Factors Affecting Water
Quality
Chapter 6
Introduction
 Many
types of pollutants and many factors
affecting the toxic effect of those pollutants
 Factors include






physicochemical properties
Mode and time of exposure
Environmental factors
Interactions among toxicants in a mixture
Biological factors
Nutritional factors
Chemical Characterization of Water
I. Structure
•
Chemical Structure
1.
limited in
freshwater
Inorganic
Ca++
Cations
Mg++ Na++ (K+)
Anions
HCO-3 SO4- Cl- PO4- NO3bicarbonate
mg/L 15
8
Normal environmental concentrations
6
23
120
12
8
v. low (<1)
limited in
oceans
Note: because NO3- is not limited in freshwater  casual about disposal (i.e. Spring River)
2.
Organic
Carbonate-bicarbonate
equilibrium
Normal range
pH is the master variable but pH of aquatic system is intricately linked to
the relative abundance of carbonate, bicarbonate and carbon dioxide.
Hardness



Degree of difficulty in precipitating soap
Based on combined concentrations of calcium,
magnesium and other cations
Can have great effect of toxicity (increasing hard =
decreasing toxicity)


Units – CaCO32- mg/L (accounts for all metals which are +2)
Typical values (as CaCO32-)
• <5- - 100 mg/L soft
• 100 - 200 mg/L
• >200
“

moderately hard
hard
Carbonate vs. Non-carbonate hardness
Note: heat can change hardness -> forms scale on boilers,
coffee pots
Alkalinity

Measurement of the capacity to accept protons
(esp. H+)  called buffering capacity



Units also expressed as CaCO32Really measures CaCO32- (bicarbonate)
Alkalinity directly correlated with hardness in many
systems
• Soft water = low alkalinity
• Hard water = high “
(but exceptions  AMD)


Measured by titrating with H2SO4  drives
bicarbonate to CO2
Rule of thumb  water of low hardness, low
alkalinity (headwaters) = higher effect of
toxicants (especially true of metals, acid)
Alkalinity (con’t)

Rule of thumb: water
of low hardness, low
alkalinity (headwaters)
= higher effect of
toxicants (especially
true of metals, acid)
Photo by R. Grippo
Headwaters of the Hudson River
Oxygen

Amount of oxygen that can be dissolved in water (solubility) is highly
dependent on temperature
Note: atmosphere = 210,000 mg/L but ~10 mg/L in most water so O2 is is
usually in very short supply in water
Physical structure
B.
Stream order – rough numerical sequence that allows characterization of a
stream
1.
springs
headwaters
1
Note: streams of same order have to
come together to form next order
1
2
Mid-reach
2
3
1
3
Lower reach
4
6-12 = river
6
Note: headwaters generally straight, starts to wander (form bends = sinuosity) as hit
order 4-6. Sinuosity is a function of slope, hardness of substrate (mud<silt<gravel)
Hard substrate = low sinuosity
Soft substrate = high sinuosity
II. Function
- function always based on structure 
can infer function from structure
A. Rivers
1.
River Continuum Concept
- RCC based on two concepts
a.
b.
From headwaters to mouth = continuous change
(gradient) in physical conditions within a stream system
Gradient produces a continuous and predictable
change in the make-up of the assemblages of
organisms within a stream system
Upper reaches ---------------- mid-reach --------------------- lower reach
(headwater to 3rd order)
(order 4 to 6)
(>6)
Continuous and predictable changes in biotic assemblages
Use bioassessment (sample, enumerate organisms)  if do not find what is
predicted  problem!!
B. Lakes



systems are dynamic but slow
Pollution stays put (reason why sewage treatment plants
are built on rivers, not lakes
More likely to
• Serve a pollution sinks (bioremediation slow if lake is deep (e.g.
Great Lakes)
• Can be highly influenced by aerial deposition
C. Groundwater
Pollutants usually
introduced as
leachate from
contaminated soils

Dependent on
physical/chemical
properties of soils
in addition to water
