Secchi Disk Marine Project e-News

Welcome to the the Secchi Disk Project e-news. The Secchi Disk Marine Project is a citizen science project investigating water turbidity in Gulf St Vincent. Along with nutrient discharges, turbid inputs into the Gulf have the greatest impact of coastal water quality and seagrass health. The project is managed by the Friends of Gulf St Vincent with support from Adelaide and Mt Lofty Ranges NRM.


News and upcoming events

11th - 19th of August is National Science Week 
The school theme for 2018 is "Game changers and change makers". Learn how to get your school or kids involved in National Science Week here:

We have had several coastal schools involved in secchi disk monitoring along the coast. If you have a class studying marine quality you may be interested in learning more about ocean turbidity and/or taking readings at your local jetty. Contact us via email to discuss.
Plastic Free July 
Plastics, especially single use plastics, have been the focus of this years' World Environment Day and the issue has been gaining momentum and public support due to their impact on the marine environment.

In Australia, only 21% of our plastic is recycled, and globally there are around 18,000 pieces of plastic in every square kilometres of ocean.

Plastic Free July was founded in 2011 and now has over 2 million participants from 150 countries. If you would like to participate visit: 

National Tree Day - July 29th 

National Tree Day has been going for 22 years. In most areas of Australia it is celebrated on the 29th of July. The aim is to re-connect to nature and reintroduce native plants to the environment.

Revegetating our catchments can help reduce ocean turbidity by binding soil and reducing stormwater runoff.

Australian Marine Sciences Association's Conference: 1st - 5th July

This year the Australian Marine Sciences Association's conference will be held in Adelaide at the Convention Centre. The conference is themed "Canyons to coast" and will focus on the connections between the coast and the deep sea geology and formations.

Registration and more information can be found on their website including at least one free panel discussion at The Science Exchange.

Water Clarity Matters for me: seagrass

With National Tree Day close, it is a good to talk about one of the most abundant plants on Earth. Like terrestrial plants, seagrass has roots which help to stabilise their substrate. they produce flowers and seeds, and provide habitat for animals and invertebrates. Like planting a windbreak on land which slows wind energy, seagrass meadows can slow wave energy and reduce beach erosion. Seagrass also stores more carbon dioxide than any forests on land.

Since 1990, seagrass decline has risen to 7% per year. Causes of seagrass loss along Adelaide's coastline include epiphyte growth caused by excess nutrients and turbid waters reducing light needed by these plants.

Replanting native seagrass was been trialed on substrates such as hessian bags in Gulf St Vincent with some success. But broadscale seagrass rehabilitation still remains challenging, especially broadscale revegetation.

Given that replanting seagrass is still more difficult than replanting terrestrial vegetation, it is vital we create a marine habitat that encourages rehabilitation and prevents further loss.
The impact of variables on secchi readings
Analysis of variables: Tides
Our secchi monitoring process includes recording a number of variables that could affect secchi readings, such as weather, shade and sea conditions.

Analysing secchi depths in relation to these variables can show if it is having a significant impact that may be skewing results. It also helps validate that recording these measurements is important.

Impact of tides on secchi depths
Most organisations taking secchi readings suggest that monitoring occur on the low tides, as this is when secchi depth is expected to be the lowest (i.e. the water is clearest). This is because sediment input is minimised at this time.

The graph below shows the average secchi readings at a few sites at different tidal conditions. Overall, the average secchi depths are lower during low tide. 

There is a possible error here as it is more likely that during low tides when water is shallow that the disk will hit the sea floor (meaning readings are always going to be less than the actual turbidity).

However, when those readings where the secchi disk has hit the sea floor are removed, the same trend appears with the clearer water on the low tide, and more turbid water on the high tide. The table below is an example at Semaphore showing the same trend for all readings versus only those readings where the disk is not visible on the ocean floor.

In an ideal world, sampling would be undertaken on the low tide at all sites but that is not practical. Firstly, volunteers have other commitments and sample when they have time. Secondly, some jetties are over very shallow water and so taking readings on a higher tide makes it more likely that the disk will not touch the sea floor and the reading will be of the actual secchi depth versus the depth of water alone.
Tides are definitely a variable that we should continue to take note of during sampling. Although it appears to influence secchi readings, more data is probably needed to work out if that influence is significant enough to consider some kind of corrective factor should be introduced to normalise data.

Recent Turbidity Trends

Turbidity in May was good despite increased rains with an average secchi depth along the Gulf of 427cm. Port Noarlunga had secchi depths up to 730cm, and Largs as low as 164cm. 

In the first two weeks of June, the average secchi reading along the metropolitan coast ihas been 345cm so far, the highest reading 650cm at Port Noarlunga, and the lowest readings was at Brighton with 105cm.
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Secchi Disk Marine Monitoring Project · Secchi Project · Adelaide, South Austrlia 5000 · Australia

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