Lecture 3

Question 1

Any shortage of a nutrient can ____ primary production

Answer 1

Any shortage of a nutrient can reduce primary production

Question 2

Can a nutrient still limit rates of primary production

when it is present in large concentrations?

Answer 2

Yes, many nutrients can occur at high concentrations in ecosystems, but are not bioavailable

• Nutrients may be bound in compounds that cannot be broken down and transported into biota, or they can be bound in complexes that render them inaccessible (e.g., dead organic material).
• The rate at which a nutrient may be mineralized (or become bioavailable) can be the limiting step controlling primary production
• Nutrient concentrations alone are often poor predictors of primary production

Question 3

As the _______ of a limiting nutrient increases, primary production also increases

Answer 3

As the mineralization rate of a limiting nutrient increases, primary production also increases

Question 4

aquatic ecosystems: conditions

Answer 4

1. Quantity of light (PAR): northerly latitudes have shorter seasons for
   production (already covered in terrestrial section)
2. Temperature: like terrestrial plants, algal productivity increases
   with water temperature (already covered in terrestrial section)
3. Nutrient supply: nutrients limit algal production in most aquatic
   environments

Question 5

Factors that control primary production in aquatic ecosystems

Potential Limiting Nutrients

Marine systems:

Answer 5

N, P, Fe and Si

Note:

Freshwater systems: N, P and Si

Question 6

Factors that control primary production in aquatic ecosystems

Potential Limiting Nutrients

Freshwater systems:

Answer 6

N, P and Si

Note:

Marine systems: N, P, Fe and Si

Question 7

Nitrogen

Answer 7

• Ammonium (NH4), nitrate and nitrite are the most important bioavailable forms
• For protein synthesis in phytoplankton and bacterioplankton

Question 8

Phosphorus

Answer 8

• Phosphate (PO4) is the most important bioavailable form

* For energy transfer (ATP), nucleic acid synthesis and cell membranes in algae and bacteria

Question 9

Iron

Answer 9

• Bioavailable forms: ferrous iron (Fe2+) and iron bound to organic ligands
• Used to fix nitrogen (N2) and other functions in bacteria and algae

Question 10

Silica

Answer 10

• Silicic acid H4SiO4 most important bioavailable form

* Used in the skeleton of diatoms (a major algal group)

Question 11

Too Much Nutrient (N & P):

Answer 11

Lake Winnipeg Algal Blooms

Question 12

In general, primary production in many lakes is limited by the availability of _____

Answer 12

In general, primary production in many lakes is limited by the availability of P

Question 13

Open ocean nutrient fertilization experiments have also been conducted, For example,

1. CYCLOPS = what limitation and where?
2. IronEx I & II = what limitation and where?

Answer 13

(P-limitation, Mediterranean)

Fe-limitation, South Pacific Ocean

Question 14

Iron dumped in ocean
Proposed Outcome:
Ocean Surface Water

Answer 14

Fe (added) + CO2 (from atmosphere)—-> Algal biomass

Question 15

In addition to abiotic factors, biotic factors such as grazing may also __________ on primary
production

Answer 15

In addition to abiotic factors, biotic factors such as grazing may also have a significant affect on primary
production