Ecosystems 1. Energy Flow 2. Chemical...

Ecosystems

1. Energy Flow

2. Chemical cycles

water, carbon, nitrogen

3. Human effects on cycles

eutrophication, acid rain

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Ecosystem = community plus abiotic factors

- Conditions (temp, light) Resources (water, nutrients)

• Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat

• Chemicals are recycled between air, water, soil, and organisms


• A terrarium ecosystem / Biosphere II

Figure 36.8

Chemical cycling (C, N, etc.)

Light energy

Chemical energy

Heat energy


–Water cycle

- Carbon cycle

–Nitrogen cycle

Chemicals are recycled between organic matter and abiotic reservoirs


Figure 36.14

Solar heat

Precipitation over the sea (283)

Net movement of water vapor by wind (36)

Flow of water from land to sea (36)

Water vapor over the sea

Oceans

Evaporation from the sea (319)

Evaporation and transpiration (59)

Water vapor over the land

Precipitation over the land (95)

Surface water and groundwater

oceans

salt water = 97.5%

freshwater = 2.5%

ice caps

and

glaciers

1.97%

ground-

water

0.5%

lakes,

rivers,

and soil

0.03%

atmosphere

0.001%


• Carbon is taken from the atmosphere by photosynthesis

–used to make organic molecules

returned to the atmosphere by cellular respiration, decomposers

Carbon cycle


Figure

36.15

CO2 in atmosphere

Cellular respiration

Higher-level consumers

Primary consumers

Plants, algae,

cyanobacteria

Photosynthesis

Wood and fossil fuels

Detritivores (soil microbes

and others) Detritus

Decomposition

Burning


• Nitrogen is plentiful in the atmosphere as N2

–But plants and animals cannot use N2

• Some bacteria in soil and legume root nodules convert N2 to compounds that plants can use:

ammonium (NH4+) and nitrate (NO3

–)

The nitrogen cycle relies heavily on bacteria


• Legumes and certain other plants have nodules in their roots that contain nitrogen-fixing bacteria

Legumes and certain other plants house nitrogen-fixing bacteria

Figure 32.14A

Shoot

Nodules

Roots


Figure 32.13

ATMOSPHERE

N2

N2 Nitrogen-fixing bacteria

Ammonifying bacteria

Organic material

NH4+

(ammonium) Nitrifying bacteria

NO3–

(nitrate)

Root

NH4+

Amino acids

Soil


Nitrogen (N2) in atmosphere

Amino acids and proteins in

plants and animals Assimilation by plants

Denitrifying bacteria

Nitrates (NO3

–)

Nitrifying bacteria

Detritus

Detritivores

Decomposition

Ammonium (NH4+)

Nitrogen fixation

Nitrogen-fixing bacteria in soil

Nitrogen-fixing bacteria in root

nodules of legumes

Nitrogen fixation

76%

naturally

occurring

24%

naturally

occurring

24%

human-

caused

58%

human-

caused

46%

available

54%

used

Atmospheric

CO2

concentration

Terrestrial

nitrogen

fixation

Accessible

surface

water

Human impact on chemical cycles


• Environmental changes caused by humans can unbalance nutrient cycling over the long term

–Example: acid rain

–Sulfur dioxide, nitrogen oxides create strong acids when dissolved in rain water.

–Low pH kills aquatic life, leaches nutrients from soil

–Calcium deficiency affects everything in food chain: plants, insects, birds. Weak egg shells.

eutrophication • Algal bloom can cause a lake

to lose its species diversity


–Human-caused eutrophication wiped out fisheries in Lake Erie in the 1950s and 1960s

Figure 36.19B

– classic experiments on eutrophication led to the ban on phosphates in detergents


What are the limits to human alteration of chemical cycles and habitats?

• What should the limits be?

• How do we set priorities for what we value in the natural world? Aesthetic, economic, conservation, humans

Ecosystems 1. Energy Flow 2. Chemical...

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