The Nitrogen Cycle

The largest single source of nitrogen is in the atmosphere.

N2 makes up 78% of our air!

Nitrogen is NOT a greenhouse gas!

What happens to atmospheric nitrogen in the nitrogen cycle?

NAtmospheric Nitrogen (N2)

Ammonia (NH3)Nitrogen combines with Hydrogen to make Ammonia

Bacteria

(cyanobacteria in soil and water or rhizobium bacteria on the roots of plants)

Nitrates (NO3)

Nitrogen combines with Oxygen to make Nitrates

Lightning

N

Nitrogen Fixation

Nitrogen Fixation

• the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms.

• Nitrogen gets “fixed” when it is combined with oxygen or hydrogen.

• N2 + 3H2 → NH3 → (dissolves) → NH4+ (ammonia)

(ammonium)

But……

• Very few plants can use NH3 (ammonia) or NH4+ (ammonium)

• Nitrification can help

Nitrification

• Nitrifying bacteria in the ground first combine ammonia or ammonium with oxygen to form nitrites. Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use!

• NH4+→NO2-→NO3- [nitrite (toxic)] [nitrate (nutrient)]

• How do plants and animals get the nitrogen they need?

Assimilation

Assimilation

• Roots: absorb NH3, NH4+, NO3- to make DNA, amino acids, proteins

• Animals: eat plants or plant-eating animals to make DNA, amino acids, proteins

How does the nitrogen return to the atmosphere?

• 2 more steps!– Ammonification– Denitrification

• Bacteria and fungi decomposers break down amino acids from dead animals and wastes into ammonium

• Decaying organisms→NH3 → NH4+ dissolves

What happens to the NH4+?

Ammonification

Denitrification

• Denitrifying bacteria live deep in soil and in aquatic sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle!

• NH3 → NO2- → N2 and N2O (nitrous oxide)

NH4+ NO3-

Soil

Atmosphere

How are humans affecting the nitrogen cycle?

• Use of nitrogen-rich fertilizers– can cause eutrophication

• Burning fossil fuels and forests– Releases solid forms of nitrogen

• Farming– Livestock wastes release

nitrogen into soil and water

Human Population

Exponential vs. Logistical Growth Curve

Carrying Capacity

Transitions in birth and death rates

Demographic Transitions

Improvement in sanitation, diseases

Cure of chronic diseases

Population Age Structure• Three basic shapes:

Zero growth

Human Population• IMR

– Infant mortality rate – the number of infants that die before their 1st birthday

– good indicator of quality of life because it reflects the general level of nutrition and health care for a geographic region.

• CBR – Crude birth rate = number of live births per 1,000

people in a population in a given year.

• CDR – Crude death rate – number of deaths per 1,000

people in a population in a given year.

• ZPG – Zero population growth

Population Growth

• TFR– Total Fertility Rate – estimate of the average number

of children a female will have during reproductive years (15-45).

– Global TFR = 2.8 children per woman.– Developing Countries TFR = 3.1, some African

countries have a TFR of 6!– Developed Nations are steady with a TFR of 1.6– Not until Developing Nations reach a TFR of 2.1 will

world populations stabilize!• GOAL = Replacement Level Fertility (RLF)

Why Are TFR’s So High In Africa?

• No government supported family planning.• Low literacy rate among woman.• Few economic roles for woman.• Woman’s rights…are there any?• Poor health care for mothers/mothers-to-be.• AIDS rampant.• Need many children for labor.• High infant mortality due to poor quality of life.• Abortions, legal or safe?

How to Achieve Zero Population Growth

• Delay age of first child• Birth control• Education• Cultural Changes

2. Population Dynamics & Carrying CapacityPopulation size is governed by births, deaths,

immigration, and emigration:

– [Population Change] = [Births + Immigration] –[Deaths + Emigration]

Population Change = (B + I) – (D + E)

• If the number of individuals added by births & immigration are balanced by those lost by deaths & emigration then there is zero population growth

Population Growth Rate

• If Thailand’s population growth rate is was 1% in 2000, when will it’s population double?

• Use the “Rule of 70”

• 70/growth rate = doubling time• 70/1.0 = 70 years• Therefore, Thailand’s population is expected to

double in the year 2070.

Agriculture and the Environment

Industrial vs. Sustainable Farms

-Traditional subsistence agriculture- just enough food for person's family- Slash and burn- vegetation cut and burned down before being planted- higher use of chemical fertilizers and pesticides now- Salinization- repeated irrigation forces soil salts to the top- GMO's can add nutrients and vitamins to plants, increase crop yield, cause deformities if bred with native species- Monoculture- planting one crop- Plantation farming- uses monoculture cash crops

FactsFood Supply and Distribution

• Wheat and rice supply half calorie intake worldwide

• 90% grain grown in U.S is for animal feed!• Cows contribute to increase in greenhouse

gases through methane emissions

The Green Revolution

• Today’s style of agriculture began after WWII• Overcoming lands limiting factors• High yields , on smaller acreages,

mechanization, hybrids, pesticides, synthetic fertilizer

• Monocultures• Increase in fossil fuel use

Today’s agriculture

• Large corporate farms• Organic farms• Family farms• Specialty farms• Loss arable land to development• GMCs

Conservation Practices

No-till

Drip irrigation

Integrated pest management

Contour plowing

SOIL

Horizons- O horizon- surface and plant litter, lots organic matter, fungi, freshly fallen, brown or black- A horizon- topsoil, lots of organic matter, mineral material, humus, partially decomposed, darker, looser than deeper layers- B horizon- subsoil, iron, aluminum, clay , humus, zone of accumulation- C horizon- regolith, partially broken down inorganic materials, parent material

Vocabulary:Sheet erosion- thin layer taken off land surface- Rill erosion- little rivulets of running water cut small channels in soil- Gully erosion- bigger channels of water that erode- Waterlogging- soil saturated with water, kills plants from lack of oxygen- Salinization- mineral salts accumulate in soil, saline irrigation

-Soil Fertility- capacity to supply nutrients (nitrogen, phosphorus, potassium) for plant growth- Soil Porosity/Infiltration- pore spaces filled with water= saturated, otherwise it is unsaturated- Infiltration- water through soil-Permeability- ease with which water moves through a material- Corrosion- slow weathering or chemical decomposition that proceeds from surface into ground

Forestry-Deforestation- removing trees for agri. or selling as lumber- Old growth forest- never cut, growing for hundreds of years- Second growth forests- cutting has occurred, new forest grew naturally- Clear-cutting- removing all trees- Selective cutting- removing some trees

-Agroforestry- trees and crops planted together-Fires are necessary for the health of forests (surface fires, not crown or ground fires)

Succession- Primary succession- lichens grow in lifeless area- Secondary succession- grasses, existing community has been cleared with soil leftover- Pioneer species- species in first stages of primary or secondary succession- Climax community- final stage of succession

Rangelands• Overgrazing- animals eat grass faster than

it grows^ Tragedy of the Commons ^Solution: rotate animals on different fields or control herd numbersAnimal waste is source of water pollutionGrazing animals eat 70% of grain in US

Energy Problems!

• 2007 Question 2

Fishing• Capture fisheries- catch fish in wild

- By-catch- untargeted fish caught- Driftnets- nets dragged through water that catch everything- Long lining- lines with baited hooks that take lots of marine organisms- Bottom trawling- ocean floor scraped with destructive netsTragedy of the Commons (again)47-50% fish stocks fully exploited

Ecosystems/Biomes

Chaparral-50-75 cm rain, shallow infertile soil-Small trees w/ big leaves, shrubs-Western North America, Mediterranean

Deserts-Less than 25 cm rain per year, sandy soil-Lots of cacti b/c water-adapted-30 degrees north and south of equator

Tundra-Less than 25 cm rain, permafrost for soil-Small herbaceous plants-Northern parts of North America, Europe, and Russia

Grasslands-10-60 cm rain, rich soil-Many types of grasses-N. America prairies, S. African velds, Russian steppes, Argentinean pampas

Deciduous Forest-75-250 cm, high rainfall, rich soil-Hardwood trees-N. America, E. Asia, Europe, Australia

Tropical Rainforest-200-400 cm, high rainfall, poor soil-Tall trees, vines-S. America, W. Africa, Southeast Asia

Taiga (Coniferous Forest)-20-60 cm rainfall, acidic soil-Coniferous trees-Northern parts of N. America and Eurasia

AtmosphereLayer of gases covering Earth = troposphere (weather, clouds), tropopause (temp increases), stratosphere (greenhouse effect from ozone), mesosphere (meteors burn up), thermosphere (aka ionosphere, absorbs solar wind from Sun)

Climate-Weather- day to day temperature, pressure, sunlight, wind speed, humidity- Climate- constant patterns of an area over a long period of time (avg 30 yrs)- Tilt on Earth's axis causes seasons- Convection currents- vertical currents that rise from warm gases expanding and becoming less dense- Dew point- temperature water vapor condenses into liquid- Precipitation- fallen condensation (frozen or liquid)

Weather- Monsoon- hot air rises from hot land, creates low-pressure system, rising air cools and moisture falls, MASSIVE RAINFALL- Rain shadow effect- air from body of water moves inland and runs into mountain, rises and on other side, no moisture left- Hurricane- intense tropical storms (typhoon or cyclone in Pacific Ocean)

Water Pollution- Dead zone- oxygen poor water- Eutrophication- warm, nutrient-rich freshwater mixes with cold saltwater and makes plankton populations explode- Hypoxic zone- area of low oxygen Wastewater- any water used by humans

Thermal Pollution-Urban areas known as heat islands-Increased photochemical smog-Adding trees can lower temperature

Noise PollutionAny noise that causes stress or can potentially damage human health

Practice Test

• http://www.learnerator.com/ap-environmental-science?utm_source=sendy&utm_medium=sendy&utm_campaign=usercampaign