The investigation of sediment accumulation rate has been carried out in Jakarta Bay. The aim of this study is to estimate the accumulation rate of sediment  using natural radionuclide 210Pb as a tracer, through the profile of unsupported 210Pb. Sediment cores of 40 cm and 30 cm length were collected using gravity core from 2 locations (TJ22 and TJ17A) in Jakarta Bay. Samples were sliced at 2 cm length, prepared and analyzed using PIPS detector Alpha Spectrometer. The result shows that in TJ22 consist of 3 layers; LS1 in the depth of (0-2) cm as a mixing layer, LS2 (2-16) and LS3 (16-26) cm and TJ17A has 3 layers; LS1 in the depth of (0-6) cm, LS2 (6-18) cm and LS3 (18-24) cm. Accumulation rate of sediment of LS2 and LS3 in TJ22 are 0.583 cm/y and 0.074 cm/y and in TJ17A are 0,852 cm/y and 0.115 cm/y, respectively. The accumulation rate of sediment since 30 years ago is higher than previous period.   Keywords: Natural radionuclide, 210Pb, sediment, accumulation rate.

AbstrakPenelitian ini dilakukan untuk mengetahui efektifitas biokompos, rumput gajah dan kelompok mikroba yang efektif dalam bioremediasi lahan tercemar minyak bumi yang dilakukan dalam skala laboratorium, dan bahan tambahan yang digunakan urea sebagai sumber nitrogen. Pada penelitian ini dilakukan berdasarkan rasio C/N yaitu 15, 10, dan 5. Parameter uji yang dilakukan untuk mengetahui kondisi optimal yang dicapai pada remediasi terdiri atas pH, kadar air, kadar abu, dan kemampuan ikat air/water holding capacity (WHC). Hasilnya menunjukan degradasi TPH (Total Petroleum Hidrokarbon) sebesar 91,15% dengan komposisi medium (100 g berat kering lumpur minyak bumi, 100 g berat kering biokompos, 9 g urea, rasio C/N = 5) menggunakan perlakuan dari kombinasi rumput gajah, mikroorganisme, urea dan biokompos selama 35 hari. Faktor lingkungan yang menghasilkan kondisi optimal ini dicapai pada remediasi diperoleh melalui kondisi awal pH 8,25; kadar air 49,97%; WHC 101,64%; dan kadar abu 63,76% dan kondisi akhir pH 6,25; kadar air 55,04%; kadar abu 73,39%; dan WHC 124,11%. Penambahan kompos dan urea dapat meningkatkan efisiensi degradasi TPH dan diperoleh hubungan positif antara jumlah penambahan kompos dan urea terhadap tingkat degradasi TPH. AbstractThis research was conducted to determine the effectiveness of biocompost and elephant grass of rehabilitating oil polluted land using landfarming methods, in combination with the addition of urea as sources of nitrogen. This research was conducted based on the 15, 10, and 5 of C/N ratios, respectively. Test parameters needed to knowing the optimal condition in remediation were pH, water content, ash content, and water holding capacity (WHC). Results show the Total Petroleum Hydrocarbon (TPH) was degraded until 91,15% for 35 days. Under treatment of elephant grass, urea, biocompost combination within composition medium of (100 g dry mass soil polluted hydrocarbon, 100 g dry mass biocompost, 9 g fertilizer, and C/N ratio : 5) using combined treatment of elephant grass, microorganisme, fertilizer, and biocompost after 35 days. The environmental factor yielding this optimal remediation reached was obtained through initial condition of pH 8,25; water content 49,97%; WHC 101,64%; ash content 63,76% and final condition of pH 6,25; water content 55,04%; ash content 73,39%; and WHC 124,11%, respectively. The addition of compost and urea has increased the efficiency of TPH degradation and obtained positive relationship between addition amounts of compost and urea to the level of TPH degradation.

Hydraulic interconnection of Jomblangan cave (Petung) with other caves and water discharges in Gunungkidul karst area has been investigated using tracer techniques and variationof stable isotopes and hydrochemical data interpretation from water samples near the cave. Many studies related to the interconnections of underground rivers around Gunungkidul Karst area have been conducted, most of them, however, focused on the area around Bribin and Seropan caves. This is because of the development activites of microhydro turbines to lift the water from underground river were still focused around Bribin and Seropan caves. Petung cave, located in the north of Bribin and Seropan caves, was believed to be one of the caves at the upstream river system of Bribin and Seropan, however, there is no evidence yet of the hydraulic interconnection between Petung cave with either Bribin or Seropan caves. The results of tracer technique at the current study showed that there was no hydraulic interconnection between Petung cave with either Bribin and Seropan caves.On the other hand, the study showed an indication of a direct flow from Petung cave to Sriti and Beton springs. The travel times from Petung to Sriti and Beton springs were found to be around 2 and 10 hours, respectively. This finding is also in agreement with the results of chemical and stable isotopes analysis from the research location. AbstrakPenelitian keterhubungan Gua Jomblangan (Petung) dengan gua lainnya dan keluaran air di sekitar daerah karst Gunungkidul telah dilakukan dengan menggunakan teknik perunut dan variasi kandungan isotop stabil serta hidrokimia sampel air di sekitar gua. Penelitian yang berkaitan dengan keterhubungan antara sistim aliran bawah tanah di sekitar daerah karst Gunungkidul telah banyak dilakukan, namun sebagian besar dari penelitian tersebut hanya berpusat pada gua di sekitar Bribin dan Seropan. Hal ini terjadi karena kegiatan pembangunan turbin-turbin mikrohidro untuk mengangkat air dari sungai bawah permukaan tanah masih terfokus di daerah gua Bribin dan Seropan. Gua Petung, yang berada di sebelah utara gua Bribin dan Seropan, dipercaya merupakan salah satu gua yang berada di hulu sistim sungai bawah tanah Bribin dan Seropan, namun, sampai sekarang belum ada bukti keterhubungan hidrolika antara gua Petung dengan gua Bribin maupun dengan gua Seropan.Hasil uji perunut dalam penelitian ini menunjukkan bahwa aliran air bawah tanah di gua Petung tidak berhubungan langsung dengan aliran bawah tanah di gua Bribin maupun di gua Seropan. Sebaliknya, hasil penelitian ini menunjukkan adanya aliran langsung dari gua Petung ke mata air Sriti dan Beton. Waktu tempuh yang dibutuhkan dari gua Petung ke mata air Sriti adalah sekitar 2 jam dan ke mata air Beton adalah sekitar 10 jam. Temuan ini sangat bersesuaian dengan hasil analisis kimia air dan isotop stabil dari lokasi penelitian.