[A-CG40] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG40-05] Main driver of short-term variation in pH and Ω_ara around the Japan coastal areas

*Tsuneo Ono¹, Daisuke Muraoka¹, Goh Onitsuka¹, Tomohiro Okamura¹, Kenji Sudo¹, Masahiro Hayashi², Mikiko Yorifuji², Akihiro Dazai³, Shigeyuki Omoto⁴, Takehiro Tanaka⁵, Masahiko Fujii⁶, Masahide Wakita⁷ (1.Fisheries Research and Education Agency, 2.Marine Ecology Research Institute, 3.Center for sustainable Society, 4.Eight-Japan Engineering Consultants Inc., 5.NPO Satoumi Research Institute, 6.Faculty of Environmental Earth Science, Hokkaido University, 7.Japan Agency for Marine-Earth Science and Technology)

Keywords:pH, saturation state of aragonite, acidification, coastal areas, terrestrial imput

We occupied continuous pH monitoring at five stations in Japan coastal areas (Miyako, Shizugawa, Kashiwazaki, Hinase and Hatsukaichi) to analyze variation of pH and W_ara with various temporal scales. In addition to seasonal variation, both pH and W_ara showed significant short-term variation with the time length of less than 10 days, and most of such short-term variation was linked to the rain fall event in each area. It was also found that both pH and W_ara decrease to the critical level for the organisms (e.g., sublethal threshold of pacific oyster Ω_ara=1.5, Waldbusser et al., 2015) only in the midst of these short-term perturbations in present Japanese coastal areas. Present risk of ocean acidification in the coastal areas, therefore, can be diminished if we can control amplitude of short-term variation in pH and W_ara.
Main factor that determines amplitude of short-term variations in pH and W_ara was investigated by analyzing relationship among multiple parameters during the short-term variation. In addition to the data from original five stations, we add data from Tokyo Bay (TBEIC monitoring post at Kawasaki Artificial Island, https://www.tbeic.go.jp/MonitoringPost/Top) in this analysis. It was found that standard deviation of pH in ten-days time length (10dSD_pH) is in proportion to that of salinity (10dSD_sal) with constant proportional coefficient (D10dSD_pH/ D 10dSD_sal) in all 10dSD_sal ranges in Tokyo Bay (Fig.1). In other coastal areas, however, D10dSD_pH/ D 10dSD_sal becomes lower when 10dSD_sal exceeds 0.7. Furthermore, value of D10dSD_pH/ D 10dSD_sal at 10dSD_sal > 0.7 showed linear relationship with the nitrate concentration of main river that flows into each area (Fig.2). These feature implied that main driver of the short-term variation of pH (and W_ara) is POM that is produced in river mouth and estuaries based on riverine nutrient, and hence we can reduce amplitude of short-term variation in pH and W_ara if we can reduce riverine nutrient imput in each coastal area.