Indicator description

The indicator reports on water quality values and exceedences of ANZECC water quality guidelines for turbidity. Water quality is a recommended NRM indicator of river condition for the Inland Aquatic Ecosystems Integrity (Rivers and other Wetlands) Matter for Target.

Data were sourced from the DPIPWE network of stream gauging sites (see acknowledgements) as shown in the following maps for the period January 2000 to January 2006. The maps show DPIPWE site names and numbers (below left), locations in relation to rainfall distribution (centre), and locations in relation to elevation (right).

Streamflow and water quality internal SOE link to larger image

Rainfall isohyets internal SOE link to larger image

Site elevation internal SOE link to larger image

Why is it indicative?

Turbidity is a measure of the light-scattering properties of water and hence an index of the amount of suspended particles. Suspended particles in stream runoff may originate from a variety of natural and human or management related sources including stream bank erosion, urban/agricultural runoff, road-related sediment, and a host of other natural and management-related causes. It is difficult to characterise the erosion of entire river basins from measurements of turbidity because of the large effects of localised land use and geology. East coast streams are generally more erosive than those in the rest of the State.

Environmental water quality is usually assessed against some criterion or guideline for each separate chemical or physical variable. The 'Australian Water Quality Guidelines for Fresh and Marine Waters' (Internal linkANZECC & ARMCANZ 2000) are applied in Tasmania. Given sufficient data availability, these guidelines take into account regional variations in the environmental values of water quality, baseline environmental conditions and allow for variation in the parameters measured and frequency of measurement for each water body. Guidelines are chosen based on the primary management aims for a water body.

Water quality data which trigger guideline values indicate a need for remedial management action or the initiation of further investigations confirming inappropriate levels of water pollution.

The term 'percentage exceedence' of water quality guidelines has been used in this indicator to gain a relative and absolute indication of water quality at a site. Percentage exceedence is defined as the percentage of samples that exceeded the guideline value over the measurement period (January 2000 to January 2006). The guideline values used within this indicator are listed in the following table. These are based on the guideline values for aquatic ecosystems (Internal linkANZECC & ARMCANZ 2000).

Water quality guidelines for aquatic ecosystems

Item	Parameter	Units	Guideline range or value
1	Dissolved oxygen	Percentage saturation (%)	81–99
2	Conductivity	micro siemens/cm	88–482
3	Turbidity	NTU	10
4	pH	pH	6.6–7.8
5	Temperature	°C	6.4–19.0
6	Total nitrogen	(mg/l)	0.48
7	Total phosphorus	(mg/l)	0.013
8	Nitrate	(mg/l)	0.19

* Temperature range is based on the 10th and 90th percentiles from the DPIW network

Source: Internal linkDPIW 2006 and Internal linkANZECC 2001

Data availability and limitations

The upgrading of the DPIPWE network of stream gauging sites has significantly improved the coverage and availability of data on water quality since the 1997 and 2003 SoE Reports. Data on turbidity were sourced from the DPIPWE Statewide Baseline Water Quality Monitoring Program consisting of monthly monitoring at 53 sites with a subset of 38 sites monitored 'continuously' for various water quality parameters. For the purposes of this indicator monthly data has generally been reported. Continuous monitoring has been used only to illustrate how parameters respond to higher flows. Supplementary data has also been sourced from the Northern Water Monitoring Program (Internal linkNRM North Water Monitoring Team 2006).

Guideline values for aquatic ecosystems for upland rivers are in the range of 2-25 NTU (Internal linkANZECC & ARMCANZ 2000). A threshold value of 10 NTU was used to assess the data for exceedences against guidelines. However, the value of 10 NTU used in this indicator should be used carefully as for some catchments it does not represent a realistic value to be used as a trigger. Rather, site specific values should be used and where it is deemed appropriate under the setting of Water Quality Objectives then the 10 NTU value for some sites/catchments may be used as an aspirational target. In the linked Internal linktable, turbidity exceedence data is shown for both the 10 NTU and 24 NTU threshold values. The 80th percentile value from the DPIW turbidity data for the period January 2000 to October 2006 is 18.7 NTU.

Limitations arise in the reporting of these data because measures of environmental quality are naturally variable. For example, even a simple measure such as temperature varies with season, flow, and time of day. Temperature also influences various other water quality parameters such as dissolved oxygen and electrical conductivity. Because of the variability of these parameters (both over time and along the river course), the values reported can only be rough guides to the overall water quality in each river. A minimum of 24 samples was required to calculate percentage exceedences of ANZECC Water Quality Guidelines.

There is now sufficient information from the DPIW Statewide Baseline Water Quality Monitoring Program to formulate site specific trigger values, and DPIW notes that this would be of greater value. However, for the purpose of this indicator to gain a relative and absolute indication of water quality a regional approach has been taken and site specific thresholds have not been used in calculating exceedences. Specific comments about the guideline values used for different parameters are discussed under each parameter heading below.

A further limitation is that the majority of DPIPWE data are from sites located towards the coastal end of catchments (see location maps) that can be considered as 'test sites' and hence are subject to influences from agricultural activities upstream.That is they represent sites that are impacted to varying degrees by anthropogenic activities.

Data

Median, minimum, maximum and percentage exceedences of guidelines for the period January 2000 to September 2006 are shown for each of the measures of water quality detailed below. The summary Internal linktable shows exceedences of guideline values from the DPIPWE Statewide Baseline Water Quality Monitoring Program.

Box and whisker plots provide a measure of the variability of the data for a number of sites over this period. The data are also presented in maps with median values shown via the thumbnail map on the left, and an interactive map (note requires External linkAdobe SVG Viewer) is provided via the thumbnail map on the right.

DPIPWE Statewide Baseline Water Quality Monitoring Program

Values for turbidity are shown in the Internal linktable and the following maps. The interactive map (at right) provides various summary measures with the data linked to the location of DPIPWE monitoring sites (requires External linkAdobe SVG Viewer).

DPIPWE stream gauging sites internal SOE link to larger image

DPIPWE stream gauging sites internal SOE link to larger image

Findings from the DPIPWE data on turbidity are outlined as follows.

• Four sampling sites experienced nil exceedences of the aspirational target of 10 NTU over the reporting period: Nile River at Deddington; Huon River u/s Frying Pan Creek; Ransom River at Sweet Hills; and, Leven River at Bannons Bridge.
   
• A further thirteen sampling sites experienced nil exceedences of the target of 24 NTU: Coal River downstream of Craigbourne Dam, Jackeys Creek downstream of Jackeys Marsh, Huon River at Judbury, Allans Rivulet upstream of Taranna, Ringarooma River at Moorina, Scamander River upstream of Scamander water supply, Tooms River downstream of Tooms Lake, Douglas River upstream of Tasman Highway, Inglis River at Emeraldvale Road, North Esk River at Ballroom, Swan River at the Grange, South Esk River at Perth and Apsley River upstream of Coles Bay Rd Bridge.
   
• The highest percentage of samples exceeding the 24 NTU guideline values occurred at the following sites: Clyde River downstream of Lake Crescent (34 of 35 samples or 97%), Duck River upstream of Scotchtown Rd (136 of 219 samples or 62%), Jordan River at Mauriceton (72 of 148 samples or 49%) and Great Forester River [upstream of Forester Rd] (42 of 117 samples or 36%).
   
• In addition to the previous sites, the highest percentage of samples exceeding the 10 NTU guideline values occurred at the following sites: Little Swanport River 3km upstream of Tasman Highway (277 of 331 samples or 84%), Brid River 2.6 km upstream of tidal limit (41 of 51 samples or 80%), Prosser River upstream of lower dam (71 of 106 samples or 67%), Montagu River at Stuarts Rd (47 of 88 samples or 53%), Little Swanport River downstream of Eastern Marshes Rivulet (105 of 175 samples or 60%) and Rubicon River at tidal limit (25 of 54 samples or 46%).
   

Turbidity during high river flows

Turbidity in rivers is influenced by flow, with very large increases occurring during flood events. Turbidity generally increases considerably during the early part of the flood event as sediment is washed into the river from the catchment and deposited sediment is resuspended (Internal linkANZECC and ARMCANZ 2000).

The following plots show how turbidity responds to rainfall events in two rivers: the Esperance and the South Esk. Channel conditions, the local intensity of a rainfall event, catchment area, the condition of riparian vegetation, and surrounding land uses are some of the factors that influence turbidity during such a rainfall event. Turbidity in smaller catchments, such as the easterly flowing rivers in Tasmania respond very quickly to rainfall. The Turbidity during a flood event, September 2005  provides further examples of turbidity during a rainfall event.

Turbidity, South Esk River internal SOE link to larger image

Turbidity, Esperance River internal SOE link to larger image

In the north of the State, a major rainfall event resulted in sediment plumes in estuaries visible from satellite. The image shows the sediment plumes with streamflow and turbidity data presented for the same period from DPIPWE stream gauging sites. The main sources of nutrients and particulate matter during flood events such as this one are from the land leaching and land erosion (Internal linkANZECC and ARMCANZ 2000).

Sediment plumes, 1 September 2005

internal SOE link to larger image

Northern Water Monitoring Program

Values for turbidity for 2005 from the Northern Water Monitoring Program (Internal linkNRM North Water Monitoring Team 2006) are shown in the Internal linktable. Findings from the Northern Water Monitoring Program data on turbidity include the following.

• Exceedences of the guideline value of 25 NTU were recorded at 15 (31%) of the 49 sites monitored for turbidity.
   
• The greatest percentage exceedences were recorded at Swamp Gum Rivulet (4 of 6 samples or 67%); Kings Meadows Rivulet, Punchbowl (4 of 13 samples or 31%); Supply River Above Old Mill (3 of 11 samples or 27%); Middle Arm Creek, West Tamar Highway (3 of 12 samples or 25%); and Brid at Duncraggen Rd (3 of 12 samples or 25%).
   
• Median values were in the range of 0.4–26.4 NTU.
   
• Characteristics of sites experiencing high percentage exceedences include poor riparian vegetation, intensive agricultural operations upstream or mixed landuse surrounding the site including agriculture.
   

Related Indicators

Related Issues

An indicator can show trends or changes that apply to one or more environmental issues. The data within an indicator is used to inform an issue report and any related recommendations. A summary of the indicator's relevance to a particular issue can be found within the 'Indicator' section of each of the linked issue reports below.

Acknowledgment

Data for this indicator is provided courtesy of the DPIW network of stream gauging sites (Internal linkDPIW 2006). The indicator is based on the Core Indicator for State of the Environment Reprting on Inland Waters and Wetlands IW8 (Internal linkAustralian and Zealand Environment and Conservation Council et al. 2000).