The Detection of Annual Hypoxia in a Low Latitude Freshwater Reservoir in Kerala, India, Using the Small AUV Maya

The Idukki Reservoir at an altitude of 748m covering an area of 53 km 2 is surrounded by tropical forests in the Western Ghats in the southwestern Indian state of Kerala.. We used the small AUV Maya with onboard sensors of dissolved oxygen, chlorophyll, turbidity, temperature and depth to monitor the water quality environment of Idukki Reservoir in May 2006. The use of AUVs in confined spaces like small lakes and reservoirs is new and uncommon requiring extra safety to be implemented. As this is a prototype AUV, we shall describe in brief key aspects of the vehicle attributes namely; its novel mechanical design, the autopilots which control the heading and cruising depth, safety and endurance of the platform. The data acquired by Maya revealed an acute oxygen deficiency at 21m, a mid-water low turbidity layer between 10 to 15m, and a prominent chlorophyll maximum in the thermocline region of Idukki waters at 6m. These experiments were repeated a year later in May 2007 are in agreement with the 2006 findings of hypoxia unambiguously. These are the first observations of hypoxic processes using a small AUV in any Indian lake. The relevance of these results in freshwater systems show similarities to hypoxia in saline coastal waters of the west coast of India and are discussed briefly.