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Sungai Kahayan di Kalimantan Tengah mengalami tekanan lingkungan karena adanya limbah merkuri yang berasal dari aktivitas penambangan emas tradisional. Di tempat tersebut terdapat 10a4 tempat penambangan emas sepanjang sungai dari hulu sampai hilir. Merkuri dalam sedimen sungai secara berturut-turut mengalami metilasi (methylation) oleh reduksi sulfat bakteri. Riset ini merupakan studi akumulasi merkuri (FIg) dalam Mytus nemurus, sedimen dan air, dari hulu ke hilir di sungai Kahayan. Total jarak dari hulu sekitar 296 km. Data dikumpulkan dari 3 lokasi sepanjang sungai. Dalam tiap lokasi tapak sampling berada di dataran baniir (floodplain). Penelitian dilaksanakan selama musim hujan. lkan ditangkap menggunakan rengge (gillnet). Penentuan metil merkuri digunakan metode modified CV-AAS (cold vapor atomic absorption spectrophotometry). Hasil penelitian menunjukkan bahwa diantara sample yang diukur, akumulasi tertinggi masing-masing berada dalam sedimen sungai (0,336 mg.) dikutip dengan daging M. numerus (0,303 mg.g-1 + 0.342). dan air (0.058 mg-1). Merkuri memiliki tendensi meninggi menuju hilir. Hal ini disebabkan oleh tekstur sedimen yang didominasi oleh silt. Kondisi ini berpotensi untuk metilasi. Turbiditas, arus, dan pH menyumbangkan kenaikan tingkat merkuri di hilir. Asupan merkuri mingguan yang dapat ditoleransi menurut WHO adalah 171,42 mg adalah sama dengan 24,4 mg sehari jika seseorang mengkonsumsi 100 g daging M. numerus sehari. dimungkinkan bahwa akan ada 30,3 mg.g-1 yang masuk ke tubuh. Hal ini berarti bahwa merkuri disepanjang sungai Kahayan mengancam penduduk yang mengkonsumsi ikan dari sungai tersebut. ABSTRACT The Kahayan River of Central Kalimantan had environmental stress due to mercury waste. This waste came from the traditional gold mining activities. There were 1014 gold mining sites along the river from upstream to downstream. Mercury in river sediment was subsequently methylated by sulfated reduction bacteria. This research were study the accumulation of mercury (Hg) on Mytus nemurus, sediment and water, from upstream to downstream in the Kahayan River. Total from up to downstream site was approximately 296 km. Data was collected from 3 location along the river. Within each location, sampling sites were at floodplain. Research was carried out during wet season. Fish were caught using rengge (gillnet). The determination of methylmercury was using modified CV-AAS (cold vapor atomic absorption spectrophotometry) methods. The results showed that among samples being measure, the accumulation was highest in river sediment (0,336 µg.g1), followed by the meat of M. numerous (0,303µg.g1 ± 0,342), and the water (0.058 mg1) respectively. Mercury had tendency higher toward downstream. This was due to sediment texture which was dominated by silt. Such condition was potential for methylation. Turbidity, water current and pH contributed to the increasing level of mercury in the downstream WHO permittable tolerarable weekly intake for mercury is 171,42 µg was equal to 24,4 µg daily if one person consume 100g M. numerous meat daily, it is possible that will be 30,3 up/g-1 enter the body. This means that mercury along the Kahayan River threaten the people who eat fish up from this river.

Perairan hutan bakau Segara Anakan merupakan ekosistem yang sedang berubah karena sedimentasi yang tinggi sejak tahun 1980, dan telah mengakibatkan pendangkalan perainan dan mengganggu proses pasang surut. Perubahan ekosistem ini direspon oleh komunitas plankton. pada musim hujan tabun 2002 salinitas perairannya adalah 0 0/00' dan musim kemarau 20 – 32%. Perubahan komunitas plankton tersebut dicirikan hadimya komunitas baik phyto maupun zooplankton dominan sungai pada musim hujan, dan sebaliknya komunitas laut pada musim kemarau. Pada tahun 2004, karena pendangkalan di perairan Bondan, mudflat dan perairannya dikeruk. Penelitian ini bertujuan untuk mempelajari respon komunitas phyto dan zooplankton terhadap pernbanan ekosistem pada musim kemarau Agustus 2005 di daerah tangkapan ikan nelayan perairan Segara Anakan. Hasil menunjukkan bahwa ada peledakan kemelimpahan phytoplankton yang didommasi olehl populasi Chaetoceros di perairan Bondan dan Klaces sebanyak 206890 dan 397273 individu per 100 liter, dan populasi Asterione/lajaponica meningkat sebanyak 69778 per 100 liter di perairan Cigatal. Peledakan kedua genus tersebut adalah merupakan respon phytoplankton terhadap meningkatnya kandungan PO4 di perairan oleh pengerukan sedimen di perairan Bondan. Kenaikan P04 di perairan berturut-berturut dari Bondan ke Cigatal sebesar 4,95 ppm, 5,88 ppm, dan 4,62 ppm. Pada musim kemarau, perairan Segara Anakan juga dicirikan dengan hadimya komunitas plankton sungai yaitu sebanyak 19 species phytoplankton, dan 9 spesies zooplankton. Peledakan populasi Chaetoceros tidak direspon oleh peledakan populasi zooplankton. Keadaan ini mencerminkan bahwa kualitas perairan Segara Anakan telah menurun. ABSTRACT The mangrove ecosystem of Segara Anakan is in the process of changing to the freshwater-wetland due to the heavy sedimentation. This change was responded by the plankton communities. In the 2002 during the rainy season, the salinity was 0 0/00, and the freshwater plankton from the river dominated this mangrove ecosystem. In contrast at the dry season, the salinities were between 20 – 32 0/00, and the estuarine plankton dominated the ecosystem. In the 2004 the Bondan area became shallower and was dredged. In responding to the changing ecosystem, the phyto and zooplankton study was carried out during the dry season of August 2005 at the fishing ground of Segara Anakan. Results showed that there were blooms of phytoplankton. At the Bondan and Klaces waters, Chaetoceros dominated the communities with 206890 and 397273 individuals per 100 liter consecutively. However, at Cigatal Asterionella japonica with 69778 individuals per 100 liter dominated the community. The plankton bloom related to the intensive dredging of sediment at Bondan areas, which increased PO4 highly in the water of Bondan, Klaces, and Cigatal inconsecutively 4.95 ppm, 5.88, and 4.62 ppm. These communities were characterized by the present of 19 species of freshwater phytoplankton and 9 species of zooplankton. Even though the population of Chaetoceros was exploded, but the zooplankton community did not response to the phytoplankton increase. This indicated that the qualities of the mangrove ecosystem waters decreased, and the ecosystem was in the process of changing to freshwater-wetland ecosystem.