nutrients Flashcards
2 things that limit phytoplankton growth
- nutrients
- light
what is usually the growth-limiting nutrient for phytoplankton
nitrogen
- But Si, P and Fe can also be limiting
what does N exist as in marine environments
Nitrate (NO3-), nitrite (NO2-) or ammonium (NH4+)
what must be recycled within the system to sustain primary production
nutrients - can be done through multiple processes and pools
top 3 most concentrated element / nutrients in seawater
silicon (Si)
nitrogen (N)
phosphorus (P)
SiNP
examples of Macronutrients + Micronutrients in seawater
Macronutrients:
- Nitrogen - NO3- and NH4+
- Phosphorus - PO43-
Micronutrients:
- iron - required for photosynthesis - very abundant on land, not in seawater
what’s the Redfield ratio
the ratio that the average elemental composition of phytoplankton follow (general guideline) - means phytoplankton need nutrients in specific proportions for optimal growth
- 106 C: 16 N: 1 P
- 106 C: 15 Si: 16 N: 1 P (for diatoms)
- Species that live in the water collum have evolved to these ratios
- Many phytoplankton species do exhibit flexible internal elemental composition
what does the oxidation number of nitrogen tell us
we can determine whether it is an oxidation (number goes up -) reaction or a reduction (number goes down +) reaction
- if oxygen was taken away from a nitrate ion, the nitrogen would have a charge of +5 aka missing 5 electrons
what is Nitrification and what does it require
Converting ammonium -> nitrite -> nitrate (Both sensitive to light)
- bacteria Nitrosomonas and Nitrobacter
- oxygen
what is Denitrification and what does it require
Converting nitrate -> nitrogen gas
- denitrifiers bacteria - break down the nitrate present in the water collum and use it to power their respiration
- low oxygen
- energy
is energy required or released when oxidation number of N increases
released
is energy required or released when oxidation number of N decreases
required
what is Nitrogen fixation and what does it require
Converting nitrogen gas -> ammonium (something that is biologically available)
- microorganisms called diazotrophs e.g Trichodesmium - prevents o2 getting in to give an anoxic environment
- enzyme nitrogenase - very sensitive to oxygen
- anoxic environment
why is Nitrification important
For primary production (photosynthesis) to happen, need inorganic form of nitrogen
what equation looks at the rate of phyto nutrient uptake (V)
Ks + S
- Ks = half-saturation constant
- S = concentration of dissolved inorganic nitrogen
what do the differences in Ks and Vmax lead to as for light
species successions
how will Changes through the year (therefore different nutrient concs) mean we are going to get a change in the species present
different species are able to make use of the different nutrients
what’s the F-ratio look at
Looks at where the nitrogen is coming from – ratio of the uptake of nitrate relative to the total uptake (nitrate + ammonium)
f-ratio equation
(Vnitrate + Vammonium)
what’s New production
phyto growth fuelled by new N, usually NO3- -> high f-ratio
- NO3- enters SML from rivers, run off or below thermocline
what’s recycled production
phyto growth fuelled by NH4+ -> low f-ratio
- NH4+ is remineralized within the SML by zooplankton
explain Thermohaline circulation
circulation that is not driven by wind but density gradients from temperature + salinity variations instead
- Drives a lot of the water around the world
- During sea ice formation, salt is expelled (brine rejection) so sea ice is mostly fresh, and the surrounding water gains additional salt - increases density
- The cold water that forms in north sinks down (as dense as water gets)
- Cold water gets pushed south + upwards as its warming
- Other water has to move to make way for the cold water + the surface water that has sank has to get replaced – global pump
- Very slow water movement; average time to complete one cycle ~1,000 years
- Global redistribution of large amount of heat; important for long-term regulation planet’s climate
- Global warming decreases sea ice formation, hence disrupts THC
Two of the major water masses in Thermohaline circulation (THC)
- North Atlantic Deep Water (NADW)
- Antarctic Bottom Water (AABW)
what happens to oxygen and nutrient conc in deep water mass flow pattern at a depth of 4000 m
- Oxygen concentration decreases as the water mass travels due to oxygen consumption for remineralisation (Note: The deep ocean is cut off from the atmosphere)
- Nutrient concentration increases as the water mass travels due to nutrient release from remineralisation
what’s the dominant form of phosphorus used by phytoplankton and where does it come from
Inorganic form (PO43-)
- Comes from terrestrial systems
- Don’t get as much recycling as nitrates
Silicon characteristics
- Less reactive – tends to sit in water collum for long time
- Needed by diatoms and other organisms with siliceous components
- After death the biogenic silica sink to the deep ocean
- Because of slow dissolution, biogenic silica may become part of opal in sediment
why are micro nutrients “Micro”
because they are needed in only a small amount - but when their concentrations are below what is needed, they can be the limiting factor
what are High Nutrient Low Chlorophyll regions and what do they suggest
In some parts of the ocean nitrate concentration is high but chlorophyll is lower than expected
- suggests phytoplankton are under-utilizing the available nitrate
examples of High Nutrient Low Chlorophyll (HNLC) regions
Subarctic Pacific
Equatorial Pacific
Southern Ocean
Possible explanations for HNLC
- Grazing keeps the standing stock low
- Phytoplankton growth is limited by something else
what does John Martin’s iron hypothesis suggest
Suggests phytoplankton growth in the HNLC regions is limited by the supply of iron
- Martin’s famous quote: “Give me a half tanker of iron and I will give you another ice age”
- Increase iron supply will stimulate phytoplankton bloom
- Increased photosynthesis will draw down extra atmospheric CO2
- Upon bloom termination phytoplankton carbon will sink to the deep ocean
- Slow thermohaline circulation means that the carbon will be kept out of atmospheric circulation for a very long time
- If enough CO2 is removed, we may reverse the global warming trend
explain IronEx II experiment
- Got a large vessel and filled it with shipping containers full of SF6 + iron sulphate (biologically available iron)
- Drove boat to high nutrient, low chlorophyll area and offloaded this off the boat and repeated over a course of a few weeks
what were the results of the IronEx II experiment
- Shift in phyto composition: start = Prochlorococcus & Synechococcus (tiny bacteria – best at making use of a limiting nutrient), end = diatoms
- Photosynthetic competence increased Fv/Fm
- Depleted surface waters of NO3- (macronutrients)
what can we conclude from the IronEx II experiment
- Iron limits phytoplankton growth in the Equatorial Pacific
- Explains HNLC
how does iron enter the oceans
naturally gets from the land to open ocean via dessert – dust that contains loads of iron gets blown from land to sea
what is Eutrophication
Excessive nutrient input into waters leads to environmental problems
Hypoxia meaning
a condition when oxygen concentrations fall below the level necessary to sustain most animal life (ca. 2 mg O2 l-1)
how do Nutrients + pollutants get into coastal waters and cause eutrophication
from anthropogenic activity - land run-off (agriculture), industrial waste, Burning organic fuels e.g. car use releases nitrogen compounds into atmos where it dissolves into clouds and rains down
- Areas of high populations are associated with high nitrate + nitrite introductions to these environments
