Stock Use – What’s in a Grade?

Our results aren‘t simply pulled out of the sky, they have been prepared using a set of formulas and scores that are applied from the indicator level all the way to the grade for a catchment. All of these steps and their application are based on best available science along with the expert knowledge and guidance of our science panel.

Stock Water Use Grades

Stock water use reports use data provided by our partners. Only data from surface water monitored in creek, rivers or on-stream storages is used. This is surface water available for stock to drink. Indicators, thresholds and normalising formula are used to determine grades as covered in more detail below.

A grade is not the same as a specific suitability test for a particular water source and a separate water analysis is required to determine a specific stock drinking water suitability.
grades

grade-n Sometimes there are no data available to assess an indicator or a water source in a particular year. When this is the case a grey N icon is displayed.

Summary

Stock water use reports have been prepared by applying a selection of the Australian and New Zealand Guidelines for Fresh and Marine Water Quality to data provided by partners. Only chemical characteristic that may affect animal health have been used.  The Australian and New Zealand Guidelines for Fresh and Marine Water Quality also include biological and radiological characteristics but there is insufficient data available in the Fitzroy Basin to include these parameters in the reports.

Livestock watering is a major agricultural use of water and good water quality is essential for successful livestock production. Production in the Fitzroy Basin relies heavily on the use of unprocessed surface water, as well as ground water resources. This report deals only with surface water quality from natural waters within creeks and rivers and on-stream storages.

Many factors influence the suitability of water for livestock watering. Requirements may differ between animal species (generally tolerances decrease in the order sheep, cattle, horses, pigs, poultry), and between different stages of growth and animal condition and climatic conditions.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality recognise that occasionally there may be test results that fall outside the guidelines and that these results are not necessarily an immediate threat to animal health. The guidelines do not require a 100% result for all parameters in all cases.

The Partnership uses data provided by companies and government agencies to score surface waters against 20 indicators. Indicators were selected using the same criteria as for the EHI and those chosen for inclusion are routinely monitored and have an available guideline for stock drinking water quality.

How are Grades Awarded?

Water quality grades are provided for salinity and chemical composition of stock drinking water.

Salinity is the dissolved salt content of water and is monitored by measuring electrical conductivity (EC). The adopted benchmark value (BM) was the level below which no adverse effect on stock is expected and the adopted worst case scenario (WCS) value was the listed trigger where loss of production and decline in animal health is expected. See Table 4.3.1 Tolerances of livestock to total dissolved solids (salinity) in drinking water of the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Nineteen chemical components were selected from those listed in Australian and New Zealand Guidelines for Fresh and Marine Water Quality as being a concern in livestock drinking water. The selected chemical components are those that are routinely measured in surface water in the Fitzroy. The threshold values adopted come from:

  • Section 4.3.3 Major ions of concern for livestock drinking water quality; and
  • Table 4.3.2 Recommended water quality trigger values (low risk) for heavy metals and metalloids in livestock drinking water

For each data point in the Fitzroy Basin, individual scores are given for salinity and each of 19 chemical toxicants.

Scores for electrical conductivity (indicator for salinity) used the following formula:

formula

Scores for chemical components used a pass/fail scoring method where each data point is given a score of 0 or 100 for each indicator. In this method, if the result for an indicator is better than the threshold it scores 100. If the result is worse than the threshold it scores a 0. The score for each indicator was converted to an overall grade based on the following table.

Grade Score Descriptor
A 80 – 100 Excellent
B 60 – 80 Good
C 40 – 60 Fair
D 20 – 40 Poor
E 0 – 20 Fail
N No data No data

An overall site score for stock water quality is a weighted score calculated using the EC (salinity) score (50%) and the worst scoring chemical component score (50%).

An overall catchment score for stock water quality is calculated by the same method. These scores are converted to a grading based on the above table.

Indicators and Thresholds

The selected indicators and thresholds for stock drinking water used in this report are based on the Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The thresholds used for each indicator (in uS/cm, mg/L or ug/L) are:

INDICATOR UNIT ALL SPECIESTHRESHOLD BEEF CATTLE BM/WCS DAIRY CATTLE BM/WCS PIGS BM/WCS HORSES BM/WCS POULTRY BM/WCS
ELECTRICAL CONDUCTIVITY uS/cm 5970/7463 3731/5970 5970/8955 5970/8955 2985/4478
ALUMINIUM ug/L 5000
ARSENIC ug/L 5000
BORON ug/L 5000
CADMIUM ug/L 10
CHROMIUM ug/L 1000
COBALT ug/L 1000
COPPER ug/L 1000 1000 5000 na 5000
FLUORIDE ug/L 2000
LEAD ug/L 100
MERCURY ug/L 2
MOLYBDENUM ug/L 150
NICKEL ug/L 1000
SELENIUM ug/L 20
URANIUM ug/L 200
ZINC ug/L 2000
CALCIUM mg/L 1000
NITRATE mg/L 400
NITRITE mg/L 30
SULFATE mg/L 1000