1. Unit 4 - Nutrient Cycles in Marine Ecosystems
AICE Marine

2. Detritus: What is it? How does it fit in to a food web/chain?
Who/what consumes it?

3. Detritus: What is it? Dead, decaying organic matter
How does it fit into a food web/chain? Returns nutrients (so they aren’t “lost” from the system)
Who/what consumes it? Detritivores AKA Decomposers (fungi & bacteria)

4. Detritus is broken down and released as chemical elements into the soil, water, & air where P.P. can recycle them into organic compounds
Without detritivores, life would cease! Essential nutrients would be locked up & unavailable to the ecosystem

6. Chemical Cycling:
Nutrients move between organic and inorganic parts of the ecosystem in biogeochemical cycles.
Cycles may be global or local. Nutrient cycles with a gaseous component (carbon, sulfur, nitrogen) are global whereas phosphorus, potassium and calcium cycle more locally (at least on short time scales).

7. 2 Major Types of Biogeochemical Cycles:
**Based on the Primary Source of nutrient input**
Gaseous cycles—atmosphere & ocean (global circulation patterns)
Sedimentary cycles—soil & rocks of the Earth’s crust; these vary from one element to another, but essentially each has two abiotic phases:
Salt Solution phase
Rock phase

8. Draw me! Fig. 1

9. Fill me in! Fig. 1

10. General Structure of Nutrient Cycles:
Nutrients can move from one reservoir to another by a variety of processes
Some examples:
Photosynthesis (makes organic nutrients available from inorganic)
Respiration (makes inorganic nutrients available from organic)
Decomposition (makes inorganic nutrients available from organic)
Excretion (makes inorganic nutrients available from organic)

11. Nutrient Cycling: Global Scale
H2O (+ volatile biochemicals)
Precipitation
Volatile bioelements only
Volatile bioelements only
Terrestrial Food Web
Uptake
Death
Evaporation
Bioelements in solution
Detritus
Decomposition
Marine Food Web
OCEAN
Weathering
Losses by water runoff
Detritus
Terrestrial Biosphere
Sinking
*Volatile=evaporates rapidly

12. Decomposition and nutrient cycling rates
Rate of nutrient cycling is affected by rate of decomposition
In the tropics, warmer temperatures cause organic material to decompose 2-3 X faster than it does in temperate regions!

13. Decomposition and nutrient cycling rates
In aquatic ecosystems decomposition in anaerobic sediments can be very slow (50 + years)
As a result, sediments are often a nutrient sink and only when there is upwelling* are marine ecosystems highly productive.
(*Upwelling is when ocean currents move water vertically from the depths to the surface—more to come)

14. Human effects on nutrient cycles (1):
Recent studies suggest that human activities (fertilization & increased planting of legumes) have approximately doubled the supply of nitrogen available to plants.
Fertilizers that are applied in amounts greater than plants can use or that are applied when plants are not in the fields leach into groundwater or run off into streams and rivers therefore getting to the ocean.

15. Human effects on nutrient cycles (2):
A major problem with intensive farming is fertilizer runoff.
The heavy supply of nutrients causes blooms of algae and cyanobacteria as well as explosive growth of water weeds.
Because respiration by plants depletes the oxygen levels at night this process of eutrophication can cause fish kills.
Eutrophication of Lake Erie, for example, wiped out commercially important populations of fish including lake trout, blue pike and whitefish in the 1960’s.

16. Limits on primary productivity
Nutrient limitation is a major factor affecting NPP in aquatic biomes.
In marine environments the nutrients limiting primary productivity are usually nitrogen and phosphorus, which are scarce in the photic zone.

17. 5 Marine Nutrient Cycles:
Carbon
Nitrogen
Phosphorus
Magnesium
Calcium

18. Carbon Cycle
Carbon forms the basis of all organic molecules (organic chemistry is the study of carbon chemistry). Fats, sugars, DNA, proteins etc. all contain carbon.
Photosynthetic organisms take in CO2 from the air and using energy from sunlight join carbon atoms to make sugars (energy is stored in the chemical bonds).

19. Carbon Cycle
Major reservoirs of carbon include: atmospheric CO2, ocean (dissolved carbon compounds), biomass of organisms, fossil fuels and sedimentary rocks.

20. Carbon Cycle Photosynthesis removes large amounts of atmospheric CO2
An approximately equal amount of CO2 is returned to atmosphere by cellular respiration.
Burning of fossil fuels adds large amounts CO2 to the atmosphere.

22. Nitrogen Cycling N is an essential element in
Protein: each amino acid has at least 1 N
Nucleic acids: nitrogenous bases
N2 makes up about 79% of the atmosphere
N2 is only usable by prokaryotes with the enzyme nitrogenase
Cyanobacteria like Anabaena carry their nitrogenase in a low oxygen package, the heterocyst.

23. The bacterial processes involved in nitrogen cycling.
The width of each arrow is an approximation of the process rate.

25. Fixation
Converts N2 to
ammonia (bacterial)- NH4 : kg N/ha=90%
N2 --> 2N
2N + 3H2 --> 2NH3
Rhizosphere bacteria: mutualistic, some nodule formers
Free-living bacteria (+cyanobacteria) ~ 12,000 species
Nitrate (high energy discharge, like lightning) - NO3
NO3 in atmosphere + water vapor = H2NO3
Atmospheric fixation low: 8.9 kg N/ha/yr

26. Mineralization (ammonification)
Major step in N cycle
Biomolecules (proteins,nucleic acids) from dead organisms broken down by bacteria and fungi to amino acids then to CO2 + H2O + NH4 + energy
Fate: dissolved in H2O, trapped in soil, fixed in clay

27. NH3 + 11/2 O2 -> HNO2 + H2 + 165 kcal
Nitrification
Nitrosomonas bacteria use ammonia in soil as sole E source
NH3 + 11/2 O2 -> HNO2 + H kcal
HNO2 -> H+ + NO2
Nitrobacter bacteria use the remaining E in nitrite ion and oxidize it to nitrate
NO2 + 1/2O2 -> NO3
Pollution can result if nitrates build up in aquatic ecosystems

28. Denitrification Nitrates reduced biologically to N2
Denitrifiers are facultative anaerobes
Bacteria: Pseudomonas
Fungi

29. Nitrogen Cycle