Lecture 1: The Ecosystem Concept
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Definition of ecosystem
Boundaries
Black box vs. transparent box
o Ecosystem approach vs. other divisions in ecology
o Gradient diagram from abiotic vs. biotic
Mass balance
How do we study ecosystems?
Ecosystem components:
o Boundaries
o Abiotic vs. biotic
o Fluxes + pools
Evolution of the ecosystem concept
o Tansley – originated the concept
o All those people after. Odum. Likens. Redfield.
o How is ecosystem science the same/different from when it originated?
o Black box to mechanistic approach
o Energy budgets and mass balance vs. mechanisms.
o Original purpose – flow of energy through a system. Later included nutrients, etc.
Lecture 2: Terrestrial PP
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GPP vs. NPP vs. NEP vs. NEE
NEE – used by meteorologists/ measured by flux towers.
NEE integrated over time = NEP. NEE is instantaneous, NEP has units per time.
Different ways of measuring productivity, what measures what, at what scale?
Liebig’s law, limits on PP
Lecture 3: Aquatic PP
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Measurement
o Light dark bottles, C14, free water oxygen, remote sensing
Regulation of PP – what limits it?
o Light
o Season, depth turbidity
o Nutrients
o Temperature
o Etc.
Oceanic limitation –
Table comparing NPP in aquatic vs. terrestrial environments
Heterotrophic vs. autotrophic systems
What limits PP in water vs. on land?
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Light –
o Turbidity
o canopy
Herbivory
o More important in aquatic systems –
o With comparable NPP, you have less biomass in aquatic systems b/c of herbivory
o Savannahs and grasslands herbivores and fire can be important.
Nutrients
o N more on land
 Changes with age of ecosystem- more weathered ecosystems are more P
limited (Vitousek hawaii study)
o P more important in the water
o Fe in the ocean
Temperature
CO2 – not really limiting
Productivity to respiration ratio less than one in lots of aquatic systems.
In terms of carbon storage – terrestrial ecosystems have much more standing stock. Very high
turnover in primary producers in aquatic systems.
Lecture 4: Secondary production
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Energy budget: I = A + E (Ingestion, assimilation, egestion)
A = R + P + U (respiration, production, excretion [urine])
Metabolism = oxidation of stored compounds to produce energy. Same as respiration. Produces
CO2
Q10 – change in metabolic rate w/ 10 degree increase in temperature. ~2.
Metabolic rate per unit mass declines w/ body size. Slope = -0.25 (that’s allometry, folks!)
How do you measure metabolic rate?
o Measure inputs and outputs
o Rate of oxygen consumption
Efficiencies: assimilation vs. net growth vs. gross growth
o Assimilation eff.= A/I
o NGE = P/A
o GGE = P/I
Secondary production definition – all heterotrophic production, regardless of its fate (even if the
rabbits die of disappointment)
Ways to measure SP
Controls on SP
o Changes depending on whether you’re looking at populations, communities, guilds
o We can calculate community level SP based on mass balance
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Mentioned as possible exam question: what’s an application for SP in terrestrial ecology that
would improve our understanding?
o Terrestrial people don’t use this as much
o Most of the biomass in aquatic systems is in secondary production but in terr systems
it’s more in plants
o Or maybe just b/c it’s hard
Secondary production can exceed PP b/c organic matter gets recycled over and over.
Is there a Loch Ness Monster? Could it survive based on Loch Ness NPP?
o How much terrestrial subsidy?
o Energy flow through trophic levels
Lecture 5: Decomposition
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Different ways things can be decomposed – release of soluble components, oxidized or respired,
fine POM
Mass loss
Intrinsic controls on decomp
o Cellulose vs. lignin vs. glucose example. Different tools microbes would need to break
them down depend on complexity of the molecule
o Higher N or P = faster decomposition
o Nutritional quality of detritus
Extrinsic
o Temperature
o Nutrients – exogenous nitrogen can speed up decomposition if low N content in detritus
o Control by terminal electron receptor
 Chart of terminal electron receptors in the redox appendix
o Organisms – microbes, bugs
C:N ratio important to predict
C: N ratios generally lower in aquatic systems – less structural investment in aquatic systems
Lecture 6: The origin of things
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The onion – the outer layer is what we’re interested in.
Distribution of elements is the result of “global star processes” and coalescence.
Triple negative valence of P – reason P is necessary for life even though it’s pretty rare.
o Important for ATP – high energy density
Formation of oxygen in the atmosphere, banded iron formations
o Oxygen couldn’t build up in the atmosphere til iron was oxidized. Sulfur, nitrogen might
have also oxidized free oxygen.
Oxygenic Photosynthesis has higher Gibbs Free Energy – would be favored energetically.
Secondary atmosphere vs. primary
o Primary – Ar36
o Secondary Ar40
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o Primary – stuff that didn’t totally coalesce when the planets were formed.
o Secondary atmosphere comes from outgassing
o Secondary comes from the planet
o Primary comes from outer space
Characteristics of life
o Membrane
o Growth + reproduction (Genetic code)
o Metabolism
Lecture 7: The global C cycle
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Carpenter’s table – experiments, theory, long term studies, comparisons
Carbon burial
No one thing controls the C cycle.
What you perceive as the control depends on the time scale you look at.
o Current elevations of CO2 are transient compared to burial of sediments
Subsidies – If you have C entering a system, some may leave and some may be buried or stored.
o Aquatic system – respiration > production, but some C is buried too.
Partial pressure
o Pressure by specific gas
o 0.2 O2
o 0.03 CO2
Why is there so much less CO2 in the atmosphere than O2?
o Carbon gets buried in sediments (reduced C that doesn’t contain much O2)
o Origin of oxygen is photosynthesis. Balance of GPP and R regulates oxygen
o Carbonate system in the ocean – the more CO2 you have the more goes into the ocean,
then it get’s locked into that system (has more to do with ocean acidification than O2)
o Carbonate ooze – at the bottom of the ocean. Places rich in carbonate.
o Bicarbonate in the ocean – lots of dissolved inorganic C in the ocean. The C is from the
atmosphere. CO2 + something alkaline
o Some of the products of respiration end up as bicarbonate in the ocean.
o On the other hand, most of the O2 from photosynthesis ends up in the atmosphere
(analogous sinks are small)
o Limestone – uplifted ocean bottom. Inorganic carbon.
Lecture 8: Nitrogen
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Ways people mess up the N cycle
Most N is in the atmosphere
C:N of substrate important for the balance of mineralization vs. immobilization
Annamox – anaerobic ammonium oxidation. Breakdown of NH4 in the presence of NO2 releases
N gas
Regulation of the N cycle on the ecosystem scale
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Nutrient richness – tight vs. loose cycles.
Low productivity – tighter N cycle – less leaky, less loss after disturbance
High productivity – “looser” N cycle – more leaky
Ecosystem age/succession – young systems have more loss (less control over abiotic
environment, no plants), growing system has maximum efficiency, old ecosystems might
have higher losses
In a mature system, losses may increase, but denitrification goes on too.
Enigma of the missing N – our N budgets don’t balance out – N is either lost or stored.
Might be denitrification or might be stored in a way we don’t really understand.
Lecture 9: The Phosphorus cycle
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Not really a cycle on biological time scales.
Inputs: chemical weathering. There’s not biological fixation.
Mostly found in phosphate form.
Internal cycling –
o Losses – leaching, erosion, fire, harvest.
Major pool – surface sediments.
Ocean is largest pool of phosphorus (sediments on the bottom of the ocean)
Weathering
Mycorrhizae
Redox drives eutrophication
o P builds up in sediments
o Released in anoxic conditions
o Increased production leads to anoxic conditions in which Fe3+ is reduced to Fe2+. Fe2+
P is like N in its internal cycling. But unlike N in that it is stored in sediments (P doesn’t leach).
No important gas phase, main pools in soils and sediments.
Redfield ratio (N:P=16:1 - aquatic) can tell you if a system is N or P limited
P does leach (but most sorbs). Soil can only absorb so much P – in places with a long history of P
fertilizer the soil can saturate.
o 20% of N applied will end up in aquatic system
o ~2% of P leaches.
Coupled biogeochemical cycles:
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History – Liebig. Exceptions to Liebig show us what’s interesting.
Redfield – stoichiometry in phytoplankton
Sulfur wars – people reporting rates of sulfate reduction that were stoichiometrically impossible
Chelation – metals bind to organic matter – effects cycling of those metals. Cycling of carbon is
related to cycling of lead.
Geoengineering – dumping iron in the ocean vs. fertilizing soils to increase NPP. Sulfates in the
stratosphere.