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Hello, I'm Glenn Paterson. We hope you've been enjoying the course so far. In this lecture,
I'd like to address the issue of water quality. We'll follow the general line of discussion
presented by Peter Glick and others in Chapter 3 of the recommended course textbook, The
World's Water Volume 7. I recommend that chapter for additional coverage of the topic. We'll
take a look at the major types of contaminants that affect water quality, where they come
from, how they affect ourselves and the aquatic environment, and some of the ways in which
people are working to improve water quality. The status of the world's water quality is
a combination of good news and not so good news. The good news generally pertains to
developed countries. In these countries, tap water is generally safe to drink thanks to
measures taken to protect source areas and to upgrade drinking water treatment. Second,
sewage and industrial waste generally received adequate treatment before being discharged
to receding waters. These types of discharges that emerge from a pipe, known as point-source
pollution, have been heavily targeted by pollution control programs in these countries since
about the 1970s. Also in these countries, steps are being made to control non-point
source pollution or pollution that enters waterways via diffuse sources such as overland
runoff or groundwater seepage. Effective non-point source pollution control is a more difficult
and more recent effort compared with point-source control. Solutions tend to involve management
practices for land or materials that reduce non-point source pollution and hence protect
the environment. The story is not so rosy for many countries
in the developing world. For various reasons generally having more to do with social and
political issues than with technological or financial ones, all three of the previous
statements are typically reversed in these countries. To put the human toll into perspective,
consider how the world would treat the news that a plane carrying 300 children had crashed
and all were lost. Then consider how the world would react if 13 such plane crashes were
to occur on the same day, killing over 4100 children. You can imagine what's next. According
to UNICEF, the death toll for water-borne disease among children is equivalent to 13
such plane crashes every day month after month, year after year. And that's just the children.
Add another two daily plane crashes for the adults. You get a total of 1.7 million deaths
per year. This carnage is inflicted by diseases that were tamed nearly a century ago in developed
countries. From a technological and engineering standpoint, there are relatively straightforward
solutions that would provide safe drinking water and adequate sanitation. The problem
lies mostly in shaping the political role in the organizational structure to implement
the solutions. To more fully understand these pollution issues,
it's helpful to review some of the basics of water quality problems. Let's take a look
at the most common categories of water quality contaminant.
Nutrients exemplify the old saying that pollution is resources out of place. Plant nutrients,
primarily nitrogen and phosphorus, are necessary for the growth of all plants. We spend billions
of dollars each year to apply these nutrients in the form of chemical and biological fertilizers
to our agricultural fields to boost crop production. Nitrogen and phosphorus are also required
by microscopic algae and other aquatic plants that are the basis for healthy aquatic ecosystems.
The problems start when rivers and lakes get too much of a good thing. Known as the process
of eutrophication, excess nutrients cause too much growth of aquatic plants so that
plant production exceeds the capacity of grazers to keep it in check. When the blooms of algae
and other plants die, their decay uses up so much oxygen that frequently there's not
enough left for fish and other organisms. In addition to causing eutrophication in the
environment, nitrogen in the form of nitrate can also be a human health hazard, especially
for babies. Ingesting water with more than 10 milligrams per liter of nitrogen as nitrate
can cause Blue Baby Syndrome in which the nitrate interferes with the blood's ability
to carry oxygen, hence drinking water provides are required to keep nitrate concentrations
below this level. As mentioned, much of the nutrient load comes from fertilizers, both
those used on the farm and those used on yards, parks, and golf courses. But, there are numerous
other sources of nutrients for rivers and lakes, too, including sewage effluent, industrial
waste, storm runoff, decaying organic matter, and even fallout from air pollution.
Like nutrients, sediment is a natural component of stream flow. And like nutrients, too much
of a good thing can cause big problems. When erosion is accelerated following disturbance
of the land surface and vegetation, downstream habitats can become choked with sediment.
Effects on the environment can include smothering the fish eggs in fry and gravel bars and effects
on human infrastructure can include accelerated wear on impellers of hydroelectric plants,
expenses for dredging sediment out of the navigable rivers, and expenses for additional
treatment of drinking and industrial water. Elevated concentrations of suspended sediment
is one of the three most common reasons for water quality impairment of streams in Colorado.
Temperature is not typically thought of as a pollutant, but heat can be detrimental to
streams. Temperature is a regulator of metabolic activity, so abnormally high temperatures
can interfere with aquatic life processes. Warm water holds less dissolved oxygen than
cold water, so as water temperatures rise fish and other aquatic life can become stressed
by low oxygen levels. Increased water temperatures can happen in several ways such as removal
of stream side vegetation that normally provides shade, addition of effluent that is warmer
than the stream, and warming associated with climate change.
Both people and aquatic organisms have fairly narrow tolerance for variations in pH, which
is the measure of the acidity of water. pH values that are too low, meaning too acidic,
or too high meaning too basic, can be detrimental or even toxic to aquatic life. Excess acidity
can come from acid rain, acid runoff from abandoned mining sites, or addition of acidic
effluence. Salt is another natural component of aquatic
environments that can cause problems when there is too much of it. Drinking water with
more than 250 milligrams per liter chloride tastes too salty to drink. Excess salt can
also disrupt metabolism in fish and other aquatic organisms that are adapted to freshwater
environments. Salt contamination comes from natural processes such as discharge from natural
salt springs, and from human activities such as road salting, agricultural drainage, discharge
of salty groundwater from oil and gas production sites, and discharge of salt from industrial
effluence. Sodium chloride or table salt is not the only salt that can cause water quality
problems. Water draining from naturally saline soils or rock formations can pick up other
salts as well. As indicated other, pathogens or disease causing
microorganisms are among the most widespread and serious of water quality problems. Dozens
of different types of pathogens have developed life cycles that are exquisitely adapted to
invading humans and turning them into breeding grounds for endless new generations of pests.
Examples include bacteria such as Vibrio Cholerae, the bacteria that causes cholera or Salmonella
Typhi, the cause of typhoid fever as well as viruses such as Hepatitis A and a host
of gastrointestinal viruses that cause diarrhea and larger microorganisms or protozoa such
as cryptosporidium and giardia which also cause debilitating diarrhea. Many of these
pathogens thrive in the fecal-oral root of infection in which they breed in the digestive
tracts of their victims, are excreted by the billions in human waste, are then ingested
when people drink water contaminated with sewage, and then begin the breeding process
anew. One of the great scientific advances in the field of public health was the discovery
in the mid-19th century of this cycle of infection. Its discovery came about because of advances
such as the discovery of microorganisms themselves, development of the germ theory of disease,
and the recovery of viable cholera bacteria from rivers that served as water supplies.
Once the fecal-oral root was recognized, the field of waterborne disease epidemiology was
born thanks to people like Dr. John Snow. He removed the handle from the public water
pump in the SoHo district of London in 1858 after noticing the geographic clustering of
cholera cases around this contaminated pump. Some of these pathogens such as Vibrio Cholerae
or Salmonella Typhi were virtually eliminated as public health concerns in developed countries
following the introduction of the chlorination of drinking water in the early 18th century,
but they continue to wreak havoc in developing countries. Others, such as cryptosporidium
and giardia, strike victims at both ends of the socioeconomic spectrum due to their ability
to form durable cysts that are resistant to this infection.
A few metals are required in tiny amounts for normal nutrition but many metals become
toxic at even moderate concentrations. Abandoned hard rock mining sites frequently leach quantities
of lead, copper, zinc, chromium, cadmium, and other toxic metals into streams where
they interfere with fish and other aquatic life. Metal related industries also discharge
metal-containing water into streams. Coal-burning power plants can release some coal related
metals into the air. This is one of the primary pathways by which mercury makes its way into
streams. Some may be leached out of naturally occurring deposits in soils and rocks. In
certain areas, this is a frequent problem associated with drainage of irrigation water
from agricultural soils naturally high in selenium. Two of these metals, mercury and
selenium, are frequent causes of water quality impairment in Colorado.
The final category of water pollutants is the largest. Humans have developed thousands
of chemicals to help us in various ways in our daily lives. Each year, about 700 new
chemicals are developed. Some, such as many petroleum distillates, are found in nature.
Many are entirely synthetic and are not known to occur naturally. Examples of human developed
chemicals include pesticides, herbicides, repellents, pharmaceuticals, flame-retardants,
solvents, cleaning agents, dyes, fragrances, and other personal care products. Ironically,
a few chemicals known as disinfection by-products are produced in drinking water as by-products
of the very process, chlorine disinfection, that was developed to make drinking water
safe from waterborne diseases. Some chemicals are acutely toxic to humans and aquatic life,
others exhibit chronic toxicity, gradually building up to a toxic effect over years of
exposure, some cause cancer or birth defects, and some mimic the effects of hormones, those
natural metabolic regulators that control growth and development in tiny amounts. Not
all of these chemicals are toxic, but testing them all for toxicity is a daunting task.
The task is complicated because some of the compounds interact with each other, magnifying
their effects in synergistic actions. Since some of these compounds are recently developed
and their testing, regulation, and treatment are in developmental stages, they are known
as emerging contaminants. Next, let's take a look at some of the processes
and activities that contribute contaminants to water resources. Not all of these processes
are mediated by humans. A number of natural processes have been contributing certain contaminants
to water since long before humans were around. Natural mineral deposits can produce significant
concentrations of some contaminants such as salt and some metals. Millions of people in
Bangladesh and the Ganges Delta Region drink shallow groundwater naturally contaminated
with arsenic. This is also a common problem in many other parts of the world. Wildfires
create large amounts of ash and charcoal which are frequently washed into streams along with
massive amounts of sediment mobilized from the burned-over forests. We'll hear more about
this topic from a lecture by Sarah Rathburn on Rivers After Fire. One additional example
of a naturally occurring contaminant is the radioactive gas radon. Some radioactive contaminants
of course come from human activities but radon is derived from the radioactive decay of naturally
occurring radium. The gas produced gradually in the soil can enter aquifers, wells, water
pipes, and basement cisterns where water is stored.
While natural process are responsible for some contaminants in water, the great bulk
of contaminants enter water as a result of human activities. We've already mentioned
agriculture which applies large amounts of fertilizers, herbicides, and pesticides to
the soil where the chemicals not absorbed by the plants may be washed into ditches,
streams, lakes, and aquifers. Animal production farms produce manure which contains pathogens,
nutrients, and sometimes synthetic chemicals. Farms also can produce sediment derived from
erosion in the fields and salt from drainage of naturally saline soils or soils irrigated
with slightly saline water. Industrial activities produce a wide range of chemicals in their
waste water effluence. Extractive industries such as oil and gas development can result
in water pollution in the form of petrochemicals from the natural formations, salt from saline
groundwater, and chemicals used in processes such as hydraulic fracturing or fracking.
Mining can contribute acidity from acid mine drainage and metals from waste rock. Some
human activities have indirect effects on water quality. As population grows and urban
and suburban development spreads over larger parts of the landscape, most of the types
of contaminants we just discussed become more abundant. In addition, the increased impervious
area generates urban runoff that transports such pollutants directly to streams rather
than filtering them gradually through soil. To the extent that humans are contributing
to climate change, we are also contributing to warmer stream temperatures and in some
places, higher pollutant concentrations due to lower diluting flows. I've saved one final
area of human activity for last because of its immense impact. This has to do with how
we handle and transport water and waste. Over the last two centuries we've made tremendous
investments in infrastructure to carry clean water to our taps and sewage to our treatment
plants and receding waters. During the last two decades however we have fallen far behind
in our efforts to keep up with the level of maintenance required to keep that infrastructure
in good condition. If we can't keep clean water isolated in the surrounding soil, we
cannot guarantee its purity when it gets to the tap. If we cannot keep sewage confined
to sewer lines, the leaks are bound to put untreated sewage into lakes, streams, and
aquifers. Similarly, investments in upgraded treatment plants for both drinking water and
waste water are needed to keep them operating efficiently. On the other hand, many parts
of the world still have little or no water and sewage infrastructure at all. This is
where the most serious water quality problems occur.
What happens when poorly treated or untreated sewage enters a stream? First of all, viable
pathogens may be released into the stream, potentially affecting downstream water supplies.
Second, nutrients and solids are added to the stream increasing the turbidity and potentially
leading to eutrophication and resulting in algal blooms and related problems. Finally,
sewage represents residual food material that has not been fully digested. This means that
sewage contains reduced organic matter that can produce energy when oxidized, as occurs
inside most living cells in the process called respiration that fuels aerobic metabolism.
Naturally occurring aquatic bacteria and other microbes derive their own energy by consuming
or oxidizing this residual reduced organic matter. Since this process requires oxygen
and is mediated in water by microorganisms, the reduced organic matter is referred to
as biochemical oxygen demand or BOD. The more sewage enters a stream and the less treatment
in receives, the higher the level of BOD. Water, even cold water, contains much less
oxygen in dissolved form than is present in the air, at most about 12 milligrams per liter.
As the dissolved oxygen is taken up by bacteria to oxidize the biochemical oxygen demand,
the concentration of dissolved oxygen remaining in the stream declines, creating a characteristic
dissolved oxygen sag downstream from the sewage discharge. This graph shows the levels of
biochemical oxygen demand and dissolved oxygen downstream from a discharge of poorly treated
sewage that occurs at the left edge of the graph. You can see the dissolved oxygen sag
that develops downstream. The bottom of the BOD sag where the oxygen concentration is
at a minimum occurs at a distance downstream known as the critical distance, indicated
by the red dashed line. If the load of biochemical oxygen demand exceeds the available supply
of dissolved oxygen to satisfy that demand, the dissolved oxygen can be totally depleted,
leaving none in the stream to support aerobic organisms such as fish. This is one of the
water quality situations that can lead to fish kills.
How does water pollution effect the environment? Many of the water contaminants we have discussed
degrade habitat for fish and other aquatic organisms. This reduces the ability of the
stream to provide ecosystem services such as fisheries. Pollution can also degrade the
aesthetic quality of rivers. Environmental effects of water pollution are not confined
just to rivers. Wetlands, lakes, and estuaries can see impaired habitats and ecosystem functioning.
Polluted water from the land surface can make its way into groundwater aquifers as well.
In the oceans, near the mouths of some large rivers that carry significant loads of biochemical
oxygen demand and other contaminants, zones of depleted dissolved oxygen appear every
year, killing marine life and destroying... Moving to the effects of water pollution on
people, the cause for greatest distress is the continuing occurrence of waterborne diseases
discussed earlier. These diseases wreak their misfortune disproportionately on highly vulnerable
populations, on children primarily. Over 90% of the deaths caused by waterborne diseases
are among children under five years of age. Another vulnerable population segment is women
who tend to be the water gatherers and caregivers and therefore have intimate contact with polluted
water in regions that have poor sanitation. These vulnerable populations also tend to
be poor, often uneducated, and sometimes politically oppressed. Water pollution upstream causes
damage to interests of downstream water users who may find the water totally or partly unsuited
to their needs. Sometimes the downstream users are in different political entities than the
upstream polluters, exacerbating transboundary conflicts. Pollution problems create economic
damages requiring expensive outlays for alternate supplies, treatment, healthcare costs, and
lost ecosystem services. What steps are being taken to control? The
solutions to these problems are not easy and must be multifaceted in approach. Some of
the most cost effective efforts include prevention of pollution in the first place. This means
management of watersheds, farms, industries, chemicals, and people to reduce the opportunity
for contaminants to enter water resources. Solutions such as vegetative buffer strips
between farm fields and streams, green infrastructure to encourage infiltration of storm runoff,
and land use management to keep polluting activities out of vulnerable drinking water
source areas can help to avoid pollution in the first place. Additional efforts must go
into expanding and improving water infrastructure to provide treatment of both drinking water
and waste water and to transport both types of water with fewer leaks. While most of the
technologies needed to improve water quality are in place, there is still room for innovation
and technological improvement. Examples include devices such as the life straw which contains
activated carbon and other treatment technologies inside a straw so that polluted water may
be treated and drunk at the same time. Another example is innovative technology for removing
arsenic from the thousands of tube wells that serve naturally high-arsenic groundwater to
consumers in the Ganges Delta Region. Finally, and perhaps most significantly, we need to
improve our institutional and political approach to water pollution control. As pointed out
by Neil Grigg in the first module, this is a crucial aspect of water management and one
of the most difficult to accomplish. Solutions to this aspect of the problem will involve
education, financing, political action, leadership, and the collaboration of many and varied entities
and institutions who can work together toward cleaner water for all.
In summary, as a universal solvent, water picks up many types of contaminants. Contaminants
come from natural process and human activities. Pollution impacts the environment and people
and is responsible for 1.7 million deaths a year, especially among children. We've made
progress improving water quality, but there is still much left to do.
Thank you and good luck in doing your part to support cleaner water!