Identify all Reservoirs, including main res.
2) Identify “pathways” or fluxes between reservoirs
3) Describe interactions with biotic community
4) Understand key terms that apply to each cycle
5) Human impact along the way
Use your “Key Points” Sheet
Use diagrams – as many as possible
Start with one we all know…H2O
1) Make a group of 4
2) Define key terms
3) Create a diagram of the water cycle that shows all
5 key points
4) Use “Key Points” worksheet as a reference
5) Do you remember the Water Cycle Song?
Water Cycle = Hydrologic Cycle
• Reservoirs: ocean, atmosphere, surface water,
groundwater, glaciers, biomass
• Evaporation = (liquid to gas) ocean and surface water to
atmosphere
• Water vapor cools and condenses into liquid (clouds) in
atmosphere (another reservoir)
• Water falls back to surface by precipitation
• Run-off = flow across surface through streams, rivers, lakes
back to ocean (check diagram)
• Infiltration = precipitated water at surface filters into soil and
rocks
• Plants can absorb it from soil through roots after infiltration
• Water evaporates from plants by transpiration
Water (Hydrologic) Cycle
Most Consumers get water from run-off locations, not
through the food web
Water that infiltrates and does not get used by plants
will percolate through soil and flow underground
eventually back to run-off or ocean (aquifer)
Natural purification steps:
1) Evaporation = only pure H2O is moving on
2) Percolation = soil, sand and rock act as a filter for
groundwater
3) Run-off (ation) = pollutants settle out on lakes and
wetlands
Human Interactions
• Over-withdrawal = depletion of fresh water supply
(problem in western US)
• Creating an imbalance between run-off and
infiltration – increased run-off, flooding and erosion
1) clearing vegetation
2) creating impervious surfaces
• Modifying = draining wetlands, modifying riparian
zones (river banks)
• Modifications short circuit the natural purification of
run-off
• Pollution of air, groundwater, surface water, soils
And now a little game….
1) On your own…
2) Take a total of 16 trips
3) Use sheets to keep track of where you
go and how
4) Answer questions on separate sheet of
paper when finished – staple all papers
together
5) Report out findings
Nitrogen Game Analysis
Answer the following questions quietly on your own…
1) Which station did you visit most often?
2) What station was visited the most by the entire class? How
does this compare with your answer to #1
3) What does this tell you about nitrogen in nature and how it
moves?
4) What kinds of human impacts were you involved in?
5) Explain the difference between how plants and animals obtain
their nitrogen requirements.
6) Identify two ways atmospheric nitrogen is made “biologically
useable”
Nitrogen
• Main reservoir is atmospheric N2 = useless gas
• Gets to producers by being fixed into useable forms of
nitrogen = Ammonia (NH3), Nitrate (NO3)
• Nitrogen Fixation is done by bacteria and lightning  NH3
• Legume family of plants have root nodules that house these
beneficial bacteria (beans, alfalfa, peas, etc…)
• Nitrification = soil bacteria converts ammonia to nitrate
(NO3-)
• Uptake of NH3 or NO3 by autotrophs = assimilation
• Travels through food chain
• Released to soil again through plant & animal waste and
decay
• Animal wastes, dead plants, etc.. Broken down by
decomposers and returned to atmos as N2 (unusable) =
denitrification
Human Impact on Nitrogen Cycle
• Humans interfere by burning certain fossil fuels that release
nitrogen compounds to form acid rain
• Also, over-fertilization pollutes waterways – remember the
nutrient pollution lab
• Over-farming removes nitrogen from soil as crops are
removed
• Use crop rotation to reduce nitrogen loss
• Make sure your diagram is accurate and complete for this
cycle
Carbon Cycle
• Main reservoir is CO2 in atmosphere and dissolved in oceans
• Other reservoirs: Ocean sediments, biomass, fossil fuels
such as coal, petroleum, natural gas (methane)
• In the atmos. CO2 acts as nature’s thermostat (greenhouse
effect)
• Basic 3 step Cycle:
1) Taken in by plant leaves to do photosynthesis
2) Travels through consumers/food chain
3) Released back into atmos. as CO2 by animal
respiration, decay processes or burning
vegetation
Ocean part of cycle is very similar except some CO2 is
incorporated into coral and shells of clams, oysters, etc…
Human Impact
• Clearing vegetation (Deforestation) increases levels of CO2 in
the atmosphere
• Combustion (burning) of fossil fuels increases levels of CO2
in the atmosphere (fuel + O2  CO2 + H20 + Energy)
• Fossil Fuels = organic compounds made by the decay of
organisms deep underground in the presence of high heat or
pressure (coal, petroleum, natural gas, etc…)
• This could increase Greenhouse Effect  Global Climate
Change
• Push for alternative energy to avoid climate change or to
lessen our dependence on resources that are non-renewable
or difficult to obtain
• What alternatives are good? Not so good?
Traditional Fossil Fuel Usage
Traditional Fossil Fuel Usage:
Petroleum = gasoline, diesel, propane, other
fuels
Coal = burned to generate electricity
Natural Gas = heat homes, water tanks, appliances
Alternatives:
Crop Ethanol, Landfill Gas, Biodiesel still emit CO2
Wind Power, Nuclear, Geothermal, Hydrogen Fuel
cells, Solar do not emit CO2
Alternative energy sources replace
traditional fossil fuels
Use more Methane / Natural Gas – makes sense
• Methane produces less CO2 and is easier to obtain than
petroleum
• Methane (CH4) is a much stronger greenhouse gas than CO2
• Hydro-fracking for methane…safety?
• Use landfill gas as alternate energy source?
Hydro-fracking to release CH4
Phosphorus
•
•
•
•
•
•
•
•
•
P circulates through earth’s crust, organisms and water
Not in atmos, no gas phase
Very slow
Typically found as phosphate (PO4) in terrestrial rock and
ocean floor sediments = Main Res.
Enters biotic through uptake by producers’ roots
Often a limiting factor for plant growth unless added in
fertilizers
Passed on through food chains
Returns to soil through decomposition, poop and pee
(guano – seabird poop deposits)
Can move slowly from ocean to land through uplifting of rock
Phosphorus
• Human activities: mined for fertilizers and
detergents
• Removed by deforestation
• Added by run-off of animal waste, fertilizers and
sewage discharge
• When too much phosphate finds its way into runoff, it causes eutrophication in waterways
• Eutrophication = excess phosphate causing algae
to grow out of control, reducing available oxygen to
other aquatic organisms
Sulfur
• Similar to P, main reservoir = rocks and minerals in soil
• Producers obtain it through roots and pass it on to the rest of
the food web
• Decomposers return it to soil from waste and detritus
• Bacteria also return sulfur the atmosphere as…
H2S (hydrogen sulfide) gas from wetlands
DMS (Dimethyl Sulfide) from oceans
• Or SO2 (sulfur dioxide) gas from volcanoes
• SO2 reacts with O2 and H2O in clouds form sulfuric acid =
acid rain
• Acid rain returns sulfur to soil and rock reservoir
Sulfur
•
•
•
•
Human Impact involves burning soft coal and oil
Refining petroleum
Using smelting for copper lead and zinc refining
These 3 activities increase sulfur dioxide
(SO2) and sulfur trioxide (S03) levels in the
atmosphere which decreases acid rain pH
Acid Rain Effects on Trees
Acid Rain Effects on Trees
Acid Rain Effects on
Buildings
Acid Rain! – the band
If you missed class time on this…
1) Make sure your notes are complete
(Nutrient Cycles at a Glance sheet)
2) Read chapter 3 section 5 (pp.65-72), pay
special attention to diagrams
3) Ask Mr. Kearns for help on what you do
not understand
Freak Point Opportunity (up to 6 Freaks)
Make up a song!
- to the tune of a holiday song
- must incorporate key vocab and the general
story behind one of the cycles (not water)
- must be sung in front of the class
- must be accurate
- due by Tuesday (11/8)
- # of freak points earned is determined by the
teacher