How clean is our stream?

View up the creek

Well, we would like to know as we are keen to keep an eye on the health of our local stream, the Lower Swanson Stream. The stream is located behind Woodside Road (and Woodside Reserve) and flows into the Huruhuru Creek, where it mingles with the salt water adjacent to Riverpark Reserve. The stream is very popular with local children for swimming even though it had tonnes of concrete put into it by Waitakere City Council in 2006 in a misguided attempt to make a local water hole safe when this simply wasn’t possible.

The links below tell some of the story:

New Zealand Herald

Shotcrete NZ – the contractor that carried out the work –

We managed to make contact with Shelley Hackett, who runs the Wai Care program within Auckland Council and arranged for her to show us how to test the water quality on Saturday 7 October. We expected Shelley to show up with a few bottles that we would fill and drop in somewhere…

However, we found out from Shelley that there is much more to it than this. After going through the OSH requirements, we are handed a monitoring sheet that we will complete during our session and Selina volunteered to be our record keeper for the session. The results will later be entered onto the Wai Care website. So, our group of volunteers is now the proud owner of an official Wai Care water quality testing kit! We will be carrying out the testing 4 times per year. If there has been heavy rainfall, we need to wait and do the testing 2 days later.

How do we do the testing?
Well, first you need to know what location is best. At the moment, our stream is flowing fast because there’s extra volume due to all of the rain we have had this winter. Obviously, the centre of the fast moving stream isn’t suitable. Similarly, you don’t want to sample in the very shallow muddy regions. Fortunately for us, we have an area that we can sample fairly safely where the water is deep enough but not fast flowing. This is where we used to fill up our watering cans for the garden.

We have 2 testing kits. One contains the physical tests and the other is for the biological tests. High quality water should be cool and clear. We carried out the following tests under instruction from Shelley.

Stream temperature and air temperature – The thermometer needs to be held under the water in the middle of the water column for one minute. It’s best to measure it in the same location every time. Monique agrees to be the timer as it’s important to be consistent. Shelley takes the stream temperature first, then Gilles has a go as the first thermometer is faulty.

Shelley takes the temperature

The ideal temperature is below 15 degrees Celsius. Our stream temperature is 14.5 degrees Celsius so we’re happy with that. The next thing is the air temperature. For this, the thermometer should be placed away from direct sunlight for one minute. Monique takes over the role of timing as this is critical for the testing to be consistent.

Dissolved oxygen – the sample container should be rinsed out with the stream water first and then filled up to the correct line. Then a glass ampoule is placed into the container and broken. The stream water then enters the ampoule and fills it. Now we have to agitate the ampoule for 30 seconds and then wait for 2 minutes. Then it’s time to compare the colour and intensity of our ampoule with the supplied colour chart. Not as easy as it looks but we manage it and our value is…9!

Checking out the dissolved oxygen level

To check how clean the stream water is, there are 3 different tests; pH (alkalinity/acidity), phosphate (e.g. fertiliser contamination), nitrites/nitrates (indicates presence of sewerage).

pH test – We have concrete in our creek thanks to Waitakere City Council so we might expect the water to be more alkaline. Run off from roads results in water becoming more acidic. The average should be between 6-8.5. Shelley tells us that we should call the Pollution Hotline if we measure values outside this range. We should also take photos of the location. The dip stick is easy to use and we just need to compare the coloured swatches on the box with our test strip. Our result is pH 7; we’re happy with that!

Phosphate test – First we rinse the two vials with the stream water (this can be done with water collected in a bucket). The vials should be filled to the 5 ml line and need to be the same. One is the control sample (won’t have reagents added to it). The other one gets 7 drops of Reagent A (sulphuric acid base) and is mixed. Then 1 drop of the more viscous Reagent B (also has a sulphuric acid base) is added. The two vials are then compared on top of a colour chart. Our phosphate level is very low, 0.025 so this is good news.

Nitrites/nitrates – For this test, we have a dip stick with patches on it that change colour. The dip stick is dipped into the bucket of water for just one second. We wait 30 seconds and read the nitrite colour. For the nitrates, we wait 60 seconds. Unfortunately there seems initially to be a problem with our dip sticks but Shelley thinks it’s fine so we have a reading of 0.075 for nitrites and 0.5 for nitrates.

Clarity test – this is the really fun part and tests our volunteers eyesight as well. A glass cylinder is filled up with the stream water. Inside the cylinder is a magnet. Another magnet (wand) is used to draw the other magnet along the cylinder towards the top (where the bubble is) while someone looks through. The point at which the magnet disappears from sight is the measurement. Selina, Monique, Nicole and Gilles all take a turn and we get measurements of 62, 60, 63 and 66 making the average 62.5. This value measures how far animals can see in the water, i.e. the degree of clarity/turbidity. The highest value you can get is 95 and the average is 40-60. Less than 30 is not good and should be reported. We’re comfortable with being at the top end of the average for now. Our main challenge with this one is making sure we don’t lose the magnet; Shelley advises us to pour the water out into a bucket before tipping it back into the stream, seems like a good idea.

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The last part of the testing is to evaluate which creatures inhabit our stream, i.e. look for presence or absence. In our case, it’s difficult to access the stream banks and we don’t have rocks, logs that we can access for sampling under which some of the “green” species would inhabit. Shelley goes on the hunt for likely habitats with a large net while we have a look at the photos of the animals we’ll be looking for. Ideally, we’ll have a mix of the green (high sensitivity), orange and red (low sensitivity) classified creatures but today we only have orange and red.

Our collection includes  shrimp, beetle, amphipods, midge, damselfly, cranefly, flatworm snails., Shelley tells us not to be discouraged as it’s probably just a matter of not being able to access their habitats. How can we create habitats that we can access for sampling without blocking up the stream with logs…? We’ll have to think about this one. Shelley offers to come back once a year to help us with this as it’s quite hard for our untrained eyes to identify these critters.

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