The eutrophication states of Jakarta, Lampung and Semangka Bays: Nutrient and phytoplankton dynamics in Indonesian tropical waters

Eutrophication states of the three different tropical embayments in Indonesian waters were studied. Effects of anthropogenic nutrient inputs on seasonal nutrient gradients and dynamics of phytoplankton biomass were studied over a one year period in three Indonesian embayments, subjected to different levels of anthropogenic pressure. Jakarta Bay receives by far the highest estuarine nutrient load(21260 tDIN y^-1, 6741 tP yp^-1 52417t Si y^-1 )followed by Lampung Bay ( 5003 t DIN y^-1 , 1096 tPy^-1 , 14731 t Si y^-1 ) and Semangka Bay (1378 t DIN y^-1 419 tP y^-1, 16449 tSi y^-1).Asa consequence, mean annual levels of dissolved inorganic nutrients in Jakarta Bay, which accounted for 20 µM N, 5 µM P and 45 µM Si, fairly exceeded those of the two other bays, resulting in high annual means of phytoplankton biomass (13µg Chl-a l^-1 ) when compared to Lampung Bay ( 4µg Chl-a l^-1 ) and Semangk:a Bay (0.8 µg Chl-a l^-1 ). In all of the bays, the phytoplankton community was dominated by diatoms. The occurrence of Dinoflagellates, Chlorophyceae and Cyanophyceae was mainly restricted to the river mouths and their surrounding waters. In total, spatial variability of parameters was much more pronounced than temporal variability, which is congruent with the moderate meteorological fluctuations typical for tropical regions. Despite high loads into Jakarta Bay, a major part still exhibits an acceptable water quality status with respect to dissolved oxygen saturation, which never fallsbelow 50%.