Water quality

Students investigate:

Managing water: salinity

Salt of the Earth

Salt is a natural feature of the environment. It is formed from ancient ocean sediments and the weathering of rocks. Salt moves through the rivers of the Murray–Darling Basin.

Salinity is a word used to describe how much salt is in water.

Many organisms cannot live in water sources that have a high salt concentration.

Salty water is also less useful in agriculture.

The removal of deep-rooted vegetation can allow salty water tables to rise to the surface, causing saline soils and killing crops (this is known as dryland salinity).

Irrigation on top of water tables can do the same thing (irrigation salinity).

Urban salinity is a combination of both processes, and can occur when natural drainage is interfered with, parks & gardens are over-watered, or effluent and waste water is not contained or treated properly.

1.a. Before land clearing.

Salt is sitting just at the top of the water table. The tree roots are keeping the water table down.

1.b. After land clearing. Salt has risen because the water table has risen since there are no deep roots sucking it up.

2. Replanting salt-tolerant trees can help improve dryland salinity.

3. Salt naturally left rivers when sufficient flow flushed it out to sea.

Students investigate:

Managing water quality: blue-green algae

Nutrient enrichment of waterways is called eutrophication. The two main nutrients that cause problems in rivers are nitrogen and phosphorous; usually entering the waterways as runoff from farms or forestry operations. Sewage is another source.

We apply nitrogen and phosphorous to crops as fertilizers. Another source of nitrogen and phosphorus is animal droppings.

When it rains, the nutrients can be carried into nearby water-sources and contribute to algal blooms.

Various algae are always present, but when sufficient heat combines with high nutrient levels they thrive. Blue-green algae (cyanobacteria) grow faster than other types. They also boom even more when flows are low and the water still.

1. Eutrophication is when a body of water becomes overly enriched with minerals and nutrients that induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body.
2. Phosphorus, nitrogen.
3. Agriculture (fertilisers), aquaculture, septic tanks, urban wastewater, urban stormwater runoff, industry, and fossil fuel combustion.
4. Cyanobacteria (or just bacteria). Species include Dolichospermum and Microsystis.
5. Plants and animals die – especially fish.
6. Blue-green algae
7. For humans and livestock, the toxin can cause liver damage, stomach upsets, nervous system disorders, skin and eye irrigations. Wildlife and pets can be poisoned, even killed.
8. The only real current solution is to flush water down the rivers and wash the bloom away. Preventative solutions include using less fertiliser, detergents and agricultural products that contain phosphorus or nitrogen.
9. The cycle should show bacteria in water, nutrients washing off farmland or towns, sun (heating of water), slow-flowing water, and then algal growth. Students may also show fish death or similar. An example is provided in linked content.

Students investigate:

Blackwater visual explanation

For more detailed information, see Managing water quality: blackwater.

Show the blackwater visual explainer to this group of students.

Water contains dissolved oxygen, critical to aquatic life. Oxygen levels are naturally higher in fast-flowing water and in cold rather than warm water.

Oxygen levels are also affected by the presence of lots of organic matter, such as leaf litter and bacteria. This is because as carbons decay, they consume oxygen.

Blackwater can occur during floods, which wash organic matter into waterways. In the past, floods happened more often, so this process occurred without too much harm. Now with dams and human water use, they are rare. Therefore by the time a flood large enough not to be contained in dams occurs, floodplains may have accumulated many years of carbon debris. As it rots it can blacken the water, and as bacteria decompose it, oxygen levels drop significantly, and unfortunately many fish die of asphyxiation.

1. Eutrophication.
2. Organic matter (leaves, sticks); oxygen.
3. Carbon compounds/tannins released when organic matter rots are staining the river on the left (river on right has high turbidy/is muddy).
4. food, breed/hide
5. It’s been too long between floods, so there’s too much organic matter and when it washes into the rivers and breaks down it uses up all the oxygen in the water.
6. Dams now contain most floods, people using lots of water keeps river levels low.
7. Consequences include toxins (tummy/skin/eye problems or even death).
8. While there is no instant solution, in limited places fresh oxygenated water can be pumped/piped in to provide a refuge for fish. Over the long-term solution is to use environmental water to flush floodplains more often.
9. Diagram should show concepts as in example ‘blackwater diagram’ in linked resources.

Students investigate:

"Check the pH before jumping into this wetland!" (ABC)

• pH is a measure of how acidic or alkaline water is. The pH scale goes from 0 – very acidic – to 14 – very alkaline. Something that has a pH of 7 is ‘neutral’, or neither acidic nor alkaline.
• Living things in our rivers and wetlands (and humans) prefer pH closer to the neutral.
• Sulphides in soil at the bottom of wetlands and rivers is natural.  However, if these are exposed to air (like in drought or when human uses reduce flow), they turn to sulphuric acid. If this happens for long enough, heavy metals (including aluminium and arsenic) are also released from the sludge. This kills everything!

1.a. acid-suphate soils/ high acidity/ low pH

1.b. no lower than 6.5

1.c. 1.6

1.d. to 1.f. See notes at left.

1.g. The best solution is returning the wetland (or creating a man-made one). Adding lime can neutralise the acid.

Water quality: turbidity (Smithsonian Environmental Research Centre)

Turbidity is a word that describes how murky or clear water is. Higher turbidity = cloudier or murky.

A main cause of increased turbidity is erosion; whereby soil and plant matter gets washed into waterways.

The flow of water is a factor. Slow moving water makes it easier for particulate matter to settle out of the water column.

Turbid water can prevent light from reaching the plants and animals living in a river. This can be a problem for plants which need to photosynthesise to grow.

Alien carp cause turbidity by bottom-feeding and uprooting plants. This is a problem for native fish.

2.a. Turbidity is caused by soil/dirt running off the land.

(Students might also mention farming, grading etc.) From the video they won’t know about carp – see notes at left).

2b. Their writing/drawing should start with aquatic plants not surviving because light is too low.