Marine Chemistry, 24 (1988) 293-305 293 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Trace Metal Transport in a Tropical Estuary H. WINDOM, R. SMITH, Jr. and C. RAWLINSON Skidaway Institute of Oceanography, P. O. Box 13687, Savannah, GA 31416 (U.S.A.) M. HUNGSPREUGS, S. DHARMVANIJ and G. WATTAYAKORN Department of Marine Science, Chulalongkorn University, Phya Thai Road, Bangkok 10500 (Thailand) (Received August 10, 1987; revision accepted December 18, 1987) ABSTRACT Windom, H., Smith, R., Jr.,Rawlinson, C., Hungspreugs, M., Dharmvanij, S. and Wattayakorn, G., 1988. Trace metal transportin a tropicalestuary.Mar. Chem., 24: 293-309. The distributions of soluble and particulate trace metals in the Bang Pakong Estuary, Thailand were studied during high (wet) and low (dry) discharge conditions. Particulate trace metals and particulate organic C concentrations are controlled by physical processes. Dissolved Cu and Ni are, in general, conservatively mixed through the estuary. The behavior of Fe and Pb result in net removal during estuarine transport. Fe removal appears to be due to decreased solubility as pH increases in estuarine waters. Mn is removed at low salinities, when riverine concentrations are high, and remobilized at higher salinities. Dissolved Cd, Co and Zn concentration distributions have mid-estuary maxima which coincide with nutrient maxima. The metal-nutrient relationship is interpreted as the result of metal regeneration during organic matter decomposition. INTRODUCTION Much of the present understanding of the transport of trace metals through river-estuarine systems is based on studies in temperate and boreal climatic regions. Because many of the systems studied are contaminated by anthropo- genic inputs, it is often difficult to describe natural estuarine processes and how they are influenced by characteristics of the watershed or by the estuarine environment itself. The transport of trace metals through 'tropical estuaries' has been studied almost entirely in estuaries of major river systems (e.g. the Amazon), the watershed of which may include several climatic zones or biomes (Walter and Box, 1976) and weathering regimes (Stallard and Edmond, 1983) making it difficult to assess the influence of drainage basin characteristics on estuarine chemistry. The mixing zones of large rivers may also extend into ocean basins where oceanic, not estuarine, processes dominate. To better understand trace metal transport in tropical estuarine systems we 0304-4203/88/$03.50 © 1988 Elsevier Science Publishers B.V.