Husnain, Toshiyuki Wakatsuki and Tsugiyuki Masunaga
Silicon is an essential and a beneficial nutrient for aquatic and terrestrial primary producers, respectively. Previous research reported that low silica available in lowland sawahs (a leveled and bounded rice field with an inlet and outlet for irrigation and drainage) in the Citarum watershed was partially associated with low dissolved silica (DSi) concentrations in irrigation water. DSi dynamics and the effect of phytoplankton were studied in the reservoirs of three major dams on Citarum River. The concentrations of DSi and other essential nutrients, as well as phytoplankton diversity and density, were monitored at several sites in the Citarum basin from September 2006 to November 2007. DSi concentrations were highest in the upstream reaches, including the furthest upstream reservoir (Saguling), and decreased downstream. Dams contributed to a decrease of approximately 49-58% in DSi concentrations. The DSi reduction is associated with rising diatom densities (P<0.05), which utilize silica in the construction of frustules. The lowest DSi concentration was measured in Jatiluhur reservoir where diatoms were very abundant. High NO3-N and PO4-P concentrations in upstream and reservoirs which ranged from 1.3 to 18.3 mg L-1 and 0.06 to 2.3 mg L-1, respectively, were probably derived from drainage of industries and houses in upstream and feeding materials used for fish culture in the reservoirs. This condition may enhance the growth of phytoplankton including diatom. Diatom was a major species in the reservoirs, while Cyanophyceae was dominant in all segments of Citarum River. Increasing diatom population could retain more DSi as diatom accumulate abundant silica in its cell wall and depleted Si supply from irrigation water into sawah in lowland.
Key words: dam, diatom, DSi, phytoplankton, reservoir, silica retention.
Makalah diterbitkan pada Journal of Food, Agriculture & Environment Vol.7 (3&4) : - . 2009