Assessment of coastal turbidity improvement potential by terrigenous sediment load reduction and its implications on seagrass inhabitable area in Banate Bay, central Philippines

Takahiro Yamamoto; Mary Ann Cielo L Malingin; Ma Marivic Pepino; Masaya Yoshikai; Wilfredo Campos; Toshihiro Miyajima; Atsushi Watanabe; Yoshiyuki Tanaka; Naoko Morimoto; Roseanne Ramos; Homer Pagkalinawan; Kazuo Nadaoka

doi:10.1016/j.scitotenv.2018.11.243

Assessment of coastal turbidity improvement potential by terrigenous sediment load reduction and its implications on seagrass inhabitable area in Banate Bay, central Philippines

Sci Total Environ. 2019 Mar 15:656:1386-1400. doi: 10.1016/j.scitotenv.2018.11.243. Epub 2018 Nov 17.

Affiliations

¹ Department of Mechanical and Environmental Informatics, Graduate School of Information Science and Engineering, Tokyo Institute of Technology, O-okayama 2-12-1 W8-13, Meguro-ku, Tokyo 152-8552, Japan. Electronic address: tyamamoto@kisr.edu.kw.
² OceanBio Lab, College of Arts & Sciences, University of the Philippines Visayas, Miag-ao, Iloilo 5023, Philippines.
³ Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, 2-12-1 W8-13 O-okayama, Meguro-ku, Tokyo 152-8552, Japan.
⁴ Marine Biogeochemistry Group, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8564, Japan.
⁵ Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 690 Kitasekine, Mutsu, Aomori 035-0022, Japan.
⁶ Department of Geodetic Science, University of the Philippines Diliman, Quezon City, Philippines.

PMID: 30625667
DOI: 10.1016/j.scitotenv.2018.11.243

Abstract

This paper demonstrates the effects of terrigenous sediment load reduction by watershed managements on coastal turbidity in Banate Bay, Iloilo located in central Philippines, using field observations and numerical simulations. Measurements of the total suspended solid and particulate organic carbon indicated that the bulk component of the coastal turbidity comprised terrigenous mineral particles rather than phytoplankton at the rise of the river after heavy rain. The suspended sediment concentration and underwater light intensity were simulated by an atmosphere-watershed-coastal ocean model to investigate the contribution of the terrigenous sediment load to the coastal turbidity in rainy season. The coastal sediment simulation indicated that the turbidity in Banate Bay is highly impacted by terrigenous sediment inputs from distant watersheds, which are transported to the bay by coastal currents. In contrast, the contributions of sediment loads from the adjacent watersheds to the bay turbidity were limited. The simulation also indicated that the majority of the bay is not inhabitable for seagrasses due to limited light availability caused by the high turbidity. Scenario analysis of the sediment load reduction demonstrated that significant reduction of turbidity and improvement of light penetration are conditionally expected only when the remediation is implemented with cooperative management of a series of neighboring watersheds because of the significant contributions of sediment loads from multiple basins.

Keywords: Coastal zone management; Irradiance; Light attenuation; Monitoring system; Simulation analysis; Watersheds.