SEDIMENT CHARACTERISTICS IN RECONSTRUCTING PALEOENVIRONMENTAL CHANGES PRESERVED IN A MIRE IN THE HORTON PLAINS, SRI LANKA

Horton Plains (HP) located in central Sri Lanka is a national park and UN World Heritage site. An undulating landscape in HP with its mires, plains, intermontane rainforests, grassy hills, and cliffs record the evolution of the regional continental paleoenvironmental history and monsoon activity. In recent years, HP has indicated forest ‘die-backs’ and this problem remains unresolved. A multi-proxy geochemical record consisting of trace metals, organic C content, stable C isotopes, humification process, and lipid biomarkers were assessed in a 150 cm long core obtained from a mire in HP. Most selected metals analyzed in the core increase between 105 and 122 cm (maximum abundance at 118 cm) before they decline (except Fe). The high metal concentrations (15 selected elements) in the mire are unusual, and unlike other references of metal distribution in mires reported in the literature. The presence of these elements is probably of natural occurrence from weathering activity. Humification process increases with depth and humification indices (A600/TOC and Δlog K) maxed around 97-105 cm; humification process however correlates poorly with metal concentrations. Total organic C is surprisingly low and ranges from 2.1-8.1 wt% (average 5.58 wt%) in the mire. The average stable C isotope value was -25.32‰ implying vascular C₃ plant matter, however the values are more depleted (ca. 3‰) implying extensive biological activity, which extends up to nearly 85 cm depth. Lipid analyses indicate dominant input of C₂₃ and C₂₅ n-alkane followed by lower concentrations of higher n-alkanes (n-C₂₇-C₃₁). Higher n-alkanes dominate in only few intervals. The n-alkane distribution suggests a moss dominated system, which could be possibly related to a wet and moist period during the late Holocene, whereas the higher n-alkanes suggest short dryer periods.