River flow pattern and heavy metals concentrations in Pasig River, Philippines as affected by varying seasons and astronomical tides

This study explored the transport of metal pollutants in Pasig River, an important source of water for different uses in the National Capital Region of the Philippines. In particular, the study investigated the effect of varying seasons and varying levels of tides on the flow pattern and heavy metals concentrations in Pasig River. Pasig River is one of the main outlets which drain directly into the Manila Bay and Laguna de Bay. Four sampling sites were chosen along the 27 km-stretch of Pasig River which includes the following: Delpan, Lambingan, Guadalupe and Kalawaan sampling locations. Series of water samplings were conducted during the months of April, 2007 copping the dry season and November 2007 covering the wet season. Sampling design was primarily based on the height of tide at Manila Bay. Flow rate as computed from surface flow velocity was measured at each station. Concentration of heavy metals such as cadmium, copper, lead and nickel, were also measured. Results indicate that an observable backflow occurred during the dry season when the tide was high, that is, saline water from Manila Bay, intruding into the Pasig River. Further, this study established that the highest flow rate was noted during the wet season at low tide, particularly at the Kalawaan station. On the other hand, low flow rate was observed during the dry season when the tide was high. With regard to the levels of heavy metals, concentrations were found to be elevated during the dry season and also, when high tide occurs. Water samples collected from Delpan station yielded high metal concentrations with lead (Pb) as the dominant heavy metal among the four metals analysed in this study. Variability in the metal concentration due to seasonal changes, varying flow patterns and tide may indicate water quality problems not only in Pasig River but also to coastal areas such as Manila Bay. (paper)