Biogeochemical CyclesAn Application of Conservation of Matter
Conservation of Matter• Matter cannot be created or destroyed it can only change form – The amount of matter in the universe is finite (unchanging) – Atoms (of certain elements) are recycled over and over again. – 92 naturally occurring elements make up nearly all matter. – Go through innumerable chemical reactions to both form and breakdown compounds. – For example some of the atoms that now make up your body may have once been part of a dinosaur, a rock, a tree, and a panda bear at one point in their existence.
Cycles• Cycles: Track the movement of matter and energy through a system. Recurring series of events.• System: A group of independent but interrelated parts forming a unified whole. – The planet earth can be viewed as one large system.
Biogeochemical Cycle • Bio = Biosphere (Living Things) • Geo = Geosphere (Rocks / Earth) • Chem = Chemical Factors • Biogeochemical Cycles: Track the repeating movement of atoms and energy through both the living and nonliving parts of the earth system.
Long Term Storage• In most cycles only a fraction of the systems total material is in active circulation.• Reservoirs: Places where elements are stored or held for a long period of time. Effectively takes them out of circulation.• Residence Time: An estimate of how long matter is typically stored in a particular reservoir.
Human Impact• Human activities can have a large impact on biogeochemical cycles. – Alter the natural functioning of systems. – Can have unforeseen negative consequences.• The biggest anthropogenic (caused by humans) impact is mining or removing resources from storage in reservoirs and putting them back into circulation.
Biogeochemical Cycles and Life• Properly functioning cycles are essential to all life on earth.• Living things depend on cycles to provide the nutrients they need.• Living things, like all matter (and elephants) are made of elements. Cycles provide those elemental building blocks.
The Human Element?• Almost 99% of the mass of the human body (and most other life forms) is made up of 6 elements: – Oxygen – Carbon – Hydrogen – Nitrogen – Calcium – Phosphorus.• Only about 0.85% is composed of another five elements: – Potassium – Sulfur – Sodium – Chlorine – Magnesium• All are necessary to life.• Around 70% of the human body is made up of a single compound: Water.
Water• Is a compound of hydrogen and oxygen. – H20• The intermolecular forces (bonds) holding the atoms of a water molecule together are extremely strong. – Makes water a very stable molecule. • Low Reactivity. • Not easy to break H2O down to elements or to form new chemicals.• Essential to life. – You could only survive about a week without water.
The Processes of the Water Cycle Evaporation Condensation Transpiration Precipitation
EvaporationProcess in which liquidchanges to gas (vapor)
TranspirationA continuous processcaused by the evaporationof water from leaves ofplants and itscorresponding uptakefrom roots in the soil.
CondensationCondensation is theprocess by which matterchanges from a gas (orvapor) phase into a liquidphase. Ex. Dew on the grass in the morning, cold glass of liquid, fog on the inside of a car window
Precipitation• When cloud (water molecules) particles become too heavy to remain suspended in the air, they fall to the earth as precipitation.
Surface Run-off Water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle. When the ground is saturated, the water flows into lakes, streams, rivers, and eventually ends up in oceans.
Groundwater• The water that is filtered through the soil and remains under the ground.• Is a major source of drinking water as well as agricultural irrigation.
“Water, water everywhere... but not a drop to drink.”• The overall water cycle "contains" between 1.386 and 1.46 Billion km3 of water in various states (liquid, solid, or gaseous).• The vast majority of it, between 96.5 and 97.25%, is in the Oceans.• Only about 3% of Earths water is fresh water. – 2/3rds of that is frozen in the ice sheets near the poles and in glaciers. – Most of the rest of the fresh water is underground. – Less than 1% of fresh water is on the surface in lakes, wetlands, and rivers. • Only a very small fraction (~.77%) of Earth’s water is suitable for human consumption.
Residence Time in Water Cycle
Storage Reservoirs Within the Water Cycle• The oceans, glaciers and ice caps, lakes, underground aquifers and the atmosphere are some examples of reservoirs.• Most of earth’s water is in “long term storage”. – Not actively circulating.
Death of the Aral Sea• Located in present-day Kazakhstan and Uzbekistan.• 1930’s it was decided that the area surrounding the sea could be used to grow cotton.• By 1960, millions of acres of land were irrigated using water from the two large rivers that fed the Aral Sea.• The sea began to shrink
Aral Sea Impacts • Salinity increased as water was not replenished – Hurt the 60,000 employee fishery industry. – 3x saltier than the ocean. • Lost 90% of it’s original volume. • Many health impacts for the people as the dried salt/pesticide/fertilizer/herb icide laden dust is carried by winds – Increased cancer, higher infant mortality • Local climate changed, growing season shortened, switch from cotton to rice.
Tragedy of the Commons...
Tragedy of the Commons• First proposed by Garrett Hardin in 1968.• When individuals, acting independently and rationally, will use and deplete a shared resource.• Doing so is often not in the individual or larger societies best long-term interests.• Dilemma: If you don’t use it someone else will.• Short term personal gain is at odds with long term communal well being.
Water: The Ultimate Commons• In most countries water is viewed as a common resource.• If you own land, you own the rights to use the water on it and under it.• The problem: All bodies of water are interconnected.• Can use that water however you see fit.• Leads to overuse, and destruction of watershed.
Carrying Capacity• Since resources are finite Earth, and other systems, have a maximum carrying capacity.• Carrying Capacity: The number of individuals a system (such as earth) can sustainably support at a given standard of living.• Sustainable: Can be maintained over generations.• Fresh water, and many other resources, are being used at a rate that is unsustainable. We call this overconsumption.• We’re using fresh water at a rate that is faster than the water cycle can replenish it.
Determining Carrying Capacity• The carrying capacity of a system is governed by two main factors: – Population: • The total number of individuals. • Each individual has certain basic needs that have to be met by the system in order to survive. – Standard of Living: • The degree of wealth and material comfort available to a person or community. • How many resources a person is using.• Since the total amount of resources is constant, as you approach a system’s carrying capacity, an increase in population has to be accompanied by a decrease in standard of living.
Human Population• There are over 7 Billion people living on earth today.• Population is growing exponentially.• More people are being born than are dyeing.
• The human population is now growing at a rate of about 3 people/second or• 260 thousand/day or• 1.8 million per week or• 93 million/year
• Each dot represents 1 million people
Human Population and Resource Use• Conservation of matter. The total amount of water and other resources is constant.• More people means more demand for resources.• The total amount of water on earth remains the same. Even as population increases.• Growing population puts huge stress on system. – More people competing for the same amount of water.
Unequal Usage• 25% of the world’s do not have adequate access to a safe and adequate water supply.• Worldwide 1 Billion people make a daily trip of over 3 hours just to collect water.• 14,000 people die every day from water related illness.• All inclusive estimates (including water used to produce food) from the United Nations state that only about 13 gallons of water per day is the minimum required amount to sustain a human life.• With access to just 1.3 gallons of domestic water each day, more than a billion people in water poor regions around the globe survive on the same amount used to flush a toilet.• In Honduras people spend 25% of their annual income on water.
USA Water Usage • The average American uses 80-100 gallons of water a day for domestic use. • All things considered this number sky rockets to around 2000 gallons of water per day. – Over 1000 times the minimum required to sustain life. – Nearly 95 percent of your water footprint is hidden in the food you eat, energy you use, products you buy, and services you rely on. – Highest per capita water use in developed world. • Water Footprint Calculator • Americans only spend .05% of their annual income on water.
Effects of Excessive Consumption• Key Problem: Fresh water is being consumed at a faster rate than it is being replenished. – If trend continues we will eventually run out of water. – What about Iowa? • We are doing relatively well. The Jordan and Dakota Aquifers are being slightly overused but not at the high rate seen in other parts of the Midwest. – In other parts of the Midwest the water in the Ogallala Aquifer is being removed 8 times faster than it is replenished.• Only a fraction of consumption goes towards day-to-day domestic uses. – 70% Agriculture – 20% Manufacturing – 10% Domestic Use
Ogallala Aquifer: A Cautionary Tale
ANF: America Needs Farmers• As population increases, so does demands for foods.• The food that feeds the majority of Americans, and people around the world, comes from the Midwest.• How do you balance demand for food with issues related to water consumption? – The key is responsible management.
Irrigation• With increased demand for food, people have begun to farm in less than ideal climate zones. – Lack an adequate supply of natural water.• Irrigation enables crops to grow in areas where they could not survive naturally.• Problems: Uses lots of water and is inefficient. – Efficiency ranges from 50-75%• Can lead to an increase in soil salinity that eventually renders the land totally unusable.
Crop Selection• Different food crops require different amounts of water to grow.• By selecting crops appropriate to your region the need for irrigation can be vastly reduced.• For example: – Growing corn makes sense in South East Iowa where water is relatively abundant. – It doesn’t make sense in the Dakota’s where water is scarce.
Managing Runoff and Erosion• Natural vegetation slows down the flow of rainwater. More water is absorbed by the ground, and eventually percolates down into aquifers.• Clearing land for farming leads to an increase in the rate and total amount of runoff. – More fresh water flows into rivers and is ultimately lost in the ocean. – Increased erosion and loss of nutrient rich topsoil.• Faster flow rates can lead to intense Flash Floods.
Preventing Erosion• Plant Buffer Strips: Plant native grasses or trees along the edges of the field or on steep slopes. – CRP Program: Provides compensation for land that is reverted back to native species. Intended to encourage construction of buffer strips and protect highly erodible land and increase groundwater recharge.• Mulching or Cover Crops: Leave waste material on field after harvest or plant cover crop.• Contour Cultivation: Plow in such away that furrows align to natural contour of the land and act as miniature dams.
Deforestation and Urbanization• Deforestation: The removal of trees and other natural vegetation from an area. – Can be for agriculture, industrial, or civil reasons.• Urbanization: Rapid growth and physical expansion of cities. – The cement jungle.• Both Deforestation and Urbanization alter the water cycle in the local area.
The Cement Jungle• Urban Sprawl: The uncontrolled geographic expansion of development and urbanization out from the city center.• Impervious Surface: A surface covering that water cannot pass through. – All of the precipitation that falls on an impervious surface will runoff. – Common examples include cement, asphalt, and rooftops. – Around 43,000 square miles of the USA is covered with impervious surface.
Effects of Pavement• When precipitation falls on impervious surfaces it runs off immediately.• Intensifies and speeds up the water cycle. – More runoff. – Flash flooding. • Flooding occurs more quickly and with greater intensity. – More erosion. – Less ground water recharge.• Rather than being held in the local watershed for later use, this urban runoff is diverted into sewer systems and routed directly into rivers and ultimately the ocean. – Quite literally (fresh) water down the drain.
Solutions• Floodwalls and Levees – Build a large wall to hold back floodwaters. – Problem: Just sends that water downstream… someone elses problem.• Reduce Impervious Surface – Design cities with parks in key areas. – Narrow streets. – New types of permeable pavement.• Rain Water Capture Systems – Cisterns – Trap and hold rainfall for later use.
Dams• Dam: A structure that impounds (blocks) the flow of water in a stream or river.• Used to store large quantities of water for later use. – Attempt to rectify problems associated with urbanization and acceleration of runoff. – Reservoir fills with water during wet season and can be drawn from during dry season or droughts.• Allow for controlled release of water. – Protect downstream areas from flooding. – Outlet flow can be used to generate electricity • Hydroelectric power
Dam Construction Worldwide• 845,000 Number of dams in the world. – Rapid Growth• 80,000 Number of dams in USA.• 65 Percentage of the worlds river water that’s flow is impeded by dams.• 292 Number of major river systems worldwide adversely affected by dam construction (over half).• 50 Average number of years that a hydroelectric dam remains useable.• 85 Percent of the world’s dams that will be obsolete by 2020.
Problems Associated With Dams
High Rate of Evaporation• The water in a reservoir is largely stagnant (not flowing).• Reservoirs, especially in warm dry areas, are prone to solar warming and high evaporation rates.• Can also lead to the creation of a thermocline and hypoxic (oxygen deprived) zones.
Accumulation of Sediment & Toxins• All rivers contain sediments (from erosion).• When a river is stilled behind a dam, the sediments it contains sink to the bottom of the reservoir.• Effectively fills in the reservoir, eventually rendering the dam useless. – The reservoir behind China’s Three Gorges Dam is loosing capacity at a rate of 2.3 percent per year.• This sediment is no longer deposited on floodplains. – Process is crucial to the creation of fertile farmland.• Dams also trap many of the toxins and pollutants carried in river water. These accumulate in the reservoir over time.
Migratory Disruption• Many fish species, including salmon and steelhead trout, seasonally migrate along river systems to spawning grounds.• Dams block these fishes ability to travel upstream.• Dams represent a major threat to 91 percent of endangered fish species.
Geographic Footprint of Reservoir• The construction of a dam and in turn the creation of a reservoir floods a large area of land behind the dam.• This destroys the natural ecosystem of the region.• Displaces people living in the area. – Three Gorges Dam has displaced at least 1.3 million people. • Thirteen cities, 140 towns, and 1,350 villages have been intentionally flooded.• Destroys historic and cultural sites. – With 635 large dams within its borders, Turkey is one of the world’s most active dam building countries. • The proposed Ilisu Dam on the Tigris River would drown the 10,000 year-old city of Hasankeyf.
Catastrophic Failure• 49: Number of dam failures in the United States between 2000 and 2007.• Dam failure can lead to dangerous flooding downstream.• The largest catastrophic failure of a dam was the 1975 Banqiao Dam failure. – Killed 26,000 people immediately. – 145,000 dying of disease later – Displacing 11,000,000 residents.• Teton Dam Collapse• In order to prevent failure in high water seasons large releases often have to be made. – Not as effective of a flood prevention technique as often believed.
Dam Removal• There is a large push to remove the thousands of obsolete dams in the USA.• Restores river system.• Dam Removal
PSA Examples• We All Live Downstream• Funny PSA’s• Save Water• No Water No Joke