primary production & seasonality Flashcards
summarise photosynthesis in terms of the photosystems
Light into PSII -> energy transferred across membrane -> provides energy to PSI
what happens to energy as wavelength decreases
energy also decreases
explain why plants don’t utilise radio waves (low energy) and prioritise visible wavelengths instead
what happens to absorption in water as wavelength increases
absorption also increases
what wavelengths get absorbed
- ~50% infra red >780 nm
- ~50% visible spectrum ~400-~700 nm
- <1% ultraviolet <380 nm
why are only blues and blacks visible in deep waters
rest has been fully absorbed by water
what wavelengths have Things like phytoplankton have to evolve to make use of
the more blue/green parts of the visible spectrum
- also contain additional pigments to increase the amount of energy they are able to make use of e.g. photosynthetic carrotenoids
what happens to photosynthesis as light intensity increases
also increases - up to a certain point…..
what happens when phytoplankton receives too much light
sterilisation of the plankton will occur
how do plankton cope with sterilisation due to too much light
photoprotectant carrotenoids -> absorb the same light as the photosynthetic carrotenoids but do not pass it on to chlorophyll a (dissapate it as heat instead to get rid of it)
what allows us to identify groups of phytoplankton
The different proportions and types of accessory pigments
formula to calculate the diffuse attenuation coefficient (m-1) -> how mercy the water is
Iz = I0 e-kz (make K the subject)
big k = mercy water
Use k to calculate I (light) at any depth in the water column
what’s a thermocline
zone of sharply changing temperature
what’s a Halocline
zone of sharply changing salinity
what’s a Pycnocline
zone of sharply changing density
what’s a Ergocline
energy gradient (amount of energy needed to mix water down to that depth)
where does the most production occur
the mixed layer
what’s planktons movement controlled by
the surface mixed layer (SML) -> depth varies depending on wind speed and heating
how to calculate average irradiance (I) in the SML
k (attenuation) x h (depth of SML)
- Phytoplankton experience fluctuating light in this SML
Surface mixed layers in winter vs summer
- winter it is deep + less light (but more nutrients)
- summer its more shallow + more light (but less nutrients)
formula to calculate gross primary production (Pg)
Ke + (I)
- Pmax = max rate of photosynthesis
- Ke = half-saturation constant
- (I) = ambient PAR
- Pmax and Ke varies between species, leading to succession of different phytoplankton species
formula to calculate net primary production (Pn)
Ke + (I - Ic)
- takes respiration into consideration
- Ic = amount of light needed to balance respiration of the plankton at that depth
formula to calculate compensation depth (Zc)
k
- depth at which photosynthetic production = respiratory losses i.e. Depth at which = I = Ic
- Compensation depth = bottom of euphotic zone
- Describes plankton when they are still (problem – they always move with the water)
what’s critical depth (Zcrit)
depth of a SML in which respiration = photo over 24 h
- aka the depth at which the amount of light available for photosynthesis is just enough to support the metabolic needs of phytoplankton
what happens when the critical depth is smaller and bigger than the depth of SML
- If depth of SML > Zcrit -> no growth
- If depth of SML < Zcrit -> growth (spring bloom) - getting enough energy from the sun to support increase in population
what determines whether a community is able to survive
balance of total energy used for respiration in 24hr + total energy used for photo in 24hr
what kind of community do we have when enery used for respiration is more and less than that used for photosynthesis
- If total energy used for resp in 24hr > total energy used for photo in 24hr, community = heterotrophic – no growth of phytoplankton
- If total energy used for resp in 24hr < total energy used for photo in 24hr, community = autotrophic – P > R = growth
is phytoplankton conc higher in winter or summer
summer
what does Phyto productivity, biomass & composition rely on
light, nutrients, mixing & grazing
- usually follows a seasonal pattern
describe the thermocline in summer
quite steep - less energy, more light
describe the thermocline in fall/autumn
Much smaller thermocline – less light, more energy (wind etc - more mixing)
describe the thermocline in winter
very deep - Entire seabed = mixes waters - Loads of energy (more turnover), dark
describe the thermocline in spring
Build-up of thermocline again - Less energy, more light
is the winter SML more or less than Zcrit (critical depth)
SML > Zcrit = no phyto growth
is the spring SML more or less than Zcrit (critical depth)
SML < Zcrit = phyto growth
is the summer SML more or less than Zcrit (critical depth)
SML < Zcrit = phyto growth
is the autumn SML more or less than Zcrit (critical depth)
SML > Zcrit = no phyto growth
winter water characteristics
- A lot of energy in system - Water column well mixed
- Heterotrophic system
- [Nutrient] (N, P, Si) high: decomposition of OM - no phyto to eat it
- Low PAR: cloud, short days, sun low in sky
- Sea: turbid, stirred sediment
- Low ambient irradiance & high suspended particulate loading = shallow Zcrit
- Mean resp > mean photo = no phyto growth
- [Chl a] uniformly low
spring water characteristics
- Day length increases, wind speeds decrease
- Sea-surface absorbs heat faster than turbulence can redistributed it
- Thermocline forms: resists vertical mixing
- Sediment settles – water gets clearer
- High nutrients & light = high growth rate
- Diatoms dominate – high growth rate
- Result: high [chl a] = spring bloom
- 1-2 weeks: diatoms exhaust NO3- in SML
- Bloom ends quite quickly – not enough nutrients for diatom
- Mesozooplankton: slow to respond
- Most phyto OM exported to benthos
- Heterotrophic dinoflagellates can respond more rapidly to feed on diatoms
summer water characteristics
- Big change in temp
- Water column: highly stratified
- SML:👇nutrients, ^ chl a
- Small phyto: take up nutrients, maintain position
- Prey & predator growth = well matched: little export
autumn water characteristics
- Reverse of spring
- Increased turbulence: storms, lower temps
- SML deepens: nutrients entrained into SML
- Short lived diatom bloom
- Stratification breaks down completely
why does shallow water prevent phyto growth
mixed all year, high suspended sediment load
what is temperate productivity
Summer = plenty of light, not enough nutrients – between the two is where we get plenty of light and nutrients for the phytoplankton
- Zooplankton will follow this phytoplankton trend
