Diatom assemblage in the 24 cm upper sediment associated with human activities in Lake Warna Dieng Plateau Indonesia

Lake Warna is a small shallow crater lake on the Dieng Plateau, Central Java, the second highest plateau in the world after Nepal. A 24 cm sediment core was extracted from Lake Warna to reconstruct environmental changes in the Lake and its catchment from preserved diatom assemblages. Diatoms are microalgae in the Bacillariophyte that have silicious cell walls that can be preserved in sediments. As diatom species are sensitive to water quality changes in the assemblages upcore reflect changes in lake condition. Sediment cores were collected from two sites, sliced at 1 cm intervals for diatom analysis and bulked across 3 cm for 210Pb radiometric dating. Examination of diatoms in a 24 cm sediment core from Lake Warna reveals clear correlation with human activities in the catchment area over the past 124 years. The record is divided into 2 zones based on sustained changes in the diatom assemblages. The lowest zone Zone I (21-15 cm, estimated 1935-1954) was dominated by Frustulia crassinervia (Brebisson ex W. Smith) Ross, Gomph onema parvulum (Kutzing) Kutzing, Pinnularia valdetolerans Mayama & H. Kobayasi, P. viridis (Nitzsch) Ehrenberg, and Aulacoseira distans (Ehrenberg) Simonson. Zone II (15-0 cm, estimated 1980-2013), the uppermost zone was dominated by P. viridiformis Krammer, P. latevittata Cleve, E. monodon var. tro p ica (Hustedt) Hustedt, S. seminulum Grunow, P a crosphaeria W. Smith. E. zygodon Ehrenberg, P. gibba Ehrenberg, and P. viridiformis Krammer. The 15 cm core from TW3 commenced sediment accumulation 114 years ago and is divided into 2 zones as well. Zone I (15-7 cm, estimated 1901-1981) was dominated by Brachysira brebissonii R. Ross, G. parvulum (Kutzing) Kutzing, E. monodon var. tropica (Hustedt) Hustedt, E. zygodon Ehrenberg and S. seminulum Grunow. Zone II (7-0 cm, estimated 1981-2006) was dominated by P. viridiformis Krammer, P. gibba Ehrenberg, Pinnularia viridis (Nitzsch) Ehrenberg, Sellaphora bacillum (Ehrenberg) Mann, S. seminulum Grunow, and Stauroneis sp. These assemblages reflect ongoing acid, clear water conditions for the time represented by the cores. The recent rise in S. seminulum Grunow reflects recent lake eutrophication likely owing to the accelerated agricultural and urban development in the lake's catchment in recent decades.