State of the Environment Report 2009
Indicators
Water Quality in Inland Waters: pH


Indicator description

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).

Streamflow and water quality

DPIPWE streamflow and water quality monitoring sitesinternal SOE link to larger image

Rainfall isohyets

DPIPWE stream gauging sites and rainfall isohyetsinternal SOE link to larger image

Site elevation

DPIPWE streamflow and water quality monitoring sites showing site elevationinternal SOE link to larger image

Why is it indicative?

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

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 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.

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 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).

pH median values

pH median values, DPIPWE stream gauging sites, January 2000-January 2005internal SOE link to larger image

pH median values

pH median values, DPIPWE stream gauging sites, January 2000-January 2005internal SOE link to larger image

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

  • The 20th and 80 percentile values from the DPIPWE network for the period January 2000 to October 2006 were 6.6 and 7.8, respectively.
     
  • Median values for pH ranged from 4.6 (Nelson River at Temma Rd Bridge) to 8.2 (Coal River downstream of Craigbourne Dam).
     
  • The highest percentage of samples exceeding the upper guideline value of 7.8 were experienced principally at sampling sites in the south-east of the State (streams tend to be slightly alkaline in this region). Examples of the percentage of samples exceeding the upper guideline value of 7.8 include the following: Coal River downstream of Craigbourne Dam (55 of 64 samples or 86%), Jordan River at Mauriceton (83 of 115 samples or 72%) and Carlton River at tidal limit (17 of 37 samples or 46%).
     
  • The highest percentage of samples exceeding (below) the lower guideline value of 6.6 occurred at sampling sites including the following: Nelson River at Temma Rd Bridge, Ansons River downstream of Big Boggy Creek, George River at St Helens water supply, Great Forester River upstream of Forester Rd, Black River at South Forest, Ransom River at Sweet Hills, Ringarooma River at Moorina, Great Forester River at Prosperity Rd and Esperance River at Dover water supply.
     

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.

  • Median values for pH were in the range of 5.8–8.1 for all sites. Maximum values were in the range of 6.5–8.9.
     
  • Sites experiencing the highest median values for pH included: Coiler Creek at Kimberley, Supply River Above Old Mill, Isis at Macquarie Rd; Mole Creek at Den Road, Mersey at Kellys Cage Road and Lobster Creek at Chudleigh.
     
  • Sites experiencing lower median values for pH included: Tomahawk at Waterhouse Road, Great Mussleroe at Browns Bridge, Little Forester at Golconda, Ringarooma at Bells Bridge, Boobyalla at Waterhouse Rd, Little Forester at Bridport Rd and Powers Rivulet at Terryvale Rd.
     

Related Indicators

Water Quality in Inland Waters: Dissolved oxygenInternal link

Water Quality in Inland Waters: ConductivityInternal link

Water Quality in Inland Waters: NutrientsInternal link

Water Quality in Inland Waters: TemperatureInternal link

Water Quality in Inland Waters: TurbidityInternal link

StreamflowInternal link

Environmental FlowsInternal link

Algal Blooms IncidenceInternal link

Groundwater QualityInternal link

Soil Structure Decline and CompactionInternal link

Area Affected by SalinityInternal link

Potential Area Affected by ErosionInternal link

AUSRIVAS River SurveyInternal link

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.

Water QualityInternal link

Acknowledgment

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).

  External linkTasmanian Planning Commissioninternal SOE link to larger image

  Contact the Commission on:

email: External linksoe@justice.tas.gov.au
Phone: (03) 6233 2795 (within Australia)
Fax: (03) 6233 5400 (within Australia)
Or mail to: Tasmanian Planning Commission, GPO Box 1691, Hobart, TAS, 7001, Australia

 


Last Modified: 1 Mar 2010
URL: http://soer.justice.tas.gov.au/2009/indicator/72/index.php
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