Use of a telemetered dispensing system for controlling nutrient additions to experimental patch reefs in the ENCORE study at One Tree Island, Great Barrier Reef, Australia

A telemetrically controlled system was developed to add nutrients automatic ally to experimental patch reefs in a remote marine environment, The experi ment, called ENCORE, was done in the lagoon of One Tree Island, a remote re search station at the southern end of the Great Barrier Reef. Nutrient disp ensing units (NDUs), moored adjacent to patch reefs in the lagoon, were tel emetrically linked to a base station on the island, The base station, about 3 km away from the furthest NDU, consisted of a dedicated computer, contro ller and radio transmitter, which relayed coded signals to a radio receiver mounted on each NDU, This activated a solenoid valve to discharge a measur ed quantity of concentrated nutrient solution from a measuring chamber usin g compressed air from a SCUBA tank. The solution was discharged through 4-8 PVC outlets into the basins of the patch reefs to allow thorough mixing. T he base station interrogated each NDU to find out if the operation had been successful and stored the information on disk to provide a daily log of op erations. Nutrient samples taken within the patch reefs demonstrated that c alculated initial mean concentrations of 2 mug-at PO4-P I-1 and 10 mug-at N H4-N I-1 were achieved. The system we have developed can be used in many si tuations where regular perturbations need to be introduced to aquatic ecosy stems, It uses state-of-the-art technology, yet all components are commerci ally readily available and relatively inexpensive. Detailed specifications and drawings are available from the Great Barrier Reef Marine Park Authorit y. (C) 2001 EIsevier Science Ltd. All rights reserved.