240 3 primary production

8/19/2019 240 3 Primary Production

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Plants convert solar energy to biological energy via photosynthesis

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Desert!.lots of solar radiation!but very low productivity (and so biodiversitytoo)!Why? Its more than just about solar energy, must have other aspects ofthe physical environment (water). Further, deserts are typically highly variable

(diurnal / seasonal) making it further difficult.

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Arctic – lots of water and sun, but temperature and food (on land) are issues

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Open ocean!.even more barren in terms of life!.why? (Nutrients andstructure! )

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However – both polar bears and lions thrive at the Toronto Zoo so, like theNova documentary you watched suggests it is temperature and water thatstructures the Earth’s biota, it does not necessarily affect organisms directly.

Polar bears are restricted to the far north and lions to the African savannabecause of indirect effects of temp and water on communities of organisms.

Both have evolved to thrive in the physical and biological contexts they findthemselves. A polar bear is ill suited to prey on gazelle and likewise lionswould starve trying to survive on seal meat.

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The correlation between species diversity and key habitat characteristics isvery high. What kind of habitat (abiotic) traits are we referring to?

Temp, water etc.! but really, we are talking about the capacity of a habitat to

facilitate plant growth. Primary production is a necessary prerequisite forbiodiversity.

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Can think of panel c) as the product of panel a) x panel b)

e.g. algal beds, reefs and tropical rainforests (green arrows) are among the

most productive habitats on Earth (panel b), but because they make up so littleof the total surface (panel a) the contribution to total global net primaryproduction is very modest. Contrast this with Open Ocean – which is literally

equivalent to a desert. In fact aquatic and especially marine habitats are oftenfar less productive than terrestrial ones!unless there are nutrient subsidies

from the land available, thus explaining why estuaries and marshes (bluearrows) are so much more productive than most aquatic and marine habitats.

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The “fixation” of carbon locks energy into the products of photosynthesis –especially sugar which is particularly energy dense. Those calories (energy)are actual sunlight, indeed all food calories are!.and the “matter” is actual

“stardust”!.

CRITICAL to appreciate Material cycle closed and Energy cycle open. The

fact that energy cannot be conserved is the root of most environmental issuesBUT ALSO is the root of all ecological processes.

1o = primary production


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Biological energy is stored in the molecular bonds of materials you eat. Thosebonds are stripped and the energy stored in your body for you to use. Glucosehas much more energy stored in its bonds than water or carbon dioxide (the

products of respiration)

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Plants respire too (burn energy to do work)

Net productivity is the energy made available to the ecosystem in the form of

plant biomass). In other words it is the energy remaining after the energeticcosts of its production are subtracted.

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Carbon is stripped from the CO2 to make sugar, byproduct is O2.

Constant input of energy is needed to drive process (energy cycles are open).

Carbon is cycled from within (closed system)

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Why are crop plants higher than “normal” plants? We seek disproportionateproduction of high energy plant parts (fruits, seeds etc)

Why is sugarcane the highest? We seek high density of the most energy

dense of all components – sugar.

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Of the 480,000 units of energy, only 10,400 are converted for gross primaryproduction that in turn only netted 4,680 which in turn produced only 1-160units of consumer. The major message of the this and the previous slide is that

is that it takes a lot of energy to make a little bit of life – life is, in general, notvery efficient in its energy use.


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Why have we switched to kJ (energy) instead of carbon? Einstein “matter isenergy” ( E=MC2)

The production metric here is not carbon per time (material production) but

energy per time (energy production). Carbon is a proxy measure of energysince we know how much energy is consumed and stored per molecule

production.

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The ability of solar radiation to penetrate water is very limited. Certainwavelengths are lost almost immediately (reds) and others (blues) penetratemuch deeper. This greatly diminishes gross productivity after only a couple of

meters.

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98% of ocean volume is aphotic

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The warmer the colour, the greater the primary production.

Equatorial regions are the LOWEST production, not highest.

Season plays a large role in determining production in temperate zones(compare the January and July panels) but tropics are uniformly low!?

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Nitrogen completely absorbed while excess phosphorus remains

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Much of the ocean is nutrient limited. Particularly nitrogen which is completelyabsorbed in the euphotic zone (highly limiting). Always assumed phosphoruswas limiting because nitrogen is rich in air (N2) and cyanobacteria in ocean!

but biologically usable nitrogen (nitrate, ammonium) is limiting.

Not always nitrogen limitation. Often iron also limiting (iron shortage limits

cyanobacteria to fix nitrogen). Some places like eastern Mediterranean arephosphate, not nitrogen, limited.

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Iron is necessary for cyanobacteria to fix N2 – therefore those areas withstrong offshore winds carrying iron rich dust show high marine productivity

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Regardless of the season the west coast of Africa maintains high productivity(and intense fishing pressure as a result)

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BUT, Iron as well as other nutrients are all more dense than water !.and sink(marine snow).

Problem: Nutrients need to be near the surface (euphotic zone) if they to be

used.

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Note the convergence of currents at the equator

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Modest increase on the equator (light green). Strength of upwelling is muchless than temperate coastal upwelling owing to the weaker winds (“doldrums”).

Note the greater production in the boreal summer vs. austral summer !why?

Greater proportion of land mass and thus nutrient sources.

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Not everywhere is a “desert”! upwelling zones, terrestrial subsidies etc..

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Large plants are possible!.but found only in shallow waters, anchored to thesubstrate.

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Challenge – unlimited chemical resources on the bottom, unlimited solarresources at surface!.? How to bridge?

If possible, would drive marine food web to the surface, massive harnessing of

solar radiation, massive increase in biomass!

.etc!

.

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Lack of nutrients does not stop tropical forests from growing thick withbiomass!

Tropical soils very depauperate of nutrients, every bit as much as the

ocean!.but energy harnessing plants still abound and cover the surface!..?

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Large floating sponge-like plants could easily overcome the nutrient / lightchallenge

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Micro floating algae have the advantage of being able to float and sink andtherefore can retard the “conveyer effect” of currents. Macrophytes will bebroken up in storms and drift out of optimal habitat before reproduction.

Test: Is there open ocean where the currents are not a “conveyer” acrosslatitudes and climactic gradients!.?

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Massive floating mats of Sargassum sp.

Columbus calmed a mutinous crew by plucking a crab from the surface andarguing they must be close to land!..they weren’t

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Ocean carbon reserve is 60x greater than atmosphere

Nutrients are limiting in the ocean ; carbon is limiting on land!

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Average productivity on land is 10,000x that of marine surface waters

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Low primary productivity

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Medium Primary Productivity

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High Primary Productivity

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Oxygen kill can occur in both summer and winter when the bottom layers ofwater are cut off from the surface (and abundant oxygen)

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One of the many large changes that occur during eutrophication: green algaepreplaced by blue-green algae (cyanobacteria).

Blue-greens are not heavily grazed by zooplankton or fish, often can’t handle

the long filaments and many cyano produce secondary toxins – explode inabundance

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Eutrophicatiuon and hypereutrophication are typically caused by run-off ofhuman activity. An extreme case is the Gulf of Mexico dead zone (oxygen kill).

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Similar events can be seen in marine systems too. Here the Fraser R plume.Not just organic nutrients here, but as we have seen, vital inorganics too likeiron.

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The most powerful experiments are the ones where the conclusion is selfevident. This work done at the Experimental Lakes Area – closed by DFO!

Why is this design superior to simply adding carbon in one lake, nitrogen in

another and phosphorus in yet another?

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240 3 primary production

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