Ecology and Biogeochemical

CyclesAPES Review

THE EARTH’S LIFE SUPPORT

SYSTEMS

The biosphere

consists of several

physical layers that

contain:

◦ Air

◦ Water

◦ Soil

◦ Minerals

◦ Life

Figure 3-6

The atmosphere’s four layers

The atmosphere’s composition

What Sustains Life on Earth?

Solar energy,

the cycling of

matter, and

gravity sustain

the earth’s life.

Figure 3-7

What Happens to Solar Energy

Reaching the Earth? Solar energy

flowing through

the biosphere

warms the

atmosphere,

evaporates and

recycles water,

generates winds

and supports

plant growth.

Figure 3-8

ECOSYSTEM COMPONENTS Life exists on land systems called biomes

and in freshwater and ocean aquatic life

zones.

Figure 3-9

Two Secrets of Survival: Energy

Flow and Matter Recycle

An ecosystem

survives by a

combination of

energy flow and

matter recycling.

Figure 3-14

BIODIVERSITY

Figure 3-15

ENERGY FLOW IN ECOSYSTEMS

Food chains and webs show how eaters, the

eaten, and the decomposed are connected to

one another in an ecosystem.Figure 3-17

Food Webs

Trophic levels

are

interconnected

within a more

complicated food

web.

Figure 3-18

Energy Flow in an Ecosystem: Losing

Energy in Food Chains and Webs

Ecological

efficiency:

percentage of

useable energy

transferred as

biomass from

one trophic level

to the next.

Figure 3-19

Net Primary Production (NPP)

NPP = GPP – R

◦ Rate at which

producers use

photosynthesis to

store energy minus

the rate at which they

use some of this

energy through

respiration (R).

Figure 3-21

The Water Cycle

Effects of Human Activities

on Water Cycle

We alter the water cycle by:

◦ Withdrawing large amounts of freshwater.

◦ Clearing vegetation and eroding soils.

◦ Polluting surface and underground water.

◦ Contributing to climate change.

The Carbon Cycle:

Part of Nature’s Thermostat

Effects of Human Activities

on Carbon Cycle

We alter the carbon cycle by adding excess CO2 to the atmosphere through:◦ Burning fossil fuels.

◦ Clearing vegetation faster than it is replaced.

◦ CO2 levels have risen by 100ppm or more in the last 150 years.

The Nitrogen Cycle: Bacteria in

Action

Effects of Human Activities

on the Nitrogen Cycle

We alter the nitrogen cycle by:

◦ Adding gases that contribute to acid rain.

◦ Adding nitrous oxide to the atmosphere through

farming practices which can warm the

atmosphere and deplete ozone.

◦ Contaminating ground water from nitrate ions in

inorganic fertilizers.

◦ Releasing nitrogen into the troposphere through

deforestation.

The Phosphorous Cycle

Effects of Human Activities

on the Phosphorous Cycle

We remove large amounts of phosphate from

the earth to make fertilizer.

We reduce phosphorous in tropical soils by

clearing forests.

We add excess phosphates to aquatic

systems from runoff of animal wastes and

fertilizers.

The Sulfur Cycle

Figure 3-32

Effects of Human Activities

on the Sulfur Cycle

We add sulfur dioxide to the atmosphere by:

◦ Burning coal and oil

◦ Refining sulfur containing petroleum.

◦ Convert sulfur-containing metallic ores into free

metals such as copper, lead, and zinc releasing

sulfur dioxide into the environment.

SOIL: A RENEWABLE

RESOURCE

Figure 3-23

Some Soil Properties

Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.

Figure 3-25

Particle Sizes

– Clay: less than 0.002 mm

– Silt: 0.002-0.05 mm

– Sand: 0.05-2 mm

• 0.05-0.24 mm fine

• 0.25-0.49 mm medium

• 0.5-0.99 mm coarse

• 1- 2 mm very coarse

– Gravels: 2-75 mm

– Cobbles:75-250 mm

– Stones: 250-600 mm

– Boulders: >600 mm

Sand + Silt + Clay = 100%

Texture =

CLAY LOAM

34 % Sand

33 % Silt

33 % Clay

General Influence of Soil Separates on

Properties and Behaviors of Soils

Property/Behavior Sand Silt Clay

Water holding Low Med-high high

Aeration Good Med Poor

OM decomposition Fast Med Slow

Water erosion pot. Low High Low

Compact-ability Low Med High

Sealing (ponds) Poor Poor Good

Nutrient supplying Poor Med-high High

Pollutant leaching High Med Low

Soil Texture and Surface Area

• As particle size decreases, surface

area increases

–Clay has about 10,000 times as much

surface area as sand

• Surface area has a big effect on:

–Water holding capacity

–Chemical reactions

–Soil cohesion

–Ability to support microorganisms

Influences of Soil Properties

• Parent Material:– Rock or original source of soil particles

– Effects soil quality

– Glacial outwash sands tend to be infertile, or hold few minerals and nutrients important for growth

– Soils derived from other sources may be relatively rich in minerals and nutrients

– Usually a combination of weathered parent materials and organic matter make a soil

Major Causes of Soil

Degradation Overgrazing 35%

Deforestation 30%

Other Agricultural Activities 27%

Other Causes 8%

Soil Exhaustion

Agricultural systems disrupt natural

mineral cycling.

◦ The soil may become mineral deficient

and lose fertility.

◦ Plants need minerals to grow and thrive

such as nitrates, phosphates and sulfates.

Soil Erosion

The removal of trees that stabilize

slopes result in erosion.

◦ Erosion is the removal of the top soil by

physical means.

◦ Deforestation is one of the major causes

of soil erosion.

Toxic Seepage and Chemical

Contamination

Chemicals released into the environment

from industrial discharges or improperly

disposed chemicals seep into the soil

and migrate or leach.

◦ These chemicals can impact the aquifer as

well as the soil.

Salinization

• Salinization is an increase in salt (ionic compounds) in soil. Irrigation in areas where the bedrock contains high salt levels will cause these aqueous salts to be brought to the surface.–This problem is compounded by clearing native

vegetation.

– Irrigation of farmland and deforestation has in Western and South Eastern Australia has caused widespread salinization.

Desertificaion

• Desertification is the expansion of dry lands

due to poor agricultural practices, improper soil

moisture management, salinization and

erosion, forest removal, and climate change.

– Overuse of agricultural lands is the cause.

– 10% of the world’s land has been desertified.

– 25% is at risk.

– In Mali, the Sahara desert has expanded more than

650 km in less than 20 years.

Case Study: Industrialized Food

Production in the United States

Industrialized agriculture uses about 17% of all commercial energy in the U.S. and food travels an average 2,400 kilometers from farm to plate.

Figure 13-7

Traditional Agriculture: Low Input

Polyculture

Many farmers in developing countries use low-

input agriculture to grow a variety of crops on

each plot of land (interplanting) through:

◦ Polyvarietal cultivation: planting several genetic

varieties.

◦ Intercropping: two or more different crops grown

at the same time in a plot.

◦ Agroforestry: crops and trees are grown together.

◦ Polyculture: different plants are planted together.

Aquaculture

• World fish populations are plummeting– Technology and

increased demand

• Aquaculture = raising aquatic organisms for food in a controlled environment– Aquatic species are

raised in open-water pens or land-based ponds

The benefits and drawbacks of

aquaculture Benefits:

◦ A reliable protein source

◦ Sustainable

◦ Reduces fishing pressure on

overharvested wild fish stocks

◦ Energy efficient

• Drawbacks:

– Diseases can occur,

requiring expensive

antibiotics

– Reduces food security

– Large amounts of waste

– Farmed fish may escape

and introduce disease

into the wild

Pesticide Protection Laws in the

U.S.• Government regulation has banned a

number of harmful pesticides but some scientists call for strengthening pesticide laws.– The Environmental Protection Agency (EPA),

the Department of Agriculture (USDA), and the Food and Drug Administration (FDA) regulate the sales of pesticides under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).

– The EPA has only evaluated the health effects of 10% of the active ingredients of all pesticides.

Integrated Pest Management

IPM programs evaluate crops and

pests as part of the ecological system

and develop a pest control program

that includes crop management, and

biological and chemical controls.

◦ The program is intended to reduce

damage to crops to an economically

tolerable level.

Natural Controls

THE GREEN REVOLUTION AND

ITS ENVIRONMENTAL IMPACT

Lack of water, high costs for small farmers,

and physical limits to increasing crop yields

hinder expansion of the green revolution.

Since 1978 the amount of irrigated land per

person has declined due to:

◦ Depletion of underground water supplies.

◦ Inefficient irrigation methods.

◦ Salt build-up.

◦ Cost of irrigating crops.

The Second Revolution

The second Green Revolution (gene

revolution) began in the 1960’s and

has spread to developing countries.

◦ Grain crops are the focus of this

revolution.

◦ Selective breeding and genetic

engineering are used to increase yield.

What are the impacts of GM

crops?

• As GM crops expanded, scientists and

citizens became concerned

–Dangerous to human health

–Escaping transgenes could pollute ecosystems

and damage nontarget organisms

–Pests could evolve resistance

–Could ruin the integrity of native ancestral races

– Interbreed with closely related wild plants

The GM debate involves more

than science• Ethical issues plays a large role

–People don’t like “tinkering” with “natural” foods

–With increasing use, people are forced to use GM products, or go to special effort to avoid them

–Multinational corporations threaten the small farmer

–Research is funded by corporations that will profit if GM foods are approved for use

–Crops that benefit small, poor farmers are not widely commercialized

The GM industry is driven by market considerations of companies selling proprietary products

Mixing Genes

Genetic

engineering

involves splicing a

gene from one

species and

transplanting the

DNA into another

species.

Figure 13-19

Government Policies and Food

Production

Governments use three main approaches to

influence food production:

◦ Control prices to keep prices artificially low.

◦ Provide subsidies to keep farmers in business.

◦ Let the marketplace decide rather that

implementing price controls.

SOLUTIONS: SUSTAINABLE

AGRICULTURE

Three main ways to reduce hunger and

malnutrition and the harmful effects of

agriculture:

◦ Slow population growth.

◦ Sharply reduce poverty.

◦ Develop and phase in systems of more

sustainable, low input agriculture over the next

few decades.

Some more of this . . .

• Sustainable farms involve more– high yield polyculture (multiple crops)

– organic fertilizers

– biological pest controls (natural predators)

– integrated pest management

– irrigation efficiency (to reduce salinization)

– perennial crops and rotation (5-year plan)

– water efficient crops

– soil conservation

– subsidizing sustainable practices (gov’t)

And less of this . . .

• Sustainable farms involve less– soil erosion

– salinization

– aquifer depletion

– overgrazing or overfishing

– loss of biodiversity

– loss of prime cropland

– food waste

– population growth

– subsidizing unsustainable practices (gov’t)

How?

High value produce sold locally

organic produce

use earthworms to aerate soil naturally

support fungi and bacteria

plant legumes to allow bacteria to fix N2

cycle crops

use manure for fertilizer

How else?

Allow plant residue to provide

nutrients

use biological controls to limit pests

use less pesticides

less water contamination

harvest seeds for planting subsequent

years