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Primary production is the rate of synthesis of organic
material from inorganic compounds such as CO2 and water. It
is significant in that it provides the base of most of the entire
marine food chain.
The formation of organic carbon compounds from inorganic
carbon (e.g. carbon dioxide) involves a reduction reaction; the
reducing power (e.g. NADPH) comes from either the
absorption of light (photosynthesis), or the oxidation of other
compounds (chemosynthesis).
It is a rate, hence involves dimensions of time:
mg C m-3 s-1,
or in a depth integrated sense:
mg C m-2 s-1
Open ocean produces like a
desert, on the land, but given its
extension it accounts for the
major global production.
Estuaries and transitional waters
are highly productive and each
accounts for a 10% of the global
net production
Note: PP is
expressed as
kilo calories
per square
meter per
year
On a global
scale open
ocean production
together with
continental
shelf largely
exceeds all
terrestrial
productions
How is the rate of photosynthesis
measured in the ocean?
1. Most common is the so-called 14C technique.
a. Collect water sample.
b. Measure total alkalinity to detect the
amount of total CO2
c. Add radioactive inorganic carbon as a
tracer as NaH14CO2
d. Incubate under different light levels for
some time (~ 1-24 hours)
e. Filter sample, acidify to remove all
inorganic carbon
f. Measure radioactivity of what is left –
this is proportional to the rate of fixation
of carbon or primary productivity.
g. Normalize to unit time and unit pigment
concentration to express results (i.e. mol
C (mg Chl)-1 h-1).
14C
Method:
Labeled carbon is probably the most extensively used procedure
for oceanic studies of productivity. This method essentially
advantageous because it is relatively safe, weak β-emission
(0.15 Mev) as well as its long half life (4700yr), so that storage
offers no major problems.
Procedure: The activity per ml of the working solution needed
for the different productivity experiments depends on the
production rates expected, duration of incubation, bottle size,
etc. Invariably, 0.2-1 ml of the working solution is used per
bottle containing water sample.
Water samples for which production rates are to be determined
are first collected from the specified depths and are transferred
to the light and dark bottles kept in a dark box. Then, a known
dose of the working solution is injected rapidly into the bottles
with the help of a graduated hypodermic syringe having a needle
not shorter than 5 cm, or better with an automatic dispenser.
The bottles are then incubated for a known period by suspending
them at the respective depths from where the water samples
were taken for experimentation (in situ incubation).
After the incubation is over, the experimental bottles are
removed from the depths and are stored in a light-free case until
the filtration of water samples is begun. Filtration may be done
either on board the ship or in the laboratory. Aliquots of water
samples for filtration are rapidly transferred into a suitable
vacuum filtration apparatus on to a No. 2 membrane filter or
Millipore filter of about 0.5 μ porosity. The vacuum should be
applied at about 0.5 atm which will help avoiding damaging of
fragile phytoplankton cells. The filtration should be done in a
semi-darkend area.
The filters, after their removal from the filtration apparatus are
placed onto planchets which are then kept in a desiccator
containing silica gel. Filters obtained from light and dark bottles
are then subjected to counting.
To measure isotopes you need a liquid scintillation. After filtering
and acidifying the samples the filters should be placed in
scintillation vials and dried at room temperature for 24 hours.
Following the addition of scintillation liquid, the samples should
kept in the dark for at least 3 hours to reduce
chemioluminescence.
The total carbon uptake is calculated from the equation:
dpm(a) · total12CO2(c) · 12(d) · 1.05(e) · k1 · k2
dP(mgCL-1hr-1)=---------------------------------------------------dt
dpm (b)
Where dpm(a) = Sample activity (minus back-ground),
dpm(b) = Total activity added to the sample (minus background),
(c) = Total concentration of 12CO2 in the sample water,
(d) = The atomic weight of carbon
(e) correction for the effect of 14C discrimination
k1 = subsampling factor (e.g. sample 50 ml, subsample 10 ml:
k1 = subsample factor 50/10=5)
k2 = time factor (e.g. incubation time 125 minutes: k2=
60/125 = 0.48).
14C
technique measures something close to Net PP,
particularly when incubation time is short.
If incubation lasts too long part of the fixed 14C can be
respired and thus it is not more detectable by liquid
scintillation.
Accurately following the same method implies that data
obtained in different regions of the ocean can be compared.
Warning: all operational steps must be done wearing
gloves, using forcipes to handle filters. Filtration must
be done under hood and the lab has to be periodically
checked for isotopic contamination.
2. Next most common is the measurement of oxygen evolution /
uptake. It is far less sensitive than the 14C method.
a. Collect water sample
b. Measure initial oxygen
concentration
c. Incubate under different
light levels (and dark) for
some time.
d. Measure final oxygen
concentration
e. Sum dark respiration to
oxygen production in the
light bottles to obtain
Gross PP
f. Normalize to unit time
and unit pigment
concentration to
g. express results (i.e.mol
O2 (mg Chl)-1 h-1).
At the sea, before collecting water samples, you need to know the
light profile, then you can choose standard depths or optical depths
to collect water and after injection of 14C (as NaH14CO3) in the
bottles to incubate them. It is better to select hours around noon to
perform the incubation. On the basis of the daily solar radiation,
obtained by
means of
surface
sensor, you
can
extrapolate
data
obtained
during the
experiment
to the daily
primary
production.
In situ
incubation
Or in situ
simulated
incubation
The best “in situ” incubation is using a moored line from the
bottom to the surface. This implies to keep your boat or ship
stopped for the period of incubation.
It is possible also to hang a line while the ship is moving.
Otherwise you can use “on the deck” incubation using boxes
with running sea water and screened with filters to mime
light intensity of the depth of sampling.
Problems arise when water temperature changes
considerably with depth, as in well stratified situation. This
can affect the photosynthetic processes.
Simulated “In situ” incubation
At the land laboratory you can use different devices at fixed
temperatures. You can regulate light intensity to again mime light
intensities registered along the water column.
ICES incubator
Photosynthetron: Controlled
laboratory incubation (Lewis
and Smith 1983)
P vs E curves experimentally obtained with water from the Gulf
of Trieste with an ICES incubator. Note that in May light
intensity produced in the incubator was enough to reach
photosaturation, so that it was possible to apply Eilers-Peeters
function, while in June there was no saturation and thus the
linear Platt-Jassby function was applied.
Comparison between in situ and
with incubator PP production. Often
at the surface the two rates do not
properly fit.
Temporal patterns of integrated PP measured in situ at two coastal
adriatic sites (Gulf of Trieste) in the period January 1999 December 2001. Note the inter-annual differences (in 2000 PP
tripled) and among the two stations (AA1 closer to river inputs is
more productive). There are usually two seasonal maxima: the
first in late winter - beginning of spring and the second in fall.
From Fonda Umani et al., AME 2007
PP at different depth measured in the
Gulf of Trieste with in situ incubation
following the 14C method (left).
PP climatology (1998 - 2005)
300
Produzione primaria
250
200
150
100
50
0
J
F
M
A
M
J
J
A
S
O
N
D
Efficiency (e)
Entering energy
(or biomassa) u
Dissipation (heat)
or loss/consume
e = y/u
Outgoing energy
(or biomassa) y
ef (photosynthetic efficiency)= gross production (GP)
PAR
en (net photosynthetic production) = NPP
GPP
Solar radiation
losses
GPP
Phytoplankton efficiency
ef ≈ 0.002
respiration
NPP
en ≈ 0.4
Any analysis of biomass energy production must consider the
potential efficiency of the processes involved. Although photosynthesis is fundamental to the conversion of solar radiation into
stored biomass energy, its theoretically achievable efficiency is
limited both by the limited wavelength range applicable to photosynthesis, and the quantum requirements of the photosynthetic
process.
Of the total solar radiation only PAR can be utilized by plants,
effectively allowing only 45 % of total solar energy to be
utilized for photosynthesis. Furthermore, fixation of one CO2
molecule during photosynthesis, necessitates a quantum
requirement of ten (or more), which results in a maximum
utilization of only 25% of the PAR absorbed by the
photosynthetic system. On the basis of these limitations, the
theoretical maximum efficiency of solar energy conversion is
approximately 11%.
In practice, however, the magnitude of photosynthetic
efficiency observed in the field, is further decreased by
factors such as poor absorption of sunlight due to its
reflection, respiration requirements of photosynthesis and the
need for optimal solar radiation levels. The net result being
an overall photosynthetic efficiency of between 3 and 6% of
total solar radiation.
Most of the aquatic ecosystems have a low photochemical
efficiency (< 2 %). Maximally they could convert 20 % of
the captured photon energy within PAR into biomass energy.
The photosynthetic efficiency is the amount of biomass
energy that is produced per amount of light energy within
the PAR region received.
The photosynthetic efficiency can be calculated for each
wavelength and is at its maximum 33 % at a wavelength of
680 nm.
The maximum efficiency within the entire PAR area is
approximately 20 %.
In most cases the efficiency is much lower because the
sunlight absorption velocity is higher than the velocity at
which photons are converted into biomass. The excess
energy will be dissipated as heat.
PP depends on photosynthetic efficiency: the same amount of chl a
can result in different PP rates, mostly depending on nutrients’
availability.
In the figs two
different years in
the Gulf of Trieste.
In 2000 there was
a higher efficiency.
Gulf of Trieste: mean P/B on the entire data set (1999- 2005)
A Cycle of Life and Death
Surface Ocean
Light + Nutrients  Growth  Consumption

Nutrients
Decomposition
Deep Sea
Bottom
The Growth of Phytoplankton
(surface layer of the ocean)
Cell Division
Daughter
Cell
Photosynthesis
Single Cell
Doubled Biomass
Nutrient Uptake
Daughter
Cell
Result:
• More suspended particulate organic matter (food)
• Less dissolved inorganic nutrients (N, P, Si)
• Less dissolved inorganic carbon (CO2)
The Growth of Phytoplankton
(surface layer of the ocean)
Daughter
Cell
Fates:
Accumulate (Bloom)
Daughter
Cell
Be eaten
Sink
Consumption and
Decomposition
(deep ocean)
Microbial
Decomposition
Organic
Matter
DEEP-SEA
LIFE
+
Nutrients
CO2
Consumption
Respiration
Excretion
Result:
• Less suspended particulate organic matter
• More dissolved inorganic nutrients (N, P, Si)
• Supersaturated dissolved inorganic carbon (CO2)
PP is limited also by
nutrients’
availability, which is
controlled by water
mixing. PAR is thus the
primary energy, while
hydrodynamics is the
secondary one.
The both derive
from solar radiation.
Hydrodynamics
drives nutrients
from the aphotic to
the photic zone
Irradiance
Physical mixing
processes
Phytoplankton
Nutrients
Zooplankton
Higher Trophic Levels
About 10% of the carbon
fixed by photosynthesis in
the surface layer each
year, escapes this layer by
sinking into the deep
ocean or settling at the
bottom.
Irradiance
Phytoplankton
Physical mixing
processes
Nutrients
Sinkage & Senescence
Zooplankton
Particle Dynamics
Higher Trophic Levels
Particle Flux (Carbon flux)
PP based on allocthonus nutrients is called “New” while the one
based on nutrients deriving from excretion of consumers in the
upper layers is called “Regenerated”
Regenerated
New
production
production
Biologically derived
Physical mixing
Irradiance
nutrients
processes
Phytoplankton
Nutrients
Zooplankton
Higher Trophic Levels
Nutrients
Sinkage & Senescence
Particle Dynamics
Carbon Flux
Export
production
To measure C
export to the
deep layers you
must employ
sediment traps
moored or
floating.
Moored traps:
samples are taken
at fixed intervals (in
this case 1 week).
Here there is a
comparison
between surface
layers’
phytoplankton
biomass and
biomass collected
by the sediment
trap. Maxima in the
sediment trap are
delayed by one
week. This can
allow to estimate
the export velocity.
Data from a site in the Gulf of
Trieste: difference between
total flux (GROSS) and flux
without resuspension (PRIM)
on the base of phytoplankton
taxonomical analyses.
From Cibic et al, Hydrobiologia, 2007
y = -0,2141x + 1,6856
R2 = 0,7492 p<0.05
(% d-1)
Loss ratebiomass
2,5
2,0
1,5
1,0
0,5
0,0
0
2
4
6
8
Grazing
(mg C L-1 h-
Relationship between grazing on Diatoms and their loss rates
calculated as biomass (n=7) in the Gulf of Trieste.
10
La colonna di Winogradski è costituito da una recipiente chiuso di diametro > 5 cm e
alto > 25 cm (una bottiglia 1,5 l va bene), riempito approx. 1/3 da fango 1/3 da acqua
e 1/3 da aria. Il fango e l'acqua devono venir campionati da uno stagno, il fango da
uno strato scuro (anossico). Il fango va pulito a mano da ogni elemento che non sia
fango stesso (piante, vermi, legnetti, etc.). Al fango vanno addizionati nutrienti quali:
carta da giornale (cellulosa - carbonio), gusci d'uovo (carbonato di calcio) e gesso
(zolfo). La quantità di quest'ultimi può variare, senza compromettere il
funzionamento della colonna. Quando completata la colonna va sigillata, se si usa
nastro adesivo quest'ultimo è consigliabile sia trasparente. La colonna va esposta
alla luce del sole per almeno 3-4 mesi, avendo cura di non muovere la colonna o nel
caso la si muove esporre al sole sempre lo stesso lato.
MATERIALE:
- Un contenitore trasparente con coperchio (bottiglia)
- acqua e fango di uno stagno
- Carta di giornale
- Gusci d’uovo
- Gesso
.