Judul: Diversity of Bacterial Community that Contribute in Nitrogen Cycle at Lake of Situ Sawangan-Bojongsari, West Java.
Abstrak: One of the problems in freshwater management is the declining of water quality due to pollution of nitrogen compound. Mechanisms of nitrogen transformation by indigenous bacteria in water body have been considered to solve this problem. Situ Sawangan-Bojongsari is the largest lake at Depok city, West Java. Antrophogenic activities on the lake have been accused to cause nitrogen pollution. Accordingly, the aim of this research is to investigate the abundance and diversity of bacterial community that contribute in N cycle as well as to study the profile of physical and chemical parameters that influence the bacterial community. Water and sediment samples were collected from three sampling station, each with three replicate. Water samples were collected from the surface of the water column (0 cm), secchi depth (110) and the bottom (230 cm). Sediment samples were collected by sediment core and divided to three section depth (0-2 cm, 2-5 cm, and 5-10 cm). Analysis of physical factors was fermormed at the time of sampling which included temperature, pH, and DO. Wheter analysis of chemical factors from water and pore water sediment covered some parameters: TN, TOM, DOM, TOC, N-NH3, N-NO3, dan N-NO2. Analysis of the bacterial abundance that contribute in N cycle was done using MPN method. The community structure of the bacteria was analyzed using DGGE method. Amplification product of nifH, amoA, and nosZ gene were targeted for DGGE analysis. The most abundance of nitrogen fixing bacteria was found at the sediment in the depth of 2-5 cm (4.43 log cell/mL) and the less abundance was found at the water coloumn in the depth of 0 cm (2.46 log cell/mL). The most abundance of ammonia oxidizing bacteria was found in the depth of 0 cm (270 cell/mL). The less abundance of the bacteria was found in the depth of 230 cm (73 cells/Ml). The most abundance of nitrite oxidizing bacteria was found at the water column in the depth of 0 cm (2.87 log cell/mL) and the less abundance of the bacteria was found in the depth of 230 cm. There was no ammonia and nitrite oxidizing bacteria found in the sediment. The most abundance of nitrate reducing bacteria (denitrification) was found at the sediment in the depth of 2-5 and 5-10 cm (6.04 log cell/mL) and the less abundance of the bacteria was found at the water column in the depth of 0 cm (1.32 log cell/mL). The most abundance of nitrate reducing bacteria (DNRA) was found at the sedimen in the depth of 5-10 cm (4.32 log cell/ml) and the less abundance of the bacteria was found at the water column in the depth of 0 and 110 cm (1.56 log cell/mL). The most abundance of amonifying bacteria was found at the sediment in the depth of 5-10 cm (4.43 log cell/mL) and the less abundance of the bacteria was found at the water column in the depth of 0 cm (1.86 cell/mL). A total of 11 unique bands of nifH gene generated after DGGE analysis. Six of eleven unique bands of the gene selected, sequenced and identified by searching
Keyword: DGGE, nifH, amoA, nosZ

Judul: Fluks Nutrien Bentik dan Kelimpahan Bakteri Terkait Siklus Nitrogen pada Sedimen Danau Lido, Jawa Barat
Abstrak: Danau Lido dimanfaatkan untuk beberapa kegiatan seperti, Keramba Jaring Apung (KJA), perikanan tangkap, pertanian, wisata, perhotelan, rumah makan, dan pemukiman. Kegiatan tersebut telah memberikan beban masukan khususnya nitrogen yang berdampak terhadap kualitas perairan danau. Penelitian ini bertujuan untuk menentukan fluks nutrien bentik (NH3-N, NO2-N, dan NO3-N) dan kelimpahan bakteri yang terkait dengan siklus N pada sedimen di Stasiun 1 dan 2. Analisis terhadap nutrien NH3-N, NO2-N, dan NO3-N dilakukan pada air pori sedimen dan fluks nutrien bentik, serta penghitungan kelimpahan kelompok bakteri nitrifikasi (AOB dan NOB), denitrifikasi, DNRA, dan amonifikasi. Hasil fluks nutrien bentik yang terjadi di kedua stasiun menunjukkan adanya pemanfaatan NO3-N dan penyumbangan NH3-N, serta pemanfaatan dan penyumbangan NO2-N oleh bakteri. Kelimpahan kelompok bakteri aerob (bakteri nitrifikasi AOB dan NOB) di kedua stasiun lebih rendah dari kelompok bakteri anaerob (bakteri amonifikasi, DNRA, dan denitrifikasi).
Keyword: Bakteri, Danau Lido, fluks nutrien bentik, sedimen

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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