Non-destructive particle analyses from different surface sediment samples of Lake Towuti, Indonesia

At the University of Cologne, Germany, a subsample was taken from one aliquot and used to produce smear slides for identification of sedimentary components using transmitted light microscopy. On selected samples, sponge spicules and diatom frustules were additionally investigated using a Zeiss Gemini Sigma 300VP scanning electron microscope (SEM; Carl Zeiss AG, Oberkochen, Germany). Furthermore, some magnetic mineral grains were identified with energy dispersive X-ray spectroscopy (EDX) of the Sigma SEM system. Based on smear slide analyses, a set of 40 samples that contain sponge spicules, diatoms and/or tephra particles were selected for automated, non-destructive particle image analyses using a dynamic imaging system (Benchtop B3 Series VS FlowCAM®; Fluid Imaging Technologies, Inc., Scarborough, ME, USA) to quantify the abundance of these particles. Aliquots of wet bulk samples were treated with hydrogen peroxide (H2O2; 30%) for seven days at room temperature to remove organic matter (OM) and disaggregate the siliceous biogenic particles, and were subsequently sieved with 25 and 80 µm meshes. The pre-treated sample fractions were diluted with deionized water (samples 80 µm). Particle recording in the 80 µm fraction was recorded using a 300 µm flowcell, a 4x objective lens without collimator, and a 5 ml syringe-pump (flow rate 0.6 ml/min). Data were acquired using the software VisualSpreadsheet (Fluid Imaging Technologies, Inc., Scarborough, ME, USA) until 10.000 images were recorded or 30 ml of the sample was investigated. An automated catalogue based on training sets developed for sponge spicules, diatoms and tephra particles was compiled to differentiate and group components with comparable characteristics in the measured sample fractions.