Nutrient Dynamics Flashcards
Redfield Ratio
1P:16N:106C
N:P drawdown in the environment is 16:1
Si requirement in phytoplsnkton
Only those with Si shells need it
No consistent ratio of Si:N needed
Different species use varying levels of Si to N
Dependent on species, nutrient availability and iron availability
2:1 and 0.5:1 are common
Phosphorus Cycle
Nutrient consumption occurs in the euphotic zone
Respiration releases nutrients from organic matter – occurs mainly at depth
So light and nutrients are physically separated
DIP in consumed by photosynthesis and produces organic phosphate
Respiration consumes organic phosphate and produces DIP in the euphotic zone
Most organic phosphate sinks and releases DIP in deep ocean through respiration
Mixing or upwelling required to bring nutrients to surface (most nutrients come from below)
Processes that bring nutrients to the surface
Upwelling
Mixing
Surface cooling - convention q
Mix Layer in June
Shallow mix layer
Warming surface and light winds
Mix Layer November
Mixed layer cool and deepening
Fall Nutrient/Phyto Dynamics
Decreasing light and increasing nutrients
Mix layer deepens
Nutrients in the layer below the summer mixed layer are added to the fall mix layer
Mix Layer February
Mix layer coldest and deepest
Cool surface leads to convection and strong winds
Summer Nutrient/Phyto Dynamics
High light and low nutrients
Previous productivity used up nutrients in the euphotic zone
Low productivity
Some mixing at euphotic base supplying small amount of nutrients upwards
Early Spring Nutrient/Phyto Dynamics
Increasing light and high nutrients
Mix layer shoals with warming surface
Critical depth becomes deeper than mixed layer
Bloom until nutrients consumed
Winter Nutrient/Phyto Dynamics
Low light and high nutrients
Deep mixed layer with high surface nutrients
Concentrations mixed from below
Not enough light so low productivity
Hawaii Waters Nutrient Dynamics
Mix layer never deeper than critical depth
Nutrients are always depleted
Labrador Sea Nutrient Dynamics
Winter mix layer to 1500m in some places
4 Types of Ocean Nutrient Dynamics
1) High nutrient winter and low nutrients summer
Classic bloom (North Atlantic)
2) Low nutrients always
High year-round light and shallow mix layer (Hawaii)
3) Episodic High Nutrients
Coastal upwelling zone
4) High Nutrients Always
Some other factor limits (Northern Pacific or Southern Ocean)
Typical Nitrogen and Phosphorus Levels
0-3 micromol P and 0-45 micromol N
Most data close to 16:1
Some data sit below
Nitrogen Cycle
Primary production consumes nitrate or ammonium in euphotic zone
Respiration releases ammonium in euphotic zone
Phytoplankton prefer ammonium
Organic phosphate sinks into dark ocean and respired to produce ammonium
Nitrification uses ammonium and O2 to produce nitrate in dark ocean (chemosynthesis)
Light inhibits nitrification, and little ammonium in dark O2 rich waters
Mixing and upwelling brings nitrate to surface
New production fueled by nitrate
Regenerated production fueled by ammonium
Denitrification comsumes nitrate when oxygen not available (NO3 to N2)
Where does denitrification occur
Where O2 is not available
Anoxic Saanich Inlet: nitrate is consumed, ammonium builds up
North/South Eastern Tropical Pacific and Arabian Sea
Nitrogen Fixation
Adds N to cycle
Use N2 gas to create more bioavailable Nitrogen
Energy intensive – only advantageous when nitrate and ammonium low
Membrane Importance
Hydrophilic head and hydrophobic tail
Polar ions – phosphate, nitrate and ammonium can’t move across
Need transport enzymes to move through
Energy Associated with Transport Enzymes
Specific transport enzymes for each nutrient
Need to make many
Transport Requires energy
There is therefore an energetic cost to make and use enzymes
Small Size Advantage
Surface area to volume ratio
Smaller cell more SA per volume
Why does Surface area matter and why does volume matter
Surface area matters for nutrient uptake
Volume matter for growth rate
When is small cell size selected
Smaller cell more efficient nutrients supplied for growth
Nutrient limitations selects small cell size
Growth vs Nutrients
At low nutrient levels: growth increases with increasing nutrients
At high nutrients: no relationship (other factor must limit)
What does kN tell us?
Lower kN indicates more efficient nutrient uptake at low nutrient concentration
Will outcompete at low nutrients
What drives species succession over blooms?
Mix layer nutrients concentration decreases over the bloom and light levels increase
These changes drive species succession
Dominant species types in bloom successions
Early Spring: low light so low kI species dominate
Later: High nutrients and high light so higher Pmax and Gmax species dominate
Later Still: Low nutrients so low kN species dominate
Transport Enzymes and Nutrient Uptake Tradeoff
More transport enzymes per SA mean higher nutrient uptake
But energetic cost tends to suppress Gmax
Species kN can acclimatize based on the environment, and adjust transport enzymes based on conditions
The energetic cost of enzymes only advantageous at low nutrient concentrations
How are the requirements for Si different from N and P
Only phytoplankton with Si shells require Si and it has no consistent ratio
Why do you think the plankton requirements for nutrients are so similar to the ratio of their availability in ocean water?
Phytoplankton are generally very small, particularly compared to terrestrial plants. What advantages are conferred by such small size?
They don’t sink as easily and they can take up nutrients better due to SA:V ratio
