Judul: Implications of changes in nutrient availability for phytoplankton rapid growth (blooming) at Jakarta Bay Waters
Abstrak: The main inorganic nutrients are necessary for phytoplankton to grow and develop are nitrogen, phosphorus, and silica. If the input of nutrients in marine waters beyond the optimal growth of phytoplankton, it will lead to rapid growth (blooming) of certain types of phytoplankton. This study aimed to analyze and determine the concentration and ratio of N : P as well as changes in nutrient availability to the population explosion and change the structure of phytoplankton communities in Jakarta Bay, to set the amount of nutrient preparations leading to population explosions of certain phytoplankton in the Jakarta Bay, as well as to examine the relationship between increased production phytoplankton biomass with nutrient availability in the dry season and rainy season and transitional season. The experiment was conducted in Jakarta Bay in August 2009 to May 2010. Sampling was performed six times at nine stations. Phytoplankton enumeration was performed by the method of deposition. Nutrient samples were analyzed using a spectrophotometer. Canonical correspondence analysis was used to determine the relationship between phytoplankton with physico-chemical parameters of water. The results showed that the spatially and temporally there were found 47 genera of phytoplankton from four classes : Bacillariophyceae (26 genera), Chlorophyceae (8 genera), Cyanophyceae (7 genera), and Dinophyceae (6 genera). Concentration of major nutrients (N, P, and Si) was high and the ratio of N : P was less than 16 resulted in very rapid growth (blooming) of certain types of phytoplankton in Jakarta Bay waters. Very rapid growth of phytoplankton occured in the range of concentrations of nutrients, namely nitrate: 0.0105-0.0829 mg.L-1, orthophosphate : 0.0114-0.3010 mg.L-1, and silica : 0.2787-5.9946 mg.L-1. Genera of phytoplankton that were experiencing rapid growth (blooming) in the dry season were Skeletonema and Rhizosolenia, while those of phytoplankton in the transitional season were Skeletonema, Chaetoceros, Rhizosolenia, and Noctiluca. How ever, in the rainy season there was no genus of phytoplankton that grew very rapidly. Physico-chemical parameters contributing to the blooming of Skeletonema were silica, nitrate, orthophosphate, and temperature. Parameters that contributing to the blooming of Chaetoceros were pH and silica. pH also played a role in the rapid growth of the genus Rhizosolenia.
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Judul: Study of the dynamic of phytoplankton growth and its relation to variability of solar radiation intensity and dissolved inorganic nutrient in Banten Bay
Abstrak: The growth of phytoplankton in the waters mostly depends on sunlight intensity and dissolved inorganic nutrient present in euphotic zone. This research aimed to count phytoplankton growth including growth rate, doubling time, and generation time, and to analyze growth rate response of phytoplankton to solar radiation intensity and dissolved inorganic nutrient. Measurement of phytoplankton growth was conducted from April to September 2008 at five stations. Station 1 was situated at the mouth river, station 2 at the middle of the Bay toward the beach, station 3 at the middle of the bay, station 4 located at the middle toward outside the bay, and station 5 located outside the bay. Phytoplankton growth at each station was measured at various water depth. At station 1, measurement was done at three euphotic depth namely at 10%, 5%, and 1% from surface irradiance. At station 2, 3, and 4, growth measurement was conducted at 50%, 25%, 10%, and 5% from surface irradiance while at station 5, phytoplankton growth was measured at five euphotic depth namely 50%, 25%, 10%, 5%, and 1% from surface irradiance. Research result showed that phytoplankton growth occurred faster at intermediate light intensity and intermediate concentration of dissolved inorganic nutrient. However, the role of light intensity and dissolved inorganic nutrient in controlling phytoplankton growth was not synergic. Temporally, light intensity did not really control the growth of phytoplankton as compared to dissolved inorganic nutrient in term of DSi because sunlight intensity from April to September was relatively stable compared to DSi that tended to be various. Spatially, on the other hand, light intensity and dissolved inorganic nutrient in term of DIN, DIP, and DSi simultaneously controlled phytoplankton growth. This occurred due to light intensity was varied and tended to be homogenous from station 1 to station 4 and low at station 5. Different phenomena also occurred with DIN, DIP, and DSI which was varied and tended to be higher at station 1 and homogenous at station 1 to station 4. However, DSi tended to be more varied than DIN and DIP. Based on this finding, it was stated that DSi was more dominant in controlling phytoplankton growth in Banten Bay and categorized as fast growth rate ranging from 0.66-2.44 day-1, doubling time 0.34-2.04.day-1, and generation time ranging from 0.91-3.53 day-1.
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Judul: Truncated Stop Loss as a Optimal Solution of Reinsurance Agreement in One-Period Model
Abstrak: Reinsurance is one of risk management efforts of an insurance company, which is called the cedent. Similar with insurance, reinsurance constitutes the cedent to pay the premium. We consider one-period reinsurance model and derive a rule which minimizes the ruin probability of the cedent for a fixed reinsurance premium. Therefore, it is needed to construct an optimal reinsurance agreement for the cedent. The premium is calculated according to four different principles, i.e. economic, generalized zero-utility, Esscher, and mean-variance principles. Stop loss is a reinsurance contract which protect the insurance company for losses that exceed a certain amount. The result of this research shows that a truncated stop loss is an optimal agreement in the class of all reinsurance contracts with various premiums calculated using above mentioned principles.
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