Studi mengenai masukan, agihan dan dekomposisi bahan organik: dari efluen tambak udang dan aliran sungai di perairan pantai labuhan Maringgai Propinsi Lampung

Ida Bagus Made Suastika Jaya, Prof.Dr.Ir. Kamiso H.N., M.Sc.

1999 | Tesis | S2 Ilmu Lingkungan

INTISARI Penelitian mengenai masukan, agihan dan dekomposisi bahan organik dari sungai dan efluen tambak udang di perairan pantai kawasan pesisir Labuhan Lampung Maringgai Propinsi Lampung bertujuan untuk mengetahui: 1) hubungan antara debit sungai dengan muatan suspensi organiknya; 2) ada tidaknya hubungan antara beberapa aspek operasional tambak udang dengan beban organik efluennya; 3) agihan bahan organik di air dan sedimen; 4) proses dekomposisi bahan organik di sedimen; 5) hubungan antara gerakan pasang surut dengan kadar suspensi di air; dan 6) hubungan antara kadar suspensi organik dengan kualitas air. Survai dilakukan untuk pengumpulan data dengan pengambilan sampel dan wawancara di lokasi penelitian antara bulan Juni dan Agustus 1998. Pengumpulan data sungai (debit sungai, muatan suspensi total, suspensi organik, dan BOD) dilakukan sebanyak 18 kali pada waktu yang berbeda. Sebanyak 50 unit tambak udang yang ditentukan secara purposive, dijadikan sampel untuk menaksir hubungan antara kadar TSS, kadar TOS dan organik terlarut efluen tambak udang dengan beberapa aktivitas operasionalnya (bobot biomassa udang, FCR, volume ganti air, nisbah volume:frekuensi ganti air, penggunaan energi kincir). Pengukuran dan pengambilan sampel air serta sedimen di perairan pantai dilakukan pada 10 stasiun sebanyak 4 kali untuk analisis agihan, dekomposisi dan hubungannya dengan kualitas air. Pengukuran pasang surut dan pengambilan sampel air untuk mengetahui hubungan antara gerakan pasang surut dengan resuspensi partikel organik, dilakukan pada suatu titik di dekat garis pantai, masing-masing dengan interval 2 jam selama 24 jam pada saat pasang tinggi dan pasang rendah. Variabel efluen tambak udang yang nyata linier dengan kelima aspek operasional adalah organik terlarut, sedangkan kondisi tambak udang yang nyata berkorelasi adalah kerapatan biomassa udang. Debit sungai menunjukkan hubungan nyata linier dan berkorelasi positif dengan TSS, TOS maupun BOD hingga debit sekitar 4 m3.S'. Di perairan pantai, partikel organik mengalami penyebaran vertikal dan horisontal serta akumulasi di air maupun sedimen. Di air perairan pantai, kadar partikel organik relatif tinggi di lapisan dasar dan pada mintakat dekat garis pantai di selatan muara. Kadar organik sedimen tertinggi terjadi pada mintakat agak ke tengah, pada jarak sekitar 700 m dari garis pantai. Dekomposisi bahan organik di sedimen berlangsung secara anaerob, diduga melibatkan reaksi reduksi nitrat dan reduksi Mangan, menghasilkan amoniak. Kadar amonia sedimen tertinggi di dekat garis pantai, sebelah selatan muara sungai. Dinamika kadar suspensi partikel organik di sekitar garis pantai tidak selalu berkaitan dengan mekanisme pasang surut, melainkan berkaitan dengan resuspensi akibat turbulen. Kondisi turbulen pada mintakat kaya organik dapat memicu pertumbuhan plankton oportunis sehingga kepadatan plankton cenderung tinggi disertai diversitas yang rendah.

ABSTRACT Study on the coastal water organic matter inflow, distribution and decomposition were conducted in Labuhan Maringgai, Lampung province. The studies aimed to know: (1) correlation between river discharge debit and its particulate organic load; (2) correlation between some operational action of shrimp pond and its effluent organic load; (3) the spatial distribution of organic matter in water and sediment; (4) its decomposition processes in sediment; (5) interrelationship between tidal action and suspended of organic matter in coastal water; (6) interrelationship between organic matter existence and water quality. Collecting data by interviewing respondents, sampling, and measuring was taken during June to August 1998. There are 18 times measurement and sampling conducted for determination of debit and its suspension load included particulate organic matter, BOD, and dissolved organic matter (DOM). Fifty respondents and their shrimp pond were selected purposively for collecting data on its operational action by interviewing the operators and data its effluent quality by sampling. Four trip expeditions for collecting data by measurement and sampling of water and sediment in coastal water were conducted at 10 sampling stations for analyses of distribution, decomposition, and its relationship with water quality. Two around the clock sampling and measurement within neap tide and spring tide were conducted for analysis of the tidal action and its relationship to the resuspended organic matter. Dissolved organic matter (DOM) in shrimp pond effluent is significantly linear to the operational action variables (biomass density, FCR, water exchange rate, volume to frequency water exchange ratio, and aerator energy flow). The biomass density of shrimp is the only variable that correlated to the effluent DOM load. Particulate organic matter load in river discharge was increase with debit increment up to about 4 m3.s1 as well as water TSS and BOD. Particulate organic matter in coastal water was higher at near shore water, and about 700 m from shore line in coastal sediment. Organic matter decomposition in sediment is take place in anaerobic condition and facilitated by nitrate and Manganese reducing reaction. Decomposition rate in sediment, in term of ammonia content, is highest at near shore. Water level dynamic due to tidal action is not related to the suspended organic matter in near shore water, but related to the water turbulence. High organic matter content and turbulence of water may induce the bloom of opportunistic plankton and decrease its diversity. Key word: organic matter, shrimp culture, effluent, coastal and shelf environment.

Kata Kunci : bahan organik, budidaya udang, limbah, lingkungan pesisir dan landas kontinen