Terrestrial Environments & Ecosystem Energetics

Terrestrial Environments & Ecosystem Energetics

Announcements

  • Extra credit lecture assignment posted.
  • Lecture assignments 8 and 9 are posted.
  • Lab:
    • In the stream this/next week.
    • Wear closed toed shoes in case waders do not fit.
    • Bring a full set of extra clothes.
    • Water will be COLD and may be HIGH based on rainfall this week.

Pore Space in the Soil

  • Important for the movement of air and water in the soil, and root penetration.
  • Ideal soil: 50% soil particles, 50% pore space.
  • Pore space includes spaces within and between soil particles.
  • Old root channels.
  • Animal burrows.

Soil Water Content

  • Field capacity: Water content (g/cm^3) varies with soil texture.
    • Clay has the highest field capacity, followed by loam, and then sand. This is because clay has the finest particles, and sand has the coarsest.
  • Wilting point: The point at which plants can no longer extract water from the soil.
  • Available water capacity: The difference between field capacity and wilting point.
  • Topography also influences water content in the soil.

Top Hat Question

  • Which type of soil has the highest field capacity?
    • Answer: C. Clay

Soil Horizons

  • Soil profile: A sequence of horizontal layers visible in the soil.
  • Horizons have different physical, chemical, and biological characteristics.
  • Key Horizons:
    • O horizon: The uppermost horizon, composed of organic matter.
    • A horizon: Contains the topsoil.
    • B horizon: Subsoil
    • C horizon: Soil base
    • R horizon: Bedrock

Top Hat Question

  • Which horizon contains the topsoil?
    • Answer: B. A

Basic Soil Formation Processes

  • Five soil-forming processes lead to the diversity of soils:
    1. Laterization
    2. Calcification
    3. Salinization
    4. Podzolization
    5. Gleization
  • These processes lead to the geographic diversity of soils.

Soil Erosion due to Agriculture

  • Tilling the land removed horizon A (grass-covered surface soil).
  • The mat of fibrous grass roots holds the soil together.
  • In the 1930s, severe drought and high winds occurred.
  • The topsoil was dry and easily eroded by the wind.
  • Resulted in dust storms.
  • The region became known as the Dust Bowl.

Energy Source

  • The Sun!
  • Specifically, photons.
  • These can be transformed into heat.
  • Photosynthetic organisms transform light energy into chemical bond energy.
  • Energy is stored in carbon-based compounds (organic).
  • First law of thermodynamics = conservation of energy.
  • Energy is neither created nor destroyed.
  • Energy can change from one form to another.

Energy in Ecosystems

  • Gross primary productivity (GPP): Total rate of photosynthesis, or the energy assimilated by autotrophs.
  • Net primary productivity (NPP, Productivity): Rate of energy storage as organic matter after respiration. GPP=NPP+RGPP = NPP + R NPP=GPP−RNPP = GPP - R
  • RR = energy expended for cellular respiration.

Factors Affecting NPP

  • Precipitation: NPP generally increases with precipitation.
  • Soil Nutrient Availability: NPP generally increases with increasing soil nutrient availability.

NPP in Aquatic Ecosystems

  • Controlled by light & nutrient availability.
  • Photosynthetically active radiation (PAR) declines exponentially with water depth.
  • Recall: GPP=NPP+RGPP = NPP + R
  • When GPP=RGPP = R, NPP=0NPP = 0 → compensation depth.

Compensation Depth

  • Compensation Depth: GPP=RGPP = R, NPP=0NPP = 0

Top Hat Question

  • Which of the below would increase NPP?
    • Select all that apply:
      • Increase precipitation
      • Increase nutrient availability

Sources of Organic Carbon in Aquatic Ecosystems

  • Autochthonous organic carbon: Produced within an ecosystem.
    • Comes from photosynthesis by aquatic photoautotrophs (plants, algae, phytoplankton).
  • Allochthonous organic carbon: Produced outside of an ecosystem.
    • Comes from dead organic matter input from adjacent terrestrial ecosystems.
    • Can be dissolved (DOM) or particulate (POM) organic matter.

Relative Contribution to Total Organic Carbon

  • Smaller streams: Dominated by allochthonous organic matter.
  • Larger rivers: Dominated by autochthonous organic matter (phytoplankton, attached algae, macrophytes).

Most Productive Ecosystems

  • Aquatic (most to least productive):
    • Coastal wetlands
    • Algal beds and coral reefs
    • Estuaries
    • Lakes and streams
    • Open ocean
  • Terrestrial (most to least productive):
    • Freshwater wetlands!
    • Forests: Tropical > Temperate > Boreal (equatorial > mid > high latitude)
    • Grasslands: Tropical > Temperate
    • Tundra
    • Deserts

Primary Production Varies with Time

  • Primary production varies with:
    • Age/succession stage
    • Seasons/time
  • Plants are often dormant with little or no NPP in cold or dry conditions.

Top Hat Question

  • When is NPP highest in temperate forests?
    • Answer: May – October

Primary Production Varies with Time

  • Inter-annual variation can occur if there is climatic variation.
  • Disturbances can cause year-to-year variation in NPP at a site.

Primary Productivity Limits Secondary Production

  • NPP is the energy available to heterotrophs in an ecosystem.
  • Herbivores, omnivores, & detritivores → consume primary productivity.
  • What happens to this energy when consumed?
    • Used (metabolism, movement, etc.)
    • Passes as waste (feces and urine)
    • Tissue production (growth, sperm/eggs)

Secondary Production

  • Biomass: the amount of organic matter present at any given time.
    • Two ways that biomass can be lost over time:
      1. DD = death of organisms
      2. CC = consumption of organisms
  • Secondary productivity: rate of biomass formed by heterotrophs.
    • Heterotroph equivalent of autotroph NPP.
    • Proportional to birth rate and growth rate of heterotrophs.
    • Dependent on primary production.

Relationship between Primary and Secondary Production

  • Herbivore biomass increases with net primary productivity.
  • Herbivore consumption increases with net primary productivity.

Energy Flow Through a Consumer

  • 200 J of plant material ingested (I).
  • 100 J of ingested energy is expelled as waste (W).
  • 100 J of ingested energy is assimilated (A).
  • 60 J of assimilated energy is used for respiration (R).
  • 40 J of assimilated energy is used for production (P).

Consumers Vary in Efficiency of Production

  • Assimilation efficiency (A/IA/I): Measures the efficiency of extracting energy from food.
  • Production efficiency (P/AP/A): Measures how efficiently assimilated energy is incorporated into secondary production.

Two Major Food Chains in Any Ecosystem

  • Grazing food chain: Primary producers → Herbivores → Carnivores → Carnivores
  • Detrital food chain: Detritus → Decomposer herbivores → Carnivores
  • RR represents respiration at each level.

Energy Decreases in Each Successive Trophic Level

  • Trophic efficiency (TE) is the ratio of productivity in a given trophic level to the trophic level it feeds on.

Biomass Pyramids

  • Florida bog:
    • Producers: 809 g/m2
    • Primary consumers: 37 g/m2
    • Secondary consumers: 11 g/m2
    • Tertiary consumers: 1.5 g/m2
      *Biomass Pyramid- exception to the rule (small aquatic communities)
  • English Channel:
    • Producers (phytoplankton): 4 g/m2
    • Consumers (zooplankton): 21 g/m2 This demonstrates an inverted biomass pyramid, where the consumer biomass is greater than the producer biomass. This can occur when producers have a high turnover rate (rapid reproduction and consumption).