Lacustrine groundwater discharge in southern Laguna de Bay, Philippines

Abstract

Although a major potential contributor to water and nutrient budgets, lacustrine groundwater discharge (LGD) is often neglected in most lake studies. Through electrical resistivity profiling surveys, the authors examined the possible occurrence of LGD in southern Laguna de Bay, the largest freshwater lake in the Philippines. Discrete and dispersed LGDs were identified. Discrete LGDs were inferred from narrow highly resistive zones that cut vertically across the lake floor. These discrete LGDs line-up with projections of lineaments on land and are thus deemed to be fault-controlled. Dispersed LGDs, interpreted from wide swaths of resistivity signals cutting across the lake floor, were found to occur more commonly in shallower areas. Findings from radon concentrations, nutrient concentrations, and chlorophyll a analyses support the perceived patterns of LGD occurrences. Nutrient input through LGD is probably contributing to the lake’s current eutrophic condition however where discrete LGDs occur, the fisheries appear to be enhanced.