Description
This week, you have learned about our physical natural resources (water, soil & minerals) and how our lifestyle choices have put the health and availability of these resources in jeopardy.
This week, you have learned about our physical natural
resources (water, soil & minerals) and how our lifestyle choices
have put the health and availability of these resources in
jeopardy. Now, it’s time to move from an individual focus on
each resource to the inter-relatedness across these three
sources. Using publicly available data and/or figures from this
week’s readings, discuss how these three physical resources are
all linked to each other. What role have our choices played in
declining water access and soil-mineral depletion? Finally, what
practices can we adopt to improve the long-term sustainability
of soil health, in particular?
Be sure to write a detailed main post here, presenting
supporting facts and evidence from reliable sources. When
responding to your classmates, please add to the discussion
with a fact-supported addition, opinion, gentle correction, or
example, citing reliable sources.
Footprinting: Carbon, Ecological and Water from Sustainability: A Comprehensive Foundation by Tom
Theis and Jonathan Tomkin, Editors, is available under a Creative Commons Attribution License 4.0
license. © Dec 26, 2018, Tom Theis and Jonathan Tomkin, Editors.
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9.3.2 Footprinting: Carbon, Ecological and Water
42
9.3.2.1 Footprinting: Carbon, Ecological and Water
9.3.2.1.1 Learning Objectives
After reading this section, students should be able to
• understand what an environmental footprint is and its limitations
• conduct some basic footprinting calculations
• calculate and explain their own footprint
9.3.2.1.2 Basic Concepts of Footprinting
What is a common measure of the impact of an individual, institution, region or nation? This can be done
by measuring the footprint of that entity. When discussing climate change and sustainability the concepts
of carbon footprint and ecological footprint are often used. Understanding how these footprints are derived
is important to the discourse as not all calculations are equal. These footprints can be calculated at the
individual or household level, the institutional level (corporation, university, and agency), municipal level,
sub-national, national or global. They are derived from the consumption of natural resources such as raw
materials, fuel, water, and power expressed in quantities or economic value. The quantity consumed is
translated into the footprint by using conversion factors generally based in scientic or economic values.
note:
•
•
•
•
•
There are many personal calculators available on the internet. Here are a few to try:
EPA Household Emissions Calculator43
Ecological Footprint44
Earth Day Network Footprint45
Cool Climate Network (UC Berkeley)46
Carbon Footprint47
This chapter will discuss three types of footprints ecological, carbon and water and the methodologies
behind them. Although eorts have been made to standardize the calculations comparisons must be approached with caution. Comparing individual, institutional or national footprints that are calculated by the
same method can be helpful in measuring change over time and understanding the factors that contribute
to the dierences in footprints.
9.3.2.1.3 Ecological Footprint
9.3.2.1.3.1 Concept
The Merriam-Webster Dictionary denes footprint48 as:
1. an impression of the foot on a surface;
2. the area on a surface covered by something
42 This content is available online at .
43 http://www.epa.gov/climatechange/emissions/ind_calculator.html
44 http://www.myfootprint.org/
45 http://les.earthday.net/footprint/index.html
46 http://coolclimate.berkeley.edu/
47 http://www.carbonfootprint.com/
48 http://www.merriam-webster.com/dictionary/footprint
Available for free at Connexions
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Similarly, the ecological footprint (EF) represents the area of land on earth that provides for resources
consumed and that assimilates the waste produced by a given entity or region. It is a composite index (see
Module Sustainability Metrics and Rating Systems (Section 9.3.1)) that represents the amount of biologically
productive land and water area required to support the demands of the population in that entity or region
The EF is benecial because it provides a single value (equal to land area required) that reects resource
use patterns (Costanza, 2000 (p. 450)). The use of EF in combination with a social and economic impact
assessment can provide a measure of sustainability’s triple bottom line (Dawe, et al., 2004 (p. 450)). It
can help nd some of the hidden environmental costs of consumption that are not captured by techniques
such as cost-benet analysis and environmental impact (Venetoulis, 2001 (p. 450)). Using the ecological
footprint, an assessment can be made of from where the largest impact comes (Flint, 2001 (p. 450)).
Next, we will discuss the how an EF is calculated.
9.3.2.1.3.2 Methodology
The ecological footprint methodology was developed by William Rees and Mathis Wackernagel (p. 450)
(1996) (p. 450), and consists of two methodologies:
1. Compound calculation49 is typically used for calculations involving large regions and nations and
is shown in Figure Compound Calculation Steps for Ecological Footprint Analysis (p. 437). First,
it involves a consumption analysis of over 60 biotic resources including meat, dairy produce, fruit,
vegetables, pulses, grains, tobacco, coee, and wood products. That consumption is then divided by
biotic productivity (global average) for the type of land (arable, pasture, forest, or sea areas) and the
result represents the area needed to sustain that activity. The second part of the calculation includes
energy generated and energy embodied in traded goods. This is expressed in the area of forested land
needed to sequester CO2 emissions from both types of energy. Finally, equivalence factors are used
to weight the six ecological categories based on their productivity (arable, pasture, forest, sea, energy,
built-up land). The results are reported as global hectares (gha) where each unit is equal to one hectare
of biologically productive land based on the world’s average productivity. We derive sub-national
footprints based on apportioning the total national footprint between sub-national populations. The
advantage of this method is that it captures many indirect of eects of consumption so the overall
footprint is more accurate.
2. Component-based calculation50 resembles life-cycle analysis in that it examines individual products
and services for their cradle-to-grave resource use and waste, and results in a factor for a certain unit
or activity. The footprint is typically broken down into categories that include energy, transportation,
water, materials and waste, built-up land, and food. This method is better for individuals or institutions
since it accounts for specic consumption within that entity. However, it probably under-counts as not
all activities and products could practically be measured or included. It also may double-count since
there may be overlap between products and services.
49 http://www.unesco.org/education/tlsf/mods/theme_b/popups/mod09t05s01.html
50 http://www.footprintnetwork.org/en/index.php/GFN/page/glossary/#consumptioncomponents
Available for free at Connexions
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Figure 9.10: Compound Calculation Steps for Ecological Footprint Analysis Figure shows the
compound calculation steps for ecological footprint analysis. Source: C. Klein-Banai
51
.
9.3.2.1.3.3 What the Results Show
When looking at the sub-national level, it is useful to be able to examine dierent activities that contribute
to the footprint such as energy, transportation, water, waste, and food. In both types of calculations, there is
a representation of the energy ecological footprint. We utilize conversion factors that account for direct land
use for mining the energy source and the land required to sequester any carbon emitted during combustion,
construction, or maintenance of the power source. It should be noted that no actual component-based
calculations have been done for nuclear power. The practice has been to consider it the same as coal so as
to account for it in some way. A discussion of the merits of this method can be found in Wackernagel et al.
(2005) (p. 450).
Transportation is another activity that can be examined at the sub-national level. The transportation
footprint maybe considered part of the energy footprint, or separately, but is basically based on the energy
consumption for transportation. It may also include some portion of the built-up land.
The hydroprint, or water-based footprint, measures the amount of water consumed in comparison to the
amount of water in the land catchment system for the geographical area being footprinted. It can represent
whether the entity is withdrawing more or less water than is naturally supplied to the area from rainfall.
51 http://cnx.org/member_prole/cindykb
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The wasteprint, or waste-based footprint, is calculated using commonly used component-based factors
that have been calculated and compiled in a number of publications and books. Food production requires
energy to grow, process and transport, as well as land for growing and grazing. The factors are derived using
the compound calculation for a certain geographical area. See Case Study: Comparing Greenhouse Gas
Emissions, Ecological Footprint and Sustainability Rating of a University (Section 9.3.3) for an example of
this kind of ecological footprint analysis. This kind of analysis can show us how a nation, region, organization,
or individual uses the planets resources to support its operation or life style, as well as what activities are
the primary contributors to the footprint. In the next section, we will look at some national footprints.
9.3.2.1.3.4 Ecological Footprint Comparisons
Figure 9.11: Ecological Footprints of Select Nations
©
Graph shows the ecological footprints of
select nations. The bars show average EF in global hectares per person for each nation. Each color on
the bar represents the dierent types of land. Source:
Living Planet Report, 2010
53
2010 WWF (panda.org). Some rights reserved.
, gure under CC BY-SA 3.0 License
54
Available for free at Connexions
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The Living Planet Report55 prepared by the World Wildlife Fund56 , the Institute of Zoology57 in London,
and Wackernagel’s Global Footprint Network58 reports on the footprints of various nations. Figure Ecological
Footprints of Select Nations (Figure 9.11) displays the footprint of several nations as shown in the report.
The bars show average EF in global hectares per person for each nation. Each color on the bar represents
the dierent types of land. Here we see that the United Arab Emirates has the largest footprint of 10.2 gha
per person, with the majority of its footprint due to carbon (same as energy land described above). Whereas
Latvia has the lowest footprint displayed at 6.0 gha per person, with the majority of its footprint due to
forestland.
Figure 9.12: United States’ Ecological Footprint
Footprint compared to the global average. Source:
Living Planet Report, 2010
60
©
Figure shows the United States’ Ecological
2010 WWF (panda.org). Some rights reserved.
, gure under CC BY-SA 3.0 License
61
52 http://wwf.panda.org/about_our_earth/all_publications/living_planet_report/2010_lpr/
53 http://wwf.panda.org/about_our_earth/all_publications/living_planet_report/2010_lpr/
54 http://creativecommons.org/licenses/by-sa/3.0/
55 http://wwf.panda.org/about_our_earth/all_publications/living_planet_report/2010_lpr/
56 http://www.worldwildlife.org/home-full.html
57 http://www.zsl.org/science/
58 http://www.footprintnetwork.org/en/index.php/GFN/page/glossary/
59 http://wwf.panda.org/about_our_earth/all_publications/living_planet_report/2010_lpr/
60 http://wwf.panda.org/about_our_earth/all_publications/living_planet_report/2010_lpr/
61 http://creativecommons.org/licenses/by-sa/3.0/
Available for free at Connexions
59
441
Figure United States’ Ecological Footprint (p. 440) shows the national footprint in 2007 of the United
States as 7.99 gha per person both with a bar display and with specic metrics on the right that show the
exact footprint and the United States’ ranking among all nations in the report (e.g. carbon is 5.57 gha and
ranks 3rd largest overall). The bar to the left expresses the world average. The United States’ footprint
of 7.99 gha stands in contrast to the earth’s global biocapacity of 1.8 gha per person. Globally, the total
population’s footprint was 18 billion gha, or 2.7 gha per person. However, the earth’s biocapacity was only
11.9 billion gha, or 1.8 gha per person. This represents an ecological demand of 50 percent more than the
earth can manage. In other words, it would take 1.5 years for the Earth to regenerate the renewable resources
that people used in 2007 and absorb CO2 waste. Thus, earth’s population used the equivalent of 1.5 planets
in 2007 to support their lives.
9.3.2.1.4 Carbon Footprint
Since climate change (see Chapter Climate and Global Change) is one of the major focuses of the sustainability movement, measurement of greenhouse gases or carbon footprint is a key metric when addressing
this problem. A greenhouse gas emissions (GHG) inventory is a type of carbon footprint. Such an inventory
evaluates the emissions generated from the direct and indirect activities of the entity as expressed in carbon dioxide equivalents (see below). Since you cannot manage what you cannot measure, GHG reductions
cannot occur without establishing baseline metrics. There is increasing demand for regulatory and voluntary reporting of GHG emissions such as Executive Order 1351462 , requiring federal agencies to reduce
GHG emissions, the EPA’s Mandatory GHG Reporting Rule63 for industry, the Securities and Exchange
Commission’s climate change disclosure guidance64 , American College and University Presidents’ Climate
Commitment65 (ACUPCC) for universities, ICLEI66 for local governments, the California Climate Action
Registry, and numerous corporate sustainability reporting initiatives.
9.3.2.1.4.1 Scoping the Inventory
The rst step in measuring carbon footprints is conducting an inventory is to determine the scope of the
inventory. The World Business Council for Sustainable Development67 (WBCSD) and the World Resource
Institute68 (WRI) dened a set of accounting standards that form the Greenhouse Gas Protocol (GHG
Protocol). This protocol is the most widely used international accounting tool to understand, quantify,
and manage greenhouse gas emissions. Almost every GHG standard and program in the world uses this
framework as well as hundreds of GHG inventories prepared by individual companies and institutions. In
North America, the most widely used protocol was developed by The Climate Registry69 .
The GHG Protocol also oers developing countries an internationally accepted management tool to help
their businesses to compete in the global marketplace and their governments to make informed decisions
about climate change. In general, tools are either sector-specic (e.g. aluminum, cement, etc.) or crosssector tools for application to many dierent sectors (e.g. stationary combustion or mobile combustion).
62 http://www.fedcenter.gov/Bookmarks/index.cfm?id=13641
63 http://www.epa.gov/climatechange/emissions/ghgrulemaking.html
64 http://www.sec.gov/rules/interp/2010/33-9106.pdf
65 http://www.presidentsclimatecommitment.org/about/commitment
66 http://www.iclei.org/
67 http://www.wbcsd.org/templates/TemplateWBCSD5/layout.asp?type=p&MenuId=NjY&doOpen=1&ClickMenu=LeftMenu
68 http://www.wri.org/
69 http://www.theclimateregistry.org/
Available for free at Connexions
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Figure 9.13: Scopes of a Greenhouse Gas Emissions Inventory Figure shows the three scopes of a
greenhouse gas emissions inventory. Source: New Zealand Business Council for Sustainable Development,
The challenges of greenhouse gas emissions: The why and how of accounting and reporting for GHG
emissions (2002, August), gure 3, p. 10
70
.
The WRI protocol addresses the scope by which reporting entities can set boundaries (see Figure Scopes of
a Greenhouse Gas Emissions Inventory (Figure 9.13)). These standards are based on the source of emissions
in order to prevent counting emissions or credits twice. The three scopes are described below:
Scope 1: Includes GHG emissions from direct sources owned or controlled by the institution production of electricity, heat or steam, transportation or materials, products, waste, and fugitive emissions.
Fugitive emissions are due to intentional or unintentional release of GHGs including leakage of refrigerants from air conditioning equipment and methane releases from farm animals.
• Scope 2: Includes GHG emissions from imports (purchases) of electricity, heat or steam generally
those associated with the generation that energy.
• Scope 3: Includes all other indirect sources of GHG emissions that may result from the activities of the
institution but occur from sources owned or controlled by another company, such as business travel;
outsourced activities and contracts; emissions from waste generated by the institution when the GHG
emissions occur at a facility controlled by another company, e.g. methane emissions from landlled
waste; and the commuting habits of community members.
•
Depending on the purpose of the inventory the scope may vary. For instance, the EPA mandatory reporting
requirements for large carbon dioxide sources require reporting of only Scope 1 emissions from stationary
sources. However, many voluntary reporting systems require accounting for all three scopes, such as the
ACUPCC reporting. Numerous calculator tools have been developed, some publicly available and some
proprietary. For instance many universities use a tool called the Campus Carbon Calculator71 developed
by Clean Air-Cool Planet72 , which is endorsed by the ACUPCC. Numerous northeastern universities collaborated to develop the Campus Carbon Calculator and the calculator has been used at more than 200
70 http://www.nzbcsd.org.nz/climatechange/Climate_Change_Guide.pdf
71 http://www.cleanair-coolplanet.org/toolkit/inv-calculator.php
72 http://www.cleanair-coolplanet.org/toolkit/inv-calculator.php
Available for free at Connexions
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campuses in North America. It utilizes an electronic Microsoft Excel workbook that calculates estimated
GHG emissions from the data collected.
9.3.2.1.4.2 Methodology
GHG emissions calculations are generally calculated for the time period of one year. Figure Steps for
Preparing a GHG Emissions Report (Figure 9.14) shows the steps for reporting GHG emissions. It is
necessary to determine what the baseline year is for calculation. This is the year that is generally used to
compare future increases or decreases in emissions, when setting a GHG reduction goal. The Kyoto Protocol73
proposes accounting for greenhouse gas emissions from a baseline year of 1990. Sometimes calculations may
be made for the current year or back to the earliest year that data is available.
Figure 9.14: Steps for Preparing a GHG Emissions Report
Figure shows the required steps to
take when preparing a GHG emissions report. Source: C. Klein-Banai
74
Next, the institutional or geographic boundaries need to be dened. Also, the gases that are being
reported should be dened. There are six greenhouse gases dened by the Kyoto Protocol. Some greenhouse
gases, such as carbon dioxide, occur naturally and are emitted to the atmosphere through natural and
anthropogenic processes. Other greenhouse gases (e.g. uorinated gases) are created and emitted solely
73 http://ec.europa.eu/clima/policies/brief/eu/index_en.htm
74 http://cnx.org/member_prole/cindykb
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through human activities. The principal greenhouse gases that enter the atmosphere because of human
activities are:
• Carbon Dioxide (CO2)75 : Carbon dioxide is released to the atmosphere through the combustion of
fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of
non-combustion reactions (e.g. manufacture of cement). Carbon dioxide is sequestered when plants
absorb it as part of the biological carbon cycle.
• Methane (CH4)76 : Methane is emitted during the production and transport of coal, natural gas,
and oil. Methane emissions also come from farm animals and other agricultural practices and the
degradation of organic waste in municipal solid waste landlls.
• Nitrous Oxide (N2O)77 : Nitrous oxide is emitted during agricultural and industrial activities, and
combustion of fossil fuels and solid waste.
• Fluorinated Gases78 : Hydrouorocarbons, peruorocarbons, and sulfur hexauoride are synthetic,
powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases
are sometimes used as substitutes for ozone-depleting substances79 (i.e. Chlorouorocarbons (CFCs),
hydrochlorouorocarbon (HCFCs), and halons). CFCs and HCFCs are gases comprised of chloride,
uoride, hydrogen, and carbon. Halons are elemental gases that include chlorine, bromine, and uorine.
These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases,
they are sometimes referred to as High Global Warming Potential gases (High GWP gases).
Each gas, based on its atmospheric chemistry, captures dierent amounts of reected heat thus contributing
dierently to the greenhouse eect, which is known as its global warming potential. Carbon dioxide, the
least capture ecient of these gases, acts as the reference gas with a global warming potential of 1. Table
Global Warming Potentials (Table 9.5: Global Warming Potentials) shows the global warming potential for
the various GHGs.
75 http://www.epa.gov/climatechange/emissions/co2.html
76 http://www.epa.gov/methane/sources.html
77 http://www.epa.gov/nitrousoxide/sources.html
78 http://www.epa.gov/highgwp/sources.html
79 http://www.epa.gov/ozone/
Available for free at Connexions
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Global Warming Potentials
Table 9.5:
Source:
C. Klein-Banai
80
Gas
GWP
CO2
1
CH4
21
N2O
310
HFC-23
11,700
HFC-32
650
HFC-125
2,800
HFC-134a
1,300
HFC-143a
3,800
HFC-152a
140
HFC-227ea
2,900
HFC-236fa
6,300
HFC-4310mee
1,300
CF4
6,500
C2F6
9,200
C4F10
7,000
C6F14
7,400
SF6
23,900
created table using data from Climate Change 2007: The Physical
Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental
Panel on Climate Change, Cambridge University Press, section 2.10.2
81
GHG emissions cannot be easily measured since they come from both mobile and stationary sources.
Therefore, emissions must be calculated. Emissions are usually calculated using the formula:
A × Fg = E
(9.14)
where A is the quantication of an activity in units that can be combined with emission factor of greenhouse
gas g (Fg ) to obtain the resulting emissions for that gas (Eg ).
Examples of activity units include mmbtu (million British Thermal Units) of natural gas, gallons of
heating oil, kilowatt hours of electricity, and miles traveled. Total GHG emissions can be expressed as the
sum of the emissions for each gas multiplied by its global warming potential (GWP). GHG emissions are
usually reported in metric tons of carbon dioxide equivalents (metric tons CO2 -e):
X
GHG =
Eg∆GWPg (9.14)
g
Eg is usually estimated from the quantity of fuel burned using national and regional average emissions
factors, such as those provided by the US Department of Energy’s Energy Information Administration82 .
80 http://cnx.org/member_prole/cindykb
81 http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html
82 http://www.eia.doe.gov/environment/
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Emission factors can be based on government documents and software from the U.S. Department of Transportation83 , the U.S. Environmental Protection Agency (EPA)84 , and the U.S. Department of Energy85 ,
or from specic characteristics of the fuel used such as higher heating value and carbon content. Scope 3
emissions that are based on waste, materials, and commuting are more complex to calculate. Various calculators use dierent inputs to do this and the procedures are less standardized. See Case Study: Comparing
Greenhouse Gas Emissions, Ecological Footprint and Sustainability Rating of a University (Section 9.3.3)
for an example of these kinds of calculations.
Greenhouse gas emissions inventories are based on standardized practice and include the steps of scoping,
calculating, and reporting. They are not based on actual measurements of emissions, rather on calculations
based on consumption of greenhouse gas generating materials such as fossil fuels for provision of energy and
transportation or emissions from waste disposal. They can be conducted for buildings, institutions, cities,
regions, and nations.
9.3.2.1.4.3 Carbon Footprint Comparisons
Comparison of carbon footprints reveal interesting dierences between countries, particularly when compared
to their economic activity. The World Bank86 tracks data on countries and regions throughout the world as
part of their mission to ght poverty. . .and to help people help themselves and their environment (World
Bank, 2011 (p. 450)). Table Gross Domestic Product (GDP) and Emissions for Select Regions, 2007 (Table
9.6: Gross Domestic Product (GDP) and Emissions for Select Regions, 2007) shows the results for GHG
emissions and gross domestic product for various regions of the world. It is interesting to note that the
United States’ emissions per capita (19.34 mt e-CO2 ) are more than four times the world average. The
United States’ economy makes up one fourth of the world GDP.
Gross Domestic Product (GDP) and Emissions for Select Regions, 2007
Country Name
CO2 emissions
(metric ton)
CO2 emissions
(metric tons per
capita)
GDP
(current
US$ millions)
GDP per capita
(current US$)
East Asia & Pacic (all income
levels)
10,241,229
4.76
$11,872,148
$5,514
Europe & Central
Asia (all income
levels)
6,801,838
7.72
$20,309,468
$23,057
Latin America &
Caribbean (all income levels)
1,622,809
2.87
$3,872,324
$6,840
Latin America &
Caribbean (developing only)
1,538,059
2.75
$3,700,320
$6,610
continued on next page
83 http://www.dot.gov/
84 http://www.epa.gov/ozone/
85 http://energy.gov/
86 http://web.worldbank.org/
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Least developed
countries:
UN
classication
185,889
0.23
$442,336
$553
Middle East &
North Africa (all
income levels)
1,992,795
5.49
$1,924,470
$5,304
South Asia
1,828,941
1.20
$1,508,635
$991
Sub-Saharan
Africa (all income
levels)
684,359
0.86
$881,547
$1,102
United States
5,832,194
19.34
$14,061,800
$46,627
World
30,649,360
4.63
$55,853,288
$8,436
Table 9.6: Table shows the GDP and emissions for select regions in 2007.
Source: C. Klein-Banai
88
created table using data from The World Bank, “World Development Indicators”
87
9.3.2.1.5 Water Footprint
The water footprint of production is the volume of freshwater used by people to produce goods, measured
over the full supply chain, as well as the water used in households and industry, specied geographically
and temporally. This is slightly dierent from the hydroprint described above which simply compares the
consumption of water by a geographic entity to the water that falls within its watershed. If you look at the
hydrologic cycle (see module Water Cycle and Fresh Water Supply (Section 5.2)), water moves through the
environment in various ways. The water footprint considers the source of the water as three components:
• Green water footprint: The volume of rainwater that evaporates during the production of goods; for
agricultural products, this is the rainwater stored in soil that evaporates from crop elds.
• Blue water footprint: The volume of freshwater withdrawn from surface or groundwater sources that is
used by people and not returned; in agricultural products this is mainly accounted for by evaporation
of irrigation water from elds, if freshwater is being drawn.
• Grey water footprint: the volume of water required to dilute pollutants released in production processes
to such an extent that the quality of the ambient water remains above agreed water quality standards.
The water footprint of an individual is based on the direct and indirect water use of a consumer. Direct
water use is from consumption at home for drinking, washing, and watering. Indirect water use results from
the freshwater that is used to produce goods and services purchased by the consumer. Similarly, the water
footprint of a business or institution is calculated from the direct and indirect water consumption.
87 http://cnx.org/member_prole/cindykb
88 http://data.worldbank.org/indicator?display=default
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Figure 9.15: Water Footprint of Production of Select Countries Graph shows the water footprint
of production of select countries. Source:
Planet Report, 2010
90
©
2010 WWF (panda.org). Some rights reserved.
, gure under CC BY-SA 3.0 License
91
89
Living
Figure Water Footprint of Production of Select Countries (Figure 9.15) shows the water footprint of
production for several countries as a whole. In this report, due to lack of data, one unit of return ow is
assumed to pollute one unit of freshwater. Given the negligible volume of water that evaporates during
domestic and industrial processes, as opposed to agriculture, only the grey water footprint for households
and industry was included. This gure does not account for imports and exports it is only based on the
country in which the activities occurred not where they were consumed.
In contrast, the water footprint of a nation accounts for all the freshwater used to produce the goods
and services consumed by the inhabitants of the country. Traditionally, water demand (i.e. total water
withdrawal for the various sectors of economy) is used to demonstrate water demand for production within a
nation. The internal water footprint is the volume of water used from domestic water resources; the external
water footprint is the volume of water used in other countries to produce goods and services imported
and consumed by the inhabitants of the country. The average water footprint for the United States was
calculated to be 2480m3 /cap/yr, while China has an average footprint of 700m3 /cap/yr. The global average
water footprint is 1240m3 /cap/yr. As for ecological footprints there are several major factors that determine
the water footprint of a country including the volume of consumption (related to the gross national income);
consumption pattern (e.g. high versus low meat consumption); climate (growth conditions); and agricultural
practice (water use eciency) (Hoekstra & Chapagain, 2007 (p. 450)).
89 http://www.panda.org/lpr/gwater
90 http://www.panda.org/lpr/gwater
91 http://creativecommons.org/licenses/by-sa/3.0/
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449
Using average water consumption for each stage of growth and processing of tea or coee, the virtual
water content of a cup can be calculated (Table Virtual Water Content of a Cup of Tea or Coee (Table
9.7: Virtual Water Content of a Cup of Tea or Coee)). Much of the water used is from rainfall that might
otherwise not be utilized to grow a crop and the revenue from the product contributes to the economy
of that country. At the same time, the result is that many countries are importing water to support the
products they consume.
Virtual Water Content of a Cup of Tea or Coee
Drink
Coee
Tea
Preparation
Virtual
(l/cup)
Standard cup of coee
140
Strong coee
200
Instant coee
80
Standard cup of tea
34
Weak tea
17
Table 9.7: Table shows the virtual water content for a cup of tea or coee.
water
content
Source: C. Klein-Banai
92
(p. 450). alt=”Virtual Water Content of a
Cup of Tea or Coee” longdesc=”Table shows the virtual water content for a cup of tea or coee.”
created table using data from Chapagain and Hoekstra (2007)
To learn more about other countries’ water footprints, visit this interactive graph93 . To calculate your
own water footprint, visit the Water Footprint Calculator94 .
The water footprint reveals that much more water is consumed to make a product than appears in using
a simple calculation. It is not just the water content of the product but includes all water used in the process
to make it and to manage the waste generated from that process.
9.3.2.1.6 Summary
Footprinting tools can be useful ways to present and compare environmental impact. They are useful because
they can combine impacts from various activities into one measure. However, they have limitations. For
instance, in a carbon footprint or greenhouse gas emissions inventory, many of the conventional environmental impacts such as hazardous waste, wastewater, water consumption, stormwater, and toxic emissions
are not accounted for, nor are the impacts of resource consumption such as paper, food, and water generally
measured. Perhaps most importantly, certain low-carbon fuel sources (e.g. nuclear power) that have other
environmental impacts (e.g. nuclear waste) are neglected. Finally, the scope of the emissions inventory does
not include upstream emissions from the manufacture or transport of energy or materials. This suggests
that there is a need to go beyond just GHG emissions analyses when evaluating sustainability and include
all forms of energy and their consequences.
The ecological footprint can be misleading when it is looked at in isolation, for instance with an urban
area, the resources needed to support it will not be provided by the actual geographic area since food must
be imported and carbon oset by natural growth that does not t in a city. However, cities have many
other eciencies and advantages that are not recognized in an ecological footprint. When looked at on a
national level it can represent the inequities that exist between countries.
It is interesting to contrast the water and ecological footprints, as well. The water footprint explicitly
considers the actual location of the water use, whereas the ecological footprint does not consider the place
of land use. Therefore it measures the volumes of water use at the various locations where the water
92 http://cnx.org/member_prole/cindykb
93 http://www.panda.org/lpr/gwater
94 http://www.waterfootprint.org/
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CHAPTER 9.
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PROBLEM-SOLVING, METRICS, AND TOOLS FOR
SUSTAINABILITY
is appropriated, while the ecological footprint is calculated based on a global average land requirement per
consumption category. When the connection is made between place of consumption and locations of resource
use, the consumer’s responsibility for the impacts of production at distant locations is made evident.
9.3.2.1.7 Review Questions
Question 9.3.2.1
Choose a calculator from the box and calculate your own footprint. How does it compare to the
national or global average? What can you do to reduce your footprint?
Question 9.3.2.2
Discuss what kind of inequities the various footprints represent between nations and the types of
inequities.
Question 9.3.2.3
How might the food print of a vegetarian dier from a carnivore?
9.3.2.1.8 References
Chambers, N., Simmons, C. & Wackernagel, M. (2000). Sharing Nature’s Interest: Ecological Footprints as
London: Earthscan Publications Ltd.
Chapagain, A.K. & Hoekstra, A.Y. (2007). The water footprint of coee and tea consumption in the
Netherlands. Ecological Economics, 64, 109-118.
Constanza, R. (2000). The dynamics of the ecological footprint concept. Ecological Economics,32, 341345.
Dawe, G.F.M., Vetter, A. & Martin. S. (2004). An overview of ecological footprinting and other tools
and their application to the development of sustainability process. International Journal of Sustainability in
Higher Education, 4, 340-371.
Flint, K. (2001). Institutional ecological footprint analysis: A case study of the University of Newcastle,
Australia. International Journal of Sustainability in Higher Education, 2, 48-62.
Hoekstra,Y. & Chapagain, A. K. (2007). Water footprints of nations: Water use by people as a function
of their consumption pattern. Water Resour Manage, 21, 35-48.
Klein-Banai,
C. (2007).
Greenhouse gas inventory for the University of Illinois
at
Chicago.
UIC
GHG
Inventory,Retrieved
November
21,
2009
from
http://www.uic.edu/sustainability/reports/Appendix%206%20GHGEmissionsFY2005-2006.pdf95
Rees, W.E. and Wackernagal, M. (1996). Urban ecological footprints and why cities cannot be sustainable
and why they are a key to sustainability. Environmental Impact Assessment Review, 16, 223-248.
Venetoulis, J. (2001). Assessing the ecological impact of a university: The ecological footprint for the
University of Redlands. International Journal of Sustainability in Higher Education, 2, 180-196.
Wackernagel, M., Monfreda, C., Moran, D., Wermer, P., Goldnger, S., Deumling, D., &
Murray, M. (2005, May 25).
National footprint and biocapacity accounts 2005:
The underlying calculation method.
Global Footprint Network.
Retrieved March 2, 2010 from
http://www.footprintnetwork.org/download.php?id=596 .
World
Bank
(2011).
About
Us.
Retrieved
September
20,
2011
from
http://go.worldbank.org/3QT2P1GNH097 .
an Indicator of Sustainability.
95 http://www.uic.edu/sustainability/reports/Appendix%206%20GHGEmissionsFY2005-2006.pdf
96 http://www.footprintnetwork.org/download.php?id=5
97 http://go.worldbank.org/3QT2P1GNH0
Available for free at Connexions
Physical Resources: Water, Pollution, and Minerals from Sustainability: A Comprehensive Foundation by
Tom Theis and Jonathan Tomkin, Editors, is available under a Creative Commons Attribution License 4.0
license. © Dec 26, 2018, Tom Theis and Jonathan Tomkin, Editors.
Chapter 5
Physical Resources: Water, Pollution,
and Minerals
5.1 Physical Resources: Water, Pollution, and Minerals – Chapter
Introduction
1
5.1.1 Introduction
Water, air, and food are the most important natural resources to people. Humans can live only a few minutes
without oxygen, about a week without water, and about a month without food. Water also is essential for
our oxygen and food supply. Plants, which require water to survive, provide oxygen through photosynthesis
and form the base of our food supply. Plants grow in soil, which forms by weathering reactions between
water and rock.
Water is the most essential compound for Earth’s life in general. Human babies are approximately 75%
water and adults are 5060% water. Our brain is about 85% water, blood and kidneys are 83% water,
muscles are 76% water, and even bones are 22% water. We constantly lose water by perspiration; in
temperate climates we should drink about 2 quarts of water per day and people in hot desert climates should
drink up to 10 quarts of water per day. Loss of 15% of body-water usually causes death. Earth is truly the
Water Planet (see Figure Planet Earth from Space (Figure 5.1)). The abundance of water on Earth
distinguishes us from other bodies in the solar system. About 70% of Earth’s surface is covered by oceans
and approximately half of Earth’s surface is obscured by clouds at any time. There is a very large volume of
water on our planet, about 1.4 billion cubic kilometers (km3) (330 million cubic miles) or about 53 billion
gallons per person on Earth. All of Earth’s water could cover the United States to a depth of 145 km (90
mi). From a human perspective, the problem is that over 97% of it is seawater, which is too salty to drink
or use for irrigation. The most commonly used water sources are rivers and lakes, which contain less than
0.01% of the world’s water!
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Figure 5.1: Planet Earth from Space
Wikimedia Commons
2
Source:
Created by Marvel, based on a Nasa image via
One of our most important environmental goals is to provide a clean, sucient, and sustainable water
supply for the world. Fortunately, water is a renewable resource, and it is dicult to destroy. Evaporation and
precipitation combine to replenish our fresh water supply constantly and quickly; however, water availability
is complicated by its uneven distribution over the Earth. Arid climate and densely populated areas have
combined in many parts of the world to create water shortages, which are projected to worsen signicantly
in the coming years. Human activities such as water overuse and water pollution have compounded the
water crisis that exists today. Hundreds of millions of people lack access to safe drinking water, and billions
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151
of people lack access to improved sanitation as simple as a pit latrine. As a result, nearly two million people
die every year from diarrheal diseases and 90% of those deaths occur among children under the age of 5.
Most of these are easily prevented deaths.
Although few minerals are absolutely essential for human life, the things that dene modern society
require a wide range of them: iron ore for steel, phosphate minerals for fertilizer, limestone rock for concrete, rare earth elements for night-vision goggles and phosphors in computer monitors, and lithium minerals
for batteries in our laptops, cell phones, and electric cars. As global population grows and emerging large
economies expand, we will face a crisis in the supply of many important minerals because they are nonrenewable, which is to say we consume them far more quickly than nature creates them. As we consume
minerals from larger and lower grade mineral deposits there will be greater environmental impacts from
mineral mining and processing. The impending mineral crisis may be more challenging to address than the
water crisis.
This chapter introduces basic principles in water supply, water pollution, and mineral resources. The
emphasis, however, is on environmental issues and sustainable solutions for each problem.
3
5.2 Water Cycle and Fresh Water Supply
5.2.1 Learning Objectives
After reading this module, students should be able to
• understand how the water cycle operates
• understand the principles controlling groundwater resources and how they also can aect surface water
resources
• know the causes and eects of depletion in dierent water reservoirs
• understand how we can work toward solving the water supply crisis
5.2.2 Water Reservoirs and Water Cycle
Water is the only substance that occurs naturally on earth in three forms: solid, liquid and gas. It is
distributed in various locations, called water reservoirs. The oceans are by far the largest of the reservoirs
with about 97% of all water but that water is too saline for most human uses (see Figure Earth’s Water
Reservoirs (Figure 5.2)). Ice caps and glaciers are the largest reservoirs of fresh water but this water is
inconveniently located, mostly in Antarctica and Greenland. Shallow groundwater is the largest reservoir of
usable fresh water. Although rivers and lakes are the most heavily used water resources, they represent only
a tiny amount of the world’s water. If all of world’s water was shrunk to the size of 1 gallon, then the total
amount of fresh water would be about 1/3 cup, and the amount of readily usable fresh water would be 2
tablespoons.
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Figure 5.2: Earth’s Water Reservoirs Bar chart Distribution of Earth’s water including total global
water, fresh water, and surface water and other fresh water and Pie chart Water usable by humans and
sources of usable water. Source: United States Geographical Survey
4
Igor Skiklomanov’s chapter “World
fresh water resources” in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World’s Fresh
Water Resources
The water cycle shows the movement of water through dierent reservoirs, which include oceans, atmosphere, glaciers, groundwater, lakes, rivers, and biosphere (see Figure The Water Cycle (Figure 5.3)).
Solar energy and gravity drive the motion of water in the water cycle. Simply put, the water cycle involves
water moving from the ocean to the atmosphere by evaporation, forming clouds. From clouds, it falls as
precipitation (rain and snow) on both water and land, where it can move in a variety of ways. The water on
land can either return to the ocean by surface runo (unchannelized overland ow), rivers, glaciers, and
subsurface groundwater ow, or return to the atmosphere by evaporation or transpiration (loss of water
by plants to the atmosphere).
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Figure 5.3: The Water Cycle Arrows depict movement of water to dierent reservoirs located above,
at, and below Earth’s surface. Source: United States Geological Survey
5
An important part of the water cycle is how water varies in salinity, which is the abundance of dissolved
ions in water. Ocean water is called salt water because it is highly saline, with about 35,000 mg of dissolved
ions per liter of seawater. Evaporation (where water changes from liquid to gas at ambient temperatures)
is a distillation process that produces nearly pure water with almost no dissolved ions. As water vaporizes, it
leaves the dissolved ions in the original liquid phase. Eventually, condensation (where water changes from
gas to liquid) forms clouds and sometimes precipitation (rain and snow). After rainwater falls onto land,
it dissolves minerals, which increases its salinity. Most lakes, rivers, and near-surface groundwater have a
relatively low salinity and are called fresh water. The next several sections discuss important parts of the
water cycle relative to fresh water resources.
5.2.3 Primary Fresh Water Resources: Precipitation
Precipitation is a major control of fresh water availability, and it is unevenly distributed around the globe
(see Figure World Rainfall Map (Figure 5.4)). More precipitation falls near the equator, and landmasses
there are characterized by a tropical rainforest climate. Less precipitation tends to fall near 2030 ◦ north and
south latitude, where the world’s largest deserts are located. These rainfall and climate patterns are related
to global wind circulation cells. The intense sunlight at the equator heats air, causing it to rise and cool,
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which decreases the ability of the air mass to hold water vapor and results in frequent rainstorms. Around
30 ◦ north and south latitude, descending air conditions produce warmer air, which increases its ability to
hold water vapor and results in dry conditions. Both the dry air conditions and the warm temperatures of
these latitude belts favor evaporation. Global precipitation and climate patterns are also aected by the size
of continents, major ocean currents, and mountains.
Figure 5.4: World Rainfall Map The false-color map above shows the amount of rain that falls around
the world. Areas of high rainfall include Central and South America, western Africa, and Southeast Asia.
Since these areas receive so much rainfall, they are where most of the world’s rainforests grow. Areas with
very little rainfall usually turn into deserts.
The desert areas include North Africa, the Middle East,
western North America, and Central Asia.
Source:
6
United States Geological Survey
Earth Forum,
Houston Museum Natural Science
5.2.4 Surface Water Resources: Rivers, Lakes, Glaciers
Flowing water from rain and melted snow on land enters river channels by surface runo (see Figure Surface
Runo (Figure 5.5)) and groundwater seepage (see Figure Groundwater Seepage (Figure 5.6)). River
discharge describes the volume of water moving through a river channel over time (see Figure River
Discharge (Figure 5.7)). The relative contributions of surface runo vs. groundwater seepage to river
discharge depend on precipitation patterns, vegetation, topography, land use, and soil characteristics. Soon
after a heavy rainstorm, river discharge increases due to surface runo. The steady normal ow of river
water is mainly from groundwater that discharges into the river. Gravity pulls river water downhill toward
the ocean. Along the way the moving water of a river can erode soil particles and dissolve minerals, creating
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the river’s load of moving sediment grains and dissolved ions. Groundwater also contributes a large amount
of the dissolved ions in river water. The geographic area drained by a river and its tributaries is called a
drainage basin. The Mississippi River drainage basin includes approximately 40% of the U.S., a measure
that includes the smaller drainage basins (also called watersheds), such as the Ohio River and Missouri
River that help to comprise it. Rivers are an important water resource for irrigation and many cities around
the world. Some of the world’s rivers that have had international disputes over water supply include the
Colorado (Mexico, southwest U.S.), Nile (Egypt, Ethiopia, Sudan), Euphrates (Iraq, Syria, Turkey), Ganges
(Bangladesh, India), and Jordan (Israel, Jordan, Syria).
Figure 5.5: Surface Runo
7
M. Pease
Surface runo, part of overland ow in the water cycle Source: James
at Wikimedia Commons
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Figure 5.6: Groundwater Seepage Groundwater seepage can be seen in Box Canyon in Idaho, where
8
approximately 10 cubic meters per second of seepage emanates from its vertical headwall. Source: NASA
8 http://astrobiology.nasa.gov/articles/erosion-on-earth-and-mars-mere-seepage-or-megaood/
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Figure 5.7: River Discharge Colorado River, U.S..
Rivers are part of overland ow in the water cycle
and an important surface water resource. Source: Gonzo fan2007
9
at Wikimedia Commons
Lakes can also be an excellent source of fresh water for human use. They usually receive water from
surface runo and groundwater discharge. They tend to be short-lived on a geological time-scale because
they are constantly lling in with sediment supplied by rivers. Lakes form in a variety of ways including
glaciation (Great Lakes, North America, See Figure Great Lakes from Space (Figure 5.8)), recent tectonic
uplift (Lake Tanganyika, Africa), and volcanic eruptions (Crater Lake, Oregon). People also create articial
lakes (reservoirs) by damming rivers. Large changes in climate can result in major changes in a lake’s size.
As Earth was coming out of the last Ice Age about fteen thousand years ago, the climate in the western
U.S. changed from cool and moist to warm and arid, which caused more than100 large lakes to disappear.
The Great Salt Lake in Utah is a remnant of a much larger lake called Lake Bonneville.
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Figure 5.8: Great Lakes from Space The Great Lakes hold 21% of the world’s surface fresh water.
Lakes are an important surface water resource. Source: SeaWiFS Project, NASA/Goddard Space Flight
Center, and ORBIMAGE
10
Although glaciers represent the largest reservoir of fresh water, they generally are not used as a water
source because they are located too far from most people (see Figure Mountain Glacier in Argentina
(Figure 5.9)). Melting glaciers do provide a natural source of river water and groundwater. During the last
Ice Age there was as much as 50% more water in glaciers than there is today, which caused sea level to be
about 100 m lower. Over the past century, sea level has been rising in part due to melting glaciers. If Earth’s
climate continues to warm, the melting glaciers will cause an additional rise in sea level.
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Figure 5.9: Mountain Glacier in Argentina Glaciers are the largest reservoir of fresh water but they
are not used much as a water resource directly by society because of their distance from most people.
11
Source: Luca Galuzzi – www.galuzzi.it
5.2.5 Groundwater Resources
Although most people in the U.S. and the world use surface water, groundwater is a much larger reservoir of
usable fresh water, containing more than 30 times more water than rivers and lakes combined. Groundwater
is a particularly important resource in arid climates, where surface water may be scarce. In addition,
groundwater is the primary water source for rural homeowners, providing 98% of that water demand in
the U.S.. Groundwater is water located in small spaces, called pore space, between mineral grains and
fractures in subsurface earth materials (rock or sediment, i.e., loose grains). Groundwater is not located in
underground rivers or lakes except where there are caves, which are relatively rare. Between the land surface
and the depth where there is groundwater is the unsaturated zone, where pore spaces contain only air and
water lms on mineral grains (see Figure Subsurface Water Terminology (Figure 5.10)).12 Below the
unsaturated zone is the saturated zone, where groundwater completely lls pore spaces in earth materials.
The interface between the unsaturated zone and saturated zone is the water table. Most groundwater
originates from rain or snowmelt, which inltrates the ground and moves downward until it reaches the
11 http://en.wikipedia.org/wiki/File:Perito_Moreno_Glacier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG
12 Groundwater is the name for water in the saturated zone and soil moisture describes water in the unsaturated zone.
Therefore, groundwater is the underground water resource used by society but soil moisture is the principal water supply for
most plants and is an important factor in agricultural productivity.
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saturated zone. Other sources of groundwater include seepage from surface water (lakes, rivers, reservoirs,
and swamps), surface water deliberately pumped into the ground, irrigation, and underground wastewater
treatment systems, i.e., septic tanks. Recharge areas are locations where surface water inltrates the
ground rather than running o into rivers or evaporating. Wetlands and at vegetated areas in general are
excellent recharge areas.
Figure 5.10: Subsurface Water Terminology
Groundwater in pore spaces and fractures of earth
materials, saturated zone, unsaturated zone, and water table, which follows land surface but in a more
subdued way. Source: United States Geological Survey
13
Groundwater is in constant motion due to interconnection between pore spaces. Porosity is the percentage of pore space in an earth material and it gives a measure of how much groundwater an earth material
can hold. Permeability is a measure of the speed that groundwater can ow through an earth material,
and it depends on the size and degree of interconnection among pores. An earth material that is capable
of supplying groundwater from a well at a useful ratei.e., it has relatively high permeability and medium
to high porosityis called an aquifer. Examples of aquifers are earth materials with abundant, large,
well-connected pore spaces such as sand, gravel, uncemented sandstone, and any highly fractured rock. An
earth material with low hydraulic conductivity is an aquitard. Examples of aquitards include clay, shale
(sedimentary rock with abundant clay), and igneous and metamorphic rock, if they contain few fractures.
As discussed above, groundwater ows because most earth materials near the surface have nite (nonzero)
porosity and permeability values. Another reason for groundwater movement is that the surface of the
water table commonly is not completely at but mimics the topography of the land surface, especially
in humid climates. There is “topography” to the water table because groundwater moves slowly through
rock and soil, so it builds up in higher elevation areas. In fact, when groundwater ows slowly through
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aquitards and deep underground, it can take many thousands of years to move relatively short distances. An
unconned aquifer has no aquitard above it and, therefore, it is exposed to the atmosphere and surface
waters through interconnected pores (See Figure Flowing Groundwater (Figure 5.11)). In an unconned
aquifer, groundwater ows because of gravity to lower water table levels, where it eventually may discharge
or leave the groundwater ow system. Discharge areas include rivers, lakes, swamps, reservoirs, water wells,
and springs (see Figure Fatzael Springs in Jordan Valley (Figure 5.12)). Springs are rivers that emerge
from underground due to an abrupt intersection of the land surface and the water table caused by joints,
caves, or faults that bring permeable earth materials to the surface. A conned aquifer is bounded by
aquitards below and above, which prevents recharge from the surface immediately above. Instead, the major
recharge occurs where the conned aquifer intercepts the land surface, which may be a long distance from
water wells and discharge areas (see Figure Schematic Cross Section of Aquifer Types (Figure 5.13)).
Conned aquifers are commonly inclined away from recharge areas, so groundwater in a conned aquifer
is under greater-than-atmospheric pressure due to the weight of water in the upslope direction. Similar
to river discharge, groundwater discharge describes the volume of water moving through an aquifer over
time. Total groundwater discharge depends on the permeability of the earth material, the pressure that
drives groundwater ow, and the size of the aquifer. It is important to determine groundwater discharge to
evaluate whether an aquifer can meet the water needs of an area.
Figure 5.11: Flowing Groundwater
Blue lines show the direction of groundwater in unconned
aquifers, conned aquifers, and conning beds. Deep groundwater moves very slowly especially through
low permeability layers.Source: United States Geological Survey
14
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Figure 5.12: Fatzael Springs in Jordan Valley
A spring is a river that emerges from underground
due to an abrupt intersection of the water table with the land surface such as alongside a hill. Source:
Hanay
15
at Mediawiki Commons
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Figure 5.13: Schematic Cross Section of Aquifer Types
This gure shows dierent types of
aquifers and water wells, including unconned aquifer, conned aquifer, water table well, artesian well,
and owing artesian well. Point of triangle is water level in each well and water table in other parts of
gure. Water level in artesian well is at potentiometric surface and above local water table (dashed blue
line) due to extra pressure on groundwater in conned aquifer.
above land surface. Source: Colorado Geological Survey
16
Water in owing artesian well moves
Most shallow water wells are drilled into unconned aquifers. These are called water table wells because
the water level in the well coincides with the water table (See Figure Schematic Cross Section of Aquifer
Types (Figure 5.13)). 90% of all aquifers for water supply are unconned aquifers composed of sand or
gravel. To produce water from a well, you simply need to drill a hole that reaches the saturated zone and
then pump water to the surface. Attempting to pump water from the unsaturated zone is like drinking root
beer with a straw immersed only in the foam at the top.
To nd a large aquifer for a city, hydrogeologists (geologists who specialize in groundwater) use a variety
of information including knowledge of earth materials at the surface and sub-surface as well as test wells.
Some people search for water by dowsing, where someone holds a forked stick or wire (called a divining rod)
while walking over an area. The stick supposedly rotates or deects downward when the dowser passes over
water. Controlled tests show that a dowser’s success is equal to or less than random chance. Nevertheless,
in many areas water wells are still drilled on dowser’s advice sometimes for considerable money. There is no
scientic basis to dowsing.
Wells into conned aquifers typically are deeper than those into unconned aquifers because they must
penetrate a conning layer. The water level in a well drilled into a conned aquifer, which is an artesian
well, (see Figure Schematic Cross Section of Aquifer Types (Figure 5.13)), moves above the local
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water table to a level called the potentiometric surface because of the greater pressure on the groundwater.
Water in a owing well (see Figure A Flowing Well (Figure 5.14)) moves all of the way to the land surface
without pumping.
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Figure 5.14: A Flowing Well Flowing artesian well where water moves above the land surface due to
extra pressure on the groundwater in a conned aquifer. Source: Environment Canada
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A conned aquifer tends to be depleted from groundwater pumping more quickly than an unconned
aquifer, assuming similar aquifer properties and precipitation levels. This is because conned aquifers have
smaller recharge areas, which may be far from the pumping well. Conversely, an unconned aquifer tends to
be more susceptible to pollution because it is hydrologically connected to the surface, which is the source of
most pollution.
Groundwater and surface water (rivers, lakes, swamps, and reservoirs) are strongly interrelated because
both are part of the same overall resource. Major groundwater removal (from pumping or drought) can lower
the levels of surface water and vice versa. We can dene two types of streams: gaining (euent) streams
and losing (inuent) streams (see Figure Interaction of Streams and Ground Water (Figure 5.15)).
Gaining streams tend to be perennial (ow year round), are characteristic of humid climates, have the water
table sloping towards the river, and therefore gain water from groundwater discharge. Losing streams tend
to be ephemeral (ow only after signicant rain), are characteristic of arid climates, are located above the
water table (which slopes away from the river), and therefore lose water to groundwater recharge. Pollution
that is dumped into a losing stream will tend to move into the ground and could also contaminate local
groundwater.
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Figure 5.15: Interaction of Streams and Ground Water
A) Gaining stream where water table
slopes toward river and groundwater discharges into river, B) Losing stream where water table slopes
away from river and river water discharges into groundwater, C) Losing stream where water table is
separated from and below river. Source: United States Geological Survey
18
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5.2.6 Water Use in the U.S. and World
People need water to produce the food, energy, and mineral resources they usecommonly large amounts
of it. Consider, for example, these approximate water requirements for some things people in the developed
world use every day: one tomato = 3 gallons; one kilowatt-hour of electricity (from a thermoelectric power
plant) = 21 gallons; one loaf of bread = 150 gallons; one pound of beef = 1,600 gallons; and one ton of steel
= 63,000 gallons. Human beings require only about 1 gallon per day to survive, but a typical person in a
U.S. household uses approximately 100 gallons per day, which includes cooking, washing dishes and clothes,
ushing the toilet, and bathing.
The water demand of an area is a function of the population and other uses of water. There are several general categories of water use, including ostream use, which removes water from its source, e.g.,
irrigation, thermoelectric power generation (cooling electricity-producing equipment in fossil fuel, nuclear,
and geothermal power plants), industry, and public supply; consumptive use, which is a type of ostream
use where water does not return to the surface water or groundwater system immediately after use, e.g.,
irrigation water that evaporates or goes to plant growth; and instream use, which is water used but not
removed from a river, mostly for hydroelectric power generation. The relative size of these three categories
are instream use ostream use > consumptive use. In 2005, the U.S. used approximately 3,300 billion
gallons per day for instream use, 410 billion gallons per day for ostream use, and 100 billion gallons per day
for consumptive use. The major ostream uses of that water were thermoelectric (49%), irrigation (31%),
public supply (11%), and industry (4%, see Figure Trends in Total Water Withdrawals by Water-use
Category, 1950-2005 (Figure 5.16)). About 15% of the total water withdrawals in the U.S. in 2005 were
saline water, which was used almost entirely for thermoelectric power generation. Almost all of the water
used for thermoelectric power generation is returned to the river, lake, or ocean from where it came but about
half of irrigation water does not return to the original source due to evaporation, plant transpiration, and
loss during transport, e.g., leaking pipes. Total withdrawals of water in the U.S. actually decreased slightly
from 1980 to 2005, despite a steadily increasing population. This is because the two largest categories of
water use (thermoelectric and irrigation) stabilized or decreased over that time period due to better water
management and conservation. In contrast, public supply water demand increased steadily from 1950 (when
estimates began) through 2005. Approximately 77% of the water for ostream use in the U.S. in 2005 came
from surface water and the rest was from groundwater (see Figure Trends in Source of Fresh Water
Withdrawals in the U.S. from 1950 to 2005 (Figure 5.17)).
18 http://pubs.usgs.gov/circ/circ1186/html/gw_eect.html
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Figure 5.16: Trends in Total Water Withdrawals by Water-use Category, 1950-2005 Trends
in total water withdrawals in the U.S. from 1950 to 2005 by water use category, including bars for thermoelectric power, irrigation, public water supply, and rural domestic and livestock. Thin blue line represents
total water withdrawals using vertical scale on right. Source: United States Geological Survey
19 http://ga.water.usgs.gov/edu/wateruse-trends.html
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Figure 5.17: Trends in Source of Fresh Water Withdrawals in the U.S. from 1950 to 2005
Trends in source of fresh water withdrawals in the U.S. from 1950 to 2005, including bars for surface
water, groundwater, and total water. Red line gives U.S. population using vertical scale on right. Source:
United States Geological Survey
20
In contrast to trends in the U.S., global total water use is steadily increasing at a rate greater than world
population growth (see Figure Trends in World Water Use from 1900 to 2000 and Projected to
2025 (Figure 5.18)). During the twentieth century global population tripled and water demand grew by a
factor of six. The increase in global water demand beyond the rate of population growth is due to improved
standard of living without an oset by water conservation. Increased production of goods and energy entails
a large increase in water demand. The major global ostream water uses are irrigation (68%), public supply
(21%), and industry (11%).
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Figure 5.18: Trends in World Water Use from 1900 to 2000 and Projected to 2025 For each
water major use category, including trends for agriculture, domestic use, and industry. Darker colored bar
represents total water extracted for that use category and lighter colored bar represents water consumed
(i.e., water that is not quickly returned to surface water or groundwater system) for that use category.
Source: Igor A. Shiklomanow, State Hydrological Institute (SHI, St. Petersburg) and United Nations
Educational, Scientic and Cultural Organisation (UNESCO, Paris), 1999
21
5.2.7 Water Supply Problems: Resource Depletion
As groundwater is pumped from water wells, there usually is a localized drop in the water table around the
well called a cone of depression (see Figure Formation of a Cone of Depression around a Pumping
Water Well (Figure 5.19)). When there are a large number of wells that have been pumping water for
a long time, the regional water table can drop signicantly. This is called groundwater mining, which
can force the drilling of deeper, more expensive wells that commonly encounter more saline groundwater.
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The occurrence of mining does not mean that groundwater will never be recharged, but in many cases the
recharge rate is negligible on a human time-scale. Conned aquifers are more susceptible to groundwater
mining due to their limited recharge areas. Urban development usually worsens groundwater mining because
natural recharge rates drop with the proliferation of impermeable pavement, buildings, and roads. Extensive
groundwater pumping around Chicago has created a gigantic cone of depression there. Because the water
table dropped up to 250 m (800 ft) in the area (see Figure Drop in Water Table in a Conned Aquifer
in the Area of Chicago, Illinois and Milwaukee, Wisconsin, U.S. from 1864 – 1980 (Figure 5.20)),
many local public water suppliers have switched to Lake Michigan water. Chicago is fortunate to have a large
alternate supply of fresh water; many arid locations don’t have that luxury. Other places where groundwater
mining is a serious problem include the High Plains (Ogallala Aquifer) and the Desert Southwest of the U.S.,
Mexico, the Middle East, India, and China. Rivers, lakes, and articial lakes (reservoirs) can also be depleted
due to overuse. Some large rivers, such as the Colorado in the U.S. and Yellow in China, run dry in some
years. The case history of the Aral Sea discussed below involves depletion of a lake. Finally, glaciers are
being depleted due to accelerated melting associated with global warming over the past century.
Figure 5.19: Formation of a Cone of Depression around a Pumping Water Well
22
Fayette County Groundwater Conservation District, TX
22 http://www.fayettecountygroundwater.com/educational_info.htm
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Source:
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Figure 5.20: Drop in Water Table in a Conned Aquifer in the Area of Chicago, Illinois
and Milwaukee, Wisconsin, U.S. from 1864 – 1980 Source: United States Geological Survey23
23 http://pubs.usgs.gov/circ/circ1186/html/gw_storage.html
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Another water resource problem associated with groundwater mining is saltwater intrusion, where
overpumping of fresh water aquifers near ocean coastlines causes saltwater to enter fresh water zones. Saltwater intrusion is a signicant problem in many coastal areas of the U.S. including Long Island, New York;
Cape Cod, Massachusetts; and southeastern and Gulf Coastal states. The drop of the water table around a
cone of depression in an unconned aquifer can change the regional groundwater ow direction, which could
send nearby pollution toward the pumping well instead of away from it. Finally, problems of subsidence
(gradual sinking of the land surface over a large area) and sinkholes (rapid sinking of the land surface over
a small area) can develop due to a drop in the water table.
5.2.8 The Water Supply Crisis
The water crisis refers to a global situation where people in many areas lack access to sucient water or
clean water or both. This section describes the global situation involving water shortages, also called water
stress. The next section covers the water crisis involving water pollution. Figure Countries Facing Water
Stress in 1995 and Projected in 2025 (Figure 5.21) shows areas of the world experiencing water stress
as dened by a high percentage of water withdrawal compared to total available water. Due to population
growth the 2025 projection for global water stress is signicantly worse than water stress levels in 1995.
In general, water stress is greatest in areas with very low precipitation (major deserts) or large population
density (e.g., India) or both. Future global warming could worsen the water crisis by shifting precipitation
patterns away from humid areas and by melting mountain glaciers that recharge rivers downstream. Melting
glaciers will also contribute to rising sea level, which will worsen saltwater intrusion in aquifers near ocean
coastlines. Compounding the water crisis is the issue of social injustice; poor people generally get less access
to clean water and commonly pay more for water than wealthy people.
Figure 5.21: Countries Facing Water Stress in 1995 and Projected in 2025
Water stress is
dened as having a high percentage of water withdrawal compared to total available water in the area.
Source: Philippe Rekacewicz
24
(Le Monde diplomatique), February 2006
According to a 2006 report by the United Nations Development Programme, in 2005, 700 million people
24 http://maps.grida.no/go/graphic/increased-global-water-stress
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(11% of the world’s population) lived under water stress with a per capita water supply below 1,700 m3 /year25
(Watkins, 2006 (p. 179)). Most of them live in the Middle East and North Africa. By 2025, the report
projects that more than 3 billion people (about 40% of the world’s population) will live in water-stressed
areas with the large increase coming mainly from China and India. The water crisis will also impact food
production and our ability to feed the ever-growing population. We can expect future global tension and
even conict associated with water shortages and pollution. Historic and future areas of water conict
include the Middle East (Euphrates and Tigris River conict among Turkey, Syria, and Iraq; Jordan River
conict among Israel, Lebanon, Jordan, and the Palestinian territories), Africa (Nile River conict among
Egypt, Ethiopia, and Sudan), Central Asia (Aral Sea conict among Kazakhstan, Uzbekistan, Turkmenistan,
Tajikistan, and Kyrgyzstan), and south Asia (Ganges River conict between India and Pakistan).
5.2.9 Sustainable Solutions to the Water Supply Crisis?
The current and future water crisis described above requires multiple approaches to extending our fresh
water supply and moving towards sustainability. Some of the longstanding traditional approaches include
dams and aqueducts. Reservoirs that form behind dams in rivers can collect water during wet times and
store it for use during dry spells (see Figure Hoover Dam, Nevada, U.S. (Figure 5.22)). They also can
be used for urban water supplies. New York City has a large number of reservoirs and controlled lakes up to
200 km away to meet the water demands of its large population. Other benets of dams and reservoirs are
hydroelectricity, ood control, and recreation. Some of the drawbacks are evaporative loss of reservoir water
in arid climates, downstream river channel erosion, and impact on the ecosystem including a change from
a river to lake habitat and interference with sh migration and spawning. Aqueducts can move water from
where it is plentiful to where it is needed (see Figure The California Aqueduct (Figure 5.23)). Southern
California has a large and controversial network of aqueducts that brings in water from the Sierra Nevada
Mountains in the north, the valleys in northern and central California, and the Colorado River to the east
(see Figure Map of California Aqueducts (Figure 5.24)). Aqueducts can be controversial and politically
dicult especially if the water transfer distances are large. One drawback is the water diversion can cause
drought in the area from where the water is drawn. For example, Owens Lake and Mono Lake in central
California began to disappear after their river inow was diverted to the Los Angeles aqueduct. Owens Lake
remains almost completely dry, but Mono Lake has recovered more signicantly due to legal intervention.
25 Although 1,700 m3 /year sounds like a lot of water for every person, it is the minimum amount that hydrologists consider
is needed to grow food, support industry, and maintain the environment in general.
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AvailableDam,
for freeNevada,
at Connexions
Figure 5.22: Hoover
U.S.
Hoover Dam, Nevada, U.S.. Behind
the dam is Lake
Mead, the largest reservoir in U.S.. White band reects the lowered water levels in the reservoir due to
26
drought conditions from 2000 – 2010. Source: Cygnusloop99
at Wikimedia Commons
177
Figure 5.23: The California Aqueduct
27
David Jordan
California Aqueduct in southern California, U.S. Source:
at en.wikipedia
26 http://commons.wikimedia.org/wiki/File:Hoover_Dam_-_2010-12-10_-_View_from_bridge.jpg
27 http://en.wikipedia.org/wiki/File:Tupman_California_California_Aqueduct_Mile_236.JPG
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Figure 5.24: Map of California Aqueducts Map of California aqueducts that bring water to southern
California from central and northern California and from the Colorado River to the east. Source: Central
Basin Municipal Water District
28
The Colorado River, probably the most exploited river in the U.S., has many dams, some huge reservoirs,
and several large aqueducts so that it can provide large amounts of fresh water to 7 states in the arid
southwestern U.S. and Mexico. The primary use for the water is for a few large cities (Las Vegas, Phoenix,
and Tuscon) and irrigation. Allocation of Colorado River water is strictly regulated. Fortunately, not all
28 http://www.centralbasin.org/waterSupplySystem.html
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states use all of their water allocation because the total amount of allocated water is more than the typical
Colorado River discharge. Colorado River water gets so saline due to evaporation along its course that
the U.S. was forced to build a desalination plant near the border with Mexico so that it could be used for
drinking and irrigation. The wetlands of the Colorado River delta and its associated ecosystem have been
sadly degraded by the water overuse; some years, no river ow even reaches the ocean.
One method that actually can increase the amount of fresh water on Earth is desalination, which
involves removing dissolved salt from seawater or saline groundwater. There are several ways to desalinate
seawater including boiling, ltration, electrodialysis, and freezing. All of these procedures are moderately
to very expensive and require considerable energy input, making the produced water much more expensive
than fresh water from conventional sources. In addition, the processes create highly saline wastewater, which
must be disposed of. Desalination is most common in the Middle East, where energy from oil is abundant
but water is scarce.
Conservation means using less water and using it more eciently. Around the home, conservation can
involve both engineered features, such as high-eciency clothes washers and low-ow showers and toilets, as
well as behavioral decisions, such as growing native vegetation that require little irrigation in desert climates,
turning o the water while you brush your teeth, and xing leaky faucets. Rainwater harvesting involves
catching and storing rainwater for reuse before it reaches the ground. Ecient irrigation is extremely
important because irrigation accounts for a much larger water demand than public water supply. Water
conservation strategies in agriculture include growing crops in areas where the natural rainfall can support
them, more ecient irrigation systems such as drip systems that minimize losses due to evaporation, no-till
farming that reduces evaporative losses by covering the soil, and reusing treated wastewater from sewage
treatment plants. Recycled wastewater has also been used to recharge aquifers. There are a great many
other specic water conservation strategies. Sustainable solutions to the water crisis must use a variety of
approaches but they should have water conservation as a high priority.
5.2.10 Review Questions
Question 5.2.1
What is the water cycle and why is it important to fresh water resources?
Question 5.2.2
What are the relative merits of using surface water vs. groundwater as a water resource?
Question 5.2.3
What should society learn from the case history of the Aral Sea?
Question 5.2.4
Why is society facing a crisis involving water supply and how can we solve it?
5.2.11 References
Watkins,
man
K. (2006).
Development
Beyond scarcity:
Report
2006,
United
Power,
Nations
http://hdr.undp.org/en/reports/global/hdr2006/29
poverty and the global water crisis.
HuDevelopment Programme.
Retrieved from
30
5.3 Case Study: The Aral Sea – Going, Going, Gone
The Aral Sea is a lake located east of the Caspian Sea between Uzbekistan and Kazakhstan in central Asia
(see Figure Map of Aral Sea Area (Figure 5.25)). This area is part of the Turkestan desert, which is the
fourth largest desert in the world; it is produced from a rain shadow eect by Afghanistan’s high mountains
29 http://hdr.undp.org/en/reports/global/hdr2006/
30 This content is available online at .
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to the south. Due to the arid and seasonally hot climate there is extensive evaporation and limited surface
waters in general. Summer temperatures can reach 60 ◦ C (140 ◦ F)! The water supply to the Aral Sea is
mainly from two rivers, the Amu Darya and Syr Darya, which carry snowmelt from mountainous areas. In
the early 1960s the then-Soviet Union diverted the Amu Darya and Syr Darya Rivers for irrigation of one of
the driest parts of Asia to produce rice, melons, cereals, and especially cotton. The Soviets wanted cotton
or white gold to become a major export. They were successful and today Uzbekistan is one of the world’s
largest exporters of cotton. Unfortunately this action essentially eliminated any river inow to the Aral Sea
and caused it to disappear almost completely.
Figure 5.25: Map of Aral Sea Area
Map shows lake size in 1960 and political boundaries of 2011.
Countries in yellow are at least partially in Aral Sea drainage basin. Source: Wikimedia Commons
31
In 1960 Aral Sea was the fourth largest inland water body; only the Caspian Sea, Lake Superior, and
Lake Victoria were larger. Since then, it has progressively shrunk due to evaporation and lack of recharge
by rivers (see Figure Shrinking Aral Sea Blue (Figure 5.26)). Before 1965 the Aral Sea received 2060
km3 of fresh water per year from rivers and by the early 1980s it received none. By 2007 the Aral Sea
shrank to about 10% of its original size and its salinity increased from about 1% dissolved salt to about 10%
dissolved salt, which is 3 times more saline than seawater. These changes caused an enormous environmental
impact. A once thriving shing industry is dead as are the 24 species of sh that used to live there; the sh
could not adapt to the more saline waters. The current shoreline is tens of kilometers from former shing
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towns and commercial ports. Large shing boats lie in the dried up lakebed of dust and salt (see Figure
An Abandoned Ship (Figure 5.27)). A frustrating part of the river diversion project is that many of the
irrigation canals were poorly built, allowing abundant water to leak or evaporate. An increasing number of
dust storms blow salt, pesticides, and herbicides into nearby towns causing a variety of respiratory illnesses
including tuberculosis.
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Available for
free Sea
at Connexions
Figure 5.26: Shrinking
Aral
Blue area gives size of Aral Sea in 1960, 1970, 1980,
32
2004, 2008, and 2009 Source: NordNordWest
at Wikimedia Commons
1990, 2000,
183
Figure 5.27: An Abandoned Ship This abandoned ship lies in a dried up lake bed that was the Aral
33
Sea near Aral, Kazakhstan Source: Staecker
at Wikimedia Commons
The wetlands of the two river deltas and their associated ecosystems have disappeared. The regional
climate is drier and has greater temperature extremes due to the absence of moisture and moderating
inuence from the lake. In 2003 some lake restoration work began on the northern part of the Aral Sea
and it provided some relief by raising water levels and reducing salinity somewhat. The southern part of
the Aral Sea has seen no relief and remains nearly completely dry. The destruction of the Aral Sea is one
of the planet’s biggest environmental disasters and it is caused entirely by humans. Lake Chad in Africa is
another example of a massive lake that has nearly disappeared for the same reasons as the Aral Sea. Aral
Sea and Lake Chad are the most extreme examples of large lakes destroyed by unsustainable diversions of
river water. Other lakes that have shrunk signicantly due to human diversions of water include the Dead
Sea in the Middle East, Lake Manchar in Pakistan, and Owens Lake and Mono Lake, both in California.
32 http://commons.wikimedia.org/wiki/File:Aralsee.gif
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5.4 Water Pollution
34
5.4.1 Learning Objectives
After reading this module, students should be able to
•
•
•
•
•
understand the major kinds of water pollutants and how they degrade water quality
understand how and why the lack of safe drinking water in some parts of the world is a major problem
know what sewage treatment does and why it is important
know why it is more dicult to remediate groundwater pollution than surface water pollution
understand how we can work toward solving the crisis involving water pollution
5.4.2 The Water Pollution Crisis
The Module Water Cycle and Fresh Water Supply (Section 5.2) described one aspect of the global water
crisis, the water shortages that aict many arid and densely populated areas. The global water crisis also
involves water pollution, because to be useful for drinking and irrigation, water must not be polluted beyond
certain thresholds. According to the World Health Organization, in 2008 approximately 880 million people
in the world (or 13% of world population) did not have access to improved (safe) drinking water (World
Health Statistics, 2010 (p. 209)) (See Figure Proportion of Population by Country Using Improved
Drinking Water Sources in 2008 (Figure 5.28)). At the same time, about 2.6 billion people (or 40% of
world population) lived without improved sanitation (see Figure Proportion of Population by Country
Using Improved Sanitation Facilities in 2008 (Figure 5.29)), which is dened as having access to a
public sewage system, septic tank, or even a simple pit latrine. Each year approximately 1.7 million people
die from diarrheal diseases associated with unsafe drinking water, inadequate sanitation, and poor hygiene,
e.g., hand washing with soap. Almost all of these deaths are in developing countries, and around 90% of
them occur among children under the age of 5 (see Figure Deaths by Country from Diarrhea Caused
by Unsafe Water, Unimproved Sanitation, and Poor Hygiene in Children Less than 5 Years
Old, 2004 (Figure 5.30)). Compounding the water crisis is the issue of social justice; poor people more
commonly lack clean water and sanitation than wealthy people in similar areas. Globally, improving water,
sanitation, and hygiene could prevent up to 9% of all disease and 6% of all deaths. In addition to the global
waterborne disease crisis, chemical pollution from agriculture, industry, cities, and mining threatens global
water quality. Some chemical pollutants have serious and well-known health eects; however, many others
have poorly known long-term health eects. In the U.S. currently more than 40,000 water bodies t the
denition of impaired set by EPA (See Figure Percentage of Impaired Water Bodies in a Watershed
by State in USA Based on US EPA Data in 2000 (Figure 5.31)), which means they could neither
support a healthy ecosystem nor meet water quality standards. In Gallup public polls conducted over the
past decade Americans consistently put water pollution and water supply as the top environmental concerns
over issues such as air pollution, deforestation, species extinction, and global warming.
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Figure 5.28:
Proportion of Population by Country Using Improved Drinking Water
Sources in 2008 Improved drinking water sources, e.g., household connections, public standpipes,
boreholes, protected dug wells and springs, and rainwater collections, are dened as those more likely to
provide safe water than unimproved water sources, e.g., unprotected wells and springs, vendor-provided
water, bottled water (unless water for other uses is available from an improved source), and tanker
truck-provided water. Source: World Health Organization
35
35 http://gamapserver.who.int/mapLibrary/Files/Maps/phe_water_08.png
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Figure 5.29: Proportion of Population by Country Using Improved Sanitation Facilities
in 2008 Improved sanitation facilities, e.g., connection to public sewers or septic systems, pour-ush
latrines, pit latrines, and ventilated improved pit latrines, are dened as those more likely to be sanitary
than unimproved facilities, e.g., bucket latrines, public latrines, and open pit latrines. Source: World
36
Health Organization
36 http://gamapserver.who.int/mapLibrary/Files/Maps/MDG7_sanitation_08.png
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Figure 5.30: Deaths by Country from Diarrhea Caused by Unsafe Water, Unimproved
Sanitation, and Poor Hygiene in Children Less than 5 Years Old, 2004 Source: World Health
Organization
37
37 http://gamapserver.who.int/mapLibrary/Files/Maps/Global_wsh_death_under5_2004.png
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Figure 5.31: Percentage of Impaired Water Bodies in a Watershed by State in USA
Based on US EPA Data in 2000 Map of watersheds containing impaired water bodies from the U.S.
Environmental Protection Agency’s 1998 list of impaired waters Source: U.S. Geological Survey
38
5.4.3 Water Chemistry Overview
Compared to other molecules of similar molecular weight, water (H2 O) has unique physical properties including high values for melting and boiling point, surface tension (water’s cohesion, or stickiness), and
capacity to dissolve soluble minerals, i.e., act as a solvent. These properties are related to its asymmetrical
structure and polar nature, which means it is electrically neutral overall but it has a net positive charge on
the side with the two hydrogen atoms and a net negative charge on the oxygen side (see Figure Structure of
Water, Polar Charge of Water, and Hydrogen Bonds between Water Molecules (Figure 5.32)).
This separation of the electrical charge within a water molecule results in hydrogen bonds with other water
molecules, mineral surfaces (hydrogen bonding produces the water lms on minerals in the unsaturated zone
of the subsurface), and dissolved ions (atoms with a negative or positive charge). Many minerals and pollutants dissolve readily in water because water forms hydration shells (spheres of loosely coordinated, oriented
water molecules) around ions.
38 http://pubs.usgs.gov/fs/FS-130-01/
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Figure 5.32: Structure of Water, Polar Charge of Water, and Hydrogen Bonds between
Water Molecules Source: Michal Ma¬as39 at Wikimedia Commons
Any natural water contains dissolved chemicals; some of these are important human nutrients, while
others can be harmful to human health. The abundance of a water pollutant is commonly given in very
small concentration units such as parts per million (ppm) or even parts per billion (ppb). An arsenic
concentration of 1 ppm means 1 part of arsenic per million parts of water. This is equivalent to one drop of
arsenic in 50 liters of water. To give you a dierent perspective on appreciating small concentration units,
converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm to time units is 30
seconds in a year. Total dissolved solids (TDS) represent the total amount of dissolved material in water.
Average TDS (salinity) values for rainwater, river water, and seawater are about 4 ppm, 120 ppm, and 35,000
ppm. As discussed in Module Climate Processes; External and Internal Controls (Section 3.2), the
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most important processes that aect the salinity of natural waters are evaporation, which distills nearly pure
water and leaves the dissolved ions in the original water, and chemical weathering, which involves mineral
dissolution that adds dissolved ions to water. Fresh water is commonly dened as containing less than either
1,000 or 500 ppm TDS, but the US Environmental Protection Agency (EPA) recommends that drinking
water not exceed 500 ppm TDS or else it will have an unpleasant salty taste.
5.4.4 Water Pollution Overview
is the contamination of water by an excess amount of a substance that can cause harm to
human beings and the ecosystem. The level of water pollution depends on the abundance of the pollutant, the
ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical,
or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes
can cause water pollution, most pollution is derived from human, land-based activities (see Figure Water
Pollution (Figure 5.33)). Water pollutants can move through dierent water reservoirs, as the water
carrying them progresses through stages of the water cycle (see Figure Sources of Water Contamination
(Figure 5.34)). Water residence time (the average time that a water molecule spends in a water reservoir) is
very important to pollution problems because it aects pollution potential. Water in rivers has a relatively
short residence time, so pollution usually is there only briey. Of course, pollution in rivers may simply
move to another reservoir, such as the ocean, where it can cause further problems. Groundwater is typically
characterized by slow ow and longer residence time, which can make groundwater pollution particularly
problematic. Finally, pollution residence time can be much greater than the water residence time because a
pollutant may be taken up for a long time within the ecosystem or absorbed onto sediment.
Water pollution
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Figure 5.33: Water
Pollution Obvious water pollution in the form of oating debris; invisible water
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pollutants sometimes can be much more harmful than visible ones. Source: Stephen Codrington
Wikimedia Commons
at
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