Vertical Distribution Of Temperature And Dissolved Oxygen Related To Floating Cage Activitiy In Cirata Reservoir, West Java

Abstract

Cirata Reservoir was built for hydropower to supply electricity for Java and Bali Islands. It is also used for fish culture in floating cage. However, aquaculture in Cirata Reservoir has been far exceeded carriying capacity. This research aims to analyze the vertical dissolved oxygen (DO) profile, determining the factors causing the hypoxia, and qualitatively explaining the response of hypoxia related to floating cage activity. Investigation and water sampling were conducted at four sites with and without floating cage activity. Data on DO, temperature, pH and chemical oxygen demand (COD) were collected weekly for six weeks from April to May 2015. The DO concentration in intensive cage area was lower than in no cage area. DO concentration in areas with intensive cage fell to hypoxia (< 3 mg/l) at 7 m of depth in the first week and moved upward to 4 m of depth in sixth week observation. COD and pH in intensive cage areas were significantly different (P<0.05) from the area with no cage activitiy. The hypoxic and anoxic layers could be dangerous if it continues to be supported by the long rainy days because it may be followed by the upwelling events and the massive fish kills. Nitrate, nitrite and ammonium in intensive cage area have no significantly diffenrent concentration from no cage area. But generally, these parameters have higher concentration in intensive cage area. The highest nitrite concentration found in water column at 20 m (0.003 mg/l). Orthophosphate and chlorophyll-a concentration in intensive cage area is significantly higher than no cage area. Vertically, orthophosphate and chlorophyll-a also have significantly different concentration. From dendrogram graph it is showed that floating cage activities affect to the different characteristic of N, P and chlorophyll-a in Cirata Reservoir.