Major Determinants of Water Quality

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Major Determinants of Water Quality
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Major Determinants of Water Quality and the
Impact or Availability of Water Pollutants
Organisms Solubility Oxygen pH
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Solubility
The ease with which substances dissolve in water
Salts dissolve to produce ions in solution
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Ions
Ions are stable forms of elements that acquire an
electrical charge by gaining or losing electrons
11 protons (), 10 electrons (-)
Sodium ion (Na)
17 protons (), 18 electrons (-)
Chloride ion (Cl-)
By losing an electron, sodium has more protons
than electrons and becomes positively charged.
By gaining an electron, chlorine has more
electrons than protons and becomes negatively
charged.
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Dissolution and Solubility
Cl-
Cl
Cl
Na
Cl
Cl
NaCl Solid
Na
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Ionic Contaminants
Pb2 Hg2 AsO4- PO4-3 NH4 NO3- Cd2
Natural and anthropogenic sources
Weathering of Rock Industrial Processes Agricultur
e
Solubility depends on the ion to which it is
bonded
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Forms and Solubility
Pb2 Hg2 AsO4- PO4-3 NH4 NO3- Cd2
HgCl2 soluble PbCO3 poorly soluble FePO4 poorly
soluble AlPO4 poorly soluble KH2PO4 soluble CdCO3
poorly soluble CdCl2 soluble
The degree to which contaminants impact water
quality is often determined by their solubility
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Toxic organic pollutants including pesticides,
and industrial products generally are not ionic
and are not particularly soluble in water.
DDT Dioxins PCBs
Dioxin
DDT
PCB
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Oxygen is also Water Soluble
Solubility 0.043 g/L
(20oC)
In water, about one out of every 100,000
molecules is oxygen
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Temperature and Oxygen
The solubility of oxygen in water is highly
temperature dependent.
Saturated Oxygen Content
10.1 mg/L
8.3 mg/L
15oC
25oC
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Oxygen and Heat
Add heat
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Factors that Control O2 Content in Water
Photosynthesis Agitation of Water Temperature A
ctivity of Aerobic Heterotrophs
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pH
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pH is a Measure of H Concentration in Water
H ion
Responsible for Acidity
Acid any substance which increases the H
concentration in water
The greater the number of H ions, the greater
the acidity
Low pH High amount of Hydrogen ions in
water High pH Low amount of Hydrogen ions in
water
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Dissociation of acids
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pH (hydrogen)
H
Low pH High H
Each unit decrease in pH represents a 10-fold
increase in H concentration

pH 4 0.0001 g H/ L
pH 3 0.001 g H/ L
There is 10 times more H in water at pH 3
compared to pH 4
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Extra Credit

• ____is a measure of H concentration in water
• Oxygen is more or less soluble in warm water that
  cold.
• Identify one ionic contaminant.
• 4. ______are stable forms of elements that
  acquire
• an electrical charge by gaining or losing
  electrons

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pH and Availability of Nutrients and Metals
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pH and Availability and Form of Nutrients
Nitrogen
When organisms decompose organic
material nutrients are released including NH4
NH4 NH3
Low pH
High pH
High H conc.
low H conc.
soluble
Gas
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Nitrate and Ammonia
NH4 and NO3-
Forms are controlled by organisms NH4 is
converted to NO3- by aerobic bacteria
These bacteria, therefore, are controlled by
oxygen levels
They also are controlled by pH. They do not
function well at low pH.
NH4 dominant at low pH NO3- dominant at higher
pH
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Dominant Forms NH4 and NO3-
Sources fertilizers, manures, wastewater
discharge
NO3- is more mobile in the environment than NH4
NH4
NO3-
Leaching to ground or surface water
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Availability and Form of Nutrients
Phosphorus
dissolved
dissolved
H2PO4-
HPO4-2
Low pH
High pH
High H conc.
low H conc.
CaHPO4
AlPO4
Solid (unavailable)
Solid (unavailable)
Dissolved (available)
CaHPO4 H Ca2 H2PO4-
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Acids and Metals
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Minerals and Erosion
KAlSi3O8 CaAl2Si2O8 NaAlSi3O8
Feldspars
granite
Acid
KAlSi3O8 CaAl2Si2O8 NaAlSi3O8
Al3
Acid
Dissolved in water
Acid
Aluminum is toxic to plants and some organisms
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Availability and Form of Metals
PbCO3 H Pb2 HCO3-
Solid (unavailable)
dissolved (available)
CdSO4 H Cd2 SO4-2
Solid (unavailable)
dissolved (available)
Acid dissolution of metals increases their
mobility
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Mine Tailings
There are approximately 420,000 abandoned mines
in the states of California, Arizona and Nevada
Cd, Pb, Zn, Cr, Cu, Al
2H SO42-
PbCO3 H Pb2 HCO3-
soluble
solid
Direct toxicity of H plus dissolution of
associated metal contaminants such as arsenic,
lead, and cadmium
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pH and Acid Rainfall
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Natural rainfall is acidic pH 5.6
CO2 H2O H2CO3
H2CO3 gt H HCO3-
Acid
Pollution by sulfur dioxide and nitrogen
oxides contributes additional acidity to rainfall.
SO2 H2O ? H2SO4
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National Surface Water Survey (EPA)
Investigated the effects of acidic deposition in
over 1,000 lakes
Acid rain caused acidity in 75 percent of the
acidic lakes and about 50 percent of the acidic
streams
Most lakes and streams have a pH between 6 and
8. In the Northeast U.S. many lakes have pH less
than 5.
Adirondacks and Catskill Mountains
mid-Appalachian highlands
Little Echo Pond has a pH of 4.2.
The Canadian government has estimated that
14,000 lakes in eastern Canada are acidic.
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Low pH can be directly toxic to fish and other
species
As acid rain flows through soils in a watershed,
aluminum is released
Low pH and increased aluminum levels cause
chronic stress that may not kill individual fish,
but leads to lower body weight and smaller size
and makes fish less able to compete for food and
habitat.
Acid tolerances
food
Increasing acidity
At pH 5, most fish eggs cannot hatch
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Major Determinants of Water Quality and the
Impact or Availability of Water Pollutants
Organisms Solubility Oxygen pH
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