Hydrogeochemical characteristics in an urbanized tropical watershed, Kuala Lumpur area, Malaysia

There is not enough data on the hydrogeochemical characteristics of groundwater-surface water interaction in the urbanized tropical watersheds. Tropical regions are generally characterized by high annual precipitation and groundwater recharge. Especially the coastal cities of southeastern Asia have larger hydraulic gradient and subsurface water flux due to high topographical gradient in the elevation recharge area. We focus on an urbanized coastal watersheds, Langat River and Klang River watersheds, Kuala Lumpur area, capital city, Malaysia and investigate the hydrogeochemical characteristics of river water and subsurface water with the multi-tracer methods using inorganic dissolved constituents and stable isotope ratios.
    The SiO2 concentrations and (Na+K)/(Ca+Mg) ratio of river water decreases from upstream to midstream in Langat River. The decrease seems to be caused by geological setting, granite in the upper reaches and schist in the middle reaches. The stable isotope ratios (δ18O & δ2H) of the river water are plotted along with the local meteoric water line, and tend to be enriched toward to downstream. In the upstream area, hot springs are distributed along the faults and rivers. They showed Na-HCO3 type quality and much higher SiO2 concentrations than that of river water. There are wetland and lake in the midstream, and they show a significant depletion of d-excess value, suggesting an evaporation from the water surface of lakes and wetland. Na+, Cl- concentrations and stable isotope ratios increase in downstream of Langar River, suggesting seawater intrusion. On the other hand, stable isotope ratios and inorganic dissolved constituents decrease in the downstream of Klang River. This would be caused by the process that deep groundwater with depleted isotopic ratios discharges to the stream.