Chapters 21 & 22

Energy & Nutrient Flows

Harned Hall 301

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Sections

Some Physical Constraints on Flow

First Law of Thermodynamics

Second Law of Thermodynamics

Primary Production

Primary production is often measured in weight of producer (usually plants or algae, but can be bacteria in some systems) tissue added to the system

DB = NPP - G - L

There are some generalities that can be made about the relationship between productivity and standing biomass

Production Efficiency is the proportion of energy fixed to that available (sunlight for photosynthesis)

Limits to Primary Production

Terrestrial ecosystems

Aquatic Ecosystems

Question: As CO2 builds up in the atmosphere, some predict that some dry terrestrial ecosystems will become more productive and that there will be little gains in aquatic systems. What is responsible for this? I'll give you a hint - it's not the CO2 concentration, but something affected by it.

Secondary Production

Biomass produced by producers (primary production) can only move into two other components

Measuring secondary production

Gross assimilation (amount of plant/algal material eaten) is reduced by the amount of energy (and the compounds needed to supply it) used to maintain the herbivore/detritivore

Gross Assimilation - Maintenance = Net Secondary Production

Net production is measured as biomass increase

Secondary Production Efficiency of secondary producers is the ratio of Net Secondary Production/Assimilation

Lindeman Efficiency is different from the efficiencies discussed so far

Terrestrial ecosystems

Aquatic Ecosystems

Control of Secondary Production

Increase in primary production often leads to an increase in secondary production

This leads to the phenomenon that well-fertilized fields are attacked by herbivorous insects more than unfertilized fields (remember the ecosystem exploitation hypothesis)

Nutrient Cycling

Follows nutrients as they flow through the system

Nutrient cycles are the most thoroughly modeled ecological processes, also called  Biogeochemical cycles,  and are the paths of materials as they enter an ecosystem, pass through various componenets of the ecosystem, and finally exit the ecosystem

General model

Global Carbon Cycle

  • Sources

    Volcanism

    Pools Flux pathways  
      Input Output
    Producers photosynthesis respiration, herbivory, death
    Consumers herbivory respiration, carnivory (between trophic levels), death
    Decomposers death respiration
    Detritus plants, animals consumption by decomposers
    Fossil fuels anaerobic respiration human-caused combustion
    Atmosphere/Water    

    Ocean is generally considered to be in equilibrium with atmosphere, such that an alteration in one will inevitably lead to an alteration in the other

    Global Phosphorous Cycle

     

    this needs some work

    Global Nitrogen Cycle

     

    note that the role of microorganisms is key

    Terms

    biocides, target organisms, Primary production, Gross Primary Production, Net Primary Production, Terrestrial ecosystems, Soil Moisture, Evapotranspiration rate, Length of Growing Season, Nutrient Limitation, Eutrophication, secondary production, Gross Assimilation, net secondary production, the basal metabolic rate, Efficiency, Production Efficiency, Lindeman efficiency, Biomass, assimilation, maintenance, early and late succession communities, Nutrient Cycling, Local models, Global models, Biosphere, Biogeochemical cycles, Nutrient pools, Flux rates, Sources, Sinks, Global Carbon Cycle, Volcanism, Global Phosphorous Cycle, Global Nitrogen Cycle, Fixation, Denitrification

    Last updated October 26, 2006