The indicator reports on water quality values for pH and exceedences of ANZECC water quality guidelines for pH. 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 measurement of pH is important as it interacts with a number of measures of water quality. In particular, it can have a major effect on the bioavailable concentrations of most heavy metals. The water quality guidelines for ecosystems (Internal linkANZECC & ARMCANZ 2000) note that pH is naturally very variable among and within ecosystem types and seasonally, and natural biological communities are adapted to the site-specific conditions. In the region around Hobart, streams tend to be slightly alkaline. For much of the rest of the State, the rivers are slightly acidic. Streams on the west coast are generally, and naturally, more acidic as a result of the large humic acid input from buttongrass plains.
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 that 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
The upgrading of the DPIW 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. Supplementary data has also been sourced from the Northern Water Monitoring Program (Internal linkNRM North Water Monitoring Team 2006).
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 DPIW 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.
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 Baseline Water Quality Monitoring Program (BWQMP).
Box and whisker plots provide a measure of the variability of the data for a number of sites over this period. The data is 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.
The pH or acidity of Tasmanian streams is typically in the range 5.5–7.5. The Australian guidelines for aquatic ecosystems specify the desired range for the median concentration is defined by the 20th percentile and 80th percentile of the reference distribution (Internal linkANZECC & ARMCANZ 2000).
The naturally more acidic conditions should be noted in relation to the low pH values and the high percentage of exceedences recorded at the Nelson River. This also highlights the importance of site specific thresholds that better represent local conditions.
Statewide Baseline Water Quality Monitoring Program
Values for pH 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).
Findings from the DPIPWE data on pH are outlined as follows.
Northern Water Monitoring Program
Values for pH 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 pH 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, and Internal linkDPIWE 2005). 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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