unit 5

5.1: tragedy of the commons

overview

• tragedy of the commons: principle that “individuals will use shared/public resources in their own self interest, degrading them”

  • must refer to a public resource (not privately owned

  • must be degraded, overused, etc. in some way

  • ex. overgrazing, overfisihing, water and air pollution, overuse of groundwater

• this happens because:

  • when no one owns the resource, no one directly suffers the negative consequence of overusing/depleting it

  • people assume others will overuse the resource if they don’t

  • there is no penalty for overusing (many) public resources

issues and solutions

• problems that arise:

  • overfishing: leads to fishery collapse (pop. crash), loss of income, and starvation

  • air pollution (from coal power plants): can lead to bronchitis, asthma, increased healthcare costs

  • pesticide runoff: contaminates drinking water

• how to solve t.o.c:

  • private land ownership (individual or gov’t)

  • fees or taxes for use (ex. permit system for grazing)

  • taxes, fines, criminal charge for pollution or shared air/soil/water resources

  • ex. clean air act, clean water act, safe drinking water act, BLM (bureau of land management)

5.2: clearcutting

direct effects of clear cutting

• soil erosion: caused by loss of stabilizing root structure; removes organic matter and nutrients from forest

  • deposits sediments in local streams = warmer water and increases turbidity (cloudiness)

• increased soil & stream temp.: loss of tree shade increases region temp.

  • soil has lower albedo than leaves of trees

  • loss of tree shade along rivers warms them

• flooding & landslides: logging machinery compacts soil; increased sunlight dries out soil; loss of root structure = erosion of topsoil and O horizon

  • these all decrease h2o holding capacity of soil = flooding and landslides

tree plantations

• tree plantation: areas where the same tree species are repeatedly planted, grown, and harvested

• lowers biodiversity: biodiverse, mature forests are replaced with single-species forests

  • less species diversity = lower resilience and less habitat diversity for other org.

• all the same age: all trees planted at same time = same age

  • lowers biodiversity further (no dead trees for insects, decomposers, etc.)

forest benefits

• filtering of air pollutants: stomata (leaf pores) remove VOCs, no2, and PM from air and store it in the tree

• removal & storage of CO2 from atmosphere

• habitat for other organisms

deforestation consequences

• reduces air filtering and carbon-storing services

• cutting trees down releases co2 from decomp. of leftover organic material

• slash & burn method releasees co2, n2o, and water vapor to atmosphere (all GHG)

5.3: the green revolution

overview

• green revolution: shift in agriculture away from small, family-operated (subsistence) farms to large, industrial-scale agribusiness

• increased use of mechanization, GMOs, irrigation, fertilizers, and pesticides

• greatly increases efficiency of lands, short-term profitability, and food supply

  • decreased world hunger and increased global human carrying capacity

• negative consequences: soil erosion, biodiversity loss, ground water and surface water contamination

mechanization

• increased use of tractors for plowing and tilling fields and combines for harvesting = increased yield (and profit)

• increases reliance of FFs (gasoline/diesel fuel)

  • emits GHG = climate change

• heavy machinery compacts soil = decreased h2o carrying capacity = loose and erosion-prone topsoil

high-yield variety (HYV) crops

• hybrid crops that produce higher yield

  • hybrid= cross-pollinating different species (parent plants) for ideal traits

• increased food stability in regions previously prone to famine

• GMO = crops with “new” genes spliced into genome

GMOs

• genetically modified organisms with genes for drought tolerance, pest resistance, faster growth, larger fruit/grain, etc.

• increases profit with fewer plants loss

• decreases genetic diversity and resilience

synthetic fertilizer

• shift from organic fertilizers (ex. manure, compost) to synth. fertilizers (man-made ammonium, nitrate, phosphate)

• increases yield and profits with more key nutrients needed for plant growth added to soil

• excess nitrate and phosphate are washed off fields and pollute water = eutrophication (algae bloom)

• requires FFs for production, releasing co2 = climate change

irrigation

• drawing water from ground or nearby surface water to redistribute to fields and increase plant growth

• make agriculture possible in many parts of the world prone to arid climate

• can deplete groundwater (esp. aquifers)

• overwater can drown roots (no o2) and cause soil salinization (increased salt level in soil)

pesticides

• increased use of synth. pesticides (chemicals sprayed on crops to kill weeds, pesticides, rodents, etc.)

• increases yield and profit with fewer plants lost to pests

• can wash off crops in runoff and kill non-target species in local region

5.4: impact of ag. practices

monocropping

• monocropping: growing a single species of crop

  • highly efficient for harvest, pesticide, and fertilizer application

• greatly decreases biodiversity and resilience

• increases soil erosion

• decreases habitat diversity for other org. in region

tilling

• tilling: mixing and breaking up soil to make planting easier

  • also loosens soil for roots

• increases erosion by loosening topsoil and breaking root structure

• loss of organic matter and topsoil nutrients

• increased PM in air and sediments in water (turbidity)

slash and burn

• cutting down vegetation and burning it to clear areas for ag. and return nutrients in plants to soil

• deforestation:

  • loss of habitat, biodiversity, co2 sequestration, loss of air pollutant filtration

• releases GHG and increases PM in air

• lowers albedo, making region increase temp.

synth. fertilizers

• don’t return org. matter to soil; no increased h2o holding cap. or soil decomposers

• leaching: water carries excess nutrients (nitrate, phosphate) to groundwater or surface water (runoff)

  • contaminates drinking water

  • causes eutrophication of surface waters

5.5: irrigation

types of irrigation

• furrow irrigation: trench dug along crops & filled with water

  • easy & inexpensive; water seeps into soil slowly

  • ~66% efficient, 33% lost to runoff & evap.

• drip irrigation: most efficient, but also most costly; over 95% efficient

  • holes in hose allow water to slowly drip out

  • avoids waterlogging & conserves waters

• flood irrigation: flood entire field; easier but more disruptive to plants

  • can waterlog the soil & drown plants

  • 80% efficient - 20% runoff/evap.

• spray irrigation: ground or surface water pumped into spray nozzles

  • more efficient (less water loss) than flood or furrow

  • more expensive (requires energy for pumps & movement of sprinklers)

waterlogging

• waterlogging: overwatering can saturate the soil, filling all soil pore space with water

  • doesn’t allow air into pores, so roots can’t take in o2 they need

  • can stunt growth/kill crops

• solution: drip irrigation, or soil aeration (poking holes or cores in soil to allow air in & water to drain through soil)

soil salinization

• salinization: the process of salt building up in a soil over time

• groundwater is used for irrigation and naturally has small amounts of salt

  • water evaporates, and salt is left behind in soil; over time, it can reach toxic levels, dehydrating plant roots & preventing growth

• solution: drip irrigation, soil aeration, flushing with fresh water, switch to freshwater source

global human water use

• industrial (19%): power plants, metal/plastic manufacturing

• municipal (11%): households

• agriculture (70%): water for livestock, irrigation water for crops

aquifers & groundwater

• groundwater: h2o stored in pore space of permeable rock & sediment layers

  • aquifers: useable groundwater deposits for humans

• replenished by groundwater recharge (rainwater percolating down soil into aquifer)

• unconfined aquifers recharge quickly

• confined aquifers recharge are longer-term water deposits that recharge slower

depletion of aquifers

• saltwater intrusion: excessive pumping near coast lowers water table pressure, allowing saltwater to seep into groundwater

• cone of depression: forms when water table is lowered by excessive pumping, depleting water & drying nearby wells

5.6: pest control methods

pesticides

• pesticide: chemicals that are toxic to pests

  • rodenticides kill rodents, fungicides kill fungi, insecticides kill insects, herbicides kill plants

• can cause pests to become resistant to pesticide overuse

  • genetic biodiversity gives some pests resistant traits to pesticide

  • pesticide artificially selects for pests with resistance by killing all the non-resistant individuals, leaving only resistant ones

GMOs & pesticide use

• gene for pest resistant trait is added to the plant through genetic modification

  • bt corn with bacteria gene that produces bt crystals toxic to pests

    • bt corn has decreased insecticide use, since corn makes its own insecticide (bt crystals)

• roundup ready crops are genetically modified to be resistant to broad herbicides (roundup) meaning roundup will kill weeds, but not crops

  • roundup ready crops have increased herbicide (glyphosate) use since crops can’t be harmed by it

GMOs & genetic diversity

• GMOs are all genetically identical (clones) so there is no genetic diversity in the pop.

• if there is disease or pest that does affect the GMO crops, they’re all vulnerable and there’s no chance of a genetic mutation providing an adaptive trait

5.7: meat prod. methods

CAFOs

• CAFO: aka feedlots; densely crowded method where animals are fed grain (corn) to raise them to as quickly as possible

• maximizes land use and profit (most meat prod./unit of area space used)

  • minimizes cost of meat for consumers

• given antibiotics & growth hormones to prevent disease outbreak & speed meat production

• animals produce large volume of waste which can contaminate nearby surface or groundwater

• produces large amounts of CO₂, CH₄ (methane), and N₂O (greenhouse gasses → climate change)

manure lagoons

• large, open storage pits for animal waste (manure)

• waste contains: ammonia (N), hormones, antibiotics, fecal coliform bacteria (e. coli)

  • e. coli → toxic to humans

  • ammonia (N) → eutrophication

  • antibiotics & growth hormones → alter endocrine (hormonal system) of humans

• heavy rain can flood lagoons & contaminate nearby surface and ground water with runoff

• denitrification of ammonia in manure produces N₂O (extremely powerful GHG)

• can be emptied and buried in landfills, or turned into fertilizer pellets

free-range grazing

• animals (usually cows) graze on grass & grow at a natural rate without growth hormones

• no antibiotics use

• doesn’t require food prod. (corn) to feed animals

• waste is dispersed over land naturally (acts as fertilizer instead of building up)

• requires more land

  • more expensive to consumer

• animals can graze on land too dry for most crop growth (maximizes land use)

overgrazing

• too many animals grazing an area of land can remove all the vegetation (grass) which leads to topsoil erosion  

• animals also compact soil, decreasing H₂O holding capacity → more erosion

• desertification: can occur if plants are killed by overgrazing & soil is compacted so much that it can’t hold enough water anymore

• rotational grazing (moving animals periodically) can prevent overgrazing

  • can even increase growth of grass by distributing manure (natural fertilizer) & clipping grass back to size where growth is most rapid

inefficiency of meat

• producing meat for humans to eat is far less efficient than producing plants in terms of energy, land and water us

• energy: all of the energy needed to plant, grow, harvest plants to feed to animals, plus:

  • energy needed to slaughter & package

  • energy needed to house animals

  • energy needed to bring water to animals

• land: all of the energy needed to grow plants to feed animals PLUS room the animals take up

• water: all of the water for crops that animals eat + the water the animals drink

5.8: impacts of overfishing

fishery & fishery collapse

• fisheries: populations of fish used for commercial fishing

  • fishery collapse: when overfishing causes 90% population decline in a fishery

• pop. may never recover from fishery collapse due to: decreased biodiversity, inability to find mates, inbreeding depression

  • decreases genetic biodiversity of fish populations & species biodiversity of ocean ecosystems if species are lost from ecosystem

  • economic consequences: lost income for fishermen, lost tourism dollars for communities

economic impact

• overfishing in period of 1975 - 1985 leads to sharp loss of profits from 1985 - 2018

• t.o.c: no incentive or penalty to prevent overfishing from 75’ - 85’

bottom trawling

• bottom trawling: esp. harmful fishing method that involves dragging a large net along ocean floor

  • bycatch: unintended species like dolphins, whales, turtles caught in nets

  • stirs up ocean sediment (turbidity) and destroys coral reef structure

  •  decreases biodiversity by killing non-target species & removing coral reef habitat

fishing down food web & trophic cascade

• depleting large, predatory fisheries moves us down to smaller fish species

• depletion of smaller fish pop. limits fishery recovery and decreases food supply of marine mammals & seabirds

5.9: mining

mining basics

• ore: commercially valuable deposits of concentrated minerals that can be harvested and used as raw materials

• metals: elements that conduct electricity, heat, and have structural properties for building (found within ores)

• eeserve: known amount of a resource left that can be mined; usually measured in years left of extraction.

• railings & slag: leftover waste material separated from the valuable metal or mineral within ore (often stored in ponds @ mine site)

• overburden: soil, vegetation, & rocks that are removed to get to an ore deposit below

surface mining

• removal of overburden to access ore near surface

• different types: open pit, strip, mountaintop removal, placer

  • mnt. top removal = esp. damaging to landscape & habitats, streams nearby

  • as ore near surface becomes more scarce, mining moves deeper underground to subsurface mining (more dangerous & expensive)

• leads to removal of vegetation & soil, topsoil erosion, habitat loss, increased stream turb., increased PM in air

subsurface mining

• vertical “shaft” drilled down into ground

  • elevator to carry down workers & transport out resource

  • often used for coal

• more expensive due to higher insurance & health care costs for workers

• risks: poor ventilation leading to toxic gas exposure, mine shaft collapse, injury from falling rock, lung cancer, asbestos, fires, explosions

• increasingly used as surface coal deposits are depleted

env. impacts of mining

• acid mine drainage: rainwater leaks into abandoned mine tunnels & mixes with pyrite, forming sulfuric acid

• rainwater carrier sulfuric acid into nearby streams, or infiltrates ground water

• lowers pH of water, making toxic metals like mercury & aluminum more soluble in water sources (killing aquatic org.)

• methane release: coal mining releases methane gas (CH₄) from rock around coal

  • vented out of mine to prevent explosion & continues seeping out after mine closes

  • GHG = climate change

• PM release: coal mining especially, releases lots of soot and other particulates that can irritate human & animal lungs

mine reclamation

• process of restoring land to original state after mining has finished

  • filling of empty mine hold

  • restoring original land contours

  • returning topsoil with acids, metals and tailings removed

  • replanting of native plants to restore community to original state

5.10: urbanization

overview

• urbanization: removing of vegetation to convert natural landscape to city (urban)

  • eeplaces soil, vegetation, wetlands , with impervious surfaces (concrete, asphalt, cement) which don’t allow water to infiltrate into the ground

• co2 emissions:

  • cement production

  • construction machinery

  • deforestation (loss of future carbon sequestration + decomposition of cut trees)

  • landfills needed for disposing trash from large pop.

• prevents groundwater recharge = precip. runoff to local bodies of water

costal cities

• pop. growth in coastal cities can lead to  saltwater intrusion due to:

  • sea level rise due to warming of ocean (thermal expansion) and melting of ice caps (increasing ocean volume) can contaminate fresh groundwater with salt

  • excessive groundwater withdrawal near coast lowering water table pressure, allowing saltwater to seep into groundwater

trends in population

• people move from rural → urban areas for jobs, entertainment, cultural attractions

  • overall trend in u.s. & many other nations is away from less dense rural (country) areas and toward more urban (city) areas

• urban areas are more densely populated, minimizing driving & land use per person (decreases env. impact per person)

• highest growth currently is suburban population

  • suburbs: less dense areas surrounding urban areas

urban sprawl

• pop. movement out of dense, urban centers to less dense suburban areas surrounding the city

• caused by:

  • cheaper property in suburbs than in cities (larger home for same price)

  • cars make it easy to still get from the suburbs into the city for work, entertainment, cultural attractions

  • domino effect (neighbors leave, so you leave)

  • fewer residents in cities leads to decline in tax revenue for city (decrease in city services)

  • residents leave, so businesses follow

  • abandoned homes + businesses create blight (unsightly, rundown infrastructure) so more people leave

  • increased in driving increases fuel tax revenue, which is used to build more highways

  • highway expansion makes it easier and easier to commute from suburbs into urban areas

• solutions:

  • urban growth boundaries: zoning laws set by cities preventing development beyond a certain boundary

    • pub. transport & walkable city design that attract residents to stay

  • mixed land use: residential, business, and entertainment buildings all located in the same area of a city

    • enables walkability & sense of place

5.11: ecological footprint

overview

• eco. footprint: measure of how much a person/group consumes expressed in area of land

• factors (land required for):

  • food prod.

  • raw materials

  • housing

  • electricity prod.

  • disposing waste produced (landfills)

eco footprint v. carbon footprint

• eco footprint: measured in land (gha - global hectare) which is a biologically productive hectare (2.47 acres)

• carbon footprint: measured in tonnes of CO₂ produced per year

  • all co2 released from an individual or groups consumption/activities

    • material goods

    • food prod. energy use (gas, heat, electricity)

factors that affect footprint

• increase:

  • affluence (wealth) increases carbon & ecological footprint

    • larger houses

    • more travel (gas)

    • more resources needed for material goods (cars, etc.)

  • meat consumption - more land, more water, more energy

  • FF usage (heating, electricity, travel, plastic)

• decrease:

  • renewable energy use (wind, solar, hydroelectric)

  • public transportation (less gas)

  • plant-based diet

  • less consumption, less travel, less energy use

global pov

• ecological footprint can also be expressed in “number of earths” required if the entire world consumed same level of resources as a given individual or group 

• current average u.s. footprint is 5.1 earths

  • 5.1 earth’s worth of resources needed if the entire world consumed resources of avg. American

• current global footprint is 1.85 earths 

  • meaning each year humanity consumes 1.85 x what the earth can produce in a year

5.12: sustainability

overview

• sustainability: consuming a resource or using a space in a way that does not deplete or degrade it for future generations

  • ex. using compost (renewable) over synthetic fertilizer (fossil fuel dependent)

• max. sus. yield: maximum amount of a renewable resource that can be harvested without reducing or depleting the resource for future use

  • approx. ½ carrying capacity; maximizes yield (resource harvest) and regeneration rate of population

env. indicators of sustainability

• indicators: factors that help us determine the health of the env. and guide us towards sustainable use of earth’s resources

• biodiversity: higher biodiversity = healthier ecosystem

  • declining biodiv. can indicate pollution,    habitat destruction, climate change

  • global extinction rate = strong env. indicator since species extinction decreases species richness of earth 

• food prod.: indicates ability of earth’s soil, water, and climate to support ag.

  • najor threats to food prod. = climate change, soil degradation (desertification, topsoil erosion), groundwater depletion

  • increasing meat consumption = further strain on food prod. (takes away water and land from grain production)

  • global grain production per capita has leveled off & sown signs of decline recently

• atmospheric temp. and co2: life on earth depends on very narrow temperature range; CO₂ is a GHG (traps infrared radiation & warms earth’s atm.)

  • increased CO₂ = increased temp.

  • deforestation (loss of CO₂ sequestration) & combustion of FF (emission of CO₂) increase atm. CO₂

  • increasing CO₂ = unsustainable (dries out arable (farmable) land, destroys habitats, worsense storm intensity)

• human pop. & resource depletion: as human pop. grows, resource dep. grows

  • resources are harvested unsustainably from natural ecosystems and dgrade ecosystem health

    • more paper (lumber) = deforestation

    • more food = soil erosion, deforestation, groundwater depletion

    • more travel = FF mining = air, water, and soil pollution, habitat destruction

5.13: reducing urban runoff

env. consequences of urban runoff

• decreased infiltration (groundwater recharge)

• rain washes pollutants into storm drains & into local surface waters:

  • pollutants (and effects): salt (plant/insect health), sediment (turbidity), fertilizer (eutrophication), pesticides (kill nontarget species), oil and gas (suffocate fish/kill aq. insects)

solution: permeable pavement

• specially designed to allow stormwater to infiltrate & recharge ground water

  • decreases runoff, decreasing pollutants carried into storm drains & into local surface water

    • decreases likelihood of flooding during heavy rainfall

  • more costly than traditional pavement

solution: rain garden

• creates hab. for pollinators, sense of place & stores CO₂

solution: public transport

• more cars on the road = more pollutants on streets to runoff into storm drains & local waters

• more cars = more lanes & parking lots (impervious surfaces) & more stormwater runoff

• public transit decreases urban runoff, pollutants on road, CO₂ emissions & traffic

solution: building up, not out

• building vertically decreases impervious surfaces (decreasing urban runoff)

5.14: intergrated pest management

overview

• IPM: using a variety of pest control methods that minimize env. disruption and pesticide use

  • researching & monitoring pests and targeting methods to specific pest life cycles

• examples:

  • biocontrol

  • crop rotation

  • intercropping

biocontrol

• introducing a natural predator, parasite, or competitor to control the pest population

• can include actually purchasing & spreading the control organisms in fields, or building homes for them/planting habitat they need to attract them naturally

  • ex. lady bugs for aphids, spiders for many insects, parasitic wasps for catepillars

crop rotation

• many pests prefer one specific crop or crop family; they lay eggs in the soil, so when larvae hatch, they have preferred food source

• rotating crops (planting a different crop each season) can prevent pests from becoming established since it disrupts their preferred food choice

• also disrupts weed growth since diff. crops can be planted at different times, preventing bare soil from being taken over by weeds

intercropping

• push & pull system:

  • “push” plants emit volatile chemicals that naturally repel pests away from crop

  • “pull” plants emit chemicals that attract moths to lay eggs in them, instead of crop

• can provide habitat, or “pull” plants that emit chemicals that attract natural pest predators

benefits & drawbacks of IPM

• benefits:

  • reduces death & mutation of non-target species  

  • reduces effects on human consumers of produce

  • reduces contamination of surface & ground water by agricultural runoff with pesticides

• drawbacks:

  • can be more time consuming & costly than just crop dusting pesticides

5.15: sustainable agriculture

soil conserv.

• agricultural techniques that minimize erosion; u.s. is losing topsoil to erosion 10x faster than it forms

• prevents loss of:

  • nutrients in topsoil

  • soil moisture

  • decomposers in topsoil

  • organic matter that traps soil moisture

methods

• contour plowing: plowing parallel to natural slopes of the land instead of down slopes prevents water runoff & soil erosion

  • forms mini terraces that catch water running off, conserving soil & water

• terracing: cutting flat “platforms” of soil into a steep slope

  • flatness of terraces catches water & prevents it from becoming runoff and eroding soil

• perrenial crops: crops that live year round and are harvested numerous times

  • longer, more established roots & prevention of bare soil between harvest

• windbreaks: using trees or other plants to block the force of the wind from eroding topsoil

  • can be used as a source of firewood, fruit (income)

  • can provide habitat for pollinators & other species

• no till: leaving leftover crop remains in soil instead of tilling under

  • adds org. matter to soil (nutrients, soil cover, moisture)

  • prevents erosion from loosened soil

• strip cropping: aka intercropping; alternating rows of dense crops (hay, wheat) with rows of less dense crops (corn, soy, cotton) to prevent runoff from eroding soil from less dense rows of crops

improving soil fertility methods

• crop rotation: methods of restoring nutrient levels in the soil (N, P, Ca, Mg)

  • replanting same crops continuously depletes soil of the same nutrients 

  • can allow soil to recover from nitrogen-demanding crops like corn

  • peas/beans (legumes) have nitrogen fixing bacteria in their root nodules that can return nitrogen to the soil

• green manure:  leftover plant matter from a cover crop; a crop planted in the offseason, between harvest & replanting of main crop

  • cover crop roots stabilize soil limiting topsoil erosion

  • rremains of cover crops (green manure) left on field breakdown to release nutrients into the soil

• limestone: releases calcium carbonate (base) which neutralizes acidic soil

  • acidic soil has high H+ ion concentration, which displaces + charge nutrients from soil (leeching them out)

  • acidic soil also makes toxic metals (aluminum) more soluble in soil

  • calcium is a needed plant nutrient as well

• rotational grazing: regular rotation of livestock to different pastures to prevent overgrazing

  • overgrazing can kill plants, compact soil, and lead to erosion of topsoil

  • can actually promote pasture growth at faster than normal rate

  • clips grass back to length where growth is fastest & encourages deeper root growth

5.16: aquaculture

benefits

• aquaculture: raising fish, or other aquatic species in cages/enclosures underwater 

  • requires only small amount of water, space, and fuel

  • reduces risk of Fishery collapse (90% pop. decline in a fishery)

  • doesn’t take up any land space (compared to beef, pork, chicken)

drawbacks

• high density produces high concentration of waste (e. coli & eutrophication risks)

• high density increases disease risk, which can be transmitted to wild populations as well

• may introduce non-native species or GMOs to local ecosystem if captive fish escape

• fish are fed antibiotics which can contaminate water via their waste

5.17: sustainable forestry

eco. sustainable forestry

• forestry (using trees for lumber) that minimizes damage to ecosystem (habitats destruction, soil erosion, etc.)

• selective cutting or strip cutting

  • strip cutting: only cutting some of the trees in an area (biggest & oldest) to preserve habitat (biodiv.) and topsoil

• using human & pack animal labor to minimize soil compaction from machinery

• replanting same species being logged

• maximizes long-term productivity of land & preserves forest for future generations

sus. forestry practics

• using recycled wood, or simply reusing without recycling (furniture, decoration)

• wood can be chipped and used as mulch for gardens or agricultural fields

• reforestation: replanting of trees in areas that have been deforested

• selectively removing diseased trees to prevent spread of infection through entire forest

  • removes host for disease

  • decreases density, making spread less likely

fire suppression

• stopping natural fires: fire supressionsion is the practice of putting out all natural forest fires as soon as they start

• leads to moe biomass buildup: putting out fires immediately leads to more dry biomass buildup; makes future fires worse

• monitoring instead: close monitoring can prevent fire damage & worse fires in the future 

prescribed burns

• dead biomass builds up: fuel for large forest fires; stored nutrients trapped in dead biomass; dead trees = susceptible to disease and pest spread

• small, controlled fires burn lots of dead biomass: uses up dead biomass (fuel) preventing larger forest fires later

• promotes nutrient recycling: nutrients in dead biomass are recycled = new growth

unit 6

6.1: renewable v. nonrenewable energy

renewable v. nonrenewable

• renewable energy sources: can be replenished naturally, at or near rate of consumption & reused

  • ex. solar, wind, hydroelectric energy

• nonrenewable energy sources: depletable renewables can run out if overused

  • ex. biomass (wood, charcoal, ethanol)

  • exist in fixed amounts on earth & can’t easily be replaced or regenerated

  • FFs: fossilized remains of ancient biomass that take millions of years to form coal, oil, nat. gas

  • nuclear: energy generated from uranium or other radioactive fuels

key to renewable energy

• rate of consumtion: rate. of use must be at. or below rate of regeneration for renewables

• FFs will run out because they take longer to replenish than the rate we use them at

6.2: global energy consumption

developed v. developing countries

• developeed nations use more energy on a per capita basis, but developed nations use more energy in total (higher pop.)

• developing nations are still industrializing & pop. is still growing rapidly

  • will also increase on a per/person basis as their economies industrialize & residents achieve higher standards of living

• avg. u.s. resident uses 5x as much energy as the world avg.

• fossil fuels: most used energy source

• hydroelectric energy (dams used to create electricity) are second largest source

  • water spins a turbine which generates electricity (oil ⇒ gasoline = main fuel for vehicles)

  • coal = main fuel for electricity gen.

  • nat. gas = secondary fuel for electricity gen. & main fuel for heating

• nuclear is the third largest source

  • uranium fission releases heat to turn water into steam to turn a turbine to gen. electricity

development increases FF consumption

• many residents of less developed nations depend on subsistence fuels - biomass that they can easily gather/purchase

  • ex: wood, charcoal, dried animal manure

    • can drive deforestation

• as developing nations develop, FF consumption will increase

  • oil = gasoline for vehicles

  • coal & nat. gas = electricity

• electricity demand for homes & manufacturing

  • econ. development → affluence (wealth) → higher per capita GDP → energy use

• availability: FF use depends on discovered reserves & accessibility of these reserves; varies heavily with availability

factors that affect energy source use

• price: FF prices fluctuate dramatically with discovery of new reserves or depletion of existing ones

• fracking opens new nat. gas reserves, increasing availability, decreasing price, increasing use

• gov’t regulation: gov’t can mandate certain energy source mixes (25% renewable by 2025)

  • gov’t cannot directly raise or lower prices of energy sources (ex: raise gas to $10/gallon)

  • gov’t can use: taxes increases to discourage companies from building FF power plants; rebates, or tax credits to encourage companies building renewable energy power plants

6.3: types of fuel and uses

subsistence fuels

• wood (and charcoal) are two of the most common fuel sources in developing nations

  • can be dried and used as a biomass fuel source

  • charcoal is made by heating wood under low oxygen conditions for a long time

• peat: partially decomposed org. matter (often ferns or other plants) found in wet, acidic ecosystems like bogs and moors

• wood: free/cheap to cut down and utilize as fuel; can cause deforestation & habitat loss

• biomass fuel sources that are easily accessible (can be found and gathered by hand); often used in developing countries as a home heating or cooking fuel

• charcoal is made by heating wood under low oxygen conditions for a long time

coal formation

• in order of energy density & quality: lignite → bituminous → anthracite

  • because higher energy density means more energy released when a fuel source is burned, anthracite is the most valuable form of coal (highest quality)

    • deeper a coal reserve is buried = more pressure from overlying rock layers & the more energy dense

      • pressure from overlying rock & sediment layers compacts peat into coal over time

• coal is burned to heat water into steam, to turn a turbine that generates electricity

  • more dense coal = hotter/longer fire = more steam = more electricity

natural gas

• mostly methane (CH4) and is found on top of trapped oil (petroleum) deposits

• considered the “cleanest” fossil fuel (produces the fewest air pollutants & least CO2 when burned)

• forms when oil is trapped in a porous, sedimentary rock, underneath a harder, impermeable rock layer that doesn’t let the gas escape

• decaying remains of plants & animals (mostly marine life) are buried under layers of rock & converted by pressure into oil (petroleum) and natural gas over time

• produces about ½ as much CO2 as coal when burned to generate electricity

  • produces virtually no PM (ash/soot)

  • produces far less SOx, NOx than coal or oil, and NO MERCURY

crude oil (petroleum)

• extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure

• can also be recovered from tar sands (combination of clay, sand, water, and bitumen)

• decaying organic matter trapped under rock layers is compressed into oil over time

• bitumen: thick, sticky, semi-solid form of petroleum (not liquid)

• extracting & using oil from tar sands is extremely energy and water intensive

  • lots of water needs to be heated (requiring energy) to create steam that’s piped down into the tar sand to melt the bitumen into a liquid that can flow up a pipe

  • lots more water is used to separate the oil from all of the impurities (sand, clay) at the refinery

FF products

• crude oil (petroleum) is converted into lots of different products through the process of fractional distillation

• crude oil is burned in a furnace and vapor passes into a column where different hydrocarbons are separated based on their boiling points

• hydrocarbons w/lower boiling points gather at the top of the column, higher boiling points gather at bottom

  • different hydrocarbons within petroleum are used for different products

• products: petroleum gas, gasoline (fuel for cars), naphtha (used to make plastic), jet fuel, diesel fuel, motor oil, bitumen (asphalt for roads)

6.4: distribution of nat. resources

overview

• coal ( ~100-150 years): 1. u.s., 2. russia, 3. china, 4. australia

• nat. gas ( ~50-60 years): 1. russia, 2. iran, 3. qatar, 4. u.s., 5. saudia arabia

• oil ( ~50 years): 1. venezuela, 2. saudi arabia, 3. iran, 4. canada, 5. iraq

fracking & shale gas

• hydraulic fracturing (aka fracking) is a method of nat. gas extraction that has extended access to nat. gas

  • gas trapped in semi-permeable, sedimentary rock layers, such as shale, is released by cracking the rock with pressurized water

• racking natural gas from shale rock increases & extends supply of nat. gas

shale gas reserves

• FFs are non-renewable, and will eventually be depleted, but short-term economic profit still drives extraction & use

• discovered, but unharvested reserves represent economic benefit to countries

tar/oil sands

• tar or oil sands are bitumen deposits where crude oil can be recovered, but with higher water & energy inputs

• canada (Alberta region) = world’s largest oil sands reserve

• just like fracking, tar/oil sands extraction extends the world’s supply of crude oil

crude oil (petroleum)

• extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure

  • can also be recovered from tar sands (combination of clay, sand, water, and bitumen)

• decaying organic matter trapped under rock layers is compressed into oil over time

• bitumen: thick, sticky, semi-solid form of petroleum (not liquid)

• extracting & using oil from tar sands is extremely energy and water intensive

  • lots of water needs to be heated (requiring energy) to create steam that’s piped down into the tar sand to melt the bitumen into a liquid that can flow up a pipe

  • lots more water is used to separate the oil from all of the impurities (sand, clay) at the refinery

6.5: fossil fuels

FF combustion

• combustion is a step in the carbon cycle:

  • hydroCARBONS (FFs) are burned to release energy & the carbon

  • stored in them reacts with O2 in the air to form CO2

• methane (natural gas), gasoline, propane, butane, coal are all fossil fuels (hydrocarbons) that release energy in the same way

• wood and biomass work the same, carbon is burned & reacts with O2 to form CO2 & give off energy

• reaction between oxygen (O2) & fossil fuels (hydrocarbons) that releases energy as heat and produces CO2 & H2O as products

FF for electricity

• steps of electricity gen. are the same, no matter what you’re burning to produce the initial heat

  • heat →water into steam →steam turns a turbine → turbine powers generator → generator produces electricity

• coal, oil, natural gas, biomass, and trash can all be burned to drive this same process and create energy.

  • even nuclear energy work similarly, with nuclear fission producing the initial heat

• FF are #1 source of electricity production globally is coal, followed by nat. gas

env. consequences of coal

• habitat destruction to clear land for mining

• produces pollutants & releases CO2 (GHG → global warming)

• releases more CO2 than any other FF when burned for electricity gen.

  • releases PM (soot, ash) which can irritate respiratory tracts of humans/animals

• produces toxic ash contaminated with lead, mercury, and arsenic

• taken to landfills or stored in ash ponds; both can leak into ground/surface waters, or into soil

• releases SOx & NOx (sulfur and nitrogen oxides) which irritate resp. systems, and contribute to smog and acid precipitation

generating electricity

• much of the energy “lost” or not converted into electricity escapes as heat

• cogeneration: when the heat produced from electricity generation is used to provide heat (air & hot water) to a building;

• CHP (combined heat & power) systems: close to 90% efficient (much better than coal/NG alone)

• coal is approx. 30% efficient as a fuel source for generating electricity

  • 30% of energy from the bonds in the hydrocarbons are converted to electricity

• nat. gas is approx. 60% efficient when it’s burned to generate electricity

oil extraction

• extracted by drilling a well through the overlying rock layers to reach the underground deposit and then pumping liquid oil out under pressure

• can also be recovered from tar sands (combination of clay, sand, water, and bitumen)

• bitumen is a thick, sticky, semi-solid form of petroleum (not liquid)

• extracting & using oil from tar sands is extremely energy and water intensive

  • lots of water needs to be heated (requiring energy) to create steam that’s piped down into the tar sand to melt the bitumen into a liquid that can flow up a pipe

  • lots more water is used to separate the oil from all of the impurities (sand, clay) at the refinery

env. consequences of tar sands

• habitat destruction to clear land for: roads, drilling equipment, digging through ground surface to reach deposits (biodiv. loss)

• ground or nearby surface water depletion (H2O needed for steam & for washing impurities from bitumen at refinery)

• water contamination: tailing ponds (holes dug for storing wastewater) can overflow & run into nearby surface waters, or leach into groundwater

• benzene (carcinogen) salts, acids, hydrocarbons, bitumen

  • all toxic to plant and animals

• CO2 released by machinery during extraction, transport, refinement

env. consequences. of crude oil

• possibility of spill (either from tanker ships or pipelines breaking

• habitat loss or fragmentation when land is cleared for roads, drilling equipment, pipelines

• spills in water = crude oil covering sun, clogging fish gills, suffocating many ocean animals, sticking to bird feathers

• spills on land = toxic to plant roots, surface or groundwater contamination (with hydrocarbons/crude oil)

• fracking (hydraulic fracturing): Used to extract natural gas from sedimentary rock

  • vertical well is drilled down to sed. rock layer, then turns horizontally into the rock layer

  • perforating gun cracks (fractures) the rock layer around hor. well, making it more permeable

  • fracking fluid (water, salt, detergents, acids) is pumped into well @ very high pressure to crack the rock even more & allow natural gas to flow out

    • nat. gas is collected @ surface & shipped for processing/use

  • flowback water (used fracking fluid) flows back out well & is collected and stored in containers or ponds nearby

env. consequences of fracking

• possibility of well leaking & contaminating groundwater with fracking fluid (salt, detergents, acids) or hydrocarbons

• depletion of ground or surface waters nearby (as they’re drawn from for fracking fluid)

• ponds can overflow or leach into ground & contaminate surface or ground waters with fracking fluid (salt, detergents, acids)

  • can be toxic to plants & animals that rely on these water sources

• increased seismic activity (earthquakes) linked with wastewater injection wells (storing fracking fluid deep underground)

• hab. loss/fragment

• methane (CH4 (GHG)) release

6.6: nuclear energy

nuclear fission & radioactivity

• neutron is fired into the nucleus of a radioactive (unstable) element (ex. uranium)

• nucleus breaks apart and releases lots of energy (heat) + more neutrons that break more nuclei apart, releasing more energy (chain reaction)

• radioactivity: refers to the energy given off by the nucleus of a radioactive isotope (uranium-235)

  • radioactive nuclei decay: breakdown and give off energy (radiation) even without fission

  • nuclear fission just releases tons of energy all at once

  • radioactive half-life: the amount of time it takes for 50% of a radioactive substance to decay (breakdown)

    • ex. ½ life of Cobalt-60 isotope = 5.27 yrs.

      • 5.27 yrs, ½ of a Co-60 sample would be decayed

generating electricity

• same electricity generation process as with FFs, just uranium fission to heat water into steam

  • heat →water into steam → steam turns a turbine → turbine powers generator → generator produces electricity

• U-235 stored in fuel rods, submerged in water in reaction core; heat from fission turns H2O → steam...

  • control rods are lowered into reactor core to absorb neutrons and slow down the reaction, preventing meltdown (explosion)

  • water pump brings in cool water to be turned into steam and also cools reactor down from overheating

  • cooling tower allows steam from turbine to condense back into liquid and cool down before being reused (this gives off H2O vapor)

nonrenewable but cleaner FFs

• nuclear energy is nonrenewable because radioactive elements are limited

• no air pollutants (PM, SOx/NOx) or CO2/CH4 released when electricity is generated; mining of uranium & plant construction still release GHGs

• other drawbacks of nuclear energy include possibility of meltdown & radioactive contamination

  • spent Fuel Rods: used fuel rods remain radioactive for millions of years & need to be stored in lead containers on site @ Nuclear PPs

  • mine tailings: leftover rock & soil from mining may have radioactive elements that can contaminate water or soil nearby

  • water use: nuclear PPs require lots of water and can deplete local surface or groundwater sources

    • only gas released from elec. gen. is water vapor (which is technically a GHG, but stays in atm, very briefly)

  • thermal pollution: hot water from PP released back into surface waters can cause thermal shock (decreased O2 & suffocation)

nuclear meltdowns

• 3 mile island (u.s.), (US), fukushima (japan), and chernobyl (ukraine) = 3 most famous nuclear meltdowns

  • fukushima: an earthquake and tsunami triggered cooling pump failure that lead to a meltdown (explosion of reactor core) & widespread radiation release

  • chernobyl: stuck cooling valve during test lead to complete meltdown (explosion of reactor core), several deaths, and widespread radiation release

  • 3 mile island: partial meltdown due to testing error; radiation released but no deaths or residual cancer cases

• env. consequences of meltdowns: genetic mutations & cancer in surrounding people, animals, and plants due to radiation released from reactor core

  • contaminated soil: radiation can remain in soil and harm plants and animals in the future (genetic mutations)

  • radiation spread: radiation can be carried by the wind over long distances, affecting ecosystems far from the meltdown site

6.7: energy frrom biomass

biomass v. biofuels

• utilized primarily in developing world for heating homes & cooking food

• easy to harvest, available, cheap/free (subsistence fuel)

• biomass: organic matter (wood/charcoal, dried animal waste, dead leaves/brush) burned to release heat - primarily for heating homes/cooking

  • can also be burned in PPs to generate electricity (less common than FFs)

• biofuels: liquid fuels (ethanol, biodiesel) created from biomass (corn, sugar cane, palm oil)

  • used as replacement fuel sources for gasoline, primarily in vehicles

modern v. fossil carboon

• biomass burning releases CO2, but doesn’t increase atmospheric CO2 levels like FF burning does

  • burning biomass releases modern carbon (CO2 that was recently sequestered, or taken out of the atmosphere)

  • FF burning releases fossil carbon that had been stored for millions of years

• biomass burning is considered “carbon neutral”

human health & env. consequences of biomass burning

• biomass burning releases CO, NOx, PM, and VOCs (all respiratory irritants)

  • 3 billion people globally cook on open, biomass fires, mostly in developing world

• lack of environmental protection laws & financial resources for other fuels lead to more biomass deforestation in developing nations

• hab. loss, soil erosion, loss of CO2 sequestration, air & H2O filtration

• biomass burn. indoors for heat/cooking worsens effects (pollutants trapped & conc.)

  • worsened asthma, bronchitis, COPD, emphysema, eye irritation

• env. consequences = deforestation & air pollutants

• NOx, VOCs, and PM all contribute to smog formation

biofuel ethanol & algae

• corn & sugar cane are fermented into ethanol which is mixed w/ gasoline

  • corn grain/sugar cane broken down & yeast ferment sugars → ethanol

• soil erosion, hab. loss, GHG release (ag. soils, tractors, fertilizers) H2O use

• lots of corn needed, relative to petroleum; can compete w/human cons. of corn

  • E85 or flex fuel = 51-83% ethanol + gasoline mix; used in flex-fuel vehicles

• decreases oil consumption for transport, but is less efficient than pure gasoline

  • env. consequences = all the neg. consequences of monocrop ag.

• “renewable” only to the extent that the production of corn is sustainable (sugar cane is a perennial, and is more sustainable)

• algae produce oils that can be used as biofuels more sustainably than corn

biodiesel

• liquid fuels produced specifically from plant oils (soy, canola, palm)

  • palm oil biodiesel has been found to produce 98% more GHGs than FFs, due to clearing of forest for palm plantations

• can be more sustainable if already cleared land is used, or if plantations are continually replanted (however, also causes all the env. impacts of ag.)

  • CO2 release, loss of hab., soil erosion, loss of air/H2O filtration

6.8: solar energy

active v. passive solar energy

• passive solar: absorbing or blocking heat from the sun, w/out use of mechanical/electrical equip.

  • using sun’s heat to cook food in a solar oven

  • orienting building design to block sunlight in warmer months & allow sunlight in during colder months

  • double paned windows, southern facing windows w/roof overhang, deciduous shade trees, skylight to decrease elect. use, dark colored sunlight abs. floor

• active solar: use of mechanical/electrical equip. to capture sun’s heat (solar water heaters or CST - concentrated solar thermal), or convert light rays directly into electricity (PV cells)

  • solar water heaters capture sun’s heat in water or circulating fluid & transfer heat to warm water for home (in place of electric/gas water heater)

  • photovoltaic cells (PV): aka “solar panels”; contain semiconductor (usually silicon) that emits low voltage electrical current when exposed to sun

    • photons (particles carrying energy from sun) cause separation of charges between two semiconductor layers (n & p); electrons separate from protons & flow through circuit to load, delivering energy (as electricity)

• drawback is intermittency (solar energy can only be generated during the day)

• could be solved by cheaper, larger batteries that can store energy generated during the day for use at night

  • currently these aren’t cost-effective yet

  • PV cells on a roof can directly power the building, or send excess electricity back to the grid for other users (earning you a credit from your utility company)

• concentrated solar thermal (CST): heliostats (mirrors) reflect sun’s rays onto a central water tower in order to heat water to produce steam to turn a turbine → electricity

  • drawback is habitat destruction & light beams frying birds in mid air

community (solar farm) v. rooftop solar

• large-scale solar “farms” can generate lots of electricity, but do take up land and cause habitat loss/fragmentation

• rooftop solar doesn’t take up land, but only produces a little electricity

solar energy pros

• no air pollutants (PM, SOx, NOx) released to gen. electricity

• no CO2 released when gen. electricity

• no mining of fossil fuels for electricity production

• renewable, unlike FFs

solar energy cons

• solar panel farms can displace habitats

• silicon is a limited resource

  • semiconductor metals (silicon) still need to be mined to produce PV cells (solar panels)

  • can disrupt habitats & pollute water with mine tailings, air with PM

6.9: hydroelectricity

overview

• kinetic energy of moving water → spins a turbine (mechanical energy) → turbine powers generator

• water moves either with natural current of river or tides, or by falling vertically through channel in a dam

• by far the largest renewable source of electricity globally

  • china, brazil, and u.s. = 3 biggest hydroelectricity producers

water impoundment (dams)

• dam built in a river creates a large artificial lake behind the dam (reservoir)

  • damming the river enables operators to allow more or less water through the channel in the dam, increasing or decreasing electricity production (water flows through channel, turns turbine, turbine powers generator → electricity)

    • also allows for control of flow downstream, prevention of seasonal flooding due to high rainfall

• reservoirs are also a source of recreation money (boating fees, tourism, increased property values, fishing, etc.)

• 2 big impacts = flooding of ecosystems behind dam & sedimentation (buildup of sediments behind dam)

run of river & tidal energy

• dam diverts the natural current of a river through man-made channel beside the river

• natural current of the river turns the turbine...powers the generator...electricity

  • less impactful to surrounding ecosystem since no reservoir is formed & ecosystems behind dam aren’t flooded

  • doesn’t stop natural flow of sediments downstream like water impoundment systems do

  • doesn’t generate nearly as much power & may be unavailable in warmer seasons when river water levels are lower

• tidal power comes from tidal ocean flow turning turbine (coastal areas only)

drawbacks of hydrodams

• reservoir floods habitats behind dam (forests/wetlands → gone; river becomes a lake)

• prevents upstream migration of fish like salmon, that need to swim up to spawning grounds to reproduce

• sedimentation changes upstream & downstream conditions

  • upstream becomes warmer (less O2) and rocky streambed habitats covered in sediment

  • downstream loses sediment (important nutrient source), decreased water level, loses streambed hab.

  • downstream wetlands especially suffer since nutrients in sediment doesn’t reach them

  env. impacts = FF combustion during dam construction, increased evap. due to larger surface area of reservoir, and methane release due to anaerobic decomp. of organic matter in reservoir

• econ. impacts = human homes & businesses must be relocated due to reservoir flooding, Initial construction is very expensive (does create long-term jobs though), sediment buildup must be dredged (removed by crane) eventually

• loss of ecosystem services from downstream wetlands, potential loss of fishing revenue if salmon breeding is disrupted

benefits of hydrodams

• no GHG emissions when producing electricity (initial construction does require cement & machines that emit GHGs)

• reservoir & dam can be tourist attractions

• jobs are created to maintain the dam

• reliable electricity source generated for surrounding area

• no air pollutants released during electricity generation (no PM/SOx/NOx)

• allows for control of downstream seasonal flooding

• in u.s., only 3% of dams are for hydroelectricity; 37% are for recreation/scenic purposes; 2nd most common purpose is flood control (allowing humans to build closer to rivers in floodplains that would normally be flooded seasonally)

  • this flood prevention is good for humans, but deprives river flood plains of nutrient-rich sediment that supports plant growth & nearby wetland habitats

fish ladders

• cement “steps” or series of pools that migratory fish like salmon can use to continue migration upstream, around or over dams

• enables continued breeding for salmon, food source for predators like large birds, bears, and fishing revenue for humans

• “salmon cannon” is a similar alternative that enables salmon to be captured or directed into a tube that carries them over the dam

6.10: geothermal energy

overview

• natural radioactive decay of elements deep in earth’s core gives off heat, driving magma convection currents which carry heat to upper portion of mantle, close to earth’s surface

• water can be piped down into the ground and heated by this heat from the mantle

  • hot water can be converted into steam → turbine → elect. or be used to heat homes directly

  • water is cooled in cooling tower & returned to the ground to start the process over

• heat from magma turns the water into steam, which is forced through pipes to spin a turbine

• geothermal for electricity: naturally heated water reservoirs underground are drilled into & piped up to the surface (or water can be piped down into naturally heated rock layers

  • renewable since heat from earth’s core won’t run out; but only if groundwater is returned after use

• often referred to as “geothermal” but technically the heat does not come from geologic activity (comes from the ground storing heat from the sun)

ground source heat pump

• more accurate name is “ground source heat pump”

• heat absorbing fluid is pumped through a pipe into the ground where it either takes on heat from the ground, or gives off heat to the ground

• in summer: heat from home transfers to liquid & liquid transfers heat to the ground, cooling house

  • 10 feet down, the ground stays a consistent 50-60o due to holding heat from sun (not warmed by geothermal energy from magma - so not technically geothermal energy)

• in winter: liquid takes heat from ground & transfers it to the house, warming house 50-600 F

geothermal heating

• true geothermal heating involves piping water deep into ground to be heated by magma & then transfering heat from water to the building

  • fifferent than ground source heat pump

• heated water is piped up to surface & sent to homes or businesses to heat them

  • well must go thousands of meters (kms) down into the ground to reach heated water reservoir

geothrmal pros & cons

• pros:

  • potentially renewable, only if water is piped back into the ground for reuse

  • no release of (PM/SOx/NOx/CO) as is case with FFs

  • not everywhere on earth has access to geothermal energy reaching close enough to surface to access it

  • much less CO2 emission than FF electricity

• cons:

  • hydrogen sulfide can be released, which is toxic and can be lethal to humans & animals

  • cost of drilling that deep in the earth can be very high initially

    • sometimes so high that it’s not even worth it

6.11: hydrogen fuel cell

overview

• H2 gas enters fuel cell where it’s split into protons (H⁺) and electrons (e^-) by an electrolyte membrane that only lets protons pass through

  • use hydrogen as a renewable, alternative fuel source to fossil fuels

  • H2 gas and O2 are the inputs used to generate electricity; H2O is given off as a waste product

    • H2 gas enters fuel cell where it’s split into protons (H+) and electrons (e-) by an electrolyte membrane that only lets protons pass through

    • e- take an alternative route (circuit) around the membrane, which generates an electrical current

    • O2 molecules enter fuel cell break apart into individual O atoms and combine with two hydrogens (H+) to form H2O as a by product (only emissions from F fuel cells)

• most common application is in vehicles

  • replaces gasoline (non-renewable, GHG releasing & air polluting) with H fuel (no air pollutants released & only H2O vapor)

creating H2 gas

• key challenge to H fuel cells is obtaining pure H gas (b/c it doesn’t exist by itself as a gas naturally)

  • separating H2 gas from other molecules like H2O or CH4 is very energy intensive

• two main processes are steam reforming (95% of all H production) and electrolysis (less common, but more sustainable)

  • steam reforming: burning natural gas (CH4) & using steam to separate the H gas from the methane (CH4)

    • emits CO2 & requires NG (FF) input

  • electrolysis: electrical current is applied to water, breaking it into O2 and H2

    • no CO2 emission, but does require electricity

pros of hydrogen carrier

• because H2 gas can be stored in pressurized tanks, it can be transported for use creating electricity later, in a different location

  • unlike solar, hydro, and wind where the electricity must be used as soon as it’s generated & relatively closely to the location of generation

• can also be used as a fuel for vehicles (replacing gasoline) or to create ammonia for fertilizer, or in the chemical industry

• as a gasoline replacement, it emits no air pollutants (NOx/PM/CO) and only H2O (tech. a GHG) no CO2

• manufacture of many different industrial chemicals requires H2 gas

• can be stored as liquid or gas, making it easy to transport

• H fuel cells are approx. 80% efficient in converting chemical energy in H2 & O2 into eleccricity (Coal PP = 35% efficient)

drawbacks of H fuel cells

• since 95% of H2 production requires methane (CH4), H fuel cells are based on a non-renewable & CO2 releasing energy source

• if electrolysis is used to produce H2, it’s only as sustainable as the electricity source

• widespread H fuel cell use would require building widespread H distribution network (similar to current system for gasoline)

• H fuel stored in gas form in vehicles would require much larger tanks than current gasoline tanks

6.12: wind energy

wind turbine electricity generation

• kinetic energy of moving air (wind) spins a turbine; generator converts mechanical energy of turbine into electricity

• blades of turbine are connected to gearbox by a shaft that rotates; rotating gears create mechanical energy that the generator transforms into electricity

• avg. turbine can power 460 homes

  • avg. wind turbine has 15-30% capacity factor (% of total possible energy it could generate)

• only produces electricity in 8-55 mph winds

• motorized drive within shaft can turn the turbine to face wind

wind turbine location

• clustered in groups (wind projects or farms) in flat, open areas (usually rural)

  • locating them together makes service, repair, and building transmission lines to them easier

• can share land with agricultural use

• capitalizes on faster wind speeds

• does require transmission lines built across long distances to reach land though

• offshore wind = wind farms in oceans or lakes

wind energy pros & cons

• pros:

  • non-depletable (isn’t decreased by its use) - even better than renewable!

  • No GHG emissions or air pollutants released when generating electricity

  • no CO2 (climate change) or NOx/SOx/PM as with burning FFs

  • nan share land uses (don’t destroy habitat or cause soil/water contamination as FFs do)

• cons:

  • intermittency (isn’t always available) can’t replace base-load power (sources that are always available like FFs, nuclear or Geothermal)

  • can’t replace base-load power (sources that are always available like FFs, nuclear or Geothermal)

  • can kill birds and bats (especially larger, migratory birds)

  • can be considered an eyesore or source of noise pollution by some

6.13: energy conservation

small-scale v. large-scale conservation

• lowering thermostat to use less heat or use AC less often

• conserving water with native plants instead of grass, low flow shower heads, efficient toilets, dishwashers, dryers

• energy efficient appliances, better insulation to keep more heat in home

  • improving fuel efficiency (fuel economy) standards

    • ex. 20 mpg → 30 mpg

• subsidizing (tax credits for) electric vehicles, charging stations, and hybrids

• increased public transport (buses & light rails), green building design

sustainable home design

• using passive solar design concepts to trap sun’s heat & decrease energy from heating system (heat absorbing walls, triple or double paned windows)

• well-insulated walls/attic to trap heat in winter & cool air from AC system in summer

  • this decreases electricity used by AC unit & energy used by heating system

• deciduous shade trees for landscaping (leaves block sun in summer, but allow it in during winter)

  • ways to either block out or take advantages of sun’s natural heat, or keep in heating/cooling to decrease energy required

water conserv.

• low-flow showers, toilets, and dishwashers do the same job with less total water (less energy to purify & pump to homes)

• rain barrels allow rain water to be used for watering plants or washing cars

• native plants require less watering than traditional lawns (also increase biodiversity of pollinators & require less fertilizer)

transport.

• approx. 28% of total u.s.s energy use comes from transport of goods & people (2019)

• improving fuel economy of u.s.s fleet of vehicles conserves energy as less gasoline/diesel is needed to travel same distance

• CAFE (corporate average fuel economy): standards are regulations set in u.s. to require auto manufacturers to make cars that meet certain MPG standards, or pay penalties

  • hybrids (Prius): have both a gasoline & electric engine, enabling them to have higher MPG ratings

• breaking system charges the electric battery, which powers electric motor

• electric vehicles (EVs or BEVs) use no gasoline, but still require electricity (only as sustainable as elect. source)

• public transit & carpooling are even better energy-saving transport options

sustainable building design

• sun lights on roof, or windows on sides can decrease electricity used for lighting

• recycled materials can reduce energy required to produce new ones (glass, wood, even fly ash from coal can be used in foundation)

• green roof or walls can decrease runoff, and absorb sun’s heat, decreasing energy needed for cooling building & surrounding area (lessens heat island effect)

• decreasing the amount of energy required to build larger buildings & heat/cool them

managing peak demand & smart grid tech.

• peak demand: time of day or year (often early night time hours or very hot weather events) that electricity demand is highest

  • if demand exceeds supply, rolling blackouts occur

• to manage peak demand, some utilities use a variable price model for electricity

  • users pay a lower rate/kWh when using a lower amount of energy (incentivizes lower overall use)

    • users pay a higher rate during peak demand hours or events, to discourage use

• “smart grid”: the idea of managing demand & energy sources in a more varied way

  • ex. using smart meters for variable price models, allowing rooftop solar to direct electricity back to grid, integrating more total energy sources (especially renewable)

unit 7

7.1: intro to air pollution

overview

• clean air act (1970): identified 6 criteria air pollutants that the EPA is required to set acceptable limits for, monitor, and enforce 

• sulfur dioxide (SO2): coal combustion (electricity); resp. irritant, smog, acid precipitation

• nitrogen oxides (NO & NO2): all FF combustion (gas esp.); O₃, photochem smog, acid precip.

• carbon monoxide (CO): incomplete combustion; O₃, lethal to humans

• particulate matter (PM): FF/biomass combustion; resp. irritant, smog

• ozone (tropospheric): photochemical oxidation of NO2; resp. irritant, smog, plant damage

• lead (Pb): metal plants, waste inceneration; nurotoxicant

air pollutants v. GHG

• co2 is not on clean air act

• co2 doesn’t diectly lower air quality from human health standpoint

  • not toxic to organisms to inhale

  • not damaging to lungs/eyes

  • doesn’t lead to smog (decreased visibility)

• co2 is a GHG (it does lead to climate change and env. imconsequences that affect humans)

• co2 isnt consideed air pollutant, but SO2, NOx, O3, and PM are

coal combustion

• releases more air pollutants than other FFs (approx. 35% of global electricity)

• releases CO, CO₂, SO₂, NO_x toxic metals (mercury, arsenic, lead), and PM (often carries the toxic metals)

• impacts of SO_2:

  • respiratory irritant (inflammation of bronchioles, lungs), worsens asthma & bronchitis

  • sulfur aerosols (suspended sulfate particles) block incoming sun, reducing visibility & photosynthesis

  • forms sulfurous (grey) smog

  • combines with water & O₂ in atmosphere to form sulfuric acid → acid precip.

nitrogen oxides (NOx)

• released by combustion of anything, especially FFs & biomass

• NO_x refers to nitrogen oxides (both NO, and NO₂) 

  • NO forms when N₂ combines with O₂ (esp. during combustion) 

  • NO can become NO₂ by reacting with O₃ or O₂

  • sunlight converts NO₂ back into NO

• env. & human health impacts:

  • esp. irritant

    lLeads to tropospheric ozone (O₃) formation, which leads to photochemical smog

  • combines with water & O₂ in atm. to form nitric acid = acid precipitation

EPA & lead

• before CAA, lwad was common gasoline additive; PA began phaseout of lead from gas in 1974

• vehicles made after 1974 are required to have catalytic converters to reduce NO_x, CO and hydrocarbon emissions (lead damages catalytic converters)

  • also a neurotoxicant (damages nervous systems of humans)

primary & secondary air pollutant

• primary: emitted directly from sources such as vehicles, power plants, factories, or natural sources (volcanoes, forest fires)

  • NO_x, CO, CO₂*, VOCs, SO₂, PM, hydrocarbons

• secondary: prrimary pollutants that have transformed in presence of sunlight, water, O₂ 

  • occur more during the day (since sunlight often drives formation)

  • tropospheric O₃ (ozone), sulfuric acid (H₂SO₄) & sulfate (SO₄^2-), nitric acid (HNO₃) & nitrate (NO₃^-)

7.2: photochemical smog

precursors & conditions

• precursors: broken by sunlight into NO + O (free O + O2 → O3): NO2  

• VOCs: volatile organic compounds (hydrocarbons) that bind with NO & form photochemical oxidants

  • carbon-based compounds that volatilize (evaporate) easily (this makes them “smelly”)

  • sources: gasoline, formaldehyde, cleaning fluids, oil-based paints, even coniferous trees (pine smell)

• O3 forms when NO2 is broken by sunlight & free O binds to O2

  • resp. irr. in troposphere (@earth’s surface) 

  • damaging to plant stomata, limiting growth

• conditions:

  • sunlight: drives O3 formation by breaking down NO2 → NO + O; then free O atom binds with O2

  • warmth: hotter atm. temp. speeds O3 formation, evaporation of VOCs & thus smog formation

normal O3 formation

impacts & reduction of smog

• impacts:

  • env.: reduces sunlight; limiting photosynthesis; decreased ag. yields due to less sunlight reaching crops & damage to plant stomata 

  • humans: resp. irritant; worsens asthma, bronchitis, COPD; irritates eyes

  • economic: increased health care costs to treat asthma, bronchitis, COPD

    • lost productivity due to sick workers missing work or dying

• reduction:

  • vehicles: decreasing the number of vehicles on the road decreases NO2 emissions

    • fewer vehicles = less gas = fewer VOCs

      • Carpooling, public transport, biking, walking, working from home

  • energy | Increased electricity production from renewable sources that don’t emit NOx (solar, wind, hydro)

    • nat. gas power plants release far less NOx than coal

      O3 damages plant stomata and irritates animal resp. tracts

7.3: thermal inversion

urban heat island effect

• urban areas tend to have higher surface & air temperature than surrounding suburban and rural areas due to:

  • lowerr albedo: concrete & asphalt absorb more of sun’s energy than areas with more vegetation (absorbed sunlight is given off as IR radiation - heat)

  • less evapotranspiration: water evaporating from surfaces and transpiration from plants carries heat from surface into the atmosphere

    • this cools off rural & suburban areas which have more vegetation

effects of thermal inversion

• air pollutants (smog, PM, ozone, SO2 , NOx)  trapped closer to earth

• respiratory irritation: asthma flare ups leading to hospitalization, worsened COPD, emphysema

• decreased tourism revenue

• decreased photosynthetic rate

7.4: atmospheric co2 & pm

natural sources of air pollutants

• lightning strikes: convert N2 in atm. to NOx

• forest fires: CO, PM, NOx

  • combustion of biomass also releases CO2 & H2O vapor (greenhouse gasses)

• plants (esp. conifers): plants emit VOCs

  • ex. terpenes & ethylene from pine, fir, spruce trees. This forms natural photochemical smog in Smoky Mountains

• volcanoes: SO2, PM, CO, NOx

natural sources of co2 and pm

• respiration: all living things (plants included) release CO2 through respiration

• natural PM sources: sea salt, pollen, ash from forest fires & volcanoes

  dust (windborne soil); leads to haze (scattering of sunlight & reduced visibility)

• aerobic decomposition → Decomposition of organic matter by bacteria & decomposers in the presence of oxygen = releases co2

• anaerobic decomposition: decomposition of organic matter by bacteria & decomposers in low or oxygen-free conditions = releases CH4 (methane)

7.5: indoor air pollutants

developing v. developed countries

• developing nations use more subsistence fuels such as wood, manure, charcoal (biomass)

  • these biomass fuels release CO, PM, NOx, VOCs ( can also cause deforestation)

  • often combusted indoors with poor ventilation, leading to high concentrations

  • est. 3 billion people globally cook with subsistence fuels, resulting in est. 3.5 - 4.3 million deaths annually

• developed nations use more commercial fuels (coal, oil, natural gas) supplied by utilities

  • typically burned in closed, well ventilated furnaces, stoves, etc.

• major indoor air pollutants in developed nations come from chemicals in products: adhesives in furniture, cleaning supplies, insulation, lead paint 

PM & asbestos

• particulates (PM): a common indoor air pollutant

  • ex. smoke (from indoor biomass combustion or cigarettes), dust, and asbestos

• asbestos: long, silicate particle previously used in insulation (since been linked to lung cancer & asbestosis)

  • phased out of use, but still remains in older buildings

    • not dangerous until insulation is disturbed and asbestos particles enter air & then resp. tract

    • should be removed by trained professionals with proper respiratory equipment, ventilation in the area it’s being removed from, plastic to seal off area from rest of the building

carbon monoxide

• CO is produced by incomplete combustion of basically any fuel

  • not all the fuel is combusted due to low O2 or temp.

• CO is an asphyxiant: causes suffocation due to CO binding to hemoglobin in blood, displacing O2

  • lethal to humans in high concentrations, especially with poor ventilation (odorless and colorless - hard to detect)

• developed nations: CO released into home by malfunctioning natural gas furnace ventilation

  • can be detected by carbon monoxide detectors (similar to smoke detectors) 

• developing nations: CO emitted from indoor biomass combustion for heating/cooking

VOCs

• chemicals used in variety of home products that easily vaporize, enter air, and irritate eyes, lungs, bronchioles

  • adhesives/sealants: chemicals used to glue carpet down, hold furniture together, seal panels 

• formaldehyde: common adhesive in particle board and carpet glues (new carpet smell) 

• cleaners: common household cleaners and deodorizers such as febreeze 

• plastics and fabrics: both can release VOCs themselves, or from adhesives used in production

radon gas

• radioactive gas released by decay of uranium naturally found in rocks underground (granite especially)

  • usually enters homes through cracks in the foundation & then disperses up from basement/foundation through home

    • can also seep into groundwater sources & enter body through drinking water

• 2nd leading cause of lung cancer after smoking

  • EPA recommends testing homes with airborne Radon monitor

  • sealing cracks in foundation can prevent it from entering and increasing ventilation in the home can disperse it if it’s detected

dust & mold

• natural indoor air pollutants that can worsen asthma, bronchitis, COPD, emphysema

• dust settles in homes naturally, is disturbed by movement, entering air and then respiratory tract

• mold develops in areas that are dark and damp and aren’t well ventilated (under sinks/showers, behind panels in walls and ceiling)

• black mold is a class of mold that releases spores into air 

  • esp. harmful to resp. system 

  • can be removed by physically cleaning mold out and fixing the water leak or ventilation issue that lead to mold forming

lead

• found in paint in old homes (EPA banned lead paint in 78’)

• paint chips off walls/windows and is eaten by small children (due to curiosity & sweet taste) or inhaled as dust

• lead water pipes can also release lead into drinking water sources (as in Flint) but it’s less common than lead paint

  • damages central nervous system of children due to smaller size and still developing brain

• can be removed from home by stripping lead paint and replacing with non-lead based paint

• lead water pipes can be replaced by cities with copper pipes

7.6: reduction of air pollutants

reducing emissions

• reducing emissions = reducing air pollutants

  • drive less, walk/bike/bus more

  • conserve electricity (smart appliances)

  • eat more plants, less meat

  • renewable, non-pollution emitting energy (solar, wind, hydro)

laws/regulations

• clean air act: allows EPA to set acceptable levels for criteria air pollutants

  • monitor emissions levels from power plants and other facilities

  • tax/sue/fine corporations that release emissions above levels

• CAFE vehicle standards (corporate avg. fuel economy): standards require the entire u.s. “fleet” of vehicles to meet certain average fuel 

  • requires vehicle manufacturers to work to make more efficient vehicles

  • more efficient vehicles burn less gasoline and release less NOx, PM, CO, and CO2 

• pollution credits: similar to ITQs for fish; companies that reduce emissions well below EPA-set levels earn pollution credits

  • can sell these to companies that release more than acceptable levels

reducing vehicle air pollutants

• vapor eecovery nozzle: capture hydrocarbon VOCs released from gasoline fumes during refueling

  • separate tube inside nozzle captures vapors & returns them to underground storage tank beneath the gas station

  • reduces VOCs, which contribute to smog & irritate resp. tracts

    • also reduces benzene (carcinogen) released from gasoline vapors 

  catalytic converter (CC):required on all vehicles after 1975

  • contains metals (platinum & palladium) that bind to NOx and CO

    • CC converts NOx, CO, and other hydrocarbons into CO2, N2, O2, and H2O

reducing SOx & NOx

• crushed limestone (SO2): used to reduce SO2 from coal power plants

  • crushed coal mixed with limestone (calcium carbonate) before being burned in boiler

  • calcium carbonate in limestone combines with SO2 to produce calcium sulfate, reducing the SO2 being emitted

  • calcium sulfate can be used to make gypsum wallboard or sheetrock for home foundations 

• fluidized bed combustion (NOx): fluidizing jets of air pumped into combustion “bed”

  • jets of air bring more O2 into rxn, making combustion more efficient and bringing SO2 into more contact with calcium carbonate in limestone

    • also allows coal to be combusted at lower temp, which emits less NOx

wet & dry scrubbers

• dry scrubbers (NOx, SOx, VOCs): large column/tube/pipe filled with chemicals that absorb or neutralize oxides (NOx, SOx, VOCs) from exhaust streams (emissions)

  • calcium oxide is a common dry scrubber additive which reacts with SO2 to form calcium sulfite

• wet scrubbers: (NOx, SOX, VOCs, & PM): may involve chemical agents that absorb or neutralize NOx, SOx, VOCs, but also include mist nozzles that trap PM in water droplets as well

  • mist droplets with pollutants and PM trapped in them fall to bottom of scrubber or get trapped @ top by mist eliminator

  • sludge collection system traps polluted water for disposal

rerducing PM

• electrostatic precipitator: power plant/factory emissions passed through device with a neg. charged electrode, giving particles a neg. charge

  • neg. charged particles stick to pos. charged collection plates, trapping them

  • plates discharged occasionally so particles fall down into collection hopper for disposal in landfills 

• baghouse filter: large fabric bag filters that trap PM as air from combustion/industrial process passes through 

  • shaker device knocks trapped particles loose into collection hopper below

    • PM collected & taken to landfill

7.7: acid rain

sources of NOx & SO2

• NOx and SO2 are the primary pollutants that cause most acid precipitation

• major sources

  • SO2: coal fired power plants, metal factories, vehicles that burn diesel fuel

  • NOx: vehicle emissions, diesel generators coal power plants 

• limiting acid rain

  • reducing NOx & SO2 emissions; reduces acid deposition

    • higher CAFE Standards

    • more public transit

    • renewable energy sources 

    • more efficient electricity use

• since passage of CAA, acid deposition has decreased significantly

env. effects of acid rain

• acidity = higher H+ ion concentration, lower pH

• soil/water acidification

  • H+ ions displace or leech other pos. charged nutrients (Ca2+, K+) from soil

  • H+ ions also make toxic metals like aluminum and mercury more soluble in soil and water

  •  This can slow growth or kill plants and animals living in the soil or water

• aquatic species have diff. pH tolerances

  • as pH decreases (more acidic) outside optimal range for a species, pop. declines

    • when pH leaves range of tolerance, they cannot survive at all, due to:

      • aluminum toxicity

      • disrupted blood osmolarity (Na+/Cl- balance disrupted at low pH)

  • indicator species: can be surveyed and used to determine conditions of an ecosystem (soil, water, etc.)

    • ex. high whitemoss/filamentous algae pop. indicates pH < 6.0

      • high crustacean pop. indicates pH > 6.0

mitigating acid rain

• limestone: natural base that can neutralize acidic soil/water

  • calcium carbonate (CaCO3) reacts with H+ ions, forming HCO3 and giving off Ca2+

    • this “neutralizes” acidic water/soil, moving it closer to a pH of 7

• regions with limestone bedrock have some natural buffering of acid rain

  • humans can also add crushed limestone to soils/waters to neutralize

  • acid rain can corrode human structures, especially those made from limestone

rerducing SO2 & NOx

• decreasing these primary pollutants that drive acid rain can reduce it

  • renewable energy sources, decreasing coal comb.

  • fluidized bed combustion & lower burning temp. for existing coal power plants

  • dry or wet scrubbers

7.8: noise pollution

urban noise pollution

• urban noise pollution: any noise at great enough volume to cause physiological stress (difficulty communicating, headaches, confusion) or hearing loss

• construction: jack hammers, trucks, concrete pouring

• transportation: cars, busses, trains  

• industrial activity: manufacturing plants

• domestic activity: neighbor’s music, lawn mowing, home projects

(land) wildlife effects

• physiological stress: caterpillar hearts beat faster when exposed to simulated highway noise pollution

• could drive pollinator species decline

• hearing: can prevent predators from hearing prey and vice versa; can prevent mates from locating each other (both of these decrease chances of survival)

(aq.) wildlife effcts

• aquatic noise pollution comes from the noise of ship engines, military sonar, and seismic air blasts from oil & gas surveying ships

• physiological stress: hearing loss, disrupted communication, mating calls, predator and prey navigation 

  • whales are especially prone to having migration routes disrupted as their vocal communication is disrupted

  • seismic surveying ships send huge air blasts down into the water, searching for oil by recording how the echo is returned from ocean floor

    • so loud that researchers off the coast of virginia can detect blasts from coast of brazil