Lecture 15 + 16 Flashcards
True or false: Divestment is the action or process of selling off subsidiary business interests or investments.
True
True or false: The Cornell board of trustees considers divesting its endowment assets from a company only when the company’s actions or inactions are morally reprehensible.
True
Which of the following types of institutions can engage in divestment? (you may select one or more answers)
- universities and colleges
- religious institutions
- insurance companies
- city pension funds
- nations
- universities and colleges
- religious institutions
- insurance companies
- city pension funds
- nations
According to the speaker’s “7 or 8 changes” portion of the talk, which 3 of the following statements are false:
1. The climate crisis is deepening over time.
2. Solar and wind power still remain more expensive that power generated by fossil fuels.
3. Developing nations do not use solar power.
4. Institutions that divest can do well financially
5. Fossil fuel companies had information concerning global warming 30 years ago.
6. Mitigating climate change will require work
7. Divestment has little support
8. Academic studies demonstrate that the divestment campaign has been successful
- Solar and wind power still remain more expensive that power generated by fossil fuels.
- Developing nations do not use solar power.
- Divestment has little support
True or false: According to the speaker we are certain to win “the climate change battle”.
False. The speaker was uncertain.
True or false: Because of the dangers associated with nuclear power the speaker prefers coal power to nuclear.
False. He considered nuclear power as a risk, while a coal power plant will certainly do damage.
What refers to the mass of organisms per unit area?
Biomass
Which of the following is an accurate definition of primary productivity?
- The rate at which a standing crop is produced or the volume at which plants photosynthesize.
- The rate at which biomass is produced per unit area or volume through photosynthesis
- The formation of essential plant structures
- The rate of formation of essential plant structures over a photosynthetic period.
- The rate at which a standing crop is produced or the volume at which plants photosynthesize.
What refers to the rate of production of biomass by heterotrophs?
Secondary productivity
Which biome has the greatest overall NPP?
Tropical rain forest
Populations
Groups of organisms of the same species in a defined area
Communities
All of the populations (different species) in a defined area
Ecosystems
The community of organisms interacting with the physical-chemical environment
- entire lakes or ponds, entire bogs or marshes, entire forests or defined parts of forest, entire pieces of oceans -> considered as a functioning unit
- boundaries are defined
Biosphere
All life interacting with the physical environment at the scale of the entire planet
Why study ecosystems?
- In general, need to study next lowest scale of organization to gain understanding of underlaying mechanisms at the scale of interest.
- Ecosystems are the appropriate scale for understanding functioning for many purposes of environmental management, including response to global change.
Why focus on primary production? All organisms need energy.
Second law of thermodynamics: increase in entropy (decrease in order) over time in the universe, and in any system…
…but only if there are no external inputs of energy to the system
Organisms and ecosystems are highly ordered systems, maintaining order through continual energy inputs.
Primary production is the source of most of that energy.
Primary production
The total amount of plant (or algal or cyanobacterial) material produced or energy captured per surface area per time. This is photosynthesis.
- this is a rate
Rate of primary production
Can be expressed in units of energy per area per time (joules m-2 yr-1), power per area (watts m-2 ), mass per area per time (g dry weight m-2 yr-1), or organic carbon per area per time (g C m-2 yr-1).
Different areas and times can be considered: square metres or square km, and hours or days or years.
The text generally uses g C m-2 yr-1
Gross primary production (GPP)
Total amount of photosynthesis per surface area per time
Total rate of CO2 fixed into organic matter per time
Represents total ecosystem photosynthesis
Net primary production
GPP minus the respiration of plants or algae carrying out photosynthesis per surface area per time
- represents the total amount of organic matter available for consumption by higher trophic levels, or for harvesting by humans
Autotrophic respiration (Ra)
Rate of respiration (energy consumption) by primary producers for their own maintenance and energy needs
How much of the energy of GPP do you think plants respire for their own metabolic needs?
50% or so on average
Across a wide range of terrestrial ecosystems, NPP = approximately 50% of GPP
That is, half of total photosynthesis is being used by the plants to meet their metabolic needs (for nutrient uptake, growth, defence against herbivory, etc.)
- terrestrial ecologists often focus on the factors controlling NPP
-> not true in aquatic ecosystems
What regulates NPP in terrestrial ecosystems?
Average pattern of NPP in terrestrial ecosystems is controlled by water availability
- highest in wetlands, tropical forests, temperate forests
- lowest in dune, rock, ice, desert, tundra
What controls terrestrial NPP?
- water is paramount
- top-down grazing by animals (“why is the world green”) may lead to rates 25% higher or lower than the mean rates set by light and water
- nutrient availability can lead to rates that are 40% higher or lower than the mean rates set by light and water
(Temperature? Remember that terrestrial biomes are structured along gradients of water and temperature…. Temperature has a major influence on both water and nutrients)
Liebig’s Law of the Minimum
“A plant’s growth is limited by the one essential mineral nutrient that is in the relatively shortest supply”
- Liebig’s barrel analogy, production is limited by shortest slat
Nutrient limitation
Constraint on rate of NPP by one or more nutrients
- caused by a low availability of the limiting nutrient relative to the needs of the plant to produce its biomass
- Generally, nitrogen (N) and phosphorus (P) are the nutrients most likely to be limiting (other nutrients are in greater abundance relative to plant needs).
Optimal ratio of N to P in plants
Optimal ratio of nitrogen to phosphorus (N:P) in plants is 15:1 (by moles, +/- 5)
NPP is N-limited if
Environmental availability is <10:1
- Nitrogen is more limiting in polar and boreal regions
NPP is P-limited if
Environmental availability is >20:1
- Phosphorus is more limiting in the tropics
Wang et al. map based on model predictions.
- includes effects of climate and soil types
- based on average conditions
- many factors can affect these predictions, including time along successional continuum
Hawaii is tropical, so P limited?
4 million years of succession and soil development
- new ecosystem, new soil: a lot of phosphorus in mineral form, ex. from volcanic ash
- overtime, lost from ecosystem, mineral disappears, organic P/occluded P, biologically unavailable
Given that the phosphorus in the soil is changing over the millions of years of primary succession, would you expect:
a) Hawaii is in the tropics, so production is limited by phosphorus, both early and late in succession;
b) Phosphorus is scarce early in succession, but becomes available over time, so it is limiting in early succession but not in late succession;
c) Phosphorus is plentiful early in succession, but becomes scarce over time, so it is limiting in late succession but not in early succession
c) Phosphorus is plentiful early in succession, but becomes scarce over time, so it is limiting in late succession but not in early succession
For tropical forests
Nitrogen is most limiting on younger soils
Phosphorus is more limiting on older soils
Plenty of available phosphorus in the very young soils on volcanic rock
Nitrogen is scarce
Plants that have nitrogen-fixing symbionts are favoured, and over geological time, they increase the amount of nitrogen to all plants
What is nitrogen fixation
The reduction of molecular N2 to biologically available forms of nitrogen
Carried out by a variety of bacteria
Essential to all life on Earth
Global pattern of nitrogen fixation in terrestrial ecosystems
- nitrogen fixation rates are highest in the tropical forests and savannahs
- rates are very low in boreal and polar areas
- nitrogen is more limiting in polar and boreal regions
- “young” soils: newly weathered P, low rates of N fixation
Phosphorus in terrestrial ecosystems
- phosphorus is more limiting in the tropics
- P has been weathered away, high rates of N fixation
- a dust storm in the Sahel Desert can place considerable phosphorus into the atmosphere, with some of this reaching as far as the Amazon rain forest over 5,000 km away
Net ecosystem production (NEP)
GPP minus the respiration of all organisms in the ecosystem per surface area per time
Net rate of organic matter accumulation in an ecosystem
NEP = NPP – Rh
NEP = GPP – Ra –Rh
Heterotrophic respiration: Rh
Rate of respiration (organic matter consumption) by all heterotrophs (microbes, herbivores, detritivores, carnivores)
Ecologists are interested in NPP because it provides the energy available to be transferred up food webs to support animal populations, and for harvest of materials to support human society (food, wood)
Why should ecologists be interest in NEP?
a) Negative rates of NEP in agricultural systems reflect a loss of organic matter that can lead to degraded soils;
b) High rates of NEP in natural ecosystems can store carbon, helping to mitigate global climate change;
c) Global climate change may change NEP in natural ecosystems, leading to feedbacks that may slow or accelerate global change
Organic carbon can be accumulating from
Positive rates of NEP in tree trunks, soils, or both
Controls on accumulation are different:
Organic carbon in tree trunks is protected from consumption and decomposition by the living trees (so forests are important)
Organic carbon in soils is the balance between
Production of new organic carbon and rates of decomposition
Temperature affects both
NPP and heterotrophic respiration, but respiration (decomposition) more strongly influenced
Therefore, storage of organic matter tends to be greatest in soils where temperatures are lower, i.e., tundra and not tropical forests
Soil is the
Largest repository or organic matter on land, storing more carbon than all vegetation
Is Net Ecosystem Production (NEP) always positive? Can it be negative?
NEP can be negative in some terrestrial ecosystems, at least for a while
Respiration (Rh) usually higher than GPP in agricultural ecosystems newly converted from natural ecosystems
-> this reflects a loss of soil organic carbon
NEP also negative immediately after disturbances such as clear-cutting and fire
-> But then rapidly becomes positive, as early succession takes over with rapidly growing tree species
Carbon accumulates in an ecosystem only when
GPP exceeds the rate of whole-ecosystem respiration
Human activity now uses
20-40% of global net primary productivity in terrestrial ecosystems
The planet is a complicated mosaic of disturbance, with some areas of recovery, with major consequences for Net Ecosystem Production globally (and therefore for global climate change)
Which community would you suspect receives high levels of radiation but does not convert much of that radiation to biomass?
- Tropical rain forest in Costa Rica
- Tropical rain forest in Ecuador
- Death Valley desert in California, United States of America
- A conifer forest in Alberta, Canada
Death Valley desert in California, United States of America
Where is the annual average rate of net primary productivity greatest (Consider only terrestrial regions)?
Between 30 degrees south and the equator
You have been informed that terrestrial plants produce 45-60 petragrams of carbon per year, and that this figure accounts for respiratory heat lost from the environment by autotrophs. What then is this 45-60 petragrams of carbon per year a measure of?
Net primary productivity
Think about a grassland that is very productive. During a one week period bison move through the grassland and consume almost 100% of the plants. Which of the following are true given this situation (multiple answers possible).
- During the time when the bison are grazing net ecosystem production would be low and perhaps even negative.
- In the week following the grazing event we should expect gross primary production to be high relative to before the grazing event.
- In the week following the grazing event we should expect gross primary production to be low relative to before the grazing event.
- The total below ground biomass will be severely reduced immediately following the grazing event.
- Respiration by animals in this system would exceed that of the plants near the end of the grazing event.
- As a result of the grazing event the amount of carbon stored in the system has increased.
- During the time when the bison are grazing, net ecosystem production would be low and perhaps even negative
- In the week following the grazing event we should expect gross primary production to be low relative to before the grazing event
- Respiration by animals in this system would exceed that of the plants near the end of the grazing event
What tends to be most important in controlling terrestrial productivity at large scales?
Water
Nitrogen is generally limiting at
300 years
Both nitrogen and phosphorous are generally limiting at
2,000 years
Phosphorus is generally limiting at
4,100,000 years
True or false: The earth is so large that humans only use ~10% of the total terrestrial primary productivity.
False. Humans use between 20% and 40% most of this is due to human activities like agriculture.
A nitrogen to phosphorous ratio by moles of 15:1 is often termed what?
The Redfield ratio
If you were interested in further understanding the relationship of abundances of elements in organisms, then you should probably do a scholarly search for which topic?
Stoichiometry
Where would NPP be lowest?
- a freshwater lake
- an estuary
- a subtropical ocean gyre
- a stream
A subtropical ocean gyre
Coastal marine ecosystem pollution
- There are coastal marine ecosystems and estuaries along the North America Atlantic coastline and throughout the Gulf of Mexico where oxygen levels are too low to fully support animal life
- Throughout Europe there are estuaries or coastal marine ecosystems that have been polluted by nutrients
- With the exception of Antarctica, every single continent has polluted estuaries or coastal marine ecosystems with nutrient pollution
What regulates NPP in aquatic (ocean) ecosystems?
Ocean biomes are structured along gradients of light and nutrients
- the interaction of light and nutrients largely controls NPP
GPP (in aquatic ecosystems) is a function of
Light and so decreases with depth as light decreases
Phytoplankton respiration (Ra) is constant over depth
Note that turbulence and flows of water move phytoplankton throughout the mixed layer
- GPP starts at deep depth, rises then flattens out
-> GPP is area of line
- phytoplankton respiration rectangle on the left
NPP =
GPP - Ra
Integrated over the mixed layer of surface waters in which phytoplankton live
Consider ecosystem with shallow “mixed” layer (relative to light)
Bottom, or bottom of mixed layer (thermocline or pycnocline)
- horizontal line, rises then flattens out
-> GPP is area
- Rphyto rectangle on the left
GPP > Ra
NPP = GPP - Ra (NPP is big)
Relationship of NPP to GPP depends upon light and mixing depths
- NPP can be as high as 95% of GPP and is quite variable across ecosystems
- it can also be negative
Too dark at depth to support
Photosynthesis
- note that “deep” is relative to light penetration (affected by turbidity and by “self shading”
- bottom of mixed layer -> horizontal line across the bottom of the graph
Note that phytoplankton are constantly mixed over the entire depth of surface to bottom of mixed layer)
GPP = 0 over much of bottom of mixed surface layer
GPP < Ra
Rphyto is large (large rectangle on left)
NPP = GPP - Ra
(NPP is negative)
How is it possible to maintain a negative rate of NPP?
Phytoplankton would respire themselves away and disappear…
Negative NPP depends on supply of phytoplankton from a time or place where NPP was positive
Tidal, freshwater Hudson River
Negative NPP at river km 118
Respiration by living phytoplankton lower concentration of dissolved oxygen, creating a water quality problem
Net ecosystem production in aquatic systems
“Rain of detritus” provides major energy source for animals in the deep, dark oceans
- no GPP in deep ocean (just Rh), so negative NEP
NEP is often negative in
Streams, rivers (i.e., respiration exceeds GPP)
GPP often low in streams due to shading
- lead input is a major source of organic matter
- respiration (Rh) can be high, driven by microbes and animals consume dead leaves
Nutrients and NPP
- nutrients come from deep ocean
- wind can deepen the surface mixed area, entraining nutrient-rich bottom water into surface
- windy latitudes have more mixing, so more nutrient entrainment, but also a deeper surface mixed layer (less light)
- NPP is regulated by the balance of light and nutrient supply
Which of the following best describes how your text
book discusses the relative importance of nutrients as a factor controlling NPP in aquatic ecosystems compared to terrestrial ecosystems?
a) Nutrients are far more important in aquatic ecosystems;
b) Nutrients are more important in terrestrial ecosystems;
c) Nutrients are equally important as a control in both aquatic and terrestrial ecosystems
Nutrients are far more important in aquatic ecosystems
Increasing N or P increases NPP by only 20-40% in terrestrial ecosystems
Nutrients are a much larger control on NPP in aquatic ecosystems
- productivity is far higher in lakes with higher concentrations of P
- productivity in marine ecosystems increases with increasing inputs of nitrogen
A more nuanced view of nutrient limitation in some ocean ecosystems such as the sub-tropical gyres, high-latitude waters, and upwelling ecosystems:
Nitrogen and phosphorus co-limiting (or nearly so)
Phytoplankton in the world’s oceans (and lakes) have a relatively constant ratio of carbon, nitrogen, and phosphorus
Redfield ratio: C:N:P = 105:15:1 (by moles)
The availability or inorganic nitrogen and phosphorus in most ocean waters (away from coasts!) is in the same proportion
N and P equally limit net primary productivity
Subtropical gyres and N and P availabilities
N and P availabilities are almost in balance with requirements of phytoplankton (Redfield ratio, 15:1)
But not quite… slight deficit in N. This is made up by nitrogen fixation in surface waters
What limits NPP in lakes?
Excess inputs of the limiting nutrient(s) leads to eutrophication – excess NPP and phytoplankton growth, leading to ecological damage
- massive problem in lakes in 1960s and 1970s
- starting to be a problem again over the past decade
Short-term, small-scalle bioassays (“bottles”)
Showed carbon limitation
Whole ecosystem phosphorus addition experiment
Showed phosphorus limitation
- more meaningful results
The whole-ecosystem P-addition experiments led rapidly to phosphate bans in detergents, and other management actions to reduce P pollution
Most lakes (including Lake Erie) recovered from eutrophication (until recently!)
Same P-control approaches applied to coastal marine ecosystems, to no avail. Eutrophication has grown worse.
Seine and Scheldt Basins and Belgian coast of North Sea
- a large scale societal “experiment”
North Sea remained N-limited throughout, and extent of phytoplankton growth just got worse over time. Reduction of P did no good.
- TN:TP ratio drastically increased (70:1)
- phytoplankton need 15:1
N or P limitation in 1979? In 2007?
N limited in 1979
In 2007 not only P limited, otherwise NPP would’ve decreased
- North Sea remained N-limited
-> coastal systems are fundamentally different than lakes
-> eutrophication when N increases
Without P-rich input of nutrients from offshore ocean waters, limits of P didn’t do much
Coastal waters of North Sea remained N-limited despite massive effort to reduce P fluxes down the rivers, leading to very high N:P ratio of inputs from rivers since 1980s
Since the ecosystem is N-limited, eutrophication grows worse as more N added from rivers.
Why is this coastal marine ecosystem and most others (which are also N-limited) so different from lakes?
If inputs of nutrients from watersheds were the only important factor, most estuaries and coastal marine ecosystems would be P limited.
So other controls are clearly important.
What determines whether N or P is more limiting to NPP?
Biogeochemical processes within the estuary:
- denitrification (vs DNRA)
- nitrogen fixation
- P absorption/desorption
N:P ratio of nutrient inputs from offshore ocean waters
- Without P-rich input of nutrients from offshore ocean waters, most coastal marine ecosystems would be P-limited (as with most lakes)
N:P ratio of watershed inputs
Nitrogen is the biggest pollution problem in coastal marine ecosystems
Phosphorus is a bigger problem in freshwater lakes
To summarize relative roles of Nitrogen & Phosphorus
- N & P nearly co-limiting in subtropical gyres and upwelling ecosystems
- P often limiting in lakes
- N often limiting in estuaries and coastal marine ecosystems
In some parts of oceans, High N & P but low phytoplankton biomass and production (“HNLC” for high nutrients, low cholorphyll)
HNLC regions
- north pacific
- west of southern mexico
- entire coast of antarctica
During 1980s, improved sampling techniques showed that dissolved iron (Fe) concentrations in oceans are thousands of times lower than previously thought.
Does low Fe limit ocean NPP?
(particularly in “high nutrient, low chlorophyll” (HNLC) regions
Iron is in short supply in HNLC regions
- data showed iron was high, John Martin said it was wrong
- to measure iron, go on steel ships, steel cables, PVC bottles which was contaminated with iron
- sample with teflon and reduce contamination, Fe concentrations 10,000-100,000x less than previously thought
The iron hypothesis
Martin suggested that we purposefully fertilize the oceans with iron in order to increase production and suck carbon dioxide in the atmosphere and solve climate warming.
- lot of issues and problems with that
Which of the following aquatic systems has the highest Net Ecosystem Production (NEP)
- An area with high nutrients and high light
- An area with low nutrients and high light
- An area with low nutrients and low light
- An area with high nutrients and low light
- There is not enough information to answer this question
There is not enough information to answer this question
- There is no information concerning Rh
If the ratio of nitrogen to phosphorous is slightly below 10:1 then _______.
- It is below the Redfield ratio
- It is at the Redfield ratio
- It is above the Redfield ratio
- None of the above
It is below the Redfield ratio
Productivity in aquatic systems can be limited by which of the following. (You may select one or more answers)
- Phosphorous
- Nitrogen
- Iron
- Fermium
- Phosphorous
- Nitrogen
- Iron
True or false: Productivity in the oceans is highest at tropical latitudes
False. Most high in polar and temperate regions.
Aquatic system: N limited
Coastal systems
Aquatic system: P limited
Freshwater systems
Aquatic system: N & P are co-limiting
Subtropical gyres
Note that the primary production equations apply to both terrestrial and aquatic systems that were covered in the last 2 lectures. Here we are using a grassland example to address these concepts.
Based on measurements from a grassland: the rate of net primary production (NPP) has been measured at 320 grams of organic carbon per square meter per year (g C m-2 yr-1); the rate of respiration by the autotrophs is 350 g C m-2 yr-1; and, the rate of respiration by all of the heterotrophs is 300 g C m-2 yr-1.
Roughly how much organic carbon (g C m-2 yr-1) is available each year for consumption by herbivores, decomposers, or for harvest?
- NPP = the C available for herbivores, decomposers, or harvest = 320 g C m-2 yr-1.
Based on measurements from a grassland: the rate of net primary production (NPP) has been measured at 320 grams of organic carbon per square meter per year (g C m-2 yr-1); the rate of respiration by the autotrophs is 350 g C m-2 yr-1; and, the rate of respiration by all of the heterotrophs is 300 g C m-2 yr-1.
By how much does the total stock of C (the amount of carbon stored in the system) in this grassland change each year (g C m-2 yr-1)?
- Change in stock = inputs – output = GPP (670) – Ra (350) – Rh (300) = NEP = 20 g C m-2 yr-1.
Based on measurements from a grassland: the rate of net primary production (NPP) has been measured at 320 grams of organic carbon per square meter per year (g C m-2 yr-1); the rate of respiration by the autotrophs is 350 g C m-2 yr-1; and, the rate of respiration by all of the heterotrophs is 300 g C m-2 yr-1.
Respiration by plants, animals, and microbes often increases with temperature. If climate change were to cause an increase in total ecosystem respiration by 50 g C m-2 yr-1, what would be the grassland’s rate of net ecosystem production (NEP; g C m-2 yr-1)?
-30. NEP = GPP – (Ra + Rh + 50) = 670 – (350 + 300 + 50) = -30 g C m-2 yr-1.
