Innovation of two established methods for monitoring water colour and clarity: participatory science using the mini- and midi- secchi disks

Brewin, Robert J W and Sun, Xuerong and Wood, Joanne L and Brewin, Thomas G and McBride, Delaney and Frensley, Troy and Bresnahan, Philip J and Simis, Stefan G H and Schmidt, Norbert and George, Grinson and Stoy, Ancy C and Menon, Nandini N and Jasmin, C and Abdulaziz, Anas and Sathyendranath, Shubha and Krug, Lilian A and Das, Nabanita and Sarker, Subrata and Pasche, Natacha and Haller, Laurence and Ghadyani, Yasmin and Odermatt, Daniel and Camus, Alexandre and Mader, Suzanne and Bonny, Adrien and Pochelon, Alexis and Edward Akinnigbagbe, Akintoye and Noernberg, Mauricio Almeida and Mahu, Edem and Diankha, Ousmane and Gonzalez-Silvera, Adriana and Ahmed, Waqar and Kidwai, Samina and Hernandez-Moresino, Rodrigo and Mohamed, Ahmed Hussein and Hernandez-Moresino, Rodrigo and Essowè Panassa, Wilfried and Primadona Purba, Noir and Betancur-Turizo, Stella Patricia and Bernawis, Lamona Irmudyawati and Smeti, Houssem and Anold Moshi, Happiness (2025) Innovation of two established methods for monitoring water colour and clarity: participatory science using the mini- and midi- secchi disks. Frontiers in Environmental Science. pp. 1-15.

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Abstract

Measurements of water colour and clarity are used to track the environmental status of lakes, estuaries and oceans. The oldest standardised methods for measuring water clarity and colour are the Secchi disk and Forel-Ule colour scale. Both techniques were developed in the 19th century and require use of the human eye. Despite the advent of optoelectronic-based sensing, these visual methods are still used today, owing to their sensitivity, affordability, simplicity and long history of use. Recently, a hand-held device was developed for measuring the Secchi depth and Forel-Ule colour (presented in two formats, named the mini- and midi-Secchi disk). Designed to be small, light and convenient-to-use, it is well suited for participatory science projects that involve monitoring water colour and clarity. To date, over 900 mini- and midi-Secchi disks have been distributed to citizens and scientists, primarily through six projects, with data mostly transferred via mobile phone applications to data servers and dashboards. In this paper, we describe the methods used in the projects and show some characteristics of the datasets collected so far. We showcase how the device can be used for scientific applications, such as verifying satellite data products, gaining new scientific insights, and supporting public engagement and education. Finally, we provide suggestions for methodological improvements and future developments.

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