ECOLOGY

TROPHIC CATEGORIES

Producers– organic vs. inorganic– autotrophs vs. heterotrophs

Consumers– predators– parasites– pathogens

Detritus Feeders and Decomposers

climate: description of the average temperature and precipitation (weather) that may be expected on each day throughout the year

patterns…– latitude– elevation

A given climate will support only those species that find the temperature and precipitation levels within their ranges of tolerance. A species will be excluded from a

region where any condition is beyond its limit of tolerance.

Ex. temperature limits forests when it becomes low enough to cause permafrost (permanently frozen subsoil)

microclimate A specific site with temperature

and moisture conditions that are significantly different from the overall, or average, climate of the region.

Ex. south-facing slope in the northern hemisphere

four spheres biosphere: layer of Earth

occupied by living things lithosphere: Earth’s crust, made

up of rocks and minerals hydrosphere: water; in oceans,

rivers, ice, groundwater atmosphere: thin layer of gases

separating Earth from space

key elements of life (C,H,N,O,P,S) carbon hydrogen nitrogen oxygen phosphorus sulfur

PHOTOSYNTHESIS reactants: light + 6CO2 + 12H2O products: C6H12O6 + 6O2 +

6H2O enzymes: promote synthesis or

breaking of chemical bonds (biological catalysts)

CELL RESPIRATION reactants: C6H12O6 + 6O2 +

6H2O products: 6CO2 + 12H2O +

energy

PRIMARY PRODUCTION– in most ecosystems, sunlight (solar

energy) is the initial source of energy absorbed by producers through the process of photosynthesis(exception: chemosynthetic bacteria)

– only about 2% of light is captured– other 98% is absorbed by

atmosphere, oceans, and land, thus heating them in the process

influences on primary productivity area light temperature water nutrients

each successive trophic level captures only a fraction of the energy that entered the previous trophic level

transfer efficiency averages 10%

(~90% loss of energy between trophic levels)

losses are critical at higher trophic levels, which explains why there are few top carnivores in ecosystems

PHOSPHORUS CYCLE– main reservoir = lithosphere– acts as limiting factor in many ecosystems– impact of fertilizer eutrophication

NITROGEN CYCLE– main reservoir = atmosphere– acts as limiting factor in many ecosystems

– plants take up nitrogen (Nr…reactive nitrogen) as ammonium ions (NH4

+) or nitrate ions (NO3-)

• incorporate nitrogen into essential organic compounds such as proteins and nucleic acids

– nitrogen is passed along food chain from producers to herbivores to carnivores

• released at points along the way as ammonium compounds

• nitrifying bacteria oxidize the ammonium to nitrate in a process that provides energy for the bacteria

NITROGEN CYCLE– nitrogen fixation

• process using nonreactive nitrogen carried out by many bacteria and cyanobacteria

• on land, Rhizobium is the most important genus– lives in the root nodules of legumes (beans, peas)– example of mutualism—legume provides food

(simple sugars) and a place to live while Rhizobium provides nitrogen

– every ecosystem has a representative legume (Ex. clover in grasslands)

• also done in 3 other ways– (1) N2 NH4 by lightning– (2) industrial fixation (fertilizer) NOx– (3) combustion of fossil fuels (N is oxidized) NOx

NITROGEN CYCLE– denitrification

• microbial process that occurs in soils depleted of oxygen

• microbes take nitrate (NO3) which is highly oxidized and use it as a substitute for oxygen

• during process, N is reduced to nitrogen gas and released to atmosphere

• farmers work to avoid process by plowing as early as possible in the spring to restore oxygen to the soil

– human impacts• use of N-rich fertilizers• burning of fossil fuels

POPULATION GROWTH– equilibrium = births and deaths are more

or less equal over time– exponential growth = increasing

population under favorable conditions (minimal limits on resources, predators, etc.); results in J-curve

• usually occurs when there are unusual disturbances

• increases are usually temporary

biotic potential = ability of populations to increase (# of offspring that a species may produce under ideal conditions)– to have an effect on the size of future generations,

young must survive and reproduce– recruitment = survival through early growth

stages to become part of breeding population reproductive strategies

– produce massive numbers of offspring– low reproductive rate with high parental care

carrying capacity

upper limit to population size of a particular organism that an ecosystem can support

whether a population grows, remains stable, or decreases depends on interactions between its biotic potential and environmental resistance

density-dependent factors:

density-independent factors:

predator-prey dynamics

Ex. Isle Royale (moose and wolves)– predation: + / -– density-dependent– other factors may influence the observed

fluctuations in population density• vegetation shortage• vulnerability to parasites and disease

– density-independent factors may also play a role (Ex. weather)

parasites

parasitism: + / -– Ex. tapeworm

density-dependent parasite can work in conjunction with a

predator to control an herbivore population relationships between a prey population and

several natural enemies (predators and parasites) is generally very stable– different enemies come into play at different prey

densities

plant-herbivore dynamics

herbivory (predation on plants): + / - overgrazing

– Ex. reindeer on St. Matthew Island– in ~20 years, herd grew from 19 to 6000– lichens were overgrazed and replaced by

unpalatable grasses and sedges– consequences of overgrazing are not only related

to herbivores predator removal

– upsets plant-herbivore relationships

keystone species

Ex. sea star, Pisaster ochraceus– feeds on mussels– allows barnacles, limpets, anemones, and

others to colonize keystone species = plays crucial role

in maintaining ecosystem structure (originates from architectural term)

KEYSTONE

competition: - / - form of bottom-up regulation

(occurs only when resource is in limited supply) interspecific intraspecific

– territoriality = individuals or groups defending a territory against the encroachment of others of the same species

• restricts breeding to individuals capable of claiming and defending territory

– self-thinning– can lead to short-term density-dependent regulation of

population, but also long-term improvements thanks to natural selection

competition

interspecific– plants

• landscapes are far from uniform as a result of microclimates

• specific abiotic conditions of moisture, temperature, and light differ between locations

• Ex. tree species• single species generally does not use all available

resources• Ex. grassland plants• epiphytes

competition

interspecific– animals

• competitive exclusion

competition

interspecific– animals

• resource partitioning

introduced species

rabbits American chestnut pests plants

adaptation through natural selection– selective pressures = environmental resistance

factors (predators, parasites, drought, etc.)– natural selection = constant selection and

consequent modification of a species’ gene pool toward features that enhance survival and reproduction

evolution = modification of the gene pool of a species by natural selection over the course of many generations

adaptations to the environment

under selective pressures exerted by the factors of environmental resistance, the gene pool of each population is continually tested

fitness = measure of traits that adapt an organism for survival and reproduction

adaptations to the environment

coping with climate and other abiotic factors obtaining food and water (animals) or nutrients,

energy, and water (plants) escaping from or protecting against predators resistance to disease or parasites finding or attracting mates (animals) or

pollinating (plants) migrating (animals) or dispersing seeds

(plants)

4.4 Ecosystem Responses to Disturbance

ecological succession = transition from one biotic community to another– occurs because the physical environment may be

gradually modified by the growth of the biotic community

– may cause the area to become more favorable for another group of species

– pioneer species are the first to colonize an opening

– final stage is a climax ecosystem

succession

primary succession = occurs in area that has not been previously occupied– species gradually prepare soil– bacteria lichens, mosses grasses shrubstrees

– Ex. bare rock after glacial recedes– Ex. volcanic island

secondary succession = occurs as a result of the disturbance of an ecosystem– starts with existing soil– Ex. fire– Ex. tornado– Ex. abandoned farm field

BIODIVERSITY

Chapter 10: Wild Species and Biodiversity

biological wealth– about 2 million species identified

– likely between 5 and 30 million

– comprised of species and ecosystems; sustains human life and economic activity with goods and services

Two kinds of value

1. instrumental value– existence or use benefits some other entity– anthropocentric

2. intrinsic value– value for its own sake– philosophical question based on moral

reasoning

general values of natural species

value as sources for agriculture, forestry, and animal husbandry

value as sources of medicine recreational, aesthetic, and scientific

value intrinsic value

medicine

Ex. rosy periwinkle on Madagascar– vincristine = leukemia treatment– vinblastine = Hodgkin’s treatment

Ex. Chinese star anise shikimic acid– raw material for Tamiflu

Ex. Pacific yew taxol– treatment for breast and ovarian cancers

protecting endangered species

Lacey Act (1900)– forbid interstate commerce in illegally killed wildlife– U.S. FWS can bring federal charges against individuals

violating wildlife laws– Ex. airline passenger from Ivory Coast with 500

pounds of bush meat– Ex. civil charges against men accused of killing first

wolf seen in Nebraska in 93 years– Ex. men in Alaska prosecuted for killing 16 black bears

for their gall bladders– Ex. FWS agent purchased leopard skin and frozen

stillborn cub on eBay, which led to prosecution

protecting endangered species

Endangered Species Act (1973, 1988)– endangered = in imminent danger of

becoming extinct if no protection is provided– threatened = in jeopardy, but not yet on the

brink of extinction– administered by FWS for terrestrial and

freshwater species– administered by National Oceanic and

Atmospheric Association (NOAA) for marine species

protecting endangered species

provisions of the Endangered Species Act– substantial fines for killing, trapping, uprooting

(plants), modifying the habitat of, or engaging in the commerce of listed species

– appropriate agency lists species with best available information (regardless of economic impact)

– critical habitat where species is found and where it is likely to spread must be designated

– agencies are required to develop recovery plans

over time, natural selection leads to speciation and extinction

over geological time, the net balance of these processes leads to an increase in biodiversity

~2 million species described examples of groups rich in species:

– insects (950 000 species)– flowering plants (250 000 species)

reasons for decline

current threats to biodiversity:– habitat change– introduced alien species– exploitation

disease, pollution, and climate change play lesser roles but could become more prominent in the future

species losses will be greatest in the developing world

habitat change

by far the greatest source of species loss natural species are adapted to specific

habitats; if the habitat changes or is eliminated, the species go with it

conversion– areas are convert to farms, subdivisions, malls, and

industrial centers– Ex. decrease in song bird population related to loss

of winter forest habitat in Central and South America, along with the fragmentation of summer forest habitat in North America

habitat change fragmentation

– human-dominated landscapes consist of a mosaic of different land uses, resulting in small, often geometrically configured, patches that frequently contrast with neighboring patches

– increases “edge” habitats simplification

– Ex. removing fallen logs for firewood, planting managed forests for a single species of tree, channeling streams and rivers

intrusion– Ex. telecommunication towers

exotic species

often decrease biodiversity of regions– ex. brown tree snake has eliminated 9 of 12

native bird species on Guam (introduced as stowaway on ships during WW II)

introduced species may drive out native species by competing with them for resources– ex. Brazilian pepper in Florida

overexploitation

often results from poor management– forests can be overcut for lumber, grasslands

overgrazed, game species overhunted, and croplands overcultivated

– overuse can set off further damage resulting from erosion and desertification

trafficking in wildlife and products from natural species– ex. tropical hardwoods, furs, traditional

medicines from animal parts

pollution

ex. nutrients from America’s heartland have runoff into the Mississippi River, creating a 6000 square mile dead zone in the Gulf of Mexico where oxygen is absent 20 meters below the surface in the summer

other examples: oil spills, DDT, human wastes

IUCN– World Conservation Union (formerly

International Union for the Conservation of Nature) maintains “Red List of Threatened Species”

– uses set of criteria to evaluate the risk of extinction for thousands of species around the world

– IUCN is not actively involved in preserving species, but its findings are often the basis for conservation work

international developments CITES

– Convention on Trade in Endangered Species of Wild Flora and Fauna was established in the early 1970s

– international agreement signed by 169 nations that focuses on trade in wildlife and wildlife parts

– best known act of CITES was the ban on the international trade of elephant ivory in 1990 (the African elephant has declined from 2.5 million animals in 1950 to about 600 000 today)

international developments

CITES (cont.)– in recent years, some countries have

requested a limited elephant harvest and ivory sale

– each time, the poaching of elephants has resumed

– monitoring has increased, but 4000 elephants are still killed each year

– ivory ends up in unregulated markets

case of the Pacific halibut

catches have been regulated since 1920s Pacific Halibut Commission would set total

allowable catch (TAC) based on its assessment of stocks

led to short fishing seasons, which caused most of the catch to be frozen, leading prices to drop

in 1990s, Canada and U.S. adopted individual quotas (IQ)– boat owners allocated a percentage of TAC based on

size of vessel and recent performance– owners would decide when to fish during season

conservation vs. preservation

conservation does not imply no use by humans– aim is to manage or regulate use so that

populations do not exceed above their carrying capacity or dip below a population size that is sustainable

preservation is meant to ensure the continuity of species, regardless of utility– often precludes making use of ecosystem

maximum sustainable yield

central question: How much continual use can be maintained without undercutting the capacity of species or system to renew itself?

MSY: the highest possible rate of use that the system can match with its own rate of replacement or maintenance

important to consider:– carrying capacity– optimal population

maximum sustainable yield

use in MSY can refer to the cutting of timber, hunting, fishing, the number of park visitations, discharge of pollution, and so on

in theory, the optimal population is just half the population at the carrying capacity– sustainable yield is increased by thinning the

population so that competition is reduced– complicated by fact that the carrying capacity

is variable based on conditions

precautionary principle

conventional approach has been to use estimated MSY to set a fixed quota– Ex. the use of total allowable catch (TAC) in fishery

management

however, if data is inaccurate, it’s easy to overestimate the TAC (especially when there is pressure to keep the number high)

precautionary principle: where there is uncertainty, resource managers should favor the protection of the living resource

tragedy of the commons

commons: owned by many people in common or by no one (open access)– Ex. federal grasslands where private ranchers graze

their livestock– Ex. coastal fisheries used by commercial fishers– Ex. groundwater drawn for private estates and farms

sustainability requires that common pool resources be maintained so that they continue to yield benefits

forest management

because trees take from 25-100 years to mature to harvestable size, usually involves rotation

even-aged management– trees of fairly uniform age are managed

until the point of harvest, cut down, then replanted

uneven-aged management

forest management

clear-cutting– typically, fast-growing but economically valuable trees

are favored– involves removing entire stand at one time– creates fragmented ecosystem with impacts on

biodiversity other methods

– selective cutting: some mature trees are removed in small groups, leaving behind much of the existing forest

– shelter-wood cutting: involves cutting the mature trees in groups over a period of 10-20 years

sustainable forestry

sustained yield: production of wood is the primary goal and the forest is managed to harvest wood continuously without being destroyed

sustainable forest management: “Forests are to be managed as ecosystems, with the objectives of maintaining the biodiversity and integrity of the ecosystem, but also to meet the social, economic, cultural, and spiritual needs of present and future generations.” –UNCED,1992

forest management

because trees take from 25-100 years to mature to harvestable size, usually involves rotation

even-aged management– trees of fairly uniform age are managed

until the point of harvest, cut down, then replanted

uneven-aged management

forest management

clear-cutting– typically, fast-growing but economically valuable trees

are favored– involves removing entire stand at one time– creates fragmented ecosystem with impacts on

biodiversity other methods

– selective cutting: some mature trees are removed in small groups, leaving behind much of the existing forest

– shelter-wood cutting: involves cutting the mature trees in groups over a period of 10-20 years

sustainable forestry

sustained yield: production of wood is the primary goal and the forest is managed to harvest wood continuously without being destroyed

sustainable forest management: “Forests are to be managed as ecosystems, with the objectives of maintaining the biodiversity and integrity of the ecosystem, but also to meet the social, economic, cultural, and spiritual needs of present and future generations.” –UNCED,1992

Georges Bank

once New England’s richest fishing ground cod and flounder were mainstays for

centuries– accounted for 2/3 of fish in 1960s

after 1976, fishing doubled in intensity, resulting in decrease in desirable species (increase in rough species like dogfish and skates)

management councils

Magnuson Act established eight regional management councils made up of government officials and industry representatives

responsible for setting management plans for regions

National Marine Fisheries Service provide advice and scientifically-based information

actions in Georges Bank

initially set TAC quotas fishers claimed that quotas were set too law and

successfully argued for indirect approach that used a net that allowed smaller fish to escape

in 10 years, number of fishing boats doubled, leading to a crash in the cod population

new regulations:– days vessels may spend at sea are restricted– areas of bank have been closed to fishing– TACs set at lower levels

actions in Georges Bank

initially set TAC quotas fishers claimed that quotas were set too law and

successfully argued for indirect approach that used a net that allowed smaller fish to escape

in 10 years, number of fishing boats doubled, leading to a crash in the cod population

new regulations:– days vessels may spend at sea are restricted– areas of bank have been closed to fishing– TACs set at lower levels

Sustainable Fisheries Act

reauthorized Magnuson Act included mandate to rebuild depleted fish

stocks and maintain them at biologically sustainable levels using IQs

also required that scientific information be employed in setting yields and steps be taken to minimize and analyze by-catch

other issues

shark-finning accurate certification of “dolphin-safe” tuna shrimping in the Gulf of Mexico that

endangers sea turtles and generates huge by-catch

declining stocks of swordfish and tuna even as fishing intensity increases

U.S. public lands

unique in setting aside nearly 40% of the country’s land– distribution is skewed toward Alaska and western states

wilderness– land given the greatest protection– authorized by Wilderness Act of 1964– provides for the permanent protection of designated

undeveloped and unexploited areas so that natural ecological processes can operate freely

– permanent structures, roads, and motor vehicles are prohibited

national parks & national wildlife refuges

national parks: administered by National Park Service (NPS)

national wildlife refuges: administered by Fish and Wildlife Service (FWS)

intent is to protect areas of great scenic or ecological significance, protect important wildlife species, and provide public access for recreation

dual goals of protection and access often conflict with each other

national parks & national wildlife refuges

increasingly, natural sites are being managed collaboratively as part of larger ecosystems

Ex. Greater Yellowstone Coalition works to conserve the larger ecosystem surrounding Yellowstone National Park– consists of Yellowstone NP, Grand Teton NP, 7

national forests, 3 wildlife refuges, and other private lands

– coalition acts to restrain forces threatening the ecosystem

• Ex. logging, hunting, development

New Forestry

practice is directed more toward protecting the ecological health and diversity of forests than producing a maximum harvest of logs– involves cutting trees less frequently (every 350

years instead of every 60 to 80)– leaves larger buffer zones around streams– leaves dead logs and debris in the forest

many practices have been adopted into the Forest Service’s new paradigm: ecosystem management (adopted during the Clinton administration)

Healthy Forests Restoration Act (2003)

little solid research on what to do about reducing the threat of wildfires

two strategies put in place by Bush administration:– fuel reduction—HFRA provides incentives to

logging companies to provide incentives to thin fire-prone forests, especially near populated areas

• ruled that environmental reviews and judicial oversight would be limited

ENERGY

drawbacks of coal

smoke and fumes made air pollution far worse at the height of the Industrial Revolution than anything we see today

hazardous to mine dirty to handle, along with the

production of large amounts of ash

energy consumption

crude oil, coal, and natural gas account for 85% of U.S. energy consumption

remaining 15% is supplied by nuclear power, hydropower, and renewable sources

electrical power production

large portion of energy used to generate electricity– technically an energy carrier– 33% of fossil fuel production dedicated to electricity

(was 10% in 1950) electric generators

– coil of wire that rotates in a magnetic field (or is still while magnetic field rotates around it)

– converts mechanical energy into electrical energy– takes about 3 units of primary energy to create one

unit of electrical power that is put to use

electrical power production

use of steam to drive a turbine, which is coupled to a generator, is the most common method of generating electrical power

any primary source (coal, oil, nuclear energy) can be used to create steam– burning garbage, solar energy, and geothermal

energy may be used more in the future

gas and water-driven turbines are also used

formation of fossil fuels

oil: found in areas where sediments were 7500 – 15000 feet under the Earth’s surface, leading large organic molecules to break down into shorter organic molecules

natural gas: produced from deeper sediments (below 15000 feet), producing methane

coal: highly compressed organic matter (mostly leafy material from swamps)

renewal of fossil fuels

additional fossil fuels are likely still forming, but they are used far faster than they are formed

takes ~1000 years to accumulate enough organic matter to produce fuel for one day

finding new oil resources depends on understanding of geology

estimated reserves represent educated guess; it’s difficult to quantify reserves without drilling

recovery

oil is a viscous fluid held in pores of sedimentary rock

primary recovery: conventional pumping (removes ~25% of oil)

secondary recovery: inject brine or steam that forces oil into wells

enhanced recovery: inject carbon dioxide, which breaks up oil droplets and enables flow

Hubbert’s peak

NATURAL GAS– most goes for industrial and residential use– about a 25-year supply of proven U.S. reserves

• gas is continually emitted from oil and gas-bearing geological deposits

• likely pushes supply to about 50 years

– about 4x more natural gas than oil around the world; however, much of it is inaccessible

– can be used to power cars and buses (compressed gas runs about 15% of cars in Argentina)

COAL

in the U.S., 50% of electricity comes from coal-fired power plants

current reserves are estimated at 225 years mining of coal can be hazardous and has

substantial environmental impacts strip mining

– destroys ecology of region by removing forests and burying streams in mining waste

– federal regulations require reclamation, but it takes decades for some sort of ecosystem to reestablish

oil shales and oil sands

oil shale: fine sedimentary rock containing a solid, wax-like hydrocarbon called kerogen– under intense heat, kerogen releases hydrocarbon

vapors that can be condensed to a liquid similar to crude oil

oil sands: sedimentary material containing bitumen, a viscous, tar-like hydrocarbon– large deposits in Canada are yielding up to 1 million

barrels per day

supply-side policies

exploring and developing domestic sources of oil and gas

increasing use of vast coal reserves for energy continuing subsidies to oil and nuclear industries removing environmental and legal obstacles to

energy development providing access to remote sources of natural

gas

demand-side policies

increasing mileage standards for motor vehicles

increase energy efficiency of appliances and buildings

encourage industries to use combined heat and power technologies

promote greater use of non-fossil-fuel sources of energy (nuclear and renewable)

Chapter 13.2How Nuclear Power Works objective is to control nuclear reactions so that

energy is released gradually as heat– as with other power plants, the heat is used to boil water

and produce steam, which drives generators nuclear energy involves changes at the atomic level:

– fission: large atom of one element is split to produce two smaller atoms of different elements

– fusion: two small atoms combine to form a larger atom of a different element

– In both cases, mass of product(s) is less than mass of reactant(s); lost mass is converted to energy (E = mc2)

fuel for nuclear power plants

all current plants use fission of uranium-235 (a radioactive isotope of uranium)

a neutron must strike a U-235 nucleus at just the right speed to trigger a fission reaction– neutron makes the atom U-236, which is highly

unstable and undergoes immediate fission– reaction releases a great deal of energy, along

with several other neutrons which have the potential to trigger a chain reaction

nuclear reactors

reactor for a power plant is designed to sustain a continuous chain reaction, but not allow it to amplify into a nuclear explosion– control is achieved by enriching the uranium to ratio of 4%

U-235 / 96% U-238– in process of fission, some faster neutrons are absorbed by

U-238 and convert it to plutonium-239, which also undergoes fission

• Pu-239 supplies about 1/3 of energy for power plant

moderator: slows down neutrons that produce fission– in slowing down the neutrons, gains heat– most U.S. plants use water as moderator

nuclear reactors

fuel rods: long metal tubes loaded with enriched UO2 and arranged geometrically to produce fission

control rods: rods made of a neutron-absorbing material control the chain reaction (rods can be inserted and withdrawn as necessary)

nuclear power plant “loss-of-coolant accident” (LOCA)

– if reactor vessel breaks, water from around the water leaks, causing the core to overheat

– sudden loss of coolant would cause fission reactions to stop (no moderator)

– nonetheless, overheating of fuel core from leftover fission could release enough heat to cause a core meltdown

– molten material falling into the remaining water could cause a steam explosion

to guard against a LOCA event:– backup systems keep reactor underwater, even if a leak

occurs– reactor is contained within a thick concrete containment tower

biological effects of radiation

high dose: radiation may cause enough damage to prevent cell division– used in cancer treatment to destroy tumors– whole body exposure results in radiation sickness

low dose: may damage DNA, leading to tumors or leukemia– damage to egg or sperm cells (mutations) may lead to

birth defects– effects may go unseen for 10 – 40 years after the event– exposures of 100-500 millisieverts or more results in an

increased risk of developing cancer

radioactive wastes

radioactive decay: process in which an unstable isotope becomes stable by releasing particles and radiation

half-life: time for half of the amount of a radioactive isotope to decay

each radioactive isotope has a characteristic half-life

disposal of radioactive wastes current problem of nuclear waste disposal is two-

fold:– short-term containment: allows radioactive decay of

short-lived isotopes; in 10 years, fission wastes lose 97% of their radioactivity

• spent fuel is first stored in deep pool-like tanks on the sites of nuclear power plants

• water in tanks helps to dissipate heat and prevent escape of radiation

• current U.S. pools will be full by 2015• after a few years of decays, spent fuel may be paced in air-

cooled dry casks until long-term storage is available (able to resist flood, tornadoes, etc.)

disposal of radioactive wastes

current problem of nuclear waste disposal is two-fold:– long-term containment: EPA recommended a

10,000 year minimum to provide protection from long-lived isotopes; government standards require isolation for 20 half-lives

nuclear power accidents

Three Mile Island (PA, 1979)– partial meltdown due to series of human

and equipment failures resulting from flawed design

– operators of the plant have paid $30 million to settle claims from the accident, although the company has never admitted that radiation-caused illnesses occurred

nuclear power accidents

Chernobyl (U.S.S.R., 1986)– disabling plant safety systems for test of

standby diesel generators eventually led to:• a steam explosion that blew the top off the reactor• core meltdown• release of 50 tons of dust and debris bearing 100-

200 million curies of radioactivity– plume rained radioactive particles over thousands of

square miles– 400x the radiation fallout associated with bombs dropped

on Hiroshima and Nagasaki

solar heating of water

solar hot-water heating is already popular in warm, sunny climates– solar collector consists of thin, broad box with a glass or

clear plastic top and a black bottom with embedded water tubes (known as flat-plate collectors)

– active system: heated water is moved by a pump– passive system: relies on natural convection currents;

system constructed so that collector is lower than tank in temperate climates where the water might

freeze, a heat-exchange coil circulates antifreeze

solar space heating uses same concept as water heating greatest efficiency is gained if building acts as

its own collector– have windows face the sun (usually south-facing)

• in winter, light can come in to heat interior• at night, shades can be drawn to insulate windows

– well-insulated buildings act as heat-storage unit– heat load for windows with sun exposure can be

minimized by using owning or overhangs

photovoltaic cells

each cell consists of two very thin layers of semiconductor material– lower layer has atoms that easily lose electrons; upper layer

has atoms that easily gain electrons– energy from light photons knock electrons from lower layer,

creating an electrical potential between the two layers– electrons flow from lower side, through motor or other

device, to upper side– light energy is converted to electrical energy with efficiency

of about 20%– lack of moving parts means they do not wear out– silicon is main material for layers

concentrated solar power (CSP) several technologies have been developed that convert

solar energy into electricity by using reflectors such as mirrors to focus concentrated light onto a receiver that transfers the heat to a generator– solar trough: light hitting collector is reflected onto pipe in

center which contains oil or other heat-absorbing fluid (9 facilities in California desert)

– power tower: array of sun-tracking mirrors that focus sunlight falling on several acres of land onto a receiver mounted to a tower in the middle of the field; receiver transfers heat to a molten-salt liquid

– dish-engine system: set of parabolic concentrator dishes focus sunlight onto a receiver

hydropower—advantages

costs and environmental effects of fossil fuel and nuclear power plants are eliminated

hydropower plants have longer lifespan than those that are fuel-fired

provide flood control on rivers provide water for irrigation of agricultural land provide recreational opportunities

wind machine designs wind-driven propeller blades have proven to be

most effective design– propeller shaft is geared directly to a generator

wind farms, with up to several thousand turbines, now produce pollution-free, sustainable power for less than 5 cents per kWh– great potential in the Midwest where land could still

be used for farming– farmers receive royalties on the order of $2000 -

$3000 per turbine per year for leasing land

wind power--disadvantages intermittent source—requires storage or

backup system disrupts aesthetic beauty of landscape

– large consideration in proposed offshore wind farm in Nantucket Sound off Cape Cod

• concerns included “visual pollution” and threats to tourism, navigation, fishing, and migrating birds

hazard to birds (a consideration near migratory routes and critical habitats)

hydropower--disadvantages reservoir created floods ecosystem behind

dam dams often displace large rural

populations dams impede migration of fish and other

species downstream ecosystems are impacted by

changing water levels

BIOMASS ENERGY biomass energy: energy derived from present-

day photosynthesis leads hydropower in renewable energy

production in the U.S. means of producing biomass energy include:

– burning wood in a stove– burning wastepaper or organic waste– generating methane from the anaerobic digestion of

manure– producing alcohol from fermenting grains

waste and methane burning wastes is a productive and

relatively inexpensive way to dispose of biological wastes– Ex. wastes from olive oil production power 3

power plants in Spain, generating over 32 MW of power to supply 100,000 homes

anaerobic digestion of sewage yields biogas (mostly methane) plus a nutrient-rich sludge that is a good organic fertilizer

hydrogen

conventional car engines can be run on hydrogen gas in the same manner as they are now able to run on methane– neither carbon dioxide nor hydrocarbon pollutants are

produced– main byproduct is water vapor, along with some nitrogen

oxides (NOx) problem with hydrogen is that it is extremely

abundant as an element, but not in the energy-rich gas form– can be extracted from water, but requires input of

significant amounts of energy

Chapter 14.4Additional Renewable Energy Options

GEOTHERMAL ENERGY– use of natural heat sources from the Earth’s interior

or volcanic sources– in 2005, provided 8900 MW of electrical power

(equal to nine large power plants)– estimates suggest that up to 80,000 more

megawatts could be generated with today’s technology

– “GeoPowering of the West” aims to provide 10% of western U.S. energy needs by 2020 (DOE program)