Low-cost autonomous in-situ multiparameter optical sensor for climate-impacted catchment monitoring

There is a pressing need to monitor, measure, understand and mitigate causes of anthropogenic activities on our aquatic environments. In situ water monitoring sensors are vital tools for decision support and risk mitigation, pollution source tracking, and regulatory monitoring. To be fit-for-purpose, sensors must withstand the challenging marine environment and provide data at an acceptable cost. If networks of sensors are to become not only a reality but common place, it is necessary to produce reliable, inexpensive, rugged sensors integrated with data analytics. In this context, this work presents the design, development and testing of an affordable, robust and reliable optical sensor for continuous measurement of chemical and physical parameters in aquatic environments. Sensor electronics are housed in a marine grade watertight housing; the optical components are mounted inside a custom designed 3D-printed optical head which joins with the sensor housing.The sensor uses multiple optical detection modes (absorption, scatter and fluorescence) over a broad spectral range (280 nm to 850 nm) to measure parameters like turbidity, fluorescent dissolved organic matter (fDOM), Chlorophyll a (Chl a) and petroleum. Sensor analytical performance was established in the laboratory using analytical standards and in the field by comparison with a commercially available multi- parameter probe. The laboratory and field trials demonstrate that the sensor is fit-for-purpose and an excellent tool for catchment monitoring where rainfall-impacted soils can cause ecological disruption in the surface water. The sensor provides high frequency time-series data with unattended operation in-situ for extended periods of times.