The electrical conductivity in estuarine waters will be variable as these waters are constantly influenced by ebb and flow of the tide. The time when the sample is taken will generally determine the salinity of the waters. For example, i f you test on an incoming or high tide, the water will be more saline , therefore the Electrical Conductivity (salinity) reading will be high and may require dilution, whereas if the tide is going out or is at low tide, you'll be collecting some of the more freshwater flowing out of the river and estuary, therefore the EC reading will generally be lower

This can affect EC results further upriver (K4, S1) also, as during the drought, the saline water which is usually kept lower in the catchment by freshwater has been able to move further upstream with the lack of rain and flow of the river(s).

Part 1. Recording tide times

When you're sampling for Bellingen Riverwatch testing, it's important for those on estuary sites to record the time and have a look at when Low or High tide is on the day - you can find this on the Bureau of Meteorology website at www.bom.gov.au/australia/tides/#!/nsw-coffs-harbour. You can search tide times for a date. It would be great if you could write in your comments when uploading data whether you have tested on a high, incoming, outgoing or low tide.

Part 2. Using your EC meter

The dual range EC meters have an upper limit of roughly 20,000 microsiemens per centimetre (µS/cm) and can only display 3-4 numbers on the screen. So if the EC is low (fresher water) then you will get a reading with three - e.g 400 - and it will read it in µS/cm.

However, if your reading is over 999µS/cm (generally on an incoming tide) then it will add a decimal place into the numbers and convert the number to millisiemens per centimetre (mS/cm) to read 1000µS/cm and above - e.g 4.00 mS/cm, which is equivalent to 4000 µS/cm.

Often on an incoming tide when the salinity is higher (e.g over 20,000µS/cm) you will get a reading of OR (over range) This means that the sample will need to be diluted - I've also added in the Estuary Senior result sheet for you to use when collecting your water quality data.

Part 3. Dilution

1. Measure 10mL of river water into ONE of the small beakers (Beaker 1).

2. Measure out 20mL of deionised water into the second beaker (Beaker 2).

3. Add the 20mL of deionised water in Beaker 2 to beaker 1 and mix gently and thoroughly.

4. Do your EC test as normal.

5. Write down the EC meter number on the screen, multiply it by 3 to get the correct dilution conversion in mS/cm, and then multiply by 1000 to get to µS/cm to upload to the database.

If you need further help, please contact Ingrid Garland on ingrid@apexenvirosolutions.com

Ingrid is happy to arrange a quick video conference with you to go through this.

Electrical conductivity is a measure of the saltiness of the water and is measured in microsiemens per centimetre (uS/cm) in freshwater and because sea water has a higher conductivity it can be expressed in uS/cm or millisiemens pe centimetre (mS/cm) (how many microsiemens in 1 millisiemens? the answer is 1000).
The EC is freshwater can vary widely due to for example the geology of the area - freshwater that runs through granite bedrock will often have a really low conductivity value, but clay and limestone soils can contribute more salts and so freshwater in these areas can contribute to higher conductivity values. The conductivity of estuaries tends to be the most variable as they are constantly influenced by freshwater and saltwater flow.
Water : 𝝻S/cm Approximate levels
- Distilled water : 0.5
- Rain in very pristine environments i.e. the rain is virtually distilled water : 0.5
- Melted snow : 2-42
- Tap water : 50-800
- Freshwater creeks : 70-2000
- Industrial wastewater : 10,000
- Seawater : 5,000-65,000 (or 55-65 mS/cm)