Sedimentation rate estimates in Sorsogon Bay, Philippines using ²¹⁰Pb method

Sorsogon Bay has experienced a long history of recurring harmful algal blooms over the past few years. In an attempt to establish a chronology of events in the sediment layer, lead-210 (²¹⁰Pb) dating method has been utilized in estimating sedimentation rates from three selected areas along the bay. Based on the unsupported ²¹⁰Pb data and by applying the Constant Initial Concentration (CIC) model, the calculated sedimentation rates were 0.8, 1.3 and 1.8 cm yr¹ for sediment cores collected near the coastal areas of Castilla (SO-01), Sorsogon City (SO-07) and Cadacan River (SO-03), respectively. High sedimentation rates were measured in sediment cores believed to be affected from frequent volcanic ash releases and from areas near human settlement combined with intensive farming and agricultural activities. The collected sediments exhibited non-uniform down core values of dry bulk density and moisture content. This variation in measurements may indicate the general quality and composition of the sediment samples, i.e., amount of organic matter and grain size. The calculated sedimentation rates obtained provided an overview of the sedimentation processes and reflect the land use pattern around the bay which may help in understanding the history and distribution of materials and nutrient input relative to the occurrence of harmful algal bloom in the sediment columns. (author)