Measuring water quality using the Secchi Project
The short film below demonstrates the monitoring method and safety requirements adopted by the Friends of Gulf St Vincents’ Secchi Porject.
The Secchi disk is used to give an indication of water clarity.
People who observe our coastal waters regularly can’t help but notice when they are dirty.
In most cases, it is possible to make a good guess as to why. Near Adelaide, stormwater is a likely culprit, and we have become accustomed to seeing murky water after rainy and windy conditions. Other causes may include dredging operations, runoff from building sites or agricultural land, waste spills etc.
The Adelaide Coastal Waters Study highlighted the importance of clean water for a healthy marine environment, particularly in relation to seagrasses, which play such a pivotal role in the gulf.
The Secchi disk disappears from view quickly in turbid water.
The Friends of Gulf St Vincent, in collaboration with the Adelaide and Mount Lofty NRM Board, have a project up and running to monitor water quality using Secchi disk. The Secchi disk is a relatively simple and inexpensive way to measure water clarity – the black and white disc is lowered into the water until it is no longer visible. This distance is the Secchi depth.
The rule of thumb is that if you can’t see your feet when you are standing in chest-deep water it is not safe to go swimming.
Similar projects have been run elsewhere – in locations where local pollution of lakes and bays was causing concern, and the benefits are that people become involved in regular observation of changes in the water quality, the data provides a baseline and record of trends, and we all learn more about the sources and impacts of pollution.
In Gulf St Vincent the Secchi depth is usually between 2 and 10 metres, but in other parts of the world measurements of 40 – 80 metres have been recorded!
The waters extending from Outer Harbour to Port Stanvac are particularly at risk from turbidity (muddy waters), but we also need to monitor coastal waters at all jetties around the gulf, so that we can identify marine areas that may be affected by turbidity now, and those which may be at risk in the future.
The project has been running since April 2012, and we are getting data for the Adelaide metropolitan jetties, but we would also really like to sign up some Secchi volunteers for the Yorke Peninsula side of the gulf.