The indicator reports on dissolved oxygen values and exceedences of ANZECC water quality guidelines for dissolved oxygen. 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).
Dissolved oxygen is an important indicator of a healthy aquatic ecosystem as oxygen is essential for aquatic animals. The measure of dissolved oxygen provides a rapid assessment of competing processes in a river system. Oxygen enters waterways from the atmosphere and from the photosynthesis of aquatic plants. Oxygen is also consumed in respiration by aquatic animals and by decomposition. High levels of organic matter and nutrients (e.g. from sewage or fertilisers) will consume dissolved oxygen, resulting in lower values. The levels of such compounds and their impacts on water quality are indicated by the biochemical oxygen demand of the water. A low dissolved oxygen level often accompanies a high biochemical oxygen demand. Reducing or changing water flows through dams or extraction can also lead to lower levels of oxygen in waterways. Increases in water temperature will also reduce the amount of oxygen in the water.
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 dissolved oxygen were sourced from the DPIPWE Baseline Water Quality Monitoring Program (BQWMP) consisting of monthly monitoring at 55 sites (Internal linkDPIPWE 2009).
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 BWQMP 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 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 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.
There can be significant variations in the level of DO with temperature, altitude, depth, season, and also during the night when plants stop photosynthesising. It is therefore important when interpreting DO that where there is the possibility of low concentrations that diurnal data is acquired to gain a comprehensive view of fluctuations in the system. Continuous data on dissolved oxygen and other water quality measures can be viewed at the External linkWater Information System of Tasmania.
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 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 guideline values for dissolved oxygen (percentage saturation) for upland rivers are in the range of 90-110 for aquatic ecosystems (Internal linkANZECC & ARMCANZ 2000). The guidelines recommend taking the 20th and 80th percentiles as the values for a reference system. Based on monitoring data from DPIPWE sites for the period January 2000-September 2006 the guideline values are 81 and 99 respectively (percentage saturation).
DPIPWE Baseline Water Quality Monitoring Program
Values for DO are shown in the Internal linktable and the following maps. The interactive map provides various summary measures for DO with the data linked to the location of DPIPWE monitoring sites.
Summary findings from the DPIPWE data on DO are:
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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