Structure of Aquatic Ecosystems

Relative importance of allochthonous versus autochthonous sources of

• nutrients• sediments• organic matter (dissolved and particulate)

Productivity within a Watershed

• Wetland very productive• Terrestrial systems moderately productive• Aquatic systems least productive

Zones of a Lake

Zones of a Reservoir

Zonation of Littoral Vegetation

Aufwuchs

Categories of Aufwuchs

• Epiphytic • Epipelic

• Episammic

• Epilithic

Phytoplankton

Zooplankton

Benthos

Nekton

Trophic Structure

Primary Producers

Primary Consumers

Secondary Consumers (carnivores)

Decomposers

Food Web

River Continuum

Productivity

Rate at which energy enters one trophic level from a lower trophic level.

Efficiency

Energy transfers not very efficient because of dissipation through metabolism, etc. Also, mechanisms of energy transfer not inherently efficient. For example photosynthesis is less than 1% efficient in water.

Diversity

Complexity of a community

Relative Sizes

Biomass

Ways to determine:• Volume and number• Weight –fresh and dry• Oxidize living matter to CO2• Total ATP• For primary producers, extract chlorophylls

Production

• New organic mass per unit of time

• Σ [new organic biomass - respiration -excretion - secretion – injury – death – grazing]

Energy Flow in an Ecosystem