2007 Wetland Inventory for the Eyre Peninsula

21.3 TurbidityTurbidity is a measure of water clarity and can be affected by the amount of suspended particles of clay,silt, plankton, industrial wastes and sewage in water. Turbidity is caused by small particles suspended inwater which are too small to settle out, but big enough to scatter light. At higher levels of turbidity, waterloses its ability to support a diversity of aquatic organisms, and it becomes warmer as suspended particlesabsorb heat from the sun. Turbidity leads to less light penetrating the water, thereby decreasingphotosynthesis, which in turn reduces dissolved oxygen concentrations. Suspended particles may also clogaquatic invertebrate and fish gills, reduce growth rates, and prevent egg and larval development. Particlesin suspension can carry heavy metals, pesticides, nutrients and bacteria. Different components ofecosystems are adapted to different levels of light. The plant community structure and biomass in anecosystem are determined by the light regime, in conjunction with nutrients and temperature. Changes inwater clarity may produce changes in the dominant phytoplankton groups. A common result from increasedclarity tends to reduce the primary productivity of systems. Changes to the primary producers will also effectthe other trophic components of the ecosystem (Liston and Maher, 1997).Turbidity can have a significant effect on the microbiological quality of drinking-water, its presence caninterfere with the detection of bacteria in drinking-water. Turbid water has been shown to stimulate bacterialgrowth since nutrients are adsorbed on to particulate surfaces, thereby enabling the attached bacteria togrow more rapidly than those in free suspension. The major problem associated with turbidity is its effect ondisinfection, high levels have been shown to protect microorganisms from the action of disinfectants and toincrease the chlorine and oxygen demand,(http://www.who.int/water_sanitation_health/GDWQ/Chemicals/turbidity.htm).Turbidity in water is measured in units called NTU's, or Nephelometric Turbidity Units. It is calculated bymeasuring the dispersion of a light beam passed through a sample of water.Fine particles, silt, and suspended matter will cause a light beam passing through the water to be scattered.It has been found that the amount of scattering is proportionate to the amount of turbidity present.Therefore, this process gives a good indication of the relative turbidity of a water sample.The measurement of NTU does not give the sizes of the particles, nor does it indicate the amount ofparticles present. It is a qualitative, rather than quantitative way of measuring turbidity.21.3.1 AnalysisTo understand the results fully, information about the natural levels of turbidity within all the survey regionsat various times of the year is required. This is important because normal levels of turbidity can vary greatlyin wetlands from clear flowing zones to murky areas. Natural variations are also related to flow events suchas floods, winter rains, road run-off which can increase levels dramatically.The Australian Water Quality Guidelines for Fresh and Marine Waters do not set a guideline for turbidity toprotect aquatic ecosystems, but recommend that increases in suspended solids should be less than 10% ofthe seasonal mean NTU. Bek and Robinson (1991) also suggest that turbidity below 50 NTU is suitable forprotecting aquatic animals and plants.The New South Wales EPA has developed the following general guidelines for turbidity:- good (< 5 NTU)- fair (5-50 NTU)- poor (> 50 NTU)Refer to: http://www.epa.nsw.gov.au/soe/97/ch3/11.htmThe National Advisory Committee to Water on the Web has developed regional trends of fresh water fishactivity with turbidity values and time. See figure 15.(See: http://wow.nrri.umn.edu/wow/under/parameters/turbidity.html)These trends correspond well with those guidelines developed by the NSW EPA mentioned above.38