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).
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 * Temperature range is based on the 10th and 90th percentiles from the DPIW network
Water quality guidelines for aquatic ecosystems
* Temperature range is based on the 10th and 90th percentiles from the DPIW network
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.
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).
Findings from the DPIPWE data on turbidity are outlined as follows.
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.
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
Sediment plumes, 1 September 2005internal 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.
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.
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).
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