INTRODUCTION TO WATER ENVIRONMENT
Without water, there would be no oceans, no lakes, no rivers, no rain, no snow, no hail, no
clouds, no polar ice caps, no Jolt cola, nothing to drink whatsoever, and probably no you, no me,
no nothing! Water is everywhere; it defines our planet; it is intricately involved in just about
every process on this planet in one way or another.
Yet how does this simple molecule, composed merely of two hydrogen atoms and one oxygen
atom (hence the chemical designation H2O) do all the amazing things that it does? That's what
we are about to find out.
Here are ten properties of water that are familiar to us all:
1. It's colorless;
2. It's tasteless;
3. It's odorless;
4. It feels wet;
5. It's distinctive in sound when dripping from a faucet or crashing as a wave;
6. It dissolves nearly everything;
7. It exists in three forms: liquid, solid, gas;
8. It can absorb a large amount of heat;
9. It sticks together into beads or drops;
10. It's part of every living organism on the planet.
The Unique Structure of Water
Polarity of water molecules results in hydrogen bonding. The water molecule is relatively simple
in structure. Two hydrogen atoms are joined to a single oxygen atom by single covalent bonds.
Oxygen is more electronegative than the hydrogen atoms which allows the electrons of the polar
bonds to spend more time closer to the oxygen side of the molecule. The oxygen side becomes
more negative in charge, and the hydrogen atoms have a slight positive charge. This forms the
polar molecule.
The water molecule is shaped like an isosceles triangle, with a slight bond angle of 104.5 degrees
at the oxygen nucleus. The weak Coulombic characteristics of the bonding of hydrogen atoms to
the weakly electronegative oxygen atom result in both ionized and covalent states that
simultaneously maintain the integrity of water. Water is one of the only compounds that possess
these characteristics.
An electrostatic attraction occurs between the polar water molecules. The slight positive charged
hydrogen atom is attracted to the slight negative charged oxygen atom of another water
molecule. This weak attraction is called a hydrogen bond. Every water molecule is hydrogen
bonded to its four nearest neighbors.
When water is in liquid form, its weak hydrogen bonds are about one-twentieth as strong as a
covalent bond. Hydrogen bonds constantly form and break. Each hydrogen bond lasts for a
fraction of a second, but the molecules continuously form new bonds with other water molecules
around them. At any time a large percentage of water molecules are bonded to neighboring water
molecules which gives water more structure than most other liquids. Collectively, the hydrogen
bonds hold water together by the property of cohesion.
Cohesion due to hydrogen bonding contributes to the formation of waves and other water
movements that occur in lakes. Water movements are integral components of the lake system
and play an important role in the distribution of temperature, dissolved gases, and nutrients.
These movements also determine the distribution of microorganisms and plankton.
Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the
surface of a liquid. Water has a greater surface tension than all other liquids except mercury. At
the interface between water and air is an ordered arrangement of water molecules which are
hydrogen bonded to one another and the water below.
Water's Specific Heat
Water has a high heat capacity. Specific heat a measure of heat capacity, is the heat required to
raise the temperature of 1 gram of water 1°C. Water, with its high heat capacity, therefore,
changes temperature more slowly than other compounds that gain or lose energy.
The heat capacity of water stems directly from its hydrogen bonded structure. Although
hydrogen bonds are weak, their combined effect is enormous. As heat is added to ice or liquid
water, the energy first breaks hydrogen bonds, which allows the molecules to move freely. Since
temperature is a measure of the average kinetic energy of molecules (the rate at which they
move), the temperature of water rises slowly with the addition of heat. When the temperature of
water drops slightly, many additional hydrogen bonds form and release a considerable amount of
energy in the form of heat.
This resistance to sudden changes in temperature makes water an excellent habitat because
organisms adapted to narrow temperature ranges may die if the temperature fluctuates widely.
The heat requiring and heat retaining properties of water provide a much more stable
environment than is found in terrestrial situations. Fluctuations in water temperature occur very
gradually, and seasonal and diurnal extremes are small in comparison to terrestrial environments.
The high specific heat can have profound effects on climatic conditions of adjacent air masses.
When it warms only a few degrees, a large lake can absorb and store a huge amount of heat from
the sun in the daytime and summer. At night and during winter, the gradually cooling water can
warm the air.
Because of water's high specific heat, the water that covers most of the earth's surface keeps
temperature fluctuations within limits that allow living organisms to survive. Also, because
organisms consist mostly of water, they are more able to resist changes in their own
temperatures.
Evaporation and Cooling
Water has a high heat of vaporization - the energy required to convert liquid water to a gas.
Because of the energy needed to break the hydrogen bonds holding a water molecule to its
neighbors, more energy is required to evaporate liquid water than most other substances. To
evaporate each gram of water at room temperature, about 580 calories of heat are needed, which
is nearly double the amount needed to vaporize a gram of alcohol or ammonia.
Water's high heat of vaporization helps moderate the earth's climate. A considerable amount of
energy from the sun is absorbed by lakes during the evaporation of its surface waters. As water
evaporates, the remaining surface water cools. This evaporative cooling occurs because the
warmest molecules are those with the greatest kinetic energy and are most likely to leave in the
gaseous state. Evaporative cooling of water contributes to the stabilization of temperature in
lakes.
Water's Liquid Temperature Range
Water remains liquid over a wide temperature range, from 0 — 100°C. Most other substances
remain liquid over a narrower range. Since the chemical reactions of metabolism depend on
interactions between molecules moving about in liquid water, the limits of life are set by water's
freezing and boiling points. This property of water makes possible a wide variety of aquatic
habitats. Some fish species survive in temperatures at or near freezing while some bacteria and
algae survive in hot springs where the water temperature is near boiling.
Water as the Universal Solvent
Water is a substance that can almost dissolve anything. Salts such as sodium chloride (NaCl),
dissolve in water by dissociating as each ion becomes surrounded by the polar water molecules.
Shielded by a shell of water molecules, the ions stay in solution because they are no longer
affected by attractive forces from other ions.
Frozen Lake Density
Water is one of the few substances that are less dense as a solid than as a liquid. While most
substances contract when they solidify, water expands. This property is due to the hydrogen
bonding. When water is above 4 °C it behaves like other liquids; it expands as it warms and
contracts when it cools. Water starts to freeze when the temperature approaches 0°C and the
molecules no longer move vigorously enough to break their hydrogen bonds. As the temperature
reaches 0°C the water molecules become locked into a crystalline lattice, and each water
molecule is bonded to the maximum of four partners.
When the surface temperature in a lake reaches 0°C, ice forms and floats on top of the lake. The
ice becomes an insulating layer on the surface of the lake; it reduces heat loss from the water
below and enables life to continue in the lake. When ice absorbs enough heat for its temperature
to increase above 0°C, the hydrogen bonds can be broken and allow the water molecules to slip
closer together. If ice sank, lakes would be packed from the bottom with ice, and many of them
would not be able to thaw out, since the energy from the air and the sunlight does not penetrate
very far.
Density Relationships of Water
A lake's physical, chemical, and metabolism dynamics are governed to a very great extent by
differences in density. The density of ice is almost ten times lighter than liquid water. Water's
density increases to a maximum at 3.98°C. Therefore, warmer waters are always found on top of
cooler water in lakes and produce layers of water called strata. This is typical of a lake that is
stratified during the summer. In winter the density differences in water cause a reverse
stratification where ice floats on top of warmer waters.
The hydrologic cycle, or water
cycle
is the cycling of water
through the earth system.
Not only is the hydrologic
cycle a cycle of water,
it is a cycle of energy as well.
The major components of the hydrologic cycle are:
•
evapotranspiration
•
condensation
•
precipitation
•
infiltration
•
percolation
•
runoff
EVAPOTRANSPIRATION
Evapotranspiration is the combined net effect of two processes: evaporation and transpiration.
Evapotranspiration uses a larger portion of precipitation than the other processes associated with
the hydrologic cycle.
Evaporation is the process of returning moisture to the atmosphere. Water on any surface,
especially the surfaces of mudholes, ponds, streams, rivers, lakes, and oceans, is warmed by the
sun's heat until it reaches the point at which water turns into the vapor, or gaseous, form. The
water vapor then rises into the atmosphere.
Transpiration is the process by which plants return moisture to the air. Plants take up water
through their roots and then lose some of the water through pores in their leaves. As hot air
passes over the surface of the leaves, the moisture absorbs the heat and evaporates into the air.
CONDENSATION
Condensation is the cooling of water vapor until it becomes a liquid. As the dew point is reached,
water vapor forms tiny visible water droplets. When these droplets form in the sky and other
atmospheric conditions are present, clouds will form. As the droplets collide, they merge and
form larger droplets and eventually, precipitation will occur.
PRECIPITATION
Precipitation is moisture that falls from the atmosphere as rain, snow, sleet, or hail. Precipitation
varies in amount, intensity, and form by season and geographic location. These factors impact
whether water will flow into streams or infiltrate into the ground. In most parts of the world,
records are kept of snow and rainfall. This allows scientists to determine average rainfalls for a
location as well as classify rainstorms based on duration, intensity and average return period.
This information is crucial for crop management as well as the engineering design of water
control structures and flood control.
INFILTRATION
Infiltration is the entry of water into the soil surface. Infiltration constitutes the sole source of
water to sustain the growth of vegetation and it helps to sustain the ground water supply to wells,
springs and streams. The rate of infiltration is influenced by the physical characteristics of the
soil, soil cover (i.e. plants), water content of the soil, soil temperature and rainfall intensity. The
terms infiltration and percolation are often used interchangeably.
PERCOLATION
Percolation is the downward movement of water through soil and rock. Percolation occurs
beneath the root zone. Ground water percolates through the soil much as water fills a sponge, and
moves from space to space along fractures in rock, through sand and gravel, or through channels
in formations such as cavernous limestone. The terms infiltration and percolation are often used
interchangeably.
RUNOFF
Runoff is the movement of water, usually from precipitation, across the earth's surface towards
stream channels, lakes, oceans, or depressions or lowpoints in the earth's surface. The
characteristics that affect the rate of runoff include rainfall duration and intensity as well as the
ground's slope, soil type and ground cover.
The hydrosphere is often called the "water sphere" as it includes all the earth's water that is found
in streams, lakes, the soil, groundwater, and in the air. The hydrosphere interacts with, and is
influenced by, all the other earth spheres. The water of the hydrosphere is distributed among
several different stores found in these other spheres. Water is held in oceans, lakes and streams at
the surface of the earth. Water is found in vapor, liquid and solid states in the atmosphere. The
biosphere serves as an interface between the spheres which aids in the movement of water
between the hydrosphere, lithosphere and atmosphere. The hydrologic cycle traces the movement
of water and energy between these various stores and spheres. Water beneath the surface
comprises the next largest store of water. Groundwater and soil water together make up about
0.5% of all water (by volume). There is a difference between ground water and soil water. Soil
water is the water held in pore spaces between soil particles. Soil pore spaces usually are usually
partially void of water most of the time but fill with water after a rain storm. Groundwater, on the
other hand, is found where earth materials are saturated throughout the year. That is, the pore
spaces are always occupied with water. Both soil and groundwater are very important sources of
water. Soil water is available for plants to extract and use. Groundwater is an important source of
water for irrigation and drinking water supplies.
Above the surface water is found stored in streams, rivers and lakes. One might expect that given
the large rivers that flow across the earth and the huge numbers of lakes we have that this store
would be rather large. Instead, streams, rivers and lakes only comprise 0.02% of all water in the
earth system. In the atmosphere, only about 0.0001 % of the water in the hydrosphere is found.
Oceans
96,5 %
Ice
1,74 %
Ground waters
1,7 %
up to 100m
0,76 %
Lakes
0,013 %
Water in soil
0,001 %
Atmosphere
0,001 %
Marsh
0,0008 %
Rivers
0,0002 %
Biological water
0,0001 %
H2O in our environment is never „pure” water
Gas (vapour pressure)
Liquid (aqueous solution)
Solid (ice)
WATER
due to the
Admixtures + Pollutants
due to the
anthropogen
ic activity of
Gases
CO2, O2, H2S, N2,
CH4, NOx, SO2
Solids
Liquids
Inorganic
compounds
NOx, SO2, CaCO3
Substances
SOLUBLE
in water
ions: Na+, Ca2+, Mg2+,
Cl-, SO42-, HCO3-,
NO3-, PO43-
Organic
compounds
CH4, PCBs, dioxines
Substances
INSOLUBLE
in water
suspended matter or
colloids
PAHs, PCBs,
man
POLLUTION OF WATERS
! Underground waters
Quality is limited by SELF-PURIFICATION
Physical processes
Chemical processes Biological processes
Dilution
Degradation
Biodegradation
Coagulation
Oxidation
Decaying
Precipitation
Reduction
Sorption
(adsorption)
Hydrolysis
Ion-exchange
Filtration
! Surface waters
Mainly microbiological activity of organisms
and sedimentation
??? DILUTION IS THE BEST
SOLUTION
OF POLLUTION ???
Subsurface water
Groundwater and soil water together make up approximately .5% of all water in the hydrosphere.
Figure illustrates the various zones of water found beneath the surface.
Water beneath the surface can
essentially be divided into three
zones, 1) the soil water zone, 2) an
intermediate zone, and 3) the
ground water zone. The top two
zones, the soil water and intermediate zones, can be grouped into the zone of aeration where
during the year air occupies the pore spaces between earth materials. Sometimes, especially
during times of high rainfall, these pore spaces are filled with water.
Zones of water beneath the surface
Beneath the zone of aeration lies the zone of saturation or groundwater zone. Here water
constantly occupies all pore spaces. The water table divides the zone of aeration from the zone
of saturation. The height of the water table will fluctuate with precipitation, increasing in
elevation during wet periods and decreasing during dry. Note in the diagram how the water table
intersects the level of the stream surface. Seepage of groundwater into a stream provides a base
flow of water for perennial streams.
Soil Water
Soil water is held in the pore spaces between particles of soil. Soil water is the water that is
immediately available to plants. Soil water can be further sub-divided into three categories, 1)
hygroscopic water, 2) capillary water, and 3) gravitational water. Hygroscopic water is found as
a microscopic film of water surrounding soil particles. This water is tightly bound to a soil
particle by molecular forces so powerful that it cannot be removed by natural forces.
Hygroscopic water is bound to soil particles by adhesive forces that exceed 31 bars and may be
as great as 10,000 bars (Recall that sea level pressure is equal to 1013.2 millibars which is just
about 1 bar!). Capillary water is held by cohesive forces between the films of hygroscopic water.
The binding pressure for capillary water is much less than hygroscopic water. This water can be
removed by air drying or by plant absorption, but cannot be removed by gravity. Plants extract
this water through their roots until the soil capillary force (force holding water to the particle) is
equal to the extractive force of the plant root.
Groundwater
Groundwater occupies the zone of saturation. As depicted in the hydrologic cycle diagram,
groundwater moves downward through the soil by percolation and then toward a stream channel
or large body of water as seepage. The water table separates the zone of saturation from the zone
of aeration. The water table fluctuates with moisture conditions, during wet times the water table
will rise as more pore spaces are occupied with water. Groundwater is found in aquifers, bodies
of earth material that have the ability to hold and transmit water. Aquifers can be either
unconfined or confined. Unconfined aquifers are "connected" to the surface above. Confined
aquifers are sandwiched in between dense impermeable layers of earth material. Groundwater is
replenished by percolation of water from the zone of aeration downward to the zone of
saturation, or in the recharge zone of a confined aquifer. The recharge zone is where the confined
aquifer is exposed at the surface and water can enter it.
Groundwater is an important source of water for human activities such as agriculture and
domestic drinking water.
Groundwater quality
BRIEF DESCRIPTION: The chemistry (quality) of groundwater reflects inputs from the
atmosphere, from soil and water-rock reactions (weathering), as well as from pollutant sources
such as mining, land clearance, agriculture, acid precipitation, domestic and industrial wastes.
The relatively slow movement of water through the ground means that residence times in
groundwaters are generally orders of magnitude longer than in surface waters. As in the case of
Surface water quality, it is difficult to simplify to a few parameters.
SIGNIFICANCE: Groundwater is almost globally important for human consumption, and
changes in quality can have serious consequences. It is also important for the support of habitat
and for maintaining the quality of baseflow to rivers. The chemical composition of groundwater
is a measure of its suitability as a source of water for human and animal consumption, irrigation,
and for industrial and other purposes.
Surface Water
Precipitation may fall directly to the surface or be intercepted by plants, ultimately
reaching the ground. Once on the ground, water can infiltrate into the soil or move
across the surface as runoff. Surface runoff generally occurs when the rainfall
intensity exceeds the rate of infiltration, or if the soil is at its water holding
capacity. Infiltration and water holding capacity are both a function of soil texture
and structure. Soils composed of high percentages of sand allow water to infiltrate
through them quite rapidly because they have large, well-connected pore spaces.
Clay soils have low infiltration rates due to their smaller sized pore spaces.
However, there is actually a smaller total amount of pore space in a unit volume of
coarse, sandy soil than that of soil composed mostly of clay. As a result, sandy
soils fill rapidly and generally generate runoff sooner than clay soils.
If the rainfall intensity exceeds the infiltration capacity of the soil, or if the soil has
reached its field capacity, surface runoff occurs.
Stream flow is measured in a variety of ways, one of which is stream discharge.
Stream discharge is the volume of water passing through a particular cross-section
of a stream in a unit of time. Stream discharge is measure in cubic feet per second
or cubic meters per second.
Surface water quality
BRIEF DESCRIPTION: The quality of surface water in rivers and streams, lakes,
ponds and wetlands is determined by interactions with soil, transported solids
(organics, sediments), rocks, groundwater and the atmosphere. It may also be
significantly affected by agricultural, industrial, mineral and energy extraction,
urban and other human actions, as well as by atmospheric inputs. The bulk of the
solutes in surface waters, however, are derived from soils and groundwater
baseflow where the influence of water-rock interactions are important [see
groundwater quality; karst activity; soil and sediment erosion; soil quality;
streamflow; wetlands extent, structure and hydrology]. Selecting the variables to
be measured depends on the objectives and economics of the monitoring. This is a
complex matter because there are so many potential chemical, physical and
biological substances that could be important in any one area. From the viewpoint
of geoindicators, the following variables may be selected:
1. Basic variables
Metals and trace elements: Al, Sb, As, Cd, Cr, Cu, Pb, Hg, Se, Ag, Zn.
Nutrients: ammonium, nitrate, nitrite, total N, orthophosphate, total P.
Major constituents and dissolved solids: Ca, Mg, Na, Cl, SO4, HCO3, TDS.
Direct field measurements: acidity, alkalinity, dissolved O, pH, temperature.
Selected organic compounds of environmental significance: 2,4-D; 2,4,5-T;
phenol, chlorophenols, cresols, atrazine, cyperquat, paraquat, benzidine, DDT,
malathion.
2. Additional parameters
Of importance to human health: Ba, Be, F, Mo, Ni, V, radionuclides (gross
alpha, gross beta, 222Rn.
Of importance to agriculture - B.
SIGNIFICANCE: Clean water is essential to human survival as well as to aquatic
life. Most is used for irrigation, with lesser amounts for municipal, industrial, and
recreational purposes: only 6% of all water is used for domestic consumption. An
estimated 75% of the populations of developing nations lacks adequate sanitary
facilities, and wastes are commonly dumped into the nearest body of flowing
water. Pathogens such as bacteria, viruses and parasites make these wastes among
the world's most dangerous environmental pollutants: water-borne diseases are
estimated to cause about 25,000 deaths daily. Water quality data are, thus, essential
for the implementation of responsible water quality regulations, for characterizing
and remediating contamination, and for the protection of the health of humans and
aquatic organisms.
HUMAN OR NATURAL CAUSE: The water quality of a lake, reservoir or river
can vary in space and time according to natural morphological, hydrological,
chemical, biological and sedimentological processes (e.g. changes of erosion
rates). Pollution of natural bodies of surface water is widespread because of human
activities, such as disposal of sewage and industrial wastes, land clearance,
deforestation, use of pesticides, mining, and hydroelectric developments.
ENVIRONMENT WHERE APPLICABLE: The main environments are those
where surface water is used for human consumption or other societal uses, or
where important freshwater fisheries, sensitive aquatic habitats or valuable
wetlands are involved.
Sea – ocean environment
About 70% of the world is covered by water. 97% of this water is in the oceans and seas.
Ocean water moves a lot! Tides, waves, surface currents, and deep water circulation are all types
of ocean water movement. The oceans have a major effect on the weather, and they moderate the
world's climate.
Oceans and seas supply most of the water that evaporates and then falls as rain in the
water cycle. Oceans and seas are salty while rivers and lakes are fresh water. When salty water
from the ocean mixes with fresh water, a special place called an estuary is formed.
There are four major oceans. From biggest to smallest they are the Pacific, Atlantic, Indian and
Arctic. The Pacific Ocean is so large it covers a third of the Earth's surface all by itself! The
largest sea is the South China Sea. People have used the oceans and seas for food and
transportation for thousands of years.
There are two basic circulation systems in our oceans. One is the wind-driven surface
circulation, and the other is the deepwater density-driven circulation. It is controlled primarily by
differences in temperature and salt content (thermohaline circulation - "thermo" for temperature
and "haline" for salinity). This section focuses on density-driven circulation.
The ocean is a single body of water, but it is not homogeneous. There are water property
differences (such as temperature, salinity, and density) in various parts of the ocean.
Oceanographers define distinct water masses based on their physical and chemical
characteristics. Temperature and salinity are the primary components used to recognize a
particular water mass. Only about 10% of the ocean volume is involved in wind-driven surface
currents. The other 90% circulates due to density differences in water masses (primarily caused
by differing temperatures and salinities).
Estuaries
An estuary is a very special place where fresh water and salt water come together. Estuaries are
found on the coast where fresh water like a river or a bay has access to the ocean. The mixing of
fresh and salt water creates a different environment, but estuaries are still home to a lot of plants,
animals and bacteria! When looking at estuaries, scientists quickly realized that these areas were
extremely nutrient-rich because of sediment deposit of rivers, creeks or streams feeding into the
salt water environment. Unfortunately, estuaries haven't always been seen as valuable. In the
past, they were seen as worthless and were even used as dumps!
Density of Ocean Water
The density of pure water is 1000 kg/m3. Ocean water is more dense because of the salt in it.
Density of ocean water at the sea surface is about 1027 kg/m3.
There are two main factors that make ocean water more or less dense than about 1027 kg/m3: the
temperature of the water and the salinity of the water. Ocean water gets more dense as
temperature goes down. So, the colder the water, the more dense it is. Increasing salinity also
increases the density of sea water.
Less dense water floats on top of more dense water. Given two layers of water with the same
salinity, the warmer water will float on top of the colder water. There is one catch though!
Temperature has a greater effect on the density of water than salinity does. So a layer of water
with higher salinity can actual float on top of
water with lower salinity if the layer with
higher salinity is quite a bit warmer than the
lower salinity layer.
The temperature of the ocean decreases and
decreases as you go to the bottom of the ocean.
So, the density of ocean water increases and
increases as you go to the bottom of the ocean.
The deep ocean is layered with the densest
water on bottom and the lightest water on top.
Circulation in the depths of the ocean is
horizontal. That is, water moves along the
layers with the same density.
The density of ocean water is rarely measured
directly.
Natural Sea Water Composition
Element
ppm
Chlorine, Cl
Sodium, Na
Magnesium, Mg
Sulphur, S
Calcium, Ca
Potassium, K
Bromine, Br
Carbon, C
Nitrogen, N
Strontium, Sr
Oxygen, O
Boron, B
Silicon, Si
Fluorine, F
Argon, Ar
Lithium, Li
Rubidium, Rb
Phosphorus, P
Iodine, I
Barium, Ba
Molybdenium, Mo
Arsenic, As
Uranium, U
Vanadium, V
Titanium, Ti
Zinc, Zn
Nickel, Ni
Aluminium, Al
Cesium, Cs
Chromium, Cr
Antimony, Sb
Krypton, Kr
Selenium, Se
Neon, Ne
Manganese, Mn
Cadmium, Cd
Copper, Cu
Tungsten, W
Iron, Fe
Xenon, Xe
Zirconium, Zr
Bismuth, Bi
Niobium, Nb
Thallium, Tl
Thorium, Th
Hafnium, Hf
Helium, He
19,500
10,770
1,290
905
412
380
67
28
11.5
8
6
4.4
2
1.3
0.43
0.18
0.12
0.06
0.06
0.02
0.01
0.0037
0.0032
0.0025
0.001
0.0005
0.00048
0.0004
0.0004
0.0003
0.00024
0.0002
0.0002
0.00012
0.0001
0.0001
0.0001
0.0001
0.000055
0.00005
0.00003
0.00002
0.00001
0.00001
0.00001
7 x 10-6
6.8 x 10-6
Beryllium, Be
Germanium, Ge
Gold, Au
Rhenium, Re
Cobalt, Co
Lanthanum, La
Neodymium, Nd
Lead, Pb
Silver, Ag
Tantalum, Ta
Gallium, Ga
Yttrium, Y
Mercury, Hg
Cerium, Ce
Dysprosium, Dy
Erbium, Er
Ytterbium, Yb
Gadolinium, Gd
Praseodymium, Pr
Scandium, Sc
Tin, Sn
Holmium, Ho
Lutetium, Lu
Thulium, Tm
Indium, In
Trebium, Tb
Palladium, Pd
Samarium, Sm
Tellurium, Te
Europium, Eu
Radium, Ra
Protactinium, Pa
Radon, Rn
5.6 x 10-6
5 x 10-6
4 x 10-6
4 x 10-6
3 x 10-6
3 x 10-6
3 x 10-6
2 x 10-6
2 x 10-6
2 x 10-6
2 x 10-6
1.3 x 10-6
1 x 10-6
1 x 10-6
9 x 10-7
8 x 10-7
8 x 10-7
7 x 10-7
6 x 10-7
6 x 10-7
6 x 10-7
2 x 10-7
2 x 10-7
2 x 10-7
1 x 10-7
1 x 10-7
5 x 10-8
5 x 10-8
1 x 10-8
1 x 10-8
7 x 10-11
5 x 10-11
6 x 10-16
It has long been
established that the
makeup of human blood
bears a haunting
resemblance to that of sea
water.
Is this a reminder that
probably all of
intelligent animal life
originated in the ocean
with the arrival of the
first true amphibians, or
is it a complete
coincidence? The latter
seems unlikely.
One of the most baffling
questions in modern
science is why the
oceans maintain an
almost constant
composition, including
every element known to
man. And these
proportions never seem
to change. In enclosed
trap basins such as the
Dead Sea or Salt Lake,
the proportions of salts
and minerals due to
runoff from the
surrounding mountains
increase daily, but this
doesn't happen in the
ocean.
Salinity - Dissolved Salts, Measuring Salinity
When we measure the salinity of water, we look at how much dissolved salt is in the water, or
the concentration of salt in the water. Concentration is the amount (by weight) of salt in water
and can be expressed in parts per million (ppm). Here are the classes of water:
•
Fresh water - less than 1,000 ppm
•
Slightly saline water - From 1,000 ppm to 3,000 ppm
•
Moderately saline water - From 3,000 ppm to 10,000 ppm
•
Highly saline water - From 10,000 ppm to 35,000 ppm
Ocean water has a salinity that is approximately 35,000 ppm. That's the same as saying ocean
water is about 3.5% salt. Sometimes, salinity is measured in different units. Another common
unit is the psu (practical salinity units). Ocean water has a salinity of approximately 35 psu.
Scientists measure salinity using a CTD instrument (CTD = conductivity, temperature, depth).
Ocean water is about 3.5% salt. That means that if the oceans dried up completely, enough salt
would be left behind to build a 180-mile-tall, one- mile-thick wall around the equator. About 90
percent of that salt would be sodium chloride, or ordinary table salt. Chlorine, sodium and the
other major dissolved salts of the ocean are listed in this table:
Dissolved salts in
sea water (atoms):
55.3 % Chlorine
30.8 % Sodium
3.7 % Magnesium
2.6 % Sulfur
1.2 % Calcium
1.1 % Potassium
This is a salinity versus depth profile for ocean
water. This salinity versus depth profile is typical of the
South Atlantic ocean. Salinity versus depth profiles at
other locations in the ocean could look quite different.
In this profile, salinity at the surface is high and then
salinity decreases until a depth of about 1,000 meters.
Salinity then increases again slightly with increasing
depth.
The halocline are layers of water where the water's
salinity changes rapidly with depth.
North Atlantic Deep Water forms in
the region around Iceland. It actually is
modified from another water mass - North
Atlantic Intermediate Water - that has come
near the surface and has been cooled by the
contact with the air. The cooling increases the
density of the water mass and it sinks (salinity
of 35 parts per thousand and temperature of
3°C or 37.4°F).
Mediterranean Outflow Water is a deep water
mass that results from high salinity, not
cooling. The high evaporation rate in the
Mediterranean increases salinity. As the water
leaves the Mediterranean basin it spreads into
the Atlantic. Mediterranean Outflow Water is
saltier (38 parts per thousand) than the North
Atlantic Deep Water, but much warmer, so it
floats above it. Because the flow is restricted
by the Straits of Gibraltar (and the sill), and the
Mediterranean Sea is in a region that has high
evaporation rates, the water of the
Mediterranean is very salty. It is a distinct
water mass in the global ocean.
Antarctic Bottom Water is the most distinct of
all deep water masses. It is cold (-0.5°C or
31.1°F) and salty (34.65 parts per thousand). It
forms at the edge of the Antarctic continent and flows under all other water masses into the deep
basins as it moves equatorward, hugging the bottom. Antarctic Bottom Water travels far from its
origin, penetrating into the North Atlantic and North Pacific basins. A cold, salty deep water
mass also forms in the Arctic, but the Arctic basin keeps most of the water contained.
Important:
The average temperature for all ocean water is 3.51°C and its average salinity
is 34.72 parts per thousand.
For the ocean surrounding Antarctica (south of 55°), the average temperature is
0.71° and the average salinity is 34.65 parts per thousand. Of the major ocean
regions, the North Atlantic is the warmest and saltiest (averages: 5.08°, 35.09
parts per thousand).
Light propagation in sea water
The processes of absorption and scattering characterise the transmission of light in water. They
are parametrised by the absorption length , the scattering length , and the scattering function
which describes the angular distribution of the scattering. The relevant window of wavelengths
for a sea water Cherenkov detector is centred on blue light. Deep sea water transparency is
maximal in the blue, with typical values of 60 m for and , and a scattering function peaked in the
forward direction with an average value for the cosine of the scattering angle . Seasonal
variations are expected to affect these values, especially the scattering parameters which are
governed by the amount of suspended particulate matter.
pH VALUE:
The pH scale ranks from 0 to 14 levels of acidity, 0 being the highest level of acidity and 14 the
base. Therefore making 7 neutral. The pH value for sea-water is 8.4, but for marine aquariums
should be between 8 to 8.3
Substance
pH
Battery Acid
Lemon Juice
Vinegar
Milk
Baking Soda
Sea water
Milk of Magnesia
Ammonia
Lye
1
2
3
6.5
8.5
8.5
10.5
12
13
Environmental problems arise when the pH level of precipitation drops below the 5.6 threshold.
The pH of the water is critical to the survival of most aquatic plants and animals. Many species
have trouble surviving if pH drops under 5.0 or rises above 9.0. Changes in pH can alter other
aspects of the water's chemistry, usually to the detriment of native species. Even small shifts in
the water's pH can affect the solubility of some metals such as iron and copper. (Higher acid
levels increases their solubility)
•
Precipitation between 5 and 6.5 pH is considered normal.
•
Streams between 6 and 8 pH is likewise within normal range.
•
Fish Reproduction is affected at pH level between 4 and 5.
•
Fish will die when levels reach between 3 and 4
Color
The "color" of the ocean and sea is determined by the interactions of incident light with
substances or particles present in the water. The most significant constituents are free-floating
photosynthetic organisms (phytoplankton) and inorganic particulates. Phytoplankton contain
chlorophyll, which absorbs light at blue and red wavelengths and transmits in the green.
Particulate matter can reflect and absorb light, which reduces the clarity (light transmission) of
the water. Substances dissolved in water can also affect its color.
Composition of Natural Water
Mostly H2O
Traces of other substances that make
each water different
"
"
Found in relatively low concentrations
They are typically charged (ions)
Units of Measurement
Gram used for mass
Liter used for volume
Prefixes:
milli = one-thousandth
For example,
1000 milligrams = 1 gram
Concentration Units
Concentrations usually given in
milligrams per liter,
or parts per million
We know 1000 mg = 1 gram,
and 1000 mL = 1 liter
Practical example:
1 ppm is about 1 ounce of tequila in 7,400 gallons of lime juice!
1 mg/L = 1/1000 of a gram in 1000 mL
1000 x 1000 = 1 million
Thus 1 mg per liter same as
1 part in 1 million.
THE BALTIC SEA ENVIRONMENT
An overview
The Baltic Sea is an almost landlocked
subsidiary sea to the Atlantic Ocean and
almost totally surrounded by land and
therefore more endangered by pollution than
other marine areas. Only narrow straits
connect it to the North Sea and the exchange
of water between the two is therefore
restricted. The residence time of water in the
central Baltic is 25–30 years. Numerous rivers
drain an area in Central and Northern Europe
of more than 1.7million km2, transporting
approximately 480 km3 freshwater annually
that increasingly dilutes the saline seawater of
the Baltic to the east and north. The salt
content decreases from about 30g l–1 in the
Kattegat deep to 2g l–1 in the innermost areas
Satelitte map of the Baltic Sea area
of the Gulfs of Bothnia and Finland. The catchment area covers 17 % of Europe. Total area is
about 415.000 km2 and a volume of water of 21.700 km3. This means that activities within a land
area 4.5 times as large as the area of the sea, and comprising parts of 14 countries, affect the
environment of the Baltic. Proceeding from the northern end, it includes the Bothnian Bay and
the Bothnian Sea. At the southern end of the Bothnian Sea, the island of Aland divides the Aland
Sea from the Archipelago Sea. The Gulf of Finland is the eastern arm of the Baltic Sea. The
central portion of the Sea, known as the Baltic Proper, includes the Eastern and Western Gotland
Seas. To the east and south are the Gulf of Riga, and the Gulf of Gdańsk. Moving to the west are
the Bornholm and Arkona basins, followed by the Sound, the Belt Sea and the Kattegat. The
Baltic Sea, including the Kattegat, is one of the world’s largest areas of brackish water.
Baltic Sea is a very young sea, it came into being after the most recent Ice Age about
12,000 years ago as the freshwater Baltic ice sea. Through openings to the North Sea, periods of
varying salt content followed. It was not until 1500 years ago that the present conditions were
reached, however, changes, particularly in coastal areas, still occur. Tides, with which we are
acquainted in the North Sea, play no role in the Baltic. This promotes the formation of stable
water layers. So it is possible for a low-salinity layer to lie over a more saline layer of deep
water. Both zones have great differences in density and are often separated by a discontinuity
layer. This is the reason why the vertical exchange of water is also very restricted.
Nine countries share the Baltic Sea coastline; Sweden and Finland to the north, Russia,
Estonia, Latvia and Lithuania to the east, followed by Poland in the south, and Germany and
Denmark in the west.
About 16 million people
live on the coast, and around 80
million in the entire catchment area
of the Baltic Sea. The catchment
area includes part of Belarus, the
Czech
Republic,
Norway,
the
Slovak Republic and Ukraine, as
some of the rivers find their
sources here. About 140 million
people live in the nine countries
surrounding the Baltic Sea, i.e., in
the so-called riparian states.
All the countries around the
Baltic
Sea
are
industrialised.
More
heavily
or
less
intensive agriculture and forestry is
also carried out over large areas in
the riparian states. Furthermore, the
sea is surrounded by a considerable number of cities, towns and harbours. There is abundant sea
traffic of pleasure craft, ferries, tankers, cargo vessels carrying oil, chemicals and other
environmentally hazardous substances in almost all parts of the sea. Fishing fleets from all Baltic
countries, and others, gather to exploit the stocks of commercially interesting species.
The Baltic is affected by human activities as well as natural processes within the entire —
and very large — drainage area. The sources of marine pollution are municipal and industrial
waste inputs directly into the sea or via rivers, and atmospheric inputs mainly from traffic and
agriculture. The increase of inorganic plant nutrients (NH3, NOx, PO4) caused eutrophication and
consequent oxygen depletion in coastal bottom waters as well as in the depths of the open sea. In
the anoxic sediments, hydrogen sulphide can be produced by protein - decomposing and
sulphate-reducing bacteria. The bottom fauna will be destroyed and only H2S tolerant
microorganisms can survive. Originating from cellulose manufacturing and from paper mills,
large amounts of poisonous chlorinated compounds contaminated the coastal waters of Sweden
and Finland until the 1980s. Most of this material is still present in sediments of the central
Baltic Sea and can be resuspended by near bottom currents.
To reduce pollution and improve the situation in the Baltic Sea, the surrounding countries
organised the Helsinki Convention, which came into force on 03.05.1980. The Helsinki
Commission (HELCOM) founded in 1974 acts as coordinator and is responsible for the
enforcement of the Baltic monitoring program and international research projects. The activities
of HELCOM have led to the reduction of dangerous pollutants.
Polish coastal zone
The Baltic Sea forms 843 km of the Polish borderline, (15% of the total length of the
country's border) i.e. 102 km of the Vistula Lagoon, 241 km the Pomeranian Bay, 76 km the Hel
Peninsula and 424 km of remaining part of the coast.
99,7% of the country is situated within
the Baltic Sea drainage area – it covers 311 900
km2 (Figure 2).
Drainage area of the Baltic Sea.
Poland is one of the major countries that considerably influenced the condition of the
Baltic Sea. Population of Poland constitutes 50% of whole population living in the basin of
Baltic Sea. The most part of Poland territory is located within two catchment areas of the two
biggest rivers: the Vistula River (54% of country area) and the Odra River (33,9 %). The
hydrological network covers also rivers of Pomorze, which flow into the Baltic Sea, i.e. Pasłęka,
Reda, Łeba, Łupawa, Słupia, Wieprza, Grabowa, Parsęta, Rega.
A considerable amount of nutrients and toxic substances are discharged to the Baltic Sea
from Poland. The majority of the pollutants are carried by river flows. While increasing
eutrophication is a consequence of elevated nutrient inputs, some of the coastal waters are
polluted also by toxic substances, such as heavy metals, chlorinated hydrocarbons and oil. The
most polluted areas of the Polish coastal waters are the Gulf of Gdańsk and the Pomeranian Bay,
both of which absorb significant pollution loads through river outflows. Intensive primary
production has been observed in these areas. Along the more open Polish coast, the problems are
similar to those in the open Baltic Sea. In the late 1980s hydrogen sulphide was detected in the
Gulf of Gdańsk in high concentrations. The decrease in fish catches along the entire Polish coast
during the last decade has been attributed to changes in living conditions for fish, but
overexploitation of certain fish stocks may have played an important role in these changes as
well.
Basins
Gulf of Gdańsk
The Gulf of Gdańsk straddles the border of Poland and the Kaliningrad Oblast (Russia)
along the southern coast of the Baltic. Excluding the Vistula Lagoon, the total surface area of the
Gulf of Gdańsk, south of 54°50' (calculated using bathymetry from the 200×200m Geological
map of the Baltic Sea bottom; Geological Map, State Geological Institute, Warsaw, 1993) is
4296 km2, with land area 304,510 km2 and coastline 491 km, and the volume of Gulf of Gdańsk
is 236 km3. The area of the Gulf of Gdańsk is extremely heavy inhabited, with the population of
38.6 mln (July 1999 estimate).
The Gulf of Gdańsk consists of several morphological subunits: the Vistula Lagoon, an
almost completely land-locked and anthropogenically stressed area, the semi-enclosed Bay of
Puck and the mouth of the Vistula. Along the southern coast of the Gulf of Gdańsk spreads the
Gdansk-Sopot-Gdynia metropolitan area with a total population exceeding 1.000 000 inhabitants.
The area of land draining into the Gulf of Gdańsk covers 194.424 km2, and land cover of the area
is distributed as follows: 27% forested lands, 63% agricultural lands, 3% urban areas, and 2%
water & wetlands.
The Gulf of Gdańsk (18.22 - 20.00° E, 54.18 - 54.50° N)
Maximum depth in the Gdańsk Deep is 118 m. The Gulf of Gdańsk is a rather shallow
water basin with a sandy bottom. It is separated from the Baltic Proper by the Hel peninsula,
which limits the exchange of water.
Annual freshwater discharge into Gulf of Gdańsk is 34.5 km3, of which the Vistula River
contributes approx. 30%. This is approx. 7% of the total input of freshwater. About 5-10% time,
the Vistula River water discharged into the Baltic flows waste - wards, resulting in dispersion of
pollutants onto the beaches of the Gulf of Gdańsk and Puck Bay.
TODAY:
European Countries
– 64 parameters to determine
Polish “rules” – 51 parameters
EPA (1995) – 120 parameters !
At the beginning of XX – 1 mg/L
Today –
1 ng/L
Physical Measures of Water Quality
! Suspended Solids
Turbidity
Color
Taste and Odour
Temperature
Types of Solids According to Size
Suspended > 1 mm (larger than bacteria)
Colloidal between 1 mm and .001 mm
Dissolved < .001 mm
Impact of Suspended Solids
Total Suspended Solids is the mass of solids that can be separated from the
water by filtration
Diameter > 1 mm (size of bacteria)
In wastewater, discharge of SS is limited to protect receiving stream.
Impact of Suspended Solids
Can include
• sand
• silt
• rust
• plant fibers
• algae
Indicator of possible bacterial or hazardous contamination
Suspended Solids Measurement
Gravimetric property
Weigh clean filter
Weigh filter after filtration
TSS = Difference in filter weight / Volume
Physical Measures of Water Quality
Suspended Solids
! Turbidity
Color
Taste and Odour
Temperature
Why it is important?
Turbidity is the measurement of the scattering properties of water. Suspended
solids in water can reduce the transmission of light either through absorption or
scattering. High turbidity can have strong negative effect
•
•
•
•
on submerged aquatic vegetation
reduce the growth of clams and oysters
slow or stop egg development
make it harder for salmon to catch food.
Turbidity
Measure of the "lack of clearness" of water.
Equivalent to looking through a fog
Solids harbour microorganisms
Pollutants attach to solids
Turbidity Definition
Capacity of solids in the water to scatter light
Caused by both suspended and colloidal solids
Physical Measures of Water Quality
Suspended Solids
Turbidity
! Colour
Taste and Odour
Temperature
Colour
Natural Sources:
• decay of plant matter,
• algae growth,
• minerals (iron and manganese)
Anthropogenic sources:
• Paper mills
• Textile mills
• Food processing
Impact of Colour
Usually an aesthetic problem, both in drinking water and wastewater
May be an indication of toxicity
May stain textiles and fixtures
Due to the presence of coloured organic substances, metals (Fe, Mg, Cu) or
industrial wastes
Colour measurement
Optical principle
Light is absorbed
Place detector in direction of incoming light source
One major factor which affects the colour of
natural water is pH => all measurements
should be done at a standard pH of 8.3
Physical Measures of Water Quality
Suspended Solids
Turbidity
Color
! Taste and Odour
Temperature
Taste and Odour
Taste and odour usually inter-related.
Inorganic chemicals can affect taste but not cause any odour:
• Salt
• Minerals
• Metals
A few inorganic chemicals can cause both taste and odour problems:
• Ammonia
• Chlorine
• Hydrogen sulfide
Organic chemicals usually affect both taste and odour:
• Biological decay products
• Petroleum products
• Pesticides
Impact of Taste and Odour
Odours from wastewater an aesthetic problem.
Taste and odour in drinking water can upset consumers.
No maximum acceptable limit
The threshold odour for some chemical
contaminants:
Chlordane
0,0003 mg/L
1,4-dichlorobenzene 0,0003 mg/L
trichloroethylene
0,5 mg/L
phenol
1-15,9 mg/L
4-chlorophenol
0,0005-1 mg/L
2,4-dichlorophenol 0,002-0,32 mg/L
hydrogen cyanide
0,001 mg/L
THE LARGEST CLASS OF CONSUMER
COMPLAINS
Physical Measures of Water Quality
Suspended Solids
Turbidity
Color
Taste and Odour
! Temperature
Why it is important?
Temperature exerts a major influence on biological activity and growth. To a point,
the higher the water temperature, the greater the biological activity.
Warm water holds less oxygen than cool water, so it may be saturated with oxygen
but still not contain enough for survival of aquatic life.
Example:
Hatching salmonids – optimal level of 9oC
Adult salmon – 12oC
Sucessful salmonid spawning at 2-21oC
Temperature
Temperature only a problem with wastewater discharges.
Sources:
• Power plants
• Industrial cooling
Fish and other organisms sensitive to temperature.
• Fish must migrate through changing temperature zones
• Sudden temperature changes affects fish more than extremes
• Higher temperature causes lower solubility of DO in water.
Reasons for natural variation
•
•
•
Change in seasonal air temperature; daily variation can hardly affect water
temperature
Thermal stratification
Restricted mixing of layers (stratification tends to persist until cooler fall
weather)
Example of Thermal Pollution
Hot water from nuclear power plants is discharged into the Pacific
Hot water is carried by currents along the coast
THE MAXIMUM ACCEPTABLE TEMPERATURE
FOR DRINKING WATER IS 25oC
Chemical Measures of Water Quality
Factors Affecting Water Quality
Dissolution of:
Minerals and soils
• Acids and bases
• Dissolved gases
Dissolved substances are found as ions (charged molecules)
•
Examples
H+ and OHCations (+): Na+, K+, Ca2+, Mg2+
Anions (-): Cl-, HCO3-, SO42Gases (0): CO2, N2, O2
Chemistry of Acids and Bases
Every water has some....
+
• H2O = H + OH
+
• Only 1 in 550,000,000 molecules is H or OH (at neutral pH)
Water with H+ = OH- is neutral (pH = 7)
Water H+ > OH- is acidic (pH < 7)
Water with OH- > H+ is basic (pH>7)
Chemistry of distilled water
Water, H2O dissociates into H+ (proton) and OH- (hydroxide)
pKw = 14.0, Kw = 10-14
By definition (H2O) = 1.0
Apply the electroneutrality concept: [H+] = [OH-]
Then (H+)2=10-14
(H+) = (OH-) = 10-7
And pH = pOH = 7.0
The pH scale
pH of Natural Waters
Surface water pH from 6.5 to 8
Groundwater pH from 5.5 to 7.5
Acid rain pH as low as 3
Lakes damaged by acid rain can have pH of 4 or less.
Typical pH Values
Strength of an acid depends on its ability to donate a proton H+. The lower the
pKa the stronger the acid.
Water: EPA: recommends that pH of water be between 6.5 and 8.5 for potable
water
Foods:
•
•
•
•
•
•
Lemons pH = 2
Apples pH = 3
Soda pH = 3 to 4
Grapes pH = 4
Carrots pH = 5
Milk pH = 7
Commercial Acids and Bases
• Sulfuric: (strong)
• Carbonic (weak)
Alkalinity
What it is?
Ability of water to neutralize acid.
Includes bicarbonate (HCO3-), carbonate (CO3-2), and hydroxide (OH-).
No drinking water standards for alkalinity (its not harmful) are presented
Mechanisms
After acid rain falls in a lake that contains alkalinity:
H+ + HCO3- ⇒ CO2,gas + H2O
If there is no alkalinity the pH of the lake will drop drastically
Acid Neutralization by Alkalinity
Sodium bicarbonate (baking soda) is used to cure acid indigestion.
Calcium hydroxide (lime) is dumped into lakes, to neutralize acidity caused by
acid rain
Water Hardness
Total concentration of multi-valent cations
Includes
+2
• Calcium Ca
+2
• Magnesium Mg
+3
• Iron Fe
+2
• Manganese Mn
Typical Hardness Values
(mg/L as CaCO3)
Soft
Moderate
Hard
Very Hard
Effects of Hardness
Causes soap scum and water spots
Causes scaling in:
• Swamp coolers
• Cooling towers
• Boilers and pipes
Sources of Hardness
Groundwater dissolves certain minerals
•
•
Ca+2 and Mg+2 from limestone
Ca+2 from gypsum
• Softening Processes
• Chemical Softening
• Ion Exchange
• Reverse Osmosis
0-50
50-150
150-300
>300
Biochemical Measures of Water Quality
Introduction to DO
DO = Dissolved oxygen
It is a critical water parameter indicating the health of an aquatic life; it is a
measurement of oxygen dissolved and available for fish and other aquatic life.
Aquatic aerobic organisms need oxygen to survive.
Maximum amount in clean water is about 9 mg/L.
DO varies with temperature, salinity, elevation, and turbulence (mixing).
Measurement of DO
DO is measured with an electronic instrument.
Concentration is given in units of mg/L
Reasons for natural variation
Oxygen is produced during photosynthesis of plants and consumed during
respiration and decomposition. Because it requires light, photosynthesis occurs
only during daylight hours. Respiration and decomposition on the other hand occur
24 hours a day. Another processes that affect DO concentration:
•
Wind (stirs the water)
•
Rivers and streams (deliver oxygen especially when they are turbulent)
•
Temperature (cold water can hold more oxygen than warmer water; warmer
temperature speeds up the photosynthesis and decomposition)
Dissolved Oxygen Problem Situations
Effect of Temperature on DO
•
Hot water from a power plant decreases DO level in the receiving water
Temperature
[oC]
0
5
10
15
20
Oxygen solubility
[mg/L]
14,6
12,8
11,3
10,2
9,2
Effect of Salinity on DO
•
Salt from roads and irrigated fields enters
streams causes DO level to decrease
Effect of Turbulence on DO
•
•
A stream with good mixing will replenish DO quickly
A slow, sluggish stream (or a lake) will replenish DO slowly
DO Requirements by Fish
Trout 4-5 mg/L
Bass 3-4 mg/L
Carp 2-3 mg/L
Catfish 1-2 mg/L
Dissolved Oxygen in Conclusion
Saturation DO decreases as temperature increases
Saturation DO decreases as salinity increases
Saturation DO decreases as elevation increases
Biochemical Measures of Water Quality
Introduction to BOD
Organic pollutants are food for bacteria
• Proteins, fats, carbohydrates, etc.
Need oxygen to consume food
HCOH + O2 # CO2 + H2O
BOD = Biochemical oxygen demand
Amount of oxygen required by bacteria to degrade a waste.
A gross indicator of water pollution
Surrogate test for total organic
pollution in water
The amount of oxygen required to
biodegrade the waste (BOD) is illustrated
in the following plot. This plot shows that
the total amount of food remaining, L,
decreases with time from an initial Lo
value. The amount of oxygen needed to
degrade the waste, y, increases asymptotically
to its ultimate value, Lo. To simplify equations,
let y equal the BOD
The BOD should not be so great as to
lower the dissolved oxygen to an
unacceptable level (6mg/L).
LOWER THE BOD, THE BETTER
DO and BOD in Conclusion
Bacteria use DO to degrade pollutants: DO Level decreases
Pollutant is completely or partially degraded to CO2
Oxygen is replenished by:
•
Reaeration (i.e., mixing)
•
Photosynthesis (algae in water)
Metals
Metals can be either beneficial or harmful, depending on
•
Chemical properties
•
Concentration
•
Some metals needed in trace amounts as nutrients.
•
High Conc. cause health problems.
Health Effects of Metals
Health Effects include:
•
Nerve damage
•
Kidney damage
•
Birth defects
Sources of Metals
Industrial wastewater
Acid mine drainage
Groundwater may be contaminated by dissolution of metals from soils,
industrial discharges, etc.
Introduction to Organic Chemicals
Organic : composed of the elements carbon (C) and hydrogen (H)
May contain other elements:
Oxygen, Nitrogen, Sulfur, Chlorine
Synthetics are made from petroleum, natural gas, or coal
Some Organic Chemicals
• Methane
Main component of natural gas
Non-toxic, flammable
• Carbon tetrachloride
Carcinogenic Solvent
Very similar in structure to methane
• Benzene
Comprises 2-5% of gasoline
Building block of many other chemicals
Flammable, carcinogenic
• Pesticides
• PAHs
• PCBs
• Dioxins
• .............
Properties of Organic Chemicals
Properties vary greatly, depending on chemical composition
•
Flammability ranges from nil to extremely flammable
•
Toxicity ranges from nil to extremely toxic
•
Solubility - amount that will dissolve in water ranges from nil to 100%
•
Density - lighter than water (will float) or heavier than water (will sink)
•
lipophylic character (bioaccumulation and biomagnification)
to be continued in the following part: HUMAN IMAPCT ON WATER RESOURCES
Conclusion on Organic Chemicals
Wide variation in properties makes organics difficult to treat and clean
up.