LAJU DEKOMPOSISI BAHAN ORGANIK DAN PRODUKSI INVERTEBRATA AIR DI SUAKA PERIKANAN TELUK RASAU, SUMATERA SELATAN

Abstract

Pembukaan lahan di lahan banjiran untuk berbagai kepentingan, mempengaruhi morfologi, siklus hidrologi, dan karakteristik fisika kimia air seperti input dan dekomposisi bahan organik yang akhirnya akan mempengaruhi struktur organisme invertebrata air dan produksi ikan di rawa banjiran. Penelitian ini bersifat percobaan lapangan yang bertujuan untuk mengetahui laju dekomposisi bahan organik dan produksi invertebrata air dilakukan di tiga stasiun di Teluk Rasau, Sumatera Selatan pada bulan September sampai Nopember 2009. Laju dekomposisi bahan organik dan produksi invertebrata air dilakukan dengan metode jaring kantong (litter bag) berukuran 20x10 cm dengan ukuran mata jaring
2 mm. Daun dari tumbuhan yang dominan yaitu pohon serpang (Caesalpina sappan) yang hampir gugur dikumpulkan dan ditimbang bobot keringnya, dan 5 g dari daun tersebut dimasukan ke dalam jaring kantong. Pada masing-masing (stasiun) percobaan diletakan 40 kantong jaring dengan posisi
20 kantong diletakan pada kedalaman air 0 m (perbatasan air dan darat) dan 20 kantong pada kedalaman 75 cm. Kantong diikatkan tiang kayu dan ditenggelamkan dengan menggunakan
pemberat. Pengukuran jumlah bahan organik yang terdekomposisi dan produksi makrozoobenthos dilakukan pada minggu ke-2, 4, 6, 8, dan 10, dengan cara mengangkat empat kantong plastik pada masing-masing kedalaman. Contoh air diambil pada kedalaman 1 m dari dasar perairan dengan
menggunakan kemmerer water sampler. Sebagian contoh dianalisis di lapangan (kedalaman air, kecerahan, suhu, pH, dan oksigen terlarut) dan sebagian lagi akan dianalisis di laboratorium (dissolved organic carbon, nitrogen total, dan fosfor total. Persentase serasah daun serpang yang terdekomposisi
selama 10 minggu pada kisaran 40-55%. Koefisien laju dekomposisi serasah daun serpang pada muara Teluk Rasau yang berhubungan dengan Sungai Lempuing pada kedalaman 0 cm (k=0,1586) lebih rendah dari stasiun lainnya baik pada kedalaman 0 cm ataupun 75 cm (k=0,2076-0,2566). Produksi makrozobenthos di muara Teluk Rasau yang berhubungan dengan Sungai Lempuing baik pada kedalaman 0 cm ataupun 75 cm (9,25; 117,25 mg bobot kering/m2) secara nyata lebih rendah dari stasiun lainnya (17,75-22,08 mg bobot kering/m2; 260-807 mg bobot kering/m2). Kedalaman air, suhu, alkalinitas total, dan unsur hara sangat mempengaruhi laju dekomposisi serasah dan produksi makrozoobenthos.

Clearance of floodplain area for multiple purposes influence morphology, hidrological cycle, and physical and chemical characteristics of water such as input and decomposition of organic matter in the waters. It finally affect the structure community of invertebrate and fish production. Experimental study in order to know decomposition rate of organic matter and aquatic invertebrate production was conducted at three sampling sites located in Teluk Rasau Fisheries Reserve Area of South Sumatera province from September to November 2009. Decomposition rate and invertebrate production was run with litter bag method. Leaf bags were constructed by placing 5 g of Caesalpina sappan in plastic with the size of 20x10 cm and mesh bags (mesh size 2 mm). Leaves were collected before abscission, air dried and stored. In each sampling sites, 20 litter bags were filled with dry leaves and placed on the sediment at water depth 0 m (transition between land and water), and another 20 litter bags were placed on the sediment at 0.75 m water depth. The litter bags were tied to the wood stake and anchored to the bottom. The leaf bags were tied together with a weighted rope and attached to a tree. Four replicate samples were removed after 2 days, to measure the leaching process, and then after 4, 6, 8, and 10 weeks for organic matter decomposition rate and invertebrate production measurement.
The bags were cut from the rope and immediately placed in sealed plastic bags and returned to the laboratory. In the laboratory, the leaves were rinsed and separated from the invertebrate. The leaves were sorted by genus, dried at 50°C and weighed. invertebrate were counted and identified to different taxonomic levels. Physical and chemical water quality parameters were measured both in and exsitu by collecting water samples with kemmmerer water sampler at 1 m depth above the bottom. Parameters measured insitu were the water depth, transparency, temperature, pH value, dissolved oxygen, while, dissolved organic carbon, total nitrogen, and total phosphorus were analyzed in the laboratory. Results indicated that decomposition rate of Caesalpina sappan leaves for 10 weeks was in the range of 40-55%. The decomposition rate coefficient in the inlet of Teluk Rasau connevting to Lempuing River at depth 0 cm ((k=0.1586) was less than that in other sampling sites both at depth ocm and 75 cm (k=0.2076-0.2566). Macrozoobenthos production in the inlet of Teluk Rasau connecting to Lempuing River at depth 0 and 75 cm (9.25; 117.25 mg dry weight/m2) were less than that in other sampling sites (17.75-22.08 mg dry weight/m2; 260-807 mg dry weight/m2). Decomposition rate and invertebrate production of Caesalpina sappan were affected by water depth, temperature, total alkalinity, and nutrient.