nutrients Flashcards
(38 cards)
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
