Ch. 9.Aquatic ecosystems

and Physiology:

Energy Flow Productivity Dissolved Oxygen

Fig. 9.1. Hypothetical Trophic Structure Model. Boxes are filled with functional groups, measured as calories of energy, or moles of chemicals, biomass, or numbers.

Fig 1.14a. Energy flow model of Cedar Bog Lake, Minnesota (Lindeman 1942)

Food Web Model:

Boxes are filled with SPECIES.

Fig 1.14b. Energy flow model of Silver Springs, Florida (Odum 1971)

PRIMARY PRODUCTIVITY: PHOTOSYNTHESIS

Fig. 9.4.

NPP = GPP – Respiration

The world's ecosystems vary tremendously in productivity.

In terms of NPP per unit area, the most productive systems are estuaries, swamps and marshes, tropical rain forests, and temperate rain forests

To calcualte the total amount of NPP in the world, these values must be multiplied by the area that the various ecosystems occupy.

The most productive systems are open oceans, tropical rain forests, savannas, and tropical seasonal forests

http://www.globalchange.umich.edu/globalchange1.html

Horne and Goldman 1994

Horne and Goldman 1994

Kalff 2002

Horne and Goldman 1994

Importance of dissolved oxygen in aquatic systems

• Affect the distribution of aerobic heterotrophic life

• Impacts the solubility of phosphorus and other nutrients

• Influences redox potential (Ch. 10) and thus the solubility of redox-sensitive materials

• May be used to estimate ecosystem productivity

Photo-inhibition

Productivity may be measured in units of mgC volume-1 time-1

Because it takes two moles of O2 to fix 1 mole of C, productivity may also be measured in units of mgO2 volume-1 time-1

CO2 + H2O CH2O + O2

Ratio of moles of C to moles of oxygen = 12/32 = 0.375; i.o.w. 1 mg O2 produced = 0.375 mg C fixed

Examples of productivity measurement techniques:

Light - dark bottles

Diel cycles in oxygen levels

14C uptake

Lingeman and Ruardij, 1981

PN=PG-R

R

Kalff 2002

Kalff 2002

Kalff 2002