KAJIAN KRITERIA NUTRIEN (NITROGEN DAN FOSFOR) SEBAGAI DASAR DALAM PENILAIAN STATUS TROFIK PERAIRAN WADUK MRICA BANJARNEGARA, JAWA TENGAH, INDONESIA

AGATHA SIH PIRANTI, Prof. Dr. H. Sudarmadji, M.Eng.Sc.

2012 | Disertasi | S3 Ilmu Lingkungan

Penelitian dilakukan di Waduk Mrica Banjarnegara Jawa Tengah selama satu tahun (Maret 2009 – Februari 2010). Tujuan penelitian adalah mengkaji besarnya input nutrien (N dan P) dari daerah tangkapan air ke waduk dan keseimbangan nutrien yang terjadi di Waduk Mrica, mengkaji dinamika nutrien secara spasial dan temporal, mengkaji hubungan konsentrasi nutrien dengan tingkat trofik perairan, dan menentukan kriteria nutrien yang tepat untuk penilaian tingkat trofik perairan Waduk Mrica yang berada di wilayah tropis. Penelitian ini menggunakan metode survai dengan teknik pengambilan sampel secara purposif di 17 (tujuh belas) lokasi yang meliputi 4 (empat) titik di sungai yang merupakan inlet waduk (Serayu, Merawu, Lumajang dan saluran Liangan), 11 (sebelas) titik di perairan waduk dan 2 titik di daerah outlet waduk serta di zona lakustrin pada 5 jeluk yaitu pada 0, 2, 5, 10, 20 dan 30 meter. Variabel penelitian meliputi nutrien (TP, TN, NO3-, PO4, NH4+), klorofil dan kualitas air yang terkait eutrofikasi (suhu, O2, HRT, pH dan turbiditas), serta inflow dan outflow waduk. Data yang diperoleh dianalisis secara kualitatif dan kuantitatif. Untuk mengkaji keseimbangan nutrien dilakukan perhitungan neraca nutrien. Distribusi TN dan TP di analisis secara deskriptif menggunakan grafik dan untuk mengetahui perbedaan antar lokasi dilakukan uji F dan dilanjutkan dengan uji BNJ 5%. Analisis regresi korelasi dilakukan untuk mengkaji hubungan nutrien dan biomassa algae dan penentuan kriteria nutrien dilakukan dilakukan dengan ekstrapolasi garis regresi tersebut. Kesimpulan penelitian menunjukkan bahwa Waduk Mrica mendapatkan input nutrien (TN 374.623,08 ton dan TP 41.117,18 ton) lebih tinggi dibandingkan output (TN 339.922,49 ton dan TP 33.179,15 ton) sehingga Waduk Mrica mengalami surplus TN dan TP masing-masing sebesar 34.700,59 ton (9,26%) dan 7.938,02 ton (19,31%). Surplus tersebut menjadi residu yang melayang dan kemudian terendapkan di sedimen Waduk Mrica. Secara spasial N dan P yang masuk ke Waduk Mrica terdistribusi merata dari zona riverin sampai zona lakustrin. Tingginya input nutrien dari DTA pada musim penghujan menyebabkan secara temporal distribusi TP pada musim penghujan lebih tinggi tinggi daripada musim kemarau, sedangkan adanya pola operasional waduk berdasarkan target level menyebabkan secara temporal distribusi TN lebih tinggi pada musim kemarau dibanding musim penghujan. Keberadaan semua jenis nutrien (TN, TP, NO3-, NH4+, dan PO4) menentukan perkembangan biomassa algae di Waduk Mrica, namun jenis nutrien yang dapat digunakan sebagai kriteria penentu perkembangan biomassa algae pada musim penghujan adalah TP dan NH4+, sedangkan pada musim kemarau adalah NO3-. Pola perkembangan biomassa algae di Waduk Mrica berfluktuatif sehingga kriteria nutrien yang diperoleh belum dapat digunakan untuk membedakan fase mesotrofik dan eutrofik namun fase hipereutrofik sudah dapat diketahui dengan jelas.

The study was conducted in Mrica Reservoir Banjarnegara Central Java during a year (March 2009 - February 2010). The research objectives were to assess the amount of nutrient (N and P) inputs from the catchment to the reservoir and the nutrient balance occured in the Mrica reservoir, examine the nutrient dynamics in Mrica reservoir spatially and temporally, to assess the relationship of nutrient concentrations to aquatic trophic status, and determine the appropriate criteria nutrient for the assessment of the trophic level of the Mrica reservoir as water located in tropical regions. This study used a survey method with purposive sampling technique in 17 (seventeen) locations including 4 (four) points in the river which were the reservoir inlet (Serayu, Merawu, Lumajang and Liangan channels), 11 (eleven) point in the waters of the reservoir and 2 points in the reservoir outlet and in the lacustrine zone of 0, 2, 5, 10, 20 and 30 meters depth. Research variables included nutrients concentration (TP, TN, NO3-, PO4, NH4+), chlorophyll and temperature, O2, CO2, HRT, pH and turbidity, and inflow as well as outflow of reservoirs. Data obtained were analysed by qualitatively and quantitatively methods. To assess the nutrient balance by calculating the different concentration between input and output of the reservoir. Distribution of TN and TP were analysed descriptively using charts and to know the difference between locations were tested using F test followed by HSD 5%. Correlation regression analysis was conducted to assess the relationship of nutrients and algal biomass. Nutrient criteria was made by extrapolating the regression line based on the empirical models. Comparison of Mrica reservoir’s nutrient criteria with the sub trophic one was analysed descriptively. The conclusions were that the Mrica reservoir had the TN input of 374.623,08 tons and TP input of 41.117,18 tonnes higher than the output of 339.922,49 tons and 33.179,15 tons). Therefore Mrica reservoir had a surplus of TN and TP respectively of 34.700,59 tons (9,26%) and 7.938,02 tons (19,31%). The surplus was as a residual drift and then deposited into the sediments of Mrica Reservoir. Spatially TN and TP entered to the Mrica reservoir were distributed evenly from riverin zone to lacustrine zone. The high nutrient input from the DTA during rainy season led to the temporal distribution of TP was higher than dry season, while the pattern of dam operation on the target level had lead in the temporal distribution of TN was higher in the dry season than the rainy season. The availability of all kinds of nutrients (TN, TP, NO3-, NH4+, and PO4) determined the development of the algae biomass in the Mrica reservoir. Where as the types of nutrients that could be used as criteria for determining the algae development in the rainy season were TP and NH4+, whereas in the dry season was NO3-. The pattern of the development of algal biomass in Mrica reservoir was fluctuated so they could not be used to distinguish between mesotrophic and eutrophic phase but the hypereutrophic phase had already be clearly known.

Kata Kunci : Waduk Mrica, kriteria nutrien, status trofik, wilayah tropis