KAJIAN KIMIA AIR GAMBUT PADA LAHAN GAMBUT DENGAN SUBSTRATUM BAHAN SULFIDIK

ZAFRULLAH DAMANIK, Dr. Ir. Benito Heru Purwanto, M.P., M.Sc.; Dr. Ir. Eko Hanudin, M.S.

2015 | Disertasi | S3 Ilmu Tanah

Penelitian ini bertujuan untuk mempelajari: 1) Perubahan karakteristik kimia air gambut akibat perbedaan kondisi hidrologi dan ketebalan lapisan gambut yang menumpangi bahan sulfidik: 2) Sifat karbon organik terlarut (KOT) berupa tingkat aromatik dan perkiraan berat molekul berdasarkan sifat serapan ultraviolet; 3) Kandungan gugus fungsional dan kandungan asam-asam organik berberat molekul rendah terlarut dalam air gambut yang diekstrak dari beberapa kategori ketebalan lapisan gambut; 4) Peranan lapisan gambut terhadap mobilitas KOT dan pelepasan unsur-unsur toksik dari bahan sulfidik di bawahnya. Sampel air gambut diambil dari situs-situs yang mewakili kategori-kategori gambut tipis, sedang, dan tebal pada kedalaman 0, 25, 50, 100, 150, 200 dan 250 cm dari permukaan tanah. Sampel diambil pada musim hujan, pada transisi musim hujan ke musim kemarau dan pada musim kemarau. Karakteristik kimia air gambut ditetapkan dengan menggunakan metode kolorimetri dan spektorofotometri. Sifat KOT ditetapkan menggunakan metode spektroskopik ultraviolet dan inframerah, serta kromatografi cair berkinerja tinggi. Hasil penelitian menunjukkan bahwa karakteristik kimia air gambut dipengaruhi secara bersama-sama oleh ketebalan gambut, jeluk muka lapisan bahan sulfidik, dan kondisi hidrologi lahan. Lapisan gambut berperan sebagai penyangga perubahan kemasaman dan kondisi redoks dan sebagai pengkhelat unsur-unsur toksik, sedangkan bahan sulfidik merupakan sumber utama ion-ion logam terlarut di lahan gambut. Karbon organik terlarut dalam gambut tebal memiliki tingkat aromatik, berat molekul dan kandungan asam-asam organik berberat molekul rendah (asam oksalat, sitrat, dan asetat) yang lebih tinggi daripada gambut tipis dan gambut sedang. Penipisan, atau hilangnya lapisan gambut di atas bahan sulfidik menyebabkan pemasaman dan pelepasan ion-ion Fe2+, Al3+, SO4 2-, Zn2+ dan Mn2+, yang dalam konsentrasi tinggi bersifat fitotoksik, akibat oksidasi bahan sulfidik, serta pelarutan senyawa-senyawa organik (yakni KOT) melalui proses oksidasi bahan gambut. Senyawa-senyawa tersebut keluar bersama air lindian yang dapat berdampak menurunkan kualitas lingkungan perairan di sekitarnya.

The objectives of this study were to investigate: 1) Changes in the chemical characteristics of peat water resulting from differences in hydrological condition, and thickness of the peat layer overlying the sulphidic material; 2) The characteristics (quality) of dissolved organic carbon (DOC) in terms of aromaticity and estimated molecular weights based on ultraviolet absorption properties; 3) Functional group content and the abundance of low molecular weight organic acids (LMWOAc) of the peat water extracted from the different categories of peat thickness; 4) The role of the peat layer on the mobility of DOC and the release of toxic elements from the sulphidic substratum. Peat water samples were taken from sites which represented shallow, medium and deep peat categories at the depths of 0, 25, 50, 100, 150, 200 and 250 cm from the soil surface. Samples were taken during the wet season, during transition from wet to dry seasons and during the dry season. Chemical characteristics of the peat water were determined using colorimetric and spectrophotometric methods. Characteristics of the DOC were determined using ultraviolet and infrared spectroscopic methods, and high-performance liquid chromatography. The results of the study showed that chemical characteristics of the peat water were influenced by peat thickness, depth of sulphidic material substratum and the hydrological condition of the peat land. The peat layer played the role of buffer for changes in the acidity and redox condition, and of chelating agent for toxic elements, whereas the sulphidic material acted as the main source of soluble metal ions in the peat land. The dissolved organic carbon in the deep peat had higher aromaticity, estimated molecular weight and abundance of LMWOAc (i.e. oxalic, acetic, and citric acids) than those of the shallow and medium peat categories. Depletion, or loss of the peat layer overlying the sulphidic material resulted in acidification and the release of Fe2+, Al3+, SO4 2-, Zn2+ and Mn2+ ions which, in high concentrations were phytotoxic, due to oxidation of the sulphidic material, as well as dissolution of organic compounds ( i.e. DOC) through oxidation of the peat material. These substances move out along with the leaching water which might have a significant impact in lowering the quality of the surrounding water environments.

Kata Kunci : gambut, sulfidik, kimia air, karbon organik terlarut, asam organik berberat molekul rendah