Vertical Temperature and Dissolved Oxygen Distribution Related to Floating Cage Activity in Cirata Reservoir, West Java E.S. Utami Department of Aquatic Resources Management of Fisheries and Marine Science, IPB S. Hariyadi Department of Aquatic Resources Management of Fisheries and Marine Science, IPB H. Effendi Center for Enviromental Research, IPB M.M. Kamal Department of Aquatic Resources Management of Fisheries and Marine Science, IPB D.A. Bengtson Department of Fisheries, Animal and Veterinary Sciences URI, Kingston, USA Introduction The concentration of oxygen dissolved plays a vital role in biogeochemical cycling and as a sensitive indicator of physical and biogeochemical changes in aquatic ecosystem. Eutrophication which is caused by nutrient loading from floating cage activities due to a considerable increase in organic matter and has caused water quality deteriorate. Floating cage activity in Cirata has been over carrying capacity (12.000 units legal; >50.000 units illegal) The most terrible problem almost every year is upwelling events, followed by massive fish kills which is might caused by hypoxia layer Aims Analyzing the vertical DO stratification profile as a response of temperature stratification, Determining the factors causing the hypoxia, Qualitatively explaining the response of hypoxia related to floating cage activity Methods The research was performed each week from April to May 2015 in Cirata Reservoir, West Java. The water sample was taken from four locations: 2 area with high floating cage activity (Cikalong Kulon and Tegal Datar) and 2 area with no floating cage activity (Maniis and Purwakarta) T, DO, and pH were conducted in-situ from the water surface to 40 m deep. The sampling for COD was carried out from two depths: 1 m and 20 m and analized in laboratory of IPB. The effect of location, depth, and observation time were analysed with repeated measurement factorial at the significance level of p<0.05 (Gomez & Gomez 1983). The distribution of physical-chemical properties (T, DO, COD and pH) of the water among the observing stations was determined using cluster analysis (Krebs 1989) and interpreted into dendrogram form. Depth (m) Secchi depth (m) pH Intensive floating cage area (mg/l) Non-floating cage area (mg/l) surface 1 – 1,6 6,64 – 6,92 6,71 – 7,07 20 - 5,52 – 6,41 5,62 – 6,32 Over the observation periods, the surface temperature of Cirata Reservoir ranged 30.2- 31.5 °C and the temperature of water column (40 m) ranged 24 °C - 26.5 °C. The interaction between floating cage activity with observation period shows a significant temperature difference in floating cage area on the 5th week The vertical profile of oxygen concentration in floating cage area is significantly lower than non-floating cage area. The low DO concentration in floating cage is likely caused by the high input of organic materials coming from the fishes food and metabolism residues (Wang et al. 2012; Young et al. 2011; Carstensen et al. 2014; Hamblin & Gale 2002; Sugiura et al. 2006). The hypoxia layer in floating cage area from the first towards third observation lies in 7 m, and then at the fourth, fifth, and sixth observation, the hypoxia layer lies within, respectively, 6 m, 5 m, and 4 m of depth. The hypoxia layer in non-floating cage area at the first, second, and third observation lies within 8 m depth, at the fourth observation lies within 7 m depth and then, fifth, and sixth, it was found in the 6 m depth. This change of hypoxia layer depth is caused by the increasing DO consumption by the accumulated organic materials decomposition process over the periods of observation. The constant raining weather condition also impacts the decreasing activity of photosynthesis and decreasing the oxygen supply (Goldman & Horne 1983; Middleburg & Levin 2009; Zhang et al, 2015). The observation station of Cikalong Kulon has a high similarity level (13.56%). This is caused by the fact that both stations (Cikalong Kulon and Tegal Datar) are two stations with intensive floating cage activity. Maniis station has high similarity level with Purwakarta station (31.47%). This is due to both Maniis and Purwakarta stations have no floating cage activity. The formation of these two stations groups shows that floating cage area and non-floating cage areas forms two different set of groups. It indicates that the existence of floating cage activity in Cirata Reservoir affects the physical and chemical properties of the water. Results Conclusion Generally, the depth profile and vertical DO stratification correlates, but it is not exactly similar, with the depth profile and vertical temperature stratification. The intensity of floating cage activity significantly affects the physical and chemical properties of the water. The high COD in water column, caused the oxygen depletion and hypoxia layer formation. The depth profile and DO stratification experiences the shallowing depth of hypoxia from one week to the next. If this hypoxia layer movement keeps occuring and supported by the continuous rain, it’s highly possible that the upwelling will occur and followed by massive fish kill. References Goldman CR & Horne AJ. 1983. Limnology. United States of America (US): McGraw-Hill. Gomez KA & Gomez A. 1983. Statistical Procedures for Agricultural Research. John Wiley and Sons, Inc. Zhang Y, Wu Z, Liu M, He J, Shi K, Zhao Y, Wang M & Liu X. 2015. Dissolved oxygen stratification and response to thermal structure and long-term climate change in a large and deep subtropical reservoir (Lake Qiandahohu, China). Water Research. 75:249-258 Asian-Pacific Aquaculture Conference Surabaya, 26-29 April 2016