The indicator reports on water quality values for temperature. 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).
Stream temperatures reflect a site's latitude, altitude, aspect, air temperature, amount of shading, proximity to the ocean, and the time of the day and the day of the year. Waters tend to be cooler in the west of the State, and in streams that rise in alpine areas. The low summer flows and more open land-cover in the east of the State mean that the waters of this region warm up more rapidly.
Stream temperature is important for reasons as outlined in Australian water quality guidelines (Internal linkANZECC & ARMCANZ 2000). Temperature can modify the effects of other water quality measures (e.g. such as dissolved oxygen and the toxicity of chemicals).
Because aquatic animals are adapted to a certain temperature range, exceeding this range (though unnaturally low or high temperatures) can change and diminish the composition of macroinvertebrate communities, aquatic health, and aquatic processes such as respiration, photosynthesis and decomposition (Internal linkNRM North Water Monitoring Team 2006). The timing or occurrence of particular life history stages may be altered by very small changes in temperature or water temperatures may exceed thermal tolerances of aquatic fauna (Internal linkDavies et al. 2004). Even a short period of high temperatures can make a waterway unsuitable for sensitive organisms (Internal linkDavies et al. 2004 and Internal linkNRM North Water Monitoring Team 2006). Some changes to temperature may also favour exotic species such as the Eastern gambusia (Gambusia holbrooki). In addition, Internal linkcarp (Cyprinus carpio)* are another exotic species that is able to utilise lower water temperatures for breeding. The replacement of native 'warm water' fish species with 'cold water' species is a common occurrence downstream of large impoundments (Internal linkKoehn et al. 1995).
Human activities that can cause stream temperature change in waterways include the removal of riparian vegetation, the discharge of warm water from industry and urban stormwater drains, excessive extraction of water leading to reduced flows, and erosion (Internal linkNRM North Water Monitoring Team 2006). Water released downstream from a dam may be released through structures well below the dam's surface, therefore tapping the cold water layer. When these releases fall outside the 20th to 80th percentile of natural stream temperatures, cold water pollution is deemed to have occurred (ANZECC and ARMCANZ 2000).
The IPCC identified that there is a high confidence that rising temperatures are impacting on hydrological systems globally, resulting in the warming of lakes and rivers, with effects on thermal structure and water quality (Internal linkIPCC 2007).
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
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 temperature were sourced from the DPIPWE Baseline Water Quality Monitoring Program (BWQMP) consisting of monthly monitoring at 55 sites (Internal linkDPIPWE 2009). 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 for this indicator to calculate percentage exceedences of ANZECC Water Quality Guidelines.
There is now sufficient information from the BQWMP to formulate site specific trigger values, and DPIPWE 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. 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). These 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 BQWMP.
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.
Because temperature is naturally very variable, the guidelines for aquatic ecosystems refer to effects of unnatural changes in temperature without providing specific recommendations for temperature (Internal linkANZECC & ARMCANZ 2000). Guidance about upper lethal temperatures for susceptible species and target temperatures to provide for aquatic health is provided by Internal linkDavies et al. 2004. Based on studies for the Tyenna River, and to ensure the survival of mayflies, the most sensitive group to elevated temperatures, 'target' temperatures of 21°C for cold water species are recommended. However, the report notes that a 'conservative' upper limit target stream temperature of 20°C has been adopted for the restoration of New Zealand streams (Internal linkDavies et al. 2004).
DPIPWE Baseline Water Quality Monitoring Program
Values for water temperature 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 temperature are as follows.
Northern Water Monitoring Program
Values for stream temperature 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 temperature include the following.
It was reported in the State of the Tamar Report (Internal linkAquenal and DEPHA 2008) that examination of long-term water quality records from Esk Water treatment plants extracting water from the North Esk and St Patricks rivers showed that there had been a steady increase in water temperature, and corresponding decline in water pH, between 1971 and 2001. This may be the result of changes in land-use and long-term changes in climatic conditions.
The following graphs track the available longer-term temperature data for DPIPWE monitoring sites on the South Esk River (left) and North Esk River (right).
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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