KONDISI LINGKUNGAN PERAIRAN DAN KEANEKARAGAMAN SUMBER DAYA IKAN DI DANAU MANINJAU, SUMATERA BARAT

Danau Maninjau merupakan perairan eutrofik yang telah mengalami degradasi kualitas air serta sering terjadi kematian ikan secara masal. Degradasi kualitas air dikhawatirkan mempengaruhi perkembangan populasi dan keanekaragaman sumberdaya ikan. Penelitian ini bertujuan untuk mengetahui kondisi kualitas air terkini dan perkembangan keanekaragaman sumber daya ikan di Danau Maninjau. Pengamatan kualitas air dilakukan pada tahun 2014 di delapan stasiun, mencakup parameter suhu, pH, DO, konduktivitas, potensi oksidasi reduksi, kecerahan perairan yang diukur secara in situ. Parameter amonia, nitrit, total nitrogen, fosfat, total fosfor, total bahan organik, klorofil-a dianalisis di laboratorium menggunakan metoda standard, dan fitoplankton menggunakan metoda Lacey Drop Microtransect. Informasi keanekaragaman sumber daya ikan diperoleh dari hasil tangkapan nelayan, pedagang ikan dan hasil pengamatan terdahulu. Kecerahan perairan menunjukkan nilai yang rendah (1,75-2,15 m). Suhu 27,5-30,33oC, nilai pH pH>9 atau di atas baku mutu untuk perikanan dijumpai di dua stasiun. Konsentrasi DO rendah (<2 mg/L) dan kondisi anoksik (0 mg/L) ditemukan pada kedalaman 9 – 15 m. Kolom anoksik terus naik ke kolom bagian atas perairan, mengindikasikan kondisi kualitas air Danau Maninjau terus mengalami degradasi. Konsentrasi amonia umumnya diatas 0,02 mg/L atau kurang mendukung kehidupan ikan. Danau Maninjau diindikasikan kaya unsur hara fosfor. Fitoplankton didominasi oleh jenis alga biru hijau (Planktolyngbia sp). Terdapat peningkatan sumber daya ikan eksotik dan beberapa diketahui merupakan species asing invasif yang mampu beradaptasi pada kondisi kualitas air yang rendah. Di sisi lain beberapa jenis sumber daya ikan asli danau jarang dan tidak dijumpai pada pengamatan ini. Lake Maninjau is a eutrophic lake which has experienced a degradation of water quality and mass fish kill frequently. It worried about their effect to the fish resources diversity and population of indigenous species. This study conducted in 2014 was to know the current of environmental condition and the development of fish resources diversity in Lake Maninjau. Water quality parameters include temperature, pH, DO, conductivity, oxidation reduction potential (ORP), transparency were measured in situ, while amonia, nitrit, total nitrogen, phosphate, total posphorous, Total organic matter (TOM) and chlorophyll-a were analyzed in the laboratory. Phytoplankton was analyzed by Lackey Drop Microtransect method. Fish resources diversity information was collected from fisherman, fish trader and previous observation. Fish resources species was indentified at the zoological Museum Bogor refer to some books reference. Water transparency was low, ranged from1.75 to 2.15 m. Temperature area ranged from 27.5 to 30.33oC, pH (pH>9) or above the standard value for fisheries was found at two stations. Low DO concentration (< 2 mg/L) and anoxic zone was found at 9 to 15 m. Low DO concentration and anoxic zone ascend continuously to the upper water column indicated that water quality continuously degradation. In general amonia concentration was above the standard value for fisheries (< 0.02 mg/L Lake Maninaju was rich of phosphorous and phytoplankton was dominated by Blue green algae (Planktolyngbia sp). Exotic species increased and some of them reported as an invasive species that tolerance to the low of water quality. On the other hand some of indigenous species was rarely and not found in this observation