Looking into the Potential Role of Sediment Processes in the Productivity of Murcielagos Bay, Philippines

Murcielagos Bay is a relatively small and shallow bay located in the northwestern part of Mindanao. It has been affected by recurring blooms of Pyrodinium bahamense var. compressum , resulting in a shellfish ban enforced by the Bureau of Fisheries and Aquatic Resources from 2009-2013. Field data, hydrodynamic and residence time models show that the small, stratified embayment in the southern part of the bay, called Sapang Dalaga, has a long residence time which may have an impact on the water quality and recurrence of blooms. A 24-hour field monitoring in November 2013 showed chlorophyll-a values ranging from 0-40 ug/L, the highest concentration relative to the concentrations from previous monitorings, and higher nutrient concentrations were observed at the bottom of the water column as well. Preliminary results from water quality modelling showed that the high chlorophyll-a concentrations near the bottom could not be reproduced if the main source is from river runoff and the sediment dynamics part of the model is turned off. As shallow waters are prone to sediment resuspension which affects the nutrient budget, the close coupling between the sediment bed and water column will be looked into and the potential role of sediments in the productivity of the bay will be examined through a sediment-water interface water quality model.