Biology 106 Lecture Topic # 24 Human Impact on Environment
I. Ecosystems = basic functional unit of living community (biotic) and nonliving (abiotic).
A. Transfer of energy from the sun is an Open System regulated within an ecosystem.
B. Nutrients and Chemicals are recycled on earth therefore they represent a Closed System.
II. Flow of Energy within an Ecosystem
- initially via solar radiation, Open System - not cyclic, but unidirectional
- ultimate source of energy for all processes of life
- green plants primary converters of solar energy to biological energy
Gross primary productivity (GPP) = total amount of energy converted to organic cmpds/unit time. Net primary productivity (NPP) = total amount of energy fixed/unit time - energy expended in metabolic activities by organism to fix energy; Energy fixed - Cost to fixing = NPP
III. Trophic Levels w/r energy flow:
1st autotrophs plants producers
2nd heterotrophs (herb.) Io cons.
3rd carnivores 2o cons.
4th 2o carnivores 3o cons.
More indiv.s at lower trophic levels than higher trophic levels
Many organisms feed at more than one tropic level
IV. Detritus Food Chain - major energy pathway in most terrestrial ecosystems
Detritivore = organism eats dead remains of other organisms
-food source for decomposers
-pathway for nutrient cycling
-turnover rates of litter important in nutrient cycling
V. Cycling within an Ecosystem
- Closed Systems = Biogeochemical Cycles - 40/90 chemical elements are cyclic
- The pathways and efficiency of nutrient cycling are integral to the structure of the ecosystem
Nutrients are stored in 4 major ways globally:
1. atmosphere 2. oceans 3. earth's crust - sedimentary cycles 4. organisms -
Nutrient movement can occur 3 main ways: 1. meterological - 2. geological - 3. biological
**Patterns and rate of nutrient fluxes are more important to an ecosystem than are the absolute amounts of nutrients**
A. Hydrological Cycle - at any one time the atmosphere holds 10-11 days of rainfall in vapor form- biogeochemical cycles could not exist w/o water, therefore ecosystems could not be maintained. Solar energy powers the evaporation of water into the atmosphere
Water movement into atmosphere also influenced by:
1. air currents 2. ocean currents 3. heat budgets 4. water balance of land and sea
Figure of Hydrological cycle:
transpiration =
evaporation =
percolation =
water table = unconfined portion of ground water
ground water = reservoir of water
- generally out of reach, unless "mined" by humans - amt's to > 90% all fresh water USA
B. In chemical terms Life can be summed up in 6 words:
-make up >95% of mass of all living things
- fixed supply, must by cycled, Closed System
ex. Carbon Cycle - responsible for global carbon balance - gaseous cycle - major element in fixation of energy by photosynthesis -Source of all fixed carbon in living organisms and fossil deposits in the form of carbon dioxide
Global consequences of increased levels of carbon dioxide in our atmosphere
-Before industrial revolution (1850) lowest levels -After industrialization levels increased- Io due to burning of fossil fuels and 2o burning of forests -Overall result is Global Warming
-Because carbon dioxide being added quicker to atmosphere then it's being removed
Carbon dioxide is called a greenhouse gas because ....
VI. Ecological Succession - ecosystems have a tendency to shift from simple to complex.
A. Two types of Succession:
1. Secondary 2. Primary
B. General Characteristics of Succession
1. increase in total biomass, decrease in net productivity 2. increase in # of spp
3. # heterotrophs increases faster than autotrophs4. later organisms more spec. than earlier ones
5. fugitive spp occur early then competitively loose out 6. increase in # spp interactions
C. Hubbard Brook Experimental Forest, New Hampshire
1963-1965 Baseline data:
1992 Long Term Update of Experimental Forest:
1963-1965 Baseline data: collected as a nutrient budget measuring input and output
Input : 1. rain gauges 2. chemical analyses 3. vegetation uptake of nutrients from biomass
Output:1. weirs in stream 2. water flow 3. nutrient flow
From Baseline Data Found:1. Undisturbed forest very efficient at retaining nutrients
2. Input via ppt.(rain and snow) equals loss via streams. Relatively very small amounts compared to whole system.
Experimental Treatment:1. Winter of 1965-1966: experimentally deforested
2. Subsequent plant regeneration suppressed by herbicide application until 1969 growing season
Initial Observations from Experimental Treatment:
1. increased water runoff by 40% 2. loss of Calcium 10 x greater
3. nitrogen decreased by 120 kg/hectare, prior nitrogen was accumulating @ 2kg/hectare
4. nitrate levels increased in stream water to unsafe levels for drinking; observed algal blooms
5. Fertility of area dramatically decreased 6. Increased probability of flooding greatly increased
1992 Long Term Update of Experimental Forest: (focus on Water Shed #2)
1. Experimental forest demonstrated a vigorous capacity for regeneration, but still will take a considerable period of time to recover
2. A shift in the "housing of nutrients"
3. Summary data on recovery of Water Shed #2 compared to 55 yr old old reference forest
Basic Steps in carbon dioxide cycling:
1. assimilation by plants into CO2
2. plants convert CO2 to glucose
3. glucose to polysaccharides and fat stored in plant tissue
4. herbivores synthesizes plant tissue into other carbon cmpds
5. carnivores eat herbivores and resynthesize into other carbon cmpds
6. light
6CO2 + 6H2O -------> 6O2 + C6H12O6 pg.202,226
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7. remaining carbon is incorporated into living biomass
8. carbon contained in animal wastes and protoplasm of plants and animals released decomposers
Rate of release dependent on environmental conditions:
1. soil moisture 2. temperature 3. precipitation