Water & Enviro Week 3

Turbidity

Measure of water clarity

Turbidity units

Nephelometric Turbidity Units (NTU)

How is turbidity measured

Using nephelometer - light shone through water & amount scattered is measured and displayed in NTU

Secchi Disk

Disk divided into black & white quarters used to gauge water clarity by measuring depth at which it is no longer visible from surface

How is turbidity caused

Suspended matter; clay, silt, inorganic / organic matter

Sources of turbidity

1. Runoff from drainage basins

2. Waste discharges

3. Algae / aquatic weeds

4. Air bubbles & particles from water treatment process

Total solids

Matter suspended and dissolved in water

How is total solids measured

Evaporating a water sample in pre weighed dish (B) at 103 degrees then weighing dish & remaining residues (A)

Total suspended solids

Particles suspended in water

How is total suspended solids measured

Filter water sample through pre-weighed 0.45um filter (B mg), dry filter at 103 degrees then weigh filter and residue (A mg)

True or false: Is turbidity and total suspended solids the same?

No, turbidity measures water clarity, TSS measures suspended particles

Effects of high TSS in water

Blocks light reaching submerged vegedation - reduces photosynthesis, reduces dissolved oxygen, plants die, risk of fish kills

How does high TSS affect fish

1. Gets trapped in gills - affect breathing

2. Sedimentation can smother fish eggs

3. Visibility affects predation

4. Deposition can cause flooding

Total dissolved solids

Anything in water other than H20 and suspended solids (anything that will pass through a 45um filter)

How is total dissolved solids measured

Evaporating water sample which has been passed through 45um filter in pre weighed dish (B mg) at 103 degrees then weighing dish & residue (A mg)

Electrical conductivity

Estimates total amount of dissolved ions by measuring ability to conduct electric current

Why is electrical conductivity important

1. Aquatic organisms require relatively constant concentration of major dissolved ions in water

2. Variations of ions from normal range indicates pollution

What can you add to increase electrical conductivity in water

Sodium chloride

How does local geology affect freshwater

Affects chemistry of freshwater

Example of local geology affecting freshwater chemistry

Limestone (calcium carbonate) dissolves leaving calcium & carbonate ions increasing electrical conductivity

How does pollution affect electrical conductivity

Addition of pollutants from wastewater from sewage works, septic tanks, agricultural works increase electrical conductivity

How can evaporation affect electrical conductivity

Concentrates dissolved substances in remaining water increasing electrical conductivity

True or false: Microbial metabolism can affect electrical conductivity

True

pH

Scale used to describe concentration of acid or base in water

Acid

Produces an excess of hydrogen ions when present in water (acidity increases)

Bases

Can accept hydrogen ions - results in excess hydroxide (aciditiy reduces)

pH =

-log10[H+]

pH scale

0 - acidic, 14 - alkaline

pH measurement

pH indicator paper - colour change indicates pH, liquid colorimetric indicators, electronic meters

How is pH controlled in unpolluted water

Carbonate buffering system

Alkalinity

Measure of ability of water to neutralise acid & resist a change in pH

Importance of high alkalinity

Resists major pH change when acid is added - neutralise pollution

Hardness

Measure of mineral content in water

How is hardness measured

In titration - acid added to water sample reactings with calcium and magnesium ions - colour indicator

Hard water originates from

Chalk and limestone areas (minerals enter water via weathering of rock)

Soft water originates from

Granite & impermeable rock (minerals enter water via weathering of rock)

Carbonate hardness

Combination of calcium and magnesium ions with carbonate and bicarbonate ions - temporary hardness

Non-carbonate hardness

Calcium and magnesium combine with anything except carbonate and bicarbonate - permanent hardness

How can carbonate hardness be removed

Water softening

Chemical precipitation

Lime or soda ash added raises pH caused precipitation of calcium & magnesium as calcium carbonate or magnesium hydroxide