The indicator reports on electrical conductivity and exceedences of ANZECC water quality guidelines for electrical conductivity. 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).
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 electrical conductivity were sourced from the DPIW 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).
Electrical conductivity (EC) is commonly used to determine salinity because of its sensitivity and ease of measurement. The Report of the Northern Water Quality Program notes that fluctuations in EC beyond the tolerance levels of endemic populations can result in a shift of community structure, with sensitive species replaced by those with higher tolerance levels (Internal linkNRM North Water Monitoring Team 2006).
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 (see table) 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
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.
At the time of writing this SoE Report, DPIPWE had 55 monitoring sites across the State (Internal linkDPIPWE 2009). The majority of these have been established to monitor water quantity rather than quality with the drivers for establishment being monitoring extraction and establishing environmental flows.
There is now sufficient information from the DPIPWE Baseline Water Quality Monitoring Program (BQWMP) to formulate site specific trigger values, and DPIPWE notes that the trigger values will be of great 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 other than to highlight key issues. 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 at the bottom 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.
In addition, DPIPWE publishes annual Waterways Reports to provide water quality information on a catchment basis, with individual template reports for 40 of the 48 Tasmanian Land and Water Management Catchments. Although each report includes information on the catchment area, streamflow and water allocation information, water quality monitoring information, and a brief report on 'riverine health', they only includes information on the data collected. The Waterways Reports provide little interpretive analysis about the results found at each monitoring site or environmental influences impacting each catchment. In addition, there appears to be little analysis of salinity trends from year to year or research on specific environmental impacts of salinisation on the State's rivers. There also appears to have been little reporting on the environmental and biological changes in salinised rivers or wetlands or any anticipated trends over time given past observations.
Conductivity is naturally variable. For example, low electrical conductivity is natural at sites such as the Nile, Ringarooma, North Esk, George, Ransom rivers and Jackeys Creek. This highlights the importance of setting guidelines that account for natural variability.
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 BQWMP for all water quality parameters reported.
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.
Tasmanian waters typically have low conductivity of 150 µS/cm or less. According to the ANZECC guidelines indicative of slightly disturbed ecosystems in south-east Australia, Tasmanian rivers are mid-range (90 µS/cm). Conductivity generally increases towards the bottom of the catchment. For example, in the Great Forester conductivity levels range from 50 µS/cm in the upper catchment to 200 µS/cm near the coast (Internal linkBobbi et al. 1999).
For a stressor such as salinity that may cause problems at both high and low values, the desired range for the median concentration is defined by the 20th percentile and 80th percentile of the reference distribution (guidelines, chapter 3). Guideline values were determined from the 80th and 20th percentile values from DPIW stream gauging sites for the period January 2000 to October 2006. Reference values for 80th percentile and 20th percentile were 482µS/cm and 88µS/cm, respectively. The upper reference value used by the Northern Water Quality Program was 350µS/cm (Internal linkNRM North Water Monitoring Team 2006), which was based on data compiled for State of the Environment Tasmania 2003 from unlogged Forestry Tasmania sites.
Statewide Baseline Water Quality Monitoring Program
Values for electrical conductivity are shown in the Internal linktable and the following maps. The interactive map provides various summary measures with the data linked to the location of DPIPWE monitoring sites (requires External linkAdobe SVG Viewer).
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. DPIW undertakes a comprehensive Statewide Baseline Water Quality Monitoring Program (BWQMP). The monitoring program commenced in November 2003 and it consists of monthly monitoring at 55 sites across the State of a range of water quality parameters. The BWQMP provides the backbone for baseline monitoring of ambient water quality in Tasmania (Internal linkDPIW 2008).
Triggers have been developed under the BWQMP utilising three years of monthly data from November 2003 to December 2006. This is with the exception of Back Creek, where the minimum of two years of monthly data (as per ANZECC 2000 guidelines) has been used due to the site being installed in April 2005. Salinity trigger values measure field conductivity as TRef 25 uS/cm (25 TRef). Trigger values can be used as default catchment values in the absence of sufficient site specific information. The DPIW trigger values for electrical conductivity are detailed in the embedded Internal linktable. Minimum, median and maximum values for electrical conductivity, as well as when the 80th percentile trigger value has been exceeded for 2007, are detailed in the embedded Internal linktable. Of the 51sites monitored across the State by DPIW, 40 sites (78%) exceeded the 80th percentile on one or more occasions during 2007.
The following two graphs show the relationship between streamflow and conductivity for stream gauging and water quality monitoring sites located on the Coal River and Back Creek. These monitoring sites are located in catchments with a greater susceptibility to salinity.
Additional graphs for data up to June 2008 showing streamflow and conductivity at selected monitoring sites are provided in the following downloadable file.
Findings from the DPIW data on electrical conductivity are outlined as follows.
Conductivity during high river flows
High flows affect electrical conductivity in Tasmanian rivers in different ways depending on river and catchment conditions. In the Meander River during a high flow event in September 2005, conductivity decreased rapidly with increasing flows due to the dilution of salts by rainwater, as shown in the following graphs. As the plot on the left shows, once the peak flow passed, electrical conductivity began to rise again. Rivers such as Pipers, North Esk, Great Forester, and Brid show a similar pattern of declining conductivity during periods of increasing streamflow.
The Conductivity during a flood event, September 2005 contains various plots of streamflow against electrical conductivity for Tasmanian rivers with continuous monitoring during a flood event.
Northern Water Monitoring Program
Values for conductivity 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 conductivity are summarised as follows.
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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