Indicator description

Why is it indicative

What does the data show

Data

Acknowledgment

Indicator description

This indicator documents the levels of, and changes in, turbidity in estuarine and coastal waters. Turbidity relates to the “murkiness” of water. It is a measure of the light-scattering properties of water and hence an index of the amount of suspended particles. It is measured in NTU.

Why is it indicative

Reasons for measuring turbidity differ slightly from those for other water quality indicators. Although increases in turbidity are often related to deterioration in water quality, it does not follow that the severity of the contamination can be assessed. For example, severe clouding of water by clay minerals and humic substances from soil disturbance may be unsightly, but not toxic to fish or other aquatic creatures. However, a lesser loading of metal rich particles from mine tailings discharge, or high clarity waters loaded with aluminium arising from runoff from acid sulphate soils, can devastate biota. Measurements of turbidity are very useful when the extent of transmission of light through water is the information sought, for example, in estimating the light available to photosynthetic organisms. The turbidity of Australian coastal waters is an important issue in relation to benthic productivity, since many highly valued seagrass and algal bed communities have evolved in, and depend on, conditions of high light penetration (low turbidity). High turbidity values are the data of interest, and change in waters from low to high values. A problem encountered is one shared with other water quality indicators - the need for national baseline data that make it possible to distinguish values and patterns that depart from the norm and may indicate environmental problems or anomalies.

What does the data show

• Indicator levels for turbidity were generally medium to high in estuaries on the north coast (Boags Bioregion) especially within Duck Bay, Port Sorell and the Mersey and Don River estuaries.
   
• A large rainfall event in July 1999 was associated with very high turbidity at Browns River (Bruny Bioregion).
   
• Medium to high turbidity (associated with high tannin levels) was recorded in the Franklin Bioregion, and within Boobyalla Inlet in the north-east.
   
• Turbidity was usually low in estuaries in the Davey and Freycinet Bioregions.
   

Data

The table shows average (each sampling event) and yearly median values for turbidity, from surface waters, for each estuary. ANZECC (2000) default trigger levels for estuarine water quality contain no Tasmanian data. Therefore, draft indicator levels, referenced against the baseline values from the TAFI study, are provided for Tasmanian estuaries. Draft indicator levels are based on the likelihood of exceeding these values during a single sampling event, using data from all estuaries. Depending on the scale of future studies, alternative indicator levels could be based on a bioregional or estuary scale. However, given that data is from surface waters and vertical stratification occurs in most estuaries, indicator levels should be applied with caution to samples taken from other depths.

Average turbidity (NTU) and yearly median for estuaries, July-August 1999 (JA99) to May-June 2000 (MJ00), by bioregion and sampling event.

		Sample						Median
Bioregion	Estuary	JA99	SO99	ND99	JF00	MA00	MJ00	(JA99-MJ00)
Boags	East Inlet	2.1	2.8	1.1	1.9	0.9	1.7	1.7
	Black River	8.9	3.9	3.8	3.0	2.9	3.1	3.4
	Little Musselroe River	4.0	5.4	1.6	6.7	3.5	3.9	3.4
	Port Sorell	39.9	6.6	5.4	-	4.8	3.1	5.4
	Mersey River	12.0	3.6	13.3	-	6.3	3.1	5.5
	Boobyalla Inlet	16.9	13.2	4.2	4.5	4.2	8.2	6.9
	Duck Bay	21.0	17.6	7.0	8.7	6.0	12.2	8.3
	Don River	50.0	9.8	125.3	-	8.1	4.5	8.6
Bruny	Cloudy Bay	1.2	0.9	1.4	1.1	1.0	1.4	1.0
	Browns River	56.0	1.8	3.9	5.0	5.1	3.1	3.2
Davey	Cockle Creek	3.5	1.0	1.3	1.3	1.6	1.5	1.4
	Catamaran River	3.1	1.2	1.2	2.0	1.1	2.0	1.5
Franklin	Pieman River	2.9	9.8	1.8	1.6	4.6	2.6	2.6
	Arthur River	10.5	5.2	8.2	2.5	2.9	4.3	4.5
	Nelson Bay River	6.2	10.7	5.9	4.2	1.3	3.1	5.2
Freycinet	Great Swanport	1.7	1.5	1.6	1.5	1.4	1.8	1.4
	Grants Lagoon	1.2	1.3	2.7	2.2	1.7	1.2	1.5
	Ansons Bay	1.4	2.6	1.8	5.3	1.7	0.8	1.7
	Douglas River	8.0	1.4	1.6	2.1	1.4	2.1	1.7
	Little Swanport	1.8	1.5	2.1	2.3	3.3	2.1	1.8
	Earlham Lagoon	3.7	1.8	2.0	2.1	3.0	0.9	2.0
	Meredith River	14.8	0.9	2.5	3.4	3.5	0.9	2.6

1. Generally, n=6 for sample and n=36 for median
    


2. Draft indicator levels for turbidity (NTU), Tasmanian estuaries:
    

Source: Murphy et. al., in preparation

Acknowledgment

Key indicator for estuaries and the sea E+S 6.3 (Ward et al. 1998)