STUDY OF ROCK MAGNETISM AND HEAVY METALS IN SEDIMENT IN VOLCANIC AND TROPICAL AREAS CASE STUDY: CITARUM RIVER BANDUNG, WEST JAVA

• Main Author: - (32314004), SUDARNINGSIH
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/24402
• Institution: Institut Teknologi Bandung

The Citarum River has a volcanic catchment area in West Java Province, and is one of the nationally strategic rivers in tropical Indonesia due to water supply and power generation. The river is economically important, but it is also polluted by industrial, agricultural, and residential wastes. Several methods, mostly based on chemistry and biology, are being used to monitor the pollution level of the river. The feasibility of using physical methods such as magnetic methods is currently being tested in the river. Due to its location in a volcanic area on a tropical island, the sediments from the river are naturally highly magnetic. In this study, sand and boulder samples from Balekambang, a relatively pristine upstream area of the river, were subjected to magnetic and geochemical characterize to establish the baseline for unpolluted sediments. Such a baseline is very important for future monitoring of the Citarum River through the application of magnetic methods. Suspended sediment samples were collected along the Citarum River profile, starting in Balekambang through the area of Bandung Regency to the downstream village of Nanjung, where the river is dammed. Similar samples were also collected from seven tributaries of the Citarum River. <br /> <br /> <br /> <br /> <br /> <br /> As expected, the results showed that the mass-specific magnetic susceptibility of boulder samples varied from 819.2 to 2,340.5 × 10&#61485;8 m3kg-1 while that of sand samples varied from 2,293.9 to 3,845.3 × 10&#61485;8 m3kg-1. Such extremely high magnetic susceptibility values infer that Citarum River sediments are highly magnetic even before being contaminated by industrial and household wastes. The predominant magnetic mineral in the samples was magnetite. However, the sand samples tended to be multi-domain (MD) while the boulder samples tended to be single domain to pseudo-single domain (PSD). These differences were supported by the results from petrographic and XRF analyses, implying that the sand and boulder samples originated from different geological formations. <br /> <br /> <br /> <br /> <br /> <br /> Magnetic and heavy metal analyses show that unlike river sediments from a nonvolcanic catchment area in temperate climates, magnetic susceptibility values tend to decrease downstream, showing that the magnetic minerals in the upstream area are mostly lithogenic in origin, containing more Fe-bearing minerals compared to those in tributary samples which are anthropogenic in origin. Anthropogenic pollution is also represented by the increase of Zn content along the river. The results suggest that applying magnetic methods for monitoring river pollution in the tropics or in the volcanic areas should be carefully analyzed and interpreted. <br />