Watershed and Pahu-anCave Stream Interconnectivity in Bonliw, Torrijos, Marinduque, Philippines

Abstract

Marinduque Island is characterized as having a karst landscape with caves having underground streams harboring a variety of freshwater organisms including freshwater shrimps which are dependent on the quality of the forest and watershed. This study aimed to characterize the forest cover overlying the cave, siltation/sedimentation rate in the surface and cave streams, nutrient contents (ammonium, phosphate. and sulfate) of the sediment and water, and freshwater shrimps and phytoplanktons present in both streams. Results of the assessment indicate that the surface stream and the cave stream in the Torrijos Watershed Forest Reserve are interconnected as shown by both streams having similar freshwater shrimps and phytoplankton species. Phytoplanktons to develop will need sunlight which is devoid in the cave, and therefore have to be transported to the caves to be present. The freshwater shrimps found in the cave are not troglobitic and therefore has found its way to the cave stream. Further, there seemed to be a similar trend on the total suspended solids, sedimentation rates and amount of nutrients (phosphates) between the two streams. Although organic matter and nutrients from the aboveground landscape are needed for the sustenance of organisms in the cave ecosystem (the abundance of which are dependent on the connectivity of the two water systems), siltation/sedimentation can ultimately threaten the water quality of cave stream. With the forest in the watershed area characterized as denuded, the threat is evident. The protection of the watersheds and its landscape is imperative.