The Northern Australian Community Groundwater Security Project

This image shows the regions of the Northern Territory & WA covered by this project

For this project we need three 50 ml vials to be filled with water. At CDU we will use this water to measure electrical conductivity/salinity and stable isotope composition, and for baseline water banking. The kit contains universal indicator papers for you to measure pH directly and record on the app. An eDNA sampling kit is provided and subsequent analyses undertaken by the Wilderlab (a commercial laboratory) will be used to characterise aquatic biota and biodiversity.

Many organisms, including humans, need freshwater to survive, that is, water that contains low concentrations of salts. One of the easiest ways to measure the saltiness, or salinity, of water is to measure the electrical conductivity (EC). The ability of water to conduct a current provides a measure of the amount of salt (dissolved ions) in the solution. The EC of the 50 ml water sample collected from your bore will be measured with a lab-based meter at CDU and the results will be provided on the project website.

Freshwaters can range in pH from very acidic (< 4) to neutral (7) to very alkaline (>9). Water is usually suitable for drinking if it is within the range of 6.5 to 8.5. You can measure the pH of a groundwater sample directly at your bore using the indicator paper and colour chart provided and entering the results onto the app.

The isotopic composition (δ¹⁸O and δ²H) of the 50 ml water sample collected from your bore will be measured in the lab at CDU using IRIS (isotope ratio infrared spectrometry). The isotopic composition provides information on whether the groundwater is mainly rain from the last major rain event, if the water has been retained for longer, or if it’s really ancient water (i.e. from rain that fell 100s or 1000s of years ago). This information makes a difference as to how we might use the resource. If it’s water from a recent rain event, then we know it's renewable. If it's very ancient water, it probably won’t be recharged, depending on the location of the aquifer, and we may need to be more cautious with water use.

One 50 ml vial of water will be frozen at CDU and stored as part of a baseline water bank. If something happens in the future, and a bore is thought to be contaminated, another sample can be collected and sent to us to determine the difference in chemical composition between the two. The water bank provides a baseline against which future changes in water quality can be assessed. This is very useful where future developments, and their impacts, are not yet known.

Groundwater can contain organisms, including microbes, fungi and invertebrates (also known as stygofauna), that are adapted to living in subterranean environments. They can contribute to maintaining good quality water and their detection is an important part of understanding how they provide this valuable ecosystem service. Groundwater can also contain DNA shed from plants and animals living in terrestrial systems above the water table. Increasingly the measurement of eDNA is being used as a biomonitoring tool (using the presence of organisms to infer water quality) as well as an indicator of biodiversity (below and above ground) The measurement of eDNA is a two-step process. It involves first filtering the water to collect the DNA and then adding a preservative. Specific sampling instructions are provided with the DNA sampling kit.