Corrosivity in A West Java Reservoir Correlated with Fish Farms and Watershed Runoff

Abstract

Cirata Reservoir, which has multiple uses including hydroelectric power for Java and Bali, is subject to environmental pressure from fish farms in its waters and human activities upstream. Corrosivity expressed as an index, LSI, was assessed four times yearly in 2013–2017 in the reservoir and in seven tributaries. Fish cages were also counted in the reservoir in 2007, 2011, 2014, 2016, and 2018. In the reservoir, yearly mean LSI in a fish farm area declined overall from - 0.83 to - 1.96 in 2013–2017, but quarterly values in 2015–2016 ranged from - 2.6 to - 0.31. Similarly upstream in the reservoir’s watershed, the yearly mean LSI of seven tributary rivers declined unsteadily in 2013–2017 from - 0.77 to - 1.55, but quarterly LSI during 2015–2016 in the Citarum River, largest tributary, ranged from - 2.4 to +0.68. Although watershed runoff may thus account for the reservoir’s corrosivity, several findings implicate fish farming increase the corrosivity even more. The number of floating net cages for fish culture nearly doubled in the past decade, from 53,031 plots in 2011, through 68,461 plots in 2014 and 77,195 plots in 2017, to 98,397 in 2018. The reservoir was previously estimated to have an environmental carrying capacity of 12,000 plots. Biological oxygen demand tends to increase in the vicinity of floating net cages.