Major Determinants of Water Quality

Major Determinants of Water Qualityand the Impact or Availability of Water Pollutants

OrganismsSolubilityOxygen

pH

Solubility

The ease with which substances dissolve in water

Salts dissolve to produce ions in solution

Ions

Ions are stable forms of elements that acquirean electrical charge by gaining or losing electrons

Sodium ion (Na+) 11 protons (+), 10 electrons (-)

By losing an electron, sodium has more protons thanelectrons and becomes positively charged.

Chloride ion (Cl-) 17 protons (+), 18 electrons (-)

By gaining an electron, chlorine has more electrons thanprotons and becomes negatively charged.

NaCl Solid

Cl-

Na+

Na ClCl

ClCl

Dissolution and Solubility

Ionic Contaminants

Natural and anthropogenic sources

Weathering of RockIndustrial ProcessesAgriculture

Solubility depends on the ion to which it is bonded

Pb2+

Hg2+

AsO4-

PO4-3

NH4+

NO3-

Cd2+

Forms and Solubility

HgCl2 solublePbCO3 poorly solubleFePO4 poorly solubleAlPO4 poorly solubleKH2PO4 solubleCdCO3 poorly solubleCdCl2 soluble

The degree to which contaminants impactwater quality is often determined by their solubility

Pb2+

Hg2+

AsO4-

PO4-3

NH4+

NO3-

Cd2+

Toxic organic pollutants including pesticides, and industrial products generally are not ionic

and are not particularly soluble in water.

DDTDioxinsPCBs

DDT

Dioxin

PCB

Solubility: 0.043 g/L(20oC)

Oxygen is also Water Soluble

In water, about one out of every 100,000 molecules is oxygen

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

Oxygen and Heat

Add heat

Factors that Control O2 Content in Water

Photosynthesis

Agitation of Water

Temperature

Activity of Aerobic Heterotrophs

pH

pH is a Measure of H+ Concentration in Water

H+ ion

Acid: any substance which increases the H+ concentration in water

Responsible for Acidity

The greater the number of H+ ions, the greater the acidity

Low pH = High amount of Hydrogen ions in waterHigh pH = Low amount of Hydrogen ions in water

HCl H+ + Cl-

HNO3 H+ + NO3-

H2SO4 H+ + HSO4-

Dissociation of acids

pH (hydrogen)

Low pH = High H+

H+

pH 3 = 0.001 g H+/ L

pH 4 = 0.0001 g H+/ L

There is 10 times more H+ in water at pH 3 compared to pH 4

Each unit decreasein pH represents a10-fold increase inH+ concentration

*

Extra Credit:

1. ____is a measure of H+ concentration in water

2. Oxygen is more or less soluble in warm water that cold.

3. Identify one ionic contaminant.

4. ______are stable forms of elements that acquire an electrical charge by gaining or losing electrons

pH and Availability of Nutrients and Metals

pH and Availability and Form of Nutrients

NH4+ NH3

Low pH High pHHigh H+ conc. low H+ conc.

Nitrogen

When organisms decompose organic materialnutrients are released including NH4

+

soluble Gas

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

Dominant Forms: NH4+ and NO3

-

NO3- is more mobile in the environment than NH4

+

_ ___

___

__

Soil particles possessa negative electrical charge

NH4+

NO3-

Leaching to groundor surface water

Sources: fertilizers, manures, wastewater discharge

CaHPO4 + H+ = Ca2+ + H2PO4-

Availability and Form of Nutrients

Low pH High pHHigh H+ conc. low H+ conc.

Solid(unavailable)

Dissolved (available)

H2PO4- HPO4

-2

CaHPO4AlPO4

Solid(unavailable)

Phosphorusdissolved dissolved

Acids and Metals

Aluminum is toxic to plants and some organisms

Dissolved in water

Acid

Acid

Acid

Minerals and ErosionMinerals and Erosion

KAlSi3O8

CaAl2Si2O8

NaAlSi3O8

Al3+

Feldspars KAlSi3O8

CaAl2Si2O8

NaAlSi3O8

granite

Solid(unavailable)

dissolved(available)

Availability and Form of Metals

Acid dissolution of metals increases their mobility

PbCO3 + H+ Pb2+ + HCO3-

Solid(unavailable)

dissolved(available)

CdSO4 + H+ Cd2+ + SO4-2

There are approximately 420,000 abandoned mines in the states of California, Arizona and Nevada

Mine Tailings

FeS2 2H2SO4

oxygen

water

Direct toxicity of H+ plus dissolution of associated metal contaminants such as arsenic, lead, and cadmium

Cd, Pb, Zn,Cr, Cu, Al

PbCO3 + H+ Pb2+ + HCO3-

solid soluble

2H+ + SO42-

pH and Acid Rainfall

Natural rainfall is acidic: pH 5.6

CO2 + H2O = H2CO3

H2CO3 => H+ + HCO3-

Acid

Pollution by sulfur dioxide and nitrogen oxidescontributes additional acidity to rainfall.

SO2 + H2O → H2SO4

The Canadian government has estimated that 14,000 lakes in eastern Canada are acidic.

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 acidiclakes and about 50 percent of the acidic streams

Adirondacks and Catskill Mountains mid-Appalachian highlands

Little Echo Pond has a pH of 4.2.

Most lakes and streams have a pH between 6 and 8.In the Northeast U.S. many lakes have pH less than 5.

Acid tolerances

Increasing acidityfood

As acid rain flows through soils in a watershed, aluminum is released

Low pH can be directly toxic to fish and other species

Low pH and increased aluminum levels cause chronic stress thatmay not kill individual fish, but leads to lower body weight and

smaller size and makes fish less able to compete for food and habitat.

At pH 5, most fish eggs cannot hatch

Major Determinants of Water Qualityand the Impact or Availability of Water Pollutants

OrganismsSolubilityOxygen

pH

Next: The History of Sewage