IB ESS Topic 3 Food resources new & Water Budget

Food Resources
Guru IB ESS TOPIC 3 1

• 3.5.1-Outline the issues involved in the
imbalance in global food supply

Food Resources
Human food systems:
1. Croplands
2. Rangelands
(livestock)
3. Oceanic fisheries

Unequal food resources
• The methods of food production differ
around the world
• Government policy and the climate of the
area influence what is grown
• The type used depends on relative
availability of land, labor, capital, and fossil
fuels

• There is enough food on the world to feed
us all, however there is an imbalance in the
food supply globally.
• Many people from the LEDCs are suffering
from not getting enough energy, proteins
and minerals.
• Around 3/4 of the world’s population is not
eating enough and an average of 1 million
are going hungry, the majority of these
people lives in the LEDCs.
Unequal food resources in LEDC

• Climate changes have also affected the
LEDCs as droughts for example reduce the
amount of growing land.
• Global warming could lead to countries
suffering from high temperatures which
could destroy crops.
• Agriculture in the LEDCs are in contrast
and have low levels of technology, lack of
capital and high levels of labour.

• However even though there is such a huge group
of people in need of food there is a surplus of food
in the MEDCs with markets producing to much
food for the population.
• This has lead to people in the MEDCs to consumer
more food then they need as the MEDCs increased
wealth has allowed them to buy more.
• There are import tariffs imposed by the MEDCs to
make the import of food more expensive, which
can ruin the exporting countries.
Food resources in MEDC

MEDC LEDC
•High food supplies for small
population
•Cause problem such as obesity
•Low cost of food and all seasonal-
supplies of food
•Low food supply for large
population
•Cause problem such as
malnutrition and under-
nourishment
•Struggle to produce enough food
and food price remain high
•In LEDC food production is used as
a way to generate foreign currency.

Cause in imbalance food distribution
• Cause in imbalance food distribution
-Ecological: some climate and soils are
better for food production
-Economic: advance technology and money
can overcome ecological limitation
(transportation of water)
-Socio-political: underinvestment in rural
area and rapid area in LEDC; poor human
health weaken available labor force

Production Methods of Agriculture
Developed Countries
– Industrialized agriculture depends heavily on
capital and fossil fuels
Developing Countries
– Intensive traditional agriculture depends heavily
on labor
– Shifting cultivation in tropical forests depends
heavily on land availability no fossil fuels
– Nomadic herding depends heavily on land

Industrialized agriculture
Shifting cultivation
Plantation agriculture
Nomadic herding
Intensive traditional agriculture
No agriculture

Population distribution in poverty
Region % in $1 a day
poverty
Population
(millions)
Pop. in $1 a day
poverty (millions)
East Asia and Pacific 9.07 1,885.0 170.0
Latin America and the Caribbean 8.63 549.0 47.0
South Asia 31.08 1,470.0 456.0
Sub-Saharan Africa 41.09 753.0 309.0
Total Developing countries 982.0
Europe and Central Asia 0.95 460.0 1.0
Middle East and North Africa 1.47 306.0 4.0
Total 987

Influence of Ecology
• Developed countries in temperate areas –
plants and soils conducive to growth of high
yield cereal crops and livestock
• Soil fertility poor in tropical areas
• Livestock native to temperate areas in most
cases as well

Influence of Socio-political factors
• Poverty is a self sustaining positive feedback
process
• Governments in LDCs focus on exploitation of
resources – Bananas in Costa Rica
• Support use of high yield green revolution crops
• Research on and use of GMOs

Poverty Malnutrition
Decreased
resistance
to disease
High death
rate for
children
Decreased
energy
Decreased
ability
to learn
Decreased
ability
to work
Shortened
life
expectancy
Feedback loop

Food Type Kilocalories of fossil fuel input per kilocalorie of protein output
Feed lot beef 20-78
Pigs
Broiler chicken
Rangeland Beef
Sheep
Vegetables
35
22
10
10
2-4

First green revolution
(developed countries)
Second green revolution
(developing countries)
Major international agricultural
research centers and seed banks

DO NOT POST TO INTERNET

Distribution of food
• Enough food produced in the world for entire
population to have 2,720 kcal per day
• Many areas no land to grow food or money to
purchase it
• 982 million people living in poverty – actually a
decrease in 20% from 1990’s
• ¼ of the world population consumes ¾ of the
food

Industrialized agriculture
in developed countries
Intensive traditional agriculture
in developing countries
Land
Labor
Capital
Fossil fuel
energy
Land
Labor
Capital
Fossil fuel energy

Shifting cultivation in tropical
forests in developing countries
Nomadic herding in
developing countries
Land
Labor
Capital
Land
Labor
Capital

Crop
Cross breeding
Desired trait
(color)
Apple
Pear
Offspring
Cross
breeding
Best results
New
offspring
Desired
result
Selective breeding
We used to breed
species for desired
traits
Takes multiple
generations
Now we just change
the genes and create
GMOs

Phase 1
Make Modified Gene
Identify and extract
gene with desired trait
Identify and remove
portion of DNA
with desired trait
Remove plasmid
from DNA of E. coli
Insert extracted DNA
(step 2) into plasmid
(step3)
Insert modified
plasmid into E. coli
Grow in tissue
culture to
make copies
cell
gene
DNA
Plasmid
E. coli
DNA
Genetically
modified
plasmid
plasmid

Phase 2
Make Transgenic Cell
Transfer plasmid
copies to a carrier
agrobacterium
Agrobacterium
inserts foreign
DNA into plant
cell to yield
transgenic cell
Transfer plasmid
to surface
microscopic metal
particle
Use gene gun
to inject DNA
into plant cell
A. tumefaciens
(agrobacterium)
Plant cell
Nucleus
Host DNA
Foreign DNA

Phase 3
Grow Genetically Engineered Plant
Transgenic cell
from Phase 2
Cell division of
transgenic cells
Culture cells
to form plantlets
Transgenic plants
with new traits

Projected
Advantages
Projected
Disadvantages
Need less fertilizer
Need less water
More resistant to
insects, plant
disease, frost, and
drought
Faster growth
Can grow in slightly
salty soils
Less spoilage
Better flavor
Less use of con-
ventional pesticides
Tolerate higher
levels of herbicide
use
Irreversible and
unpredictable
genetic and eco-
logical effects
Harmful toxins in
food from possible
plant cell mutations
New allergens
in food
Lower nutrition
Increased evolution
of pesticide-
resistant insects
and plant diseases
Creation of herbicide-
resistant weeds
Harm beneficial
insects
Lower genetic
diversity
Use of
GMOs

2,000
1,500
1,000
500
0
Grain
production
(millions
of
tons)
1950 1960 1970 1980 1990 2000 2010
Total World Grain Production
Year
Global Trend in Food Production

400
350
300
250
150
Per
capita
grain
production
(kilograms
per
person)
1950 1960 1970 1980 1990 2000 2010
World Grain Production per Capita
200
Year
But… what does this show?

In use
Not usable
Arid land
6%
Tropical
forest
8%
Cultivated
10%
Grazed
11%
Forests,
arid
lands
14%
51%
Ice, snow, deserts
mountains
© 2004 Brooks/Cole – Thomson Learning

Compare and contrast the efficiency of
terrestrial and aquatic food production
systems.

• Terrestrial systems:
• Most food is harvested from low trophic
levels (producers and herbivores).
• Systems that produce crops are more
energy efficient then those which produce
livestock.
• This is because energy is greater in
proportion in the low trophic levels.

• Even though it is efficient to use arable
systems, many cultures still use livestock as
part of their farming system.
• Taste and cultural demand play a major role
in this and the animals also provide a source
protein which is essential for the human
diet.
• Animals are also used as working animals in
some cultures.

• Terrestrial farming systems are divided into several types:
• Commercial farming & Subsistence farmer:
• Both commercial and subsistence can be intensive or
extensive farms.
• Intensive farms: take a small area of land but aim for a high
input
• Extensive farms: are large in comparison to the money and
labour put into it
• The efficiency of the system can be calculated by
comparing outputs to inputs per unit area of land.

Terrestrial vs. Aquatic Differences
Terrestrial
• Most food at low trophic
levels
• Producers or Herbivores
• Less energy loss between
initial input and level of
harvest
Aquatic
• Most food harvested at higher
trophic levels
• Makes total energy storages
smaller
• Due to tastes for fish /
particularly large predatory
ones
• Energy conversion in this
system is more efficient – sizes
and lack of structural material in
low trophic levels
• Initial amount of sunlight fixed
is less efficient because of
reflection and absorbtion by
water

Terrestrial Aquatic
-Consume from lower trophic
level e.g. cow/rice due to taste
and cultural demand
-Consume from higher trophic
level e.g. salmon due to taste
and cultural demand
-Less efficiency -higher efficiency however the
initial of available solar energy
is slower due to reflection and
absorption of light by water

• 3.5.3 Compare and contrast the inputs and outputs of
materials and energy (energy efficiency), the system
characteristics, and evaluate the relative environmental
impacts for two named food production systems.

Systems of Production
1. Croplands
- grains, 76% of worlds food
2. Rangelands
- grazing meat production, 17% worlds food
3. Oceanic fisheries
- 7% world food
Growth in production b/c technology
Challenge  providing for future population

Food Production Systems
• There are many food production systems around
the world
• They vary depending on the geography,
sociopolitical dimensions, culture, needs of the
area
• They also vary based on the characteristics of the
food being produced
• We will look at a comparison of two of these many
systems
• Many areas of the world are dependent on
fisheries for foodGuru IB ESS TOPIC 3 47

100
80
60
40
20
0
1950 1960 1970 1980 1990
2000
Year
Total World Fish Catch
Catch
(millions
of
metric
tons)

25
20
15
10
5
0
1950 1960 1970 1980 1990 2000
Year
World Fish Catch per Person
Per
capita
catch
(kilograms
per
person)

800
600
400
200
0
1960 1970 1980 1990 2000
Year
80
70
60
50
40
30
20
Harvest
(thousands
of
metric
tons)
Abundance
(kilograms/tow)
Abundance
Harvest

Demersal
(mostly bottom dwelling)
Hake
Haddock
Cod
Pelagic
(surface dwelling)
Crustaceans Mollusks
Sardine Anchovy
Herring
Mackerel
Tuna
Krill
Shrimp
Lobster
Crab
Oyster Clam
Octopus
Squid
Fish Shellfish
Major Targets of Marine Fisheries worldwide

Spotter airplane
Fish farming
in cage
Trawler
fishing
Purse-seine
fishing
sonar
trawl flap
trawl
lines
trawl bag
Long line fishing
lines with
hooks
Drift-net fishing
Fish caught
by gills
float buoy
fish school

Now we farm fish
• Fish is a major component of the human
diet
• Some countries almost exclusively based on
seafood – Japan
• With wild stocks being increasingly
depleted, we are turning to fish farming for
various reasons as an alternative

Figur
e 13-
31
Seafood type Kilocalories of fossil fuel input per kilocalorie of protein output
Marine Fisheries
Shrimp
Salmon
Cod
Ocean Aquaculture
Salmon cage
culture
Salmon ranching
Seaweed
3-98
18-52
20
50
7-12
1

Advantages
Highly efficient
High yield in small
volume of water
Increased yields
through
crossbreeding
and genetic
engineering
Can reduce
overharvesting
of conventional
fisheries
Little use of fuel
Profit not tired to
price of oil
High profits
Disadvantages
Large inputs of
land, feed, and
water needed
Produces large
and concentrated
outputs of waste
Destroys
mangrove forests
Increased grain
production
needed to feed
some species
Fish can be killed
by pesticide runoff
from nearby
cropland
Dense populations
vulnerable to
disease
Tanks too
contaminated to
use after about
5 years

• Terrestrial Systems:
• Example :Intensive Charolais beef
production in France:
• In Western Europe the Charolais beef is one of the beef
brands chosen.
• Through selective breeding and genetic engineering
bloodlines that puts weight on exist but has a low fat cover.
• Charolais lives under controlled conditions, they are fed
with high proteins and treated with antibiotics to make
sure they are healthy.
• Lots of energy is used in transporting and processing the
finished meat.

• Inputs:
• energy for food distribution
• food supplements
• selective breeding and genetic engineering
(system characteristics)
• indoor rearing
• fertilizers to maximize grass production
• antibiotics and hormones

• Outputs:
• cheap meat (socio-cultural)
• habitat destruction to make bigger fields
(environmental impact)
• antibiotic resistance
• Eutrophication

Nomadic cattle grazing of the Himba:
• The Himba people are from North West Namibia,
they survive by being Nomadic hunters/grazers.
• They also have a tight bond with the cattle they
graze.
• During the dry seasons the Himba move their
cattle from area to area until the grass is used up
until the raining season, they go to better pastures.
• Cattle to the Himba are very important as they
provide; meat, milk, skins and even dung for fires.

• Prestige between the Himba is seen by how
many cattle they have, not the size of the
cattle.
• The cattle during the dry season may start
competing with herbivores.
• This has increased especially with global
warming drought periods.
• This can lead to soil erosion as extra grazing
pressure removes the grasses that hold the
top soil together.

• Input:
• nomadic grazing moving from place to place so
land has a chance to recover
• cattle survive on low grade natural forage with no
supplements
• during drought cattle die as grass disappears
adding patches of nutrients to the soil

• Outputs:
• Himba cattle provide meat, milk and fuel
(dung)
• owning cattle gives status in community
(socio-cultural)
• during drought times Himba cattle compete
with wild grazers for food this can lead to
soil erosion as well as food shortage

System 1: Rice-Fish Farming - China

System 1: Rice-Fish Farming - China
• Fish farming in wet rice fields
• In China, Han Dynasty plate (2000 years old) shows fish
swimming from pond to field
• Ecological symbiosis in the system – fish provides
fertilizer to rice, regulates micro-climatic conditions,
softens the soil, disturbs the water, and eats larvae and
weeds in the flooded fields; rice provides shade and
food for fish.
• Provides balanced food, reduced costs and labor, less
use of chemicals in the environment

www.fao.org/DOCREP/005/Y1187E/y1187e18.htm

• Inputs –requires input of small amounts of
urea, N,P,K and optional lime or manure
• System Characteristics – uses native fish,
polyculture using natural principles of
ecosystem interaction, sustainable

• Socio-cultural - tenant farmers improve income, in
china industrialization threatens its continued use
• Environmental Impacts – may use pesticides but
generally less than alternatives, reducing CH4
emissions compared to normal systems
• Outputs – fish and rice, 2 seasonal rice crops per
year

Norwegian Salmon Farms
• Norway and Chile produce 2/3 of the
world’s farmed salmon
• 60% of world’s salmon is farmed
• High input system of penned fish in ocean
areas or on land – depends on pellet food
derived from wild caught fish
• High density high waste systems

Norwegian Salmon farms
• Inputs – need pellets for feed made from
fishing for smaller fish in the ocean,
• System characteristics – monoculture –
disease susceptible so antibiotics used,
may selectively breed stocks, human
manipulated
• Socio-cultural – farming operations
provide local jobs, if effecting local
fisheries that effects jobs as well

• Environmental Impacts – 100,000’s
escape cultivation & threaten native fish,
farmed fish less effective reproducers than
natural but their offspring are more
successful
• Outputs – antibiotics, nutrients causing
eutrophication,

Fish change form
Fish enter rivers
and head for
spawning areas
Grow to smolt
and enter the ocean...
Grow to maturity
in Pacific Ocean
in 1-2 years
Eggs and young are
cared for in the hatchery
Fry hatch in the spring...
Fingerlings migrate downstream
In the fall spawning salmon
deposit eggs in gravel nests and die
Normal
Life
Cycle
Fingerlings
are released into river
And grow in the stream
for 1-2 years
Human capture
Salmon
processing
plant
Eggs are taken from adult
females and fertilized with
sperm “milked” from males
Modified
Life
Cycle
To hatchery

3.5.4: Discuss the links that exist
between social systems and food
production systems.

• Shifting Cultivation
• Extensive subsistence farming
• Agribusiness

• Shifting cultivation is an agricultural system
in which plots of land are cultivated
temporarily, then abandoned.
• This system often involves clearing of a piece
of land followed by several years of wood
harvesting or farming, until the soil loses
fertility.
What is Shifting Cultivation?

Extensive Subsistence Agriculture?
• Farmers who grow enough food for their
own use is the definition to extensive
subsistence agriculture.
• These farmers will grow many types of
crops and have different types of animals to
sustain their family need for food until the
next year planting season.

What is agribusiness?
• In agriculture, agribusiness is the business
of agricultural production.
• It includes crop production (farming and
contract farming), seed supply,
agrichemicals, breeding, farm machinery,
distribution, processing, marketing, and
retail sales.

Comparison of 3 system

Shifting Cultivation Extensive subsistence
farming
Agribusiness
-Slash and burn and its
widely used by those who
cannot afford other
methods of land clearance.
-Fertilizers in the soil will
last for a while and people
are force to move after it.
-Low population allows it
and affected by cultural
beliefs e.g. choice of site for
land clearance
-High demand for food due
to high population which in
turn allow for high labor
inputs and it require low
technology
-High rainfall and warm
temperatures support it
-Intensive subsistence
farming
-After WWII concern of
self-sufficiency raise and
smaller farms were
combined to create large
area of the same crops.
-Intensive farming to
produce food for
commercial use.
-Maxim productivity and
profit to compete in a
global market.
-High impacts on the
environment

Food Production Systems are
linked to social systems
• Modern US
– Developed, high tech, high fossil fuel input
– Value speed and convenience
– Capitalism based revenue generation
– Removed from food production so don’t see
negative results
– We are willing to compromise environmental
health for the benefits now from pesticides,
inorganic fertilizers, machine harvest etc.

Cropland
Irrigated farm land
Rangeland
Pasture
Forest
Barren land
Wetland
Urban area

4% 2% 6% 5%
17% of total
commercial
energy use
Crops Livestock Food processing Food distribution and preparation
Food production

Think back to the rice-fish
system
• Tied to asian cultures as a historical
practice
• But asian culture is changing  more
cosmopolitan  more movement to cities
• Could threaten this model system
• It is a form that keeps soil fertility high in
areas with high population density this can
be used on the outskirts to maximize
production per area.

Can the green movement
• Swing our culture to sustainable food
production?
• People interested in organic foods
• Green production – boutique types of
grocers and restaurants
• Benefits the planet and trendy

Increase
High-yield
polyculture
Organic fertilizers
Biological pest
control
Integrated pest
management
Irrigation efficiency
Perennial crops
Crop rotation
Use of more water-
efficient crops
Soil conservation
Subsidies for
more sustainable
farming and
fishing
Decrease
Soil erosion
Soil salinization
Aquifer depletion
Overgrazing
Overfishing
Loss of
biodiversity
Loss of prime
cropland
Food waste
Subsidies for
unsustainable
farming and
fishing
Population growth
Poverty

Croplands
• Help maintain water
flow and soil infiltration
• Provide partial erosion
protection
• Can build soil organic
matter
• Store atmospheric
carbon
• Provide wildlife habitat
for some species
Ecological Services Economic Services
• Food crops
• Fiber crops
• Crop genetic
resources
• Jobs
© 2004 Brooks/Cole – Thomson Learning
Done the right way
Cropland can be
very beneficial

And don’t forget the global
trend in food production…

1950 1970 1990 2010 2030 2050
Year
0.20
0.25
0.15
0.10
0.05
Grain
area
per
person
(hectares)

• http://www.fao.org/nr/giahs/pilot-systems
• Food and agriculture organization of the
UN

• 3.6 Water resources
• 3 hours

Our Water Supply
(Water Budget)

Water Cycle
water cycle the continuous movement of water
between the atmosphere, the land, and the
oceans
• More than 2/3 of Earth’s surface is covered with
water.
• In the atmosphere, water occurs as an invisible
gas. This gas is called water vapor. Liquid water
also exists in the atmosphere as small particles
in clouds and fog.
• Earth’s water is constantly changing from one
form to another.

Earth’s Water Supply

Water Cycle
evapotranspiration the total loss of water from an
area, which equals the sum of the water lost by
evaporation from the soil and other surfaces and
the water lost by transpiration from organisms
• Each year, about 500,000 km3 of water
evaporates into the atmosphere. About 86% of
this water evaporates from the ocean.
• Water vapor also enters the air by transpiration,
the process by which plants and animals release
water vapor into the atmosphere.

Water Cycle
condensation the change of state from a
gas to a liquid
• When water vapor rises in the
atmosphere, it expands and cools.
• As the vapor becomes cooler; some of it
condenses, or changes into tiny liquid
water droplets, and forms clouds.

Water Cycle
precipitation any form of water that falls to Earth’s
surface from the clouds; includes rain, snow,
sleet, and hail
• About 75% of all precipitation falls on Earth’s
oceans. The rest falls on land and becomes
runoff or groundwater.
• Eventually, all of this water returns to the
atmosphere by evapotranspiration, condenses,
and falls back to Earth’s surface to begin the
cycle again.

Water Cycle

Water Budget
• In Earth’s water budget, precipitation is the
income. Evapotranspiration and runoff are the
expenses.
• The water budget of Earth as a whole is
balanced because the amount of precipitation is
equal to the amount of evapotranspiration and
runoff.
• However, the water budget of a particular area,
called the local water budget, is usually not
balanced.

Water Budget
Factors That Affect the Water Budget
• Factors that affect the local water budget
include temperature, vegetation, wind, and
the amount and duration of rainfall.
• The factors that affect the local water
budget vary geographically.
• The local water budget also changes with
the seasons in most areas of Earth.

Water Budget
Water Use
• On average, each person in the United States
uses about 20,890 gal of water each year.
• As the population of the United States increases,
so does the demand for water.
• About 90% of the water used by cities and
industry is returned to rivers or to the oceans as
wastewater.
• Some of this wastewater contains harmful
materials, such as toxic chemicals and metals.

Water Budget
Conservation of Water
• Scientists have identified two ways to ensure
that enough fresh water is available today and in
the future.
• One way is through conservation, or the wise
use of water resources.
• A second way to protect the water supply is to
find alternative methods of obtaining fresh water.

Water Budget
Conservation of Water, continued
desalination a process of removing salt from
ocean water
• Desalination is expensive and is impractical for
supplying water to large populations.
• Currently, the best way of maintaining an
adequate supply of fresh water is the wise use
and conservation of the fresh water that is now
available.

Conservation
• Voluntary conservation costs nothing – in
fact, it can save money
• Some conservation methods can be
enforced by law
– Florida has water restrictions
– Congress limited the water used by toilets
– These methods cost money to implement and
enforce

Household Water Usage

Conservation
• A front-loading washer uses 10-15 gal per
load, while a top-loading washer uses
about 40 gal per load.

Conservation
• Xeriscaping landscaping that does not
require artificial watering
Bad
Good

Bad
Florida Yards and
Neighborhoods Program
Good

Stormwater Runoff
Porous surfaces
allow water to
soak into the
ground; solid
surfaces, such
as concrete
cause more
evaporation and
can push
pollutants into
river systems

The end…

Florida
Aquarium
Experimental
Parking Lot

River Systems
tributaries streams that flows into a lake or into a
larger stream
watershed (AKA basin) the area of land that is
drained by a river system
• A river system is made up of a main stream and
tributaries.
• The ridges or elevated regions that separate
watersheds are called divides.

Continental Divides

Mississippi River Basin

Peace River
Watershed

River Systems
• The relatively narrow depression that a stream
follows as it flows downhill is called its channel.
• The edges of a stream channel that are above
water level are called the stream’s banks.
• The part of the stream channel that is below the
water level is called the stream’s bed.
• A stream channel gradually becomes wider and
deeper as it erodes its banks and bed.

River Systems
• River systems change continuously
because of erosion.
• In the process of headward erosion,
channels lengthen and branch out at their
upper ends, where run off enters the
streams.

River Systems
stream load the materials other than the
water that are carried by a stream
• A stream transports soil, loose rock
fragments, and dissolved mineral as it
flows downhill.
• Stream load takes three forms: suspended
load, bed load, and dissolved load.

Stream Load

River Systems
Stream Load, continued
• The suspended load consists of particles of fine sand
and silt. The velocity, or rate of downstream travel, of the
water keeps these particles suspended, so they do not
sink to the stream bed.
• The bed load is made up of larger, coarser materials,
such as coarse sand, gravel, and pebbles. This material
moves by sliding and jumping along the bed.
• The dissolved load is mineral matter transported in
liquid solution.

River Systems
Stream discharge the volume of water that flows
within a given time, expressed in m3 or ft/sec
• The faster a stream flows, the higher its
discharge and the greater the load that the
stream can carry.
• A stream’s velocity also affects how the stream
cuts down and widens its channel. Swift streams
erode their channels more quickly than slow-
moving streams do.

River Systems

River Systems
Stream gradient the change in elevation over a
given distance
• Near the headwaters, or the beginning of a
stream, the gradient generally is steep. This
area of the stream has a high velocity, which
causes rapid channel erosion.
• As the stream nears its mouth, where the
stream enters a larger body of water, its gradient
often becomes flatter.

Gradient

River Systems

Evolution of Channels
meander one of the bends, twists, or curves in a
low-gradient stream or river
• When a river rounds a bend, the velocity of the
water on the outside of the curve increase.
However, on the inside of the curve, the velocity
of the water decreases. (ex. marching band)
• This decrease in velocity leads to the formation
of a bar of deposited sediment, such as sand or
gravel.

Stream Flow

Meandering Channels, continued
• As this process continues, the curve
enlarges while further erosion takes place
on the opposite bank, where the water is
moving more quickly.
• Meanders can become so curved that they
almost form a loop, separated by only a
narrow neck of land.

Horseshoe
Bend
of the Colorado River
near Page, AZ

Braided stream a stream or river that is
composed of multiple channels that divide and
rejoin around sediment bars
• Braided streams are a direct result of large
sediment load, particularly when a high
percentage of the load is composed of coarse
sand and gravel.
• Although braided streams look very different
from meandering streams, they can cause just
as much erosion.

Braided Stream

Deltas and Alluvial Fans
delta a fan-shaped mass of rock material
deposited at the mouth of a stream; for example,
deltas form where streams flow into the ocean at
the edge of a continent
• A stream may deposit sediment on land or in
water.
• The exact shape and size of a delta are
determined by waves, tides, offshore depths,
and the sediment load of the stream.

Deltas and Alluvial Fans
alluvial fan a fan-shaped mass of rock material deposited
by a stream when the slope of the land decreases
sharply; for example, alluvial fans form when streams
flow from mountains to flat land
• When a stream descends a steep slope and reaches a
flat plain, the speed of the stream suddenly decreases.
As a result, the stream deposits some of its load on the
level plain at the base of the slope.
• Alluvial fans differ from deltas in that alluvial fans form on
land instead of being deposited in water.

Floodplains
floodplain an area along a river that forms
from sediments deposited when the river
overflows its banks
• The volume of water in nearly all streams
varies depending on the amount of rainfall
and snowmelt in the watershed.

Floodplains

Floodplains
Natural Levees
• When a stream overflows its banks and spreads
out over the floodplain, the stream loses velocity
and deposits its coarser sediment load along the
banks of the channel.
• The accumulation of these deposits along the
banks eventually produces raised banks, called
natural levees.

Natural Levees

Human Activity
• Human activity can contribute to the size and
number of floods in many areas.
• Vegetation, such as trees and grass, protects
the ground surface from erosion by taking in
much of the water that would otherwise run off.
• Logging and the clearing of land for agriculture
or housing development can increase the
volume and speed of runoff, which leads to more
frequent flooding.

Human Activity
• Indirect methods of flood control include forest
and soil conservation measures that prevent
excess runoff during periods of heavy rainfall.
• More-direct methods include the building of
artificial structures that redirect the flow of water.
• The most common method of direct flood control
is the building of dams. Another direct method of
flood control is the building of artificial levees.

New Orleans
Levees

Life Cycle of Lakes
• Most lakes are relatively short lived in geologic
terms.
• Many lakes eventually disappear because too
much of their water drains away or evaporates.
• Lake basins may also disappear if they fill with
sediments. Streams that feed a lake deposit
sediments in the lake. The lake basin may
eventually become dry land.

World Watershed Sediment
Yield

Kermit says being green is cool.
So conserve your water.

IB ESS Topic 3 Food resources new & Water Budget

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