Laju Dekomposisi dan Pelepasan Unsur Hara Sedimen Mangrove di Tambak Wanamina Blanakan Subang

Abstract

Mangrove merupakan penyumbang nutrien pada perairan melalui dekomposisi serasah mangrove yang mendominasi berupa daun dan sedimen yang menyimpan bahan organik. Penelitian ini bertujuan mengetahui laju dekomposisi dan laju pelepasan nutrien dari sedimen ke perairan. Pengamatan dilakukan di dua stasiun dengan jenis perakaran yang berbeda di kawasan wanamina Blanakan Subang. Pengukuran laju dekomposisi dilakukan selama 15 hari pada Maret 2020 dan laju pelepasan nutrien dilakukan selama 30 hari pada Juli-Agustus 2020. Sampel serasah dikumpul menggunakan litter bag. Pengukuran kandungan nutrien air menggunakan metode spektrofotometer amonia berdasarkan SNI 06.6989.30- 2005 nitrat berdasarkan SNI 69.8979.2011 dan ortofosfat berdasarkan SNI 06.6989.31-2005. Kandungan sedimen C-organik dianalisis menggunakan metode Walkey-Black, N-total Kjeldahl dan P ekstrak HCl 25%. Kerapatan vegetasi mangrove kategori pohon didominasi oleh S. alba (6100 ind Haˉˡ), A. marina dan A. lanata (400 ind Haˉˡ) di Stasiun 1 dan Stasiun 2 oleh R. mucronata (6800 ind Haˉˡ), sedangkan kategori semai hanya ditemukan untuk R. mucronata (4100 ind Haˉˡ). Laju dekomposisi tercepat secara berturut-turut diamati pada A. lanata, A. marina, S. alba dan R. mucronata. Pelepasan nutrien sedimen Tambak 1b dan Tambak 2b beturut-turut nitrat (0,026-0,041 mg Lˉˡ dan 0,048-0,069 mg Lˉˡ), amonia (0,110-0,209 mg Lˉˡ dan 0,219-0,250 mg Lˉˡ) dan ortofosfat (0,293-0,019 mg Lˉˡ dan 0,181-0,044 mg Lˉˡ).

Mangroves are a contributor to the waters through the decomposition of mangrove litter, which dominates leaves and sediments that store organic matter. This research aimed to determine the rate of decomposition and release of nutrients from sediments into the water. The research was conducted at two stations with different types of roots in the silvo-fishery Blanakan Subang district. Decomposition rate measurements were carried out for 15 days in March 2020, and the rate of nutrient release was carried out for 30 days in July-August 2020. A sample of litter decomposition was collected using litter bags. Measurement of water nutrient content using ammonia spectrophotometer method based on SNI 06.6989.30- 2005 nitrate based on SNI 69.8979.2011 and orthophosphate based on SNI 06.6989.31- 2005. Sediment content of C-organic was analyzed using the Walkey-Black method. Kjeldahl N-total, and P 25% HCl extract. Mangrove vegetation at tree category was dominated by S. alba (6100 stand Haˉˡ), A. marina dan A. lanata (400 stand Haˉˡ) at Stasiun 1 and Stasiun 2 by R. mucronata (6800 stand Haˉˡ) while the seedling category was only found for R. mucronata (4100 stands Haˉˡ). The fastest decomposition rate in succession was observed on A. lanata, A. marina, S. alba dan R. mucronata. The release of sediment nutrients in Pond 1b dan Pond 2b were nitrate (0,026-0,041 mg Lˉˡ and 0,048-0,069 mg Lˉˡ), ammonia (0,110-0,209 mg Lˉˡ and 0,219-0,250 mg Lˉˡ) and orthophosphate (0,293-0,019 mg Lˉˡ and 0,181-0,044 mg Lˉˡ).