Ecosystem energetics
description
Transcript of Ecosystem energetics
Ecosystem energetics
Outline:
• Limits on primary production• Relationship between primary and secondary
productivity• Trophic efficiency
Readings: Chapters 20
Laws of thermodynamics govern energy flow
Laws of thermodynamics govern energy flow
Energy flow in ecosystems
Ecosystem energetics - terminology
• Standing crop biomass – amount of accumulated organic matter found in an area at a given time [g/m2]
• Productivity – rate at which organic matter is created by photosynthesis [g/m2/yr]
• Primary productivity – autotrophs
• Secondary - heterotrophs
• Gross versus net primary productivity
Estimating primary productivity in aquatic ecosystems
Factors limiting primary productivity in terrestrial ecosystems
• Temperature
• Precipitation
• Light
• Nutrients
Controls on primary production in terrestrial ecosystems
Controls on primary production in terrestrial ecosystems
Controls on primary production in terrestrial ecosystems
Controls on primary production in terrestrial ecosystems
Controls on primary production in terrestrial ecosystems
Despite much variation, there is a general trend of increasing net primary productivity with decreasing latitude. a), Grassland and tundra ecosystems. b) Cultivated crops. c) Lakes
Primary production as a function of latitude
Global map of primary productivity
Factors limiting primary productivity in aquatic ecosystems
• Light
• Nutrients
Controls on primary production in aquatic ecosystems
Controls on primary production in aquatic ecosystems
Controls on primary production in aquatic ecosystems
Global map of primary productivity
Energy allocation
Primary production varies with time
Primary production varies with time
Primary production varies with time
Primary productivity limits secondary
productivity
Primary productivity limits secondary productivity
Consumption efficiency = 200/1000
Assimilation efficiency 70/200
Production efficiency = 14/70
Amt produced by trophic level n-1
Amt ingested by trophic level n
Amt egested as feces (waste) by trophic level n
Amt assimilated (i.e. absorbed into body) by trophic level n
Amt respired by trophic level n
Secondary production by trophic level n
Efficiency of energy transfer
I = ingested A = assimilated through gut wallW = expelled as waste
productOf A,
R = respiredP =
production
Efficiency of production
Food chains
Consumption efficiency determines pathways of energy
flow through ecosystem
Note: • Detrital food chain accounts for
most biomass produced in a community
• LCS plays greatest role in phytoplankton-based food chains
FOREST
GRASSLAND
PLANKTON - OCEAN
STREAM COMMUNITY
Energy loss between trophic levels
Amt produced by trophic level n-1
Amt ingested by trophic level n
Amt egested as feces (waste) by trophic level n
Amt assimilated (i.e. absorbed into body) by trophic level n
Amt respired by trophic level n
Secondary production by trophic level n
Example: a herbivore (level n) feeding on a plant (level n-1); values = kilocalories.
Trophic Efficiency = 0.2*0.35*0.2= 14/1000= 0.014
Efficiency of energy transfer
Decomposition and Nutrient cycling
Outline:• Process of decomposition
– Types of decomposers– Controls on decomposition– Decomposition in lakes and
rivers
• Nutrient cycling: generalities• Nutrient cycles
– Carbon– Nitrogen– Phosphorus
Readings: Chapters 21, 22
Decomposition
• Most material = plant• Involves:
• Release of chemical energy• Mineralization (= organic --> inorganic)
• Note immobilization = reverse of mineralization• Net mineralization rate = mineralization -
immobilization
Decomposition involves a variety of organisms
• Microfauna & microflora [<100 μm]– bacteria and fungi; nematodes, protozoa
• Mesafauna [100 μm – 2mm] – mites, potworms
• Macrofauna [2-20 mm] - millipedes
• Megafauna [> 20 mm]- earthworms, snails
Fungi: microfauna
Mites: mesofauna
Megafauna
Vertebrate scavengersConsumers of animal carrion
(highest lignin content)
(lowest lignin content)
Factors influencing decomposition rates
Decomposition of straw
Factors influencing decomposition rates
Factors influencing decomposition rates
Factors influencing decomposition rates
Factors influencing decomposition rates
Immobilization vs. mineralization
Decomposition in aquatic environments
Rate of nutrient cycling
Rate of nutrient cycling
Zones of production and decomposition
Nutrient spiraling in rivers
Nutrient spiraling in rivers
Terrestrial communities:Nutrient sources
• Weathering of rock (K, P, Ca and many others)• Fixation of CO2 (photosynthesis) and N2 • Dryfall (particles in the atmosphere)• Wetfall (snow & rain); contains
– Oxides of S, N– Aerosols
• particles high in Na, Mg, Cl, S• produced by evaporation of droplets
– Dust particles from fires, volcanoes• Ca, K, S
Terrestrial communities:Nutrient losses
• Release to atmosphere– CO2 from respiration– Volatile hydrocarbons from leaves– Aerosols– NH3 (decomposition), N2 (denitrification)
• Loss in streamflow– Dissolved nutrients– Particles
Oceans
• No outflow• Detritus sinks --> mineralization --> nutrients
end up1. Being carried back to surface in upwelling
currents, or2. Trapped in sediment
• E.g. phosphorus: 1% lost to sediment with each cycling
The Carbon Cycle
Daily variation in CO2
Annual variation in CO2
The nitrogen cycle
The phosphorus cycle
Nitrogen saturation
Nitrogen saturation
For next lecture:
• Please read Chapter 6
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