Autonomous profiling device to monitor remote water bodies

Abstract

In tropical climates, most freshwater reservoirs, dams and lakes are prone to annual summer stratification during which bottom water layers near the bed become hypoxic (<2 ml/l) with very low concentrations of dissolved oxygen (DO). This has serious implications to human health, and requires frequent and effective monitoring, particularly during summer months (March–May) when water consumption is highest. These water bodies are frequently located in remote areas away from human habitation, making it logistically difficult to access and monitor their water column properties on a regular basis. The need for monitoring temporal changes in freshwater ecosystems is addressed in this note through the description of a patented technology - Autonomous Vertical Profiler (AVP) designed and developed at the National Institute of Oceanography (NIO), Goa, for use in both coastal and freshwater bodies. The AVP was used in experiments to satellite transmit complete time and location referenced high-resolution profiles of temperature, phytoplankton concentration, turbidity and DO from the remote Tillari Dam - a freshwater reservoir near Dodamarg, Maharashtra, India. The profiles were received without errors at the Marine Instrumentation Laboratory at NIO. The benefits of in situ time-series profiling with AVP captured the onset of developing hypoxia in early April 2011 over a 9-day unsupervised profiling experiment. A similar 5-day experiment in February 2011 tracked diurnal changes in phytoplankton concentrations through night and day, suggesting a possible interplay between recycled production and photoinhibition.