WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2016 49 (CONTINUED ON PAGE 50) for the whole lake and for Haranggaol Bay. The bay has experienced a large increase in aquaculture production in recent years and had a large fish kill in 2016. To maintain a P level of 15 µg/L in the water (making it of low mesotrophic status and possibly a compromise between uses for tourism and aquaculture), the ACC for the whole lake was estimated to be about 33,000 t/yr and for Haranggaol Bay only about 69 t/yr. Both estimates are far less than the current production levels for the whole lake and the bay. Eutrophication of the water could have a long-term impact on the lake because Lake Toba has a long turnover time of about 80 years. Arif Rahman analyzed phytoplankton species composition in Lake Toba, especially around Samosir Island. Despite the lake’s attractiveness for tourism, Arif found that the phytoplankton community composition indicates a eutrophic condition, at least around the island, rather than the oligotrophic status that is desirable for tourism. Lake Cirata The team studying Lake Cirata was led by Dr. Michael Rice (URI), assisted by Dr. Niken Pratiwi (IPB), Dr. Sigid Hariyadi (IPB), Prof. Desyana Cut (SU), Prof. Billy Strothers (UoS), graduate students Terri Breeden (URI), Marius Nicolini (UoS), and Sri Utami (IPB), and a class of undergraduate students from Surya University. The Citarum River Basin in West Java contains a series of three reservoirs: Saguling (highest elevation, built in 1985); Cirata (middle elevation, built in 1987); and Jatiluhur (also known as Djuanda, lowest elevation, built in 1967). Cage aquaculture of fish occurs in all three reservoirs and Saguling also receives water contaminated by industry, so a cascade of water of increasingly impaired quality flows from Saguling to Cirata to Jatiluhur. Aquaculture production was instituted in Cirata in 1988 to provide an alternative livelihood for terrestrial farmers who were displaced by inundation of the land for the reservoir, and at the time it was expected that the lake would contain about 2,700 fish cages. Today, about 56,000 cages are officially in use in Cirata, but a study using Google Earth views indicates that the actual number may be closer to 70,000. In interviews with fish farmers, our Cirata team found that fish kills are common, especially in December and January, following annual rains. FCR varies from 1.36 to 4.76 with no correlation to farm size, according to interviews conducted by Marius Nicolini. Average P content in feed used by Cirata farmers was 1.73 percent, as determined in analyses of samples by Billy Strothers at UoS. Annual production is about 1.2-1.5 t/cage, down markedly from the 6-12 t/cage in the late 1980s and early 1990s, according to Dr. Sigid Hariyadi of our team. In her study of water quality in Lake Cirata, Sri Utami found that dissolved oxygen profiles indicated significantly reduced dissolved oxygen in areas with many cages compared to areas with no cages and that water was hypoxic below 7 m in areas with many cages. Tilapia in the double-cage system used in Lake Cirata are in cages at 5-9 m depth. Terri Breeden modeled ACC in Lake Cirata to examine the effects of improving FCR and using optimal P in feed. Currently, Lake Cirata can support about 40,000 t of fish production per year, but that could theoretically be doubled if FCR P content of feed were optimized. Terri also calculated that hydroponic production of water spinach could remove about 300 g of P per spinach production cycle per fish cage for each unit of cage area converted from fish production to spinach production, based on literature values for P uptake by water spinach (Yu 2013). Desyana Cut and Dr. Sidrotun Naim, both of Surya University, led a class of undergraduate students in an investigation of whether spinach production was feasible in Lake Cirata, with the assistance of two farmers. They encountered problems with pests in the water, excessive sunlight, and insufficient nutrients (other than P). In addition, consumers around the lake are concerned about the heavy metal content of the spinach, given the contaminants flowing in from Saguling reservoir. Clearly, further research is required before hydroponic vegetable production can be used as a mitigation measure in Lake Cirata. Lake Jatigede The Jatigede team was led by Dr. David Bengtson, assisted by Dr. Mayariana Krisanti (IPB), Dr. Taryono Kodiran (IPB) and graduate students Andri Warsa (IPB) and Pamela Booth (URI), along with GIS help from Josh Oakley and Terri Breeden. The Cimanuk River is being dammed to provide flood control and hydropower near the municipality of Sumedang. The lake that will be formed may or may not have aquaculture included as one of its uses. Terrestrial farmers will be displaced by the inundation. Because the Saguling-Cirata-Jatiluhur reservoir complex is not far away from Jatigede, some terrestrial farmers in the Jatigede area plus fish farmers from the Saguling-Cirata-Jatiluhur area are eager to become fish farmers in Jatigede, according to interviews conducted by Pamela Booth. Given the overproduction and deterioration of water quality in Lake Cirata, some government agencies want to ban aquaculture in Lake Jatigede, while others want to encourage it with safeguards applied. Calculating the ultimate ACC for Jatigede is difficult because inundation has not yet begun, so we cannot yet obtain initial P samples from lake waters. We have to rely on samples taken from the Cimanuk River and estimates of P input from the surrounding watershed. We assume that there will be an initial spike of P in the water due to decomposition of terrestrial vegetation that has been inundated (Grimard and Jones 1982, Scharf 2002). Based on projected flow rates and estimated decomposition rates, we expect that the spike will persist for about one year. Josh Oakley and Terri Breeden analyzed the Jatigede watershed using satellite imagery and GIS and employed standard estimates of P inputs in runoff from various types of land usage to calculate Dam construction at Jatigede, showing the Cimanuk River and the area to be flooded.
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