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Turbidity
Sediment
and other solids enter the waterways as a result of erosion (land, beds
and banks). It is estimated that an average of 4 million tones of
sediment are exported from the Fitzroy basin each year.
Consumption of ‘murky’ waters is not necessarily a health hazard, but
many may be risky if the suspended particles contain toxic micro
organisms. The relative Nephelometric turbidimeter (NTU) is the
preferred
Typical
values for Australian drinking water range between 1 and 60 NTU
depending on filtering. ‘Crystal’ clear water usually has a turbidity
of less than one.
Results
found in the Upper Dawson are usually 50-70 times this. In general the
· Woleebee
measures around 4200 NTU,
· Dawson
River at Taroom has an average of 800 during rainfall events and a range
of 200-400 during normal flow.
· In
depth results are available from the Landcare Office.
Nutrient
levels refer to the amount of phosphorus and nitrogen that is present in
the water. Nutrients are important as they promote healthy plankton
blooms, which are necessary to maintain turbidity levels and provide
feed for fish. Increase levels of nutrients however may be harmful. It
can cause excessive plankton growth, potential blue green algae blooms
and oxygen depletion. High levels of nutrients can be caused by high
stocking densities, over feeding (very common in winter), high
productivity, and dead plant and animal matter.
Water
quality along most of the Dawson is reasonable, with quite high
concentrations of nutrients such, especially phosphorous, algal growth
is probably limited by light.
Parameters measured include:
· Temperature,
dissolved oxygen & pH
· Electrical
Conductivity (EC) a Juandah Creek sample was 5 times the ANZECC
guideline of 110mS/cm
· Total
Suspended Solids (TDS)
· Suspended
particulate matter
· Nitrogen
under low flow conditions the Upper Dawson was well above the trigger
level, although this varied with seasons and flow volume.
· Phosphorous
levels are naturally high in the upper Dawson and as with the Nitrogen
concentrations vary with seasons and flow rates. |
Pesticides and Herbicides
Herbicides and insecticides reach waterways by running off the areas
where they were applied, either directly or indirectly when attached to
eroded soil or organic particles. They also have the potential to
contaminate groundwater by leaching through the soil.
Atrazine
a commonly used herbicides , is often found at concentrations above
guidelines in waterways throughout the upper Dawson, but particularly in
the lower Bungaban and Woleebee sub catchments. Other Herbicides such
as Diuron and Dieldron have also been detected at very high levels.
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