Siak River System — East-Sumatra

• Published in: Journal of marine systems 2009-04, Vol.77 (1), p.148-159
• Main Authors: Siegel, Herbert, Stottmeister, Iris, Reißmann, Jan, Gerth, Monika, Jose, Christin, Samiaji, Joco
• Format: Article
• Language: English
• Subjects: Brackish; CDOM; Freshwater; Marine; Ocean colour; Remote sensing; Siak River; Sumatra; Water constituents
• ISSN: 0924-7963; 1879-1573
• DOI: 10.1016/j.jmarsys.2008.12.003

Interdisciplinary pollution studies were performed in the Siak River system in the Riau Province of East-Sumatra (Indonesia). Remote sensing investigations combined with in situ measurements in different seasons of the years 2004–2006 were focused on the identification of different sources of water masses in the tributaries and on the discharge into the estuary and Malacca Strait. Ship-borne measurements comprised the determination of the concentration and composition of optically active water constituents and water colour. Satellite data of different spectral and spatial resolution were implemented. Sources of different water masses such as humic substance dominated rivers, erosion areas of high suspended matter concentration and areas of limited bio-productivity are identified. Sources of humic substances are the rivers Tapung Kanan, Mandau, Siak Kecil, and Bukit Batu which are draining peatlands. The absorption coefficients of dissolved organic substances are partly (Siak Kecil, 51.8 m − 1 ) more than double of the currently admitted coefficients. The highest suspended matter concentrations near a channel between Siak and Siak Kecil leading to lowest transparency are caused by the estuarine turbidity maximum developing at the tidal front. The lowest Chlorophyll concentrations were measured between Pekanbaru and the channel, in and downstream of an industrial area. The concentration and distribution of water constituents are characterised by distinct regional patterns independent from the monsoon phases. The high absorption of dissolved organic humic substances originated from draining peatlands shifts the maximum of spectral reflectances to 700 nm leading to the extreme brownish to red-brownish water colour. High scattering of suspended particles increases the reflectance in the entire spectral range. The strong changes in the water colour enables satellite data of the visible spectral range to follow the distribution patterns of the Siak River discharge in the estuary which are strongly related to tidal phases. During low tide, the transport of Siak River water is directed into the Malacca Strait north-westwards and during high tide into Selat Panjang. Time series of daily available MODIS images have shown that the main transport direction in all seasons is the outflow into the Malacca Strait and further north-westwards following the large scale circulation.