Magnesium and calcium concentrations in limestone groundwaters, Peninsular Malaysia

Author : J. Crowther
Publication : Bulletin of the Geological Society of Malaysia
Page : 59-83
Volume Number : 23
Year : 1989

Bulletin of the Geological Society of Malaysia, Volume 23, August 1989, pp. 59 – 83

Magnesium and calcium concentrations in limestone groundwaters, Peninsular Malaysia


Department of Geography, St. David‘s University College, Lampeter, Dyfed, U.K.


Abstract: The discharge and solute concentrations of 217 groundwaters, draining the Kuala Lumpur Limestone, the Kinta Limestone, and limestones of the Setul Formation, were monitored over a 1-year period. The mean molar Mg: Ca+Mg ratio of the groundwaters (12.8%) is very similar to that of the bedrock (13.3%), indicating the dissolution of calcium and magnesium to be broadly congruent. Extremely low (<2.5%) or high (>35%) ratios are notably less common in groundwaters than bedrock, a feature attributed to: (i) heterogeneity in bedrock mineralogy within the catchments drained by individual groundwaters; (ii) differences in the relative solubilities of calcium and magnesium in magnesian calcites and dolomites; and (iii) preferential precipitation of calcium in secondary carbonate deposits. Where groundwaters have variable discharges, their Mg:Ca+Mg ratio tends to correlate negatively with discharge, as less calcium per unit volume of water is deposited on speleothems at higher flows. The possibilities of using groundwater survey data to locate areas of dolomitization and to make specific inferences about the mineralogy of limestone formations are discussed.

Because the soil cover in the Setul Boundary Range is generally deeper and more extensive than in the steeper tower karsts of the Kuala Lumpur and Kinta Limestones, groundwater recharge has almost twice the chemical weathering potential. However, net chemical denudation rates are similar in all three limestone formations (range, 56.6-70.9 m3/km2/yr) as the higher effective rainfall in the tower karst regions compensates for their lower solute concentrations.